Geohydrology of the Yuma Area, and

GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-H

Geohydrology of the Yuma Area, Arizona and California

By F. H. OLMSTED, O. J. LOELTZ, and BURDGE IRELAN

WATER RESOURCES OF LOWER - AREA

GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-H

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1973 DEPARTMENT OF THE INTERIOR

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY

V. E. McKelvey, Director

Library of Congress catalog-card No. 73-600011

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $11.60 Stock Number 2401-02391 CONTENTS

Page Page Abstract ______HI Geology Continued Introduction ______6 Stratigraphy Continued Location of area ______6 Volcanic rocks (Tertiary) Continued History of water-resources development _____ 6 Basalt or basaltic andesite of unknown Yuma Valley ______6 age ______H38 Yuma Mesa ______9 Age of volcanic rocks ___ _ 39 Other areas ______9 Older marine sedimentary rocks (Tertiary). 39 Mexicali Valley ______10 Bouse Formation (Pliocene) ______40 Objectives of present investigation and scope of Transition zone (Pliocene) ______45 report ______11 Conglomerate of (Ter­ Methods of investigation ______12 tiary and Quaternary) _____ 45 Geologic mapping ______12 Older alluvium (Pliocene and Pleistocene) _ 45 Geophysical exploration ______12 Distribution and thickness ______46 Test drilling ______12 Age and correlation 46 Studies of formation samples ______13 Classification of deposits by source 47 Wireline logging ______14 Deposits of local origin _ ____ 47 Inventory of existing wells and well records- 14 Stream-terrace and piedmont deposits 47 Quantitative determinations of aquifer char­ Deposits of mixed origin __ _ 48 acteristics ______15 Deposits of the old Colorado and Gila Chemical analyses of ground-water samples _ 15 Rivers ______48 Measurements of ground-water temperature. 15 Younger alluvium (Quaternary) __ 53 Analog-model studies ______15 Deposits of the Colorado and Gila Rivers 53 Earlier investigations ______16 Alluvial-fan deposits _ 56 Geologic studies ______16 Wash and sheet-wash deposits 56 Hydrologic studies ______16 Windblown sand (Quaternary) __ 56 Acknowledgments ______16 Structure ______57 Well-numbering systems ______17 Regional structural patterns ______57 Geology ______18 Pre-Tertiary structural features _ 57 Geomorphology ______18 Basin and Range structural features (Ter­ Regional setting ______18 tiary) ______58 Classification of landforms ______19 Late Tertiary and Quaternary structural Mountains and hills ______19 features ______60 Dissected old river deposits __ _ 23 Algodones fault and related faults ______61 Dissected piedmont slopes ______24 Ground-water hydrology ______63 Undissected piedmont slopes ______24 The ground-water reservoir ______63 River terraces and mesas ______26 Major subdivisions of the reservoir ______63 Sand dunes ______28 Definition of fresh water 63 River valleys ______28 Poorly water-bearing rocks of Tertiary age _ 64 Stratigraphy ______30 Nonmarine sedimentary rocks ______65 Classification of rocks ______30 Older marine sedimentary rocks ____ 65 Crystalline rocks (pre-Tertiary) ______30 Bouse Formation ___ _ _ 65 Nonmarine sedimentary rocks (Tertiary) __ 32 Transition zone ______66 Red beds ______33 Water-bearing deposits of Pliocene to Holo- Breccia and conglomerate ______33 cene age 66 Kinter Formation ______34 Wedge zone ___ - 66 Other nonmarine sedimentary rocks _ _ 37 Coarse-gravel zone ______67 Volcanic rocks (Tertiary) ______37 Upper, fine-grained zone -______68 Older andesite ______37 Older alluvium, undivided ______69 Pyroclastic rocks of silicic to interme­ Origin of ground water and sources of recharge _ 70 diate composition ______37 Colorado River ______70 Basaltic andesite or basalt of Chocolate ______71 Mountains ______38 Irrigation ______71 Flows and vent tuff of Laguna Moun­ Local precipitation ______72 tains 38 Local runoff ______72 ill IV CONTENTS

Page Page Ground-water hydrology Continued Ground-water hydrology Continued Hydrologic characteristics of aquifers ______H72 Temperature of ground water Continued Definition of terms ______72 Variations in temperature with time H113 Transmissivity ______75 Vertical variations in temperature _ _ 116 Determinations by previous investiga­ Areal variations in temperature 121 tors ______75 Chemical quality of ground water 124 Determinations during present investi­ Chemical changes in ground water derived gation ______75 from the recent Colorado River __ 124 Storage coefficient ______78 Concentration by evapotranspiration 126 Movement of ground water ______82 Softening ______126 Direction of movement under natural con­ Carbonate precipitation 127 ditions ______84 Sulfate reduction ______127 Hardening ______128 Rate of movement under natural conditions- 87 Summary of hypothetical analyses 129 Alluvial section between Pilot Knob and Subdivision of Yuma area for description Cargo Muchacho Mountains ______87 of quality of water ______129 Limitrophe section of Colorado River __ 87 Gila Valley subarea __ _ - - --_ 129 Yuma Valley ______87 Gila Siphon sector _ 132 Direction of movement in 1960 ______88 East sector __ 132 Rate of movement in 1960 ______91 East-central sector 133 Alluvial section between Pilot Knob and West-central sector __ _ 133 Cargo Muchacho Mountains ______91 West sector 133 Limitrophe section of Colorado River __ 91 Upper valley subarea __ _ _ _ 134 Yuma Valley ______93 "Laguna Valley" sector __ 134 Movement after 1960 ______95 North Gila sector ___ 134 Water budgets ______95 Bard sector __ __ 135 "Laguna Valley" subarea ______98 The Island sector ____ 135 Reservation and Bard subarea ______99 Winterhaven sector _ 135 The Island subarea ______100 Yuma Valley subarea ______136 North Gila Valley subarea ______100 California sector 137 South Gila Valley subarea ______100 East sector ______137 Yuma Mesa subarea ______101 Central sector ______138 Yuma Valley subarea ______102 Floodway sector ____ 138 Summary of subarea budgets ______103 Yuma Mesa subarea _ 139 Yuma area ____-______103 Fortuna sector ______139 Ground-water discharge to the Colorado Arizona Western sector ___ _ 139 River between and the Citrus sector ______140 northerly international boundary _____ 105 City sector ______140 Analog-model studies ______107 South sector ______141 Model characteristics ______107 References _ _ __ -- 141 Transmissivity values ______108 Appendix A. Records of wells ______146 Storage-coefficient values ______109 Appendix B. Selected logs of water wells __ _ 170 Stresses applied to the modeled system ___ 109 Appendix C. Chemical analyses of ground water _ 195 Verification studies ______113 Appendix D. Selected pumping tests ______208 Reliability of the analog model ______113 Appendix E. Moisture investigations ______216 Temperature of ground water ______113 Index ______225

ILLUSTRATIONS

[Plates are in separate volume] PLATE 1. Topographic map of the "Upper Mesa" showing trace of the Algodones fault and the effect of the fault on ground-water levels, Yuma-area, Arizona and California. 2. Topographic map of the Yuma Mesa, Yuma area, Arizona and California. 3. Geologic map of the Yuma area, Arizona and California. 4. Geologic map of southeastern Laguna Mountains and north end of Gila Mountains, Yuma area, Arizona. 5. Geologic sections A-A', B-B', C-C', D-D', and E-E' across northern Yuma Valley and northwestern Yuma Mesa, Yuma area, Arizona and California. 6. Geologic sections F-F' along limitrophe section of Colorado River and G-G' along southerly international boundary, Yuma area, Arizona and California. 7. Map showing altitude of top of coarse-gravel zone, Yuma area, Arizona and California. CONTENTS v

PLATE 8. Geologic sections H~H' across margins of Yuma Valley and Yuma Mesa southeast of Somerton and /-/' across eastern South Gila Valley and northeastern Yuma Mesa, Yuma area, Arizona and California. 9. Map showing principal geologic structural features, Yuma area, Arizona and California. 10. Block diagram of the Yuma area, Arizona and California. 11. Map showing chemical character of water in the coarse-gravel zone, Yuma area, Arizona and California. 12. Maps showing thickness of clay, silty clay, and clayey silt in the upper 100 feet of the alluvium in parts of the Yuma area, Arizona and California. 13-17. Maps of the Yuma area, Arizona and California showing location of 13. Water test wells and oil test wells. 14. U.S. Geological Survey auger test holes and test wells, Yuma County Water Users' Association deep observation wells, and selected U.S. Bureau of Reclamation observation wells. 15. Drainage and supply wells. 16. Irrigation wells. 17. Miscellaneous wells. Page FIGURE 1. Map of the lower Colorado River region showing location of the Yuma area H7 2. Map showing areas irrigated in 1966 ______- -_------8 3. Photograph showing the boring of a test well with a power auger 3% miles south of Somerton, Ariz_ 13 4. Photograph showing the drilling of test well LCRP 26 1% miles west of Winterhaven, Calif 14 5. Snetch showing subdivision of U.S. land-net sections for assignment of well numbers and locations of wells by grid coordinates ______- - 18 6. Geomorphic map of the Yuma area ______20 7-9. Photographs of 7. Westward view of a ridge in the southwestern Chocolate Mountains, Calif 21 8. Dissected piedmont surfaces of reentrant of "Picacho Mesa" in eastern Cargo Muchacho Mountains, Calif ______25 9. Northern Gila Mountain from Fortuna Wash ______26 10. Photograph showing terraces in southern Laguna Mountains _ 27 11. Stratigraphic column ______31 12. Photograph showing granite breccia and conglomerate exposed in north bank of Colorado River at Yuma ______- 34 13. Photograph showing exposure of Kinter Formation in railroad cut along Kinter siding at north end of Gila Mountains ______36 14. Selected logs of test well LCRP 29 below a depth of 1,000 feet ______41 15. Map showing inferred extent and configuration of the Bouse Formation ______43 16. Selected logs of test well LCRP 26 between depths of 1,000 and 1,450 feet ______44 17-20. Photographs showing 17. Poorly sorted gravelly deposits of local origin exposed in west bank of Fortuna Wash near U.S. Interstate Highway 8 ______47 18. View of southeastern Chocolate Mountains, California, showing predominantly fine-grained older alluvium abutting basaltic andesite or basalt of Tertiary age ______49 19. Crossbedded coarse sand and fine gravel in exposure of older alluvium 6 miles west of Yuma ______50 20. Well-rounded to subrounded Colorado River gravel in an exposure of older alluvium south­ west of Pilot Knob ______51 21. Map of the southwestern part of the Yuma area showing extent and altitude of top and bottom of clay A beneath Yuma Valley and northwest margin of Yuma Mesa ______54 22. Map of the central part of the Yuma area showing extent and altitude of top and bottom of clay B beneath Yuma Mesa ______55 23. Map showing transmissivities computed from pumping tests made prior to the present investigation-- 76 24. Map showing wells for which pumping tests were made during present investigation ______77 25. Map of the Yuma area showing transmissivity of alluvium ______81 26. Hydrograph showing mean annual stages of Colorado River at Yuma ______83 27. Map of Yuma Valley showing average water-level contours in 1911 ______85 28. Map of the delta region showing average water-level contours in 1939 ______86 29. Map showing average water-level contours in 1925 ______89 30. Map of the delta region showing average water-level contours in 1960 ______90 31. Map of Yuma Valley showing average water-level contours for upper part of coarse-gravel zone in 1960 ______94 32. Map of the delta region showing average water-level contours in December 1965 ______96 33. Sketch map showing water budgets for subareas, 1960-63, inclusive ______97 34. Map of Yuma Valley showing average water-level contours for upper part of coarse-gravel zone in 1962 ______104 VI CONTENTS

Page FIGURE 35. Map of the delta region showing transmissivity of the upper transmissive layer simulated in the analog model ______- H110 36. Map of the delta region showing transmissivity of the lower transmissive layer simulated in the ana­ log model __---______-______---_--_- ______- 111 37. Map showing storage coefficients of the upper transmissive layer simulated in the analog model __ 112 38-43. Maps showing changes in 38. Water level, 1925 to December 1957, as indicated by field measurements or as estimated __ 114 39. Head in the upper transmissive layer, 1925 to December 1957, as indicated by responses of the analog model ______115 40. Water level, December 1957 to December 1962, as indicated by field measurements 116 41. Head in the upper transmissive layer, December 1957 to December 1962, as indicated by responses of the analog model ______- 117 42. Water level, December 1962 to December 1966, as indicated by field measurements 118 43. Head in the upper transmissive layer, December 1962 to December 1966, as indicated by responses of the analog model ___-_---- _ ------119 44. Temperature profiles in well (C-9-24)llccc for May and November 1967 and February 1968 120 45. Graph showing change in temperature of water pumped by well (C-9-23)20bdc (USER drainage well YV-13) from November 1966 to February 1968 121 46. Temperature profile in well (C-8-23)33cdd (LCRP 13) for March 12, 1963 ______122 47. Map showing temperature of ground water in coarse-gravel zone or at equivalent depth below the water table, 1965-68 ______-_ - - 123 48. Diagrams representative of chemical charac ter of water represented by selected chemical analyses in table 15 ______-___-__-__-__--__- 130 49. Map of the Yuma area showing subareas and sectors described in section on quality of water and listed in appendix C ______-_- 131 50-54. Graphs in appendix D showing pumping-test data for wells 50. 16S/23E-10Rcc (LCRP 23) ______209 51. 16S/22E-29Gca2 (LCRP 26) ______-___-______-___ 211 52. (C-9-22)28cbb (LCRP 25) ______213 53. (C-10-25)35bbd (LCRP 17) ______- ______214 54. (C-ll-24)23bcb (LCRP 10) ______216 55. Graph showing relation between counts per minute and moisture content ______218 56-58. Graphs showing counts per minute at various depths below land surface obtained by use of a neutron moisture probe at 56. Ten sites in South Gila Valley ______221 57. Ten sites on Yuma Mesa ______222 58. Six sites in Yuma Valley ______224

TABLES

Page TABLE 1. Irrigated acreage and water diverted to Yuma Mesa H9 2. Potassium-argon ages of volcanic rocks in the Yuma area 39 3. Summary of heavy-mineral analyses of alluvial sand (deposits of the Colorado River) of the Yuma area ______51 4. Selected data from analyses of gravel from wells in older and younger alluviums 52 5. Depths of Tertiary and pre-Tertiary horizons in wells 64 6. Miscellaneous chemical analyses ______-- ______73 7. Results of pumping tests ______79 8. Diversions, consumptive use, and ground-water recharge for Yuma Mesa _ _ _ 98 9. Summary of ground-water budgets of Yuma subareas, 1960-63 105 10. Ground-water discharge to the Colorado or Gila Rivers between Imperial Dam and northerly in­ ternational boundary, 1960-63 ______- - __ 106 11. Flow of the Colorado River at Imperial Dam and at Yuma, and differences between sum of all surface-water inflow items in the reach and flow of Colorado River at Yuma ______106 12. Flow of the Colorado River at Yuma and at northerly international boundary, and differences be­ tween sum of all surface-water inflow items in the reach and flow of Colorado River at northerly international boundary ______106 13. Design stresses for analog model of Yuma area __ _ 109 CONTENTS VII

Page TABLE 14. Effective year-end declines of water level, in feet, in Mexicali Valley at a site 12 miles west of the middle limitrophe section of the Colorado River ______H109 15. Hypothetical analyses of ground water resulting from specified chemical changes in Colorado River water ______125 16-20. In appendix A: 16. Water-test wells and oil-test wells- ______147 17. U.S. Geological Survey auger test holes and test wells, Yuma County Water Users' Associa­ tion deep observation wells, and selected U.S. Bureau of Reclamation observation wells 150 18. Drainage and supply wells ______158 19. Irrigation wells ______-______160 20. Miscellaneous wells ______164 21. In appendix E: Moisture content and storage capacity of alluvium as indicated by neutron moisture probe study ______219

WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA

By F. H. OLMSTED, O. J. LOELTZ, and BURDGE IRELAN

ABSTRACT The Yuma area includes the upstream part of the Colo­ through which are cut the present valleys (flood plains) of rado River delta within the United States, in one of the the Colorado and Gila Rivers. The landforms include seven driest regions of North America. Except for very major types: (1) Mountains and hills, (2) dissected old minor irrigation by the Indians and the Spanish before river deposits, (3) dissected piedmont slopes, (4) undissected about 1850, irrigation with Colorado River water began in piedmont slopes, (5) river terraces and mesas, (6) sand the late 19th century. By 1966, about 100,000 acres was dunes, and (7) river valleys. being irrigated, chiefly in the river valleys (flood plains) Mountains and hills composed of dense pre-Tertiary and on Yuma Mesa (a river terrace). Ground water has crystalline rocks and hard volcanic rocks of Tertiary age been the source of supply only in South Gila Valley east of form the higher, more rugged exposures; less consolidated Yuma and in small areas outside the established irrigation sedimentary and volcanic rocks of Tertiary age form the districts in the other river valleys and on Yuma Mesa. lower, more rounded hills. Some of the mountain blocks are The valley lands were the first to be irrigated, and only buried or nearly buried by alluvium, particularly those in a very small acreage was irrigated on Yuma Mesa before the southern and western parts of the area. 1923. After the middle 1940's the irrigated area on Yuma Dissected old river deposits lie at some distance from Mesa expanded rapidly so that by 1966 more than 20,000 the mountains; the chief example of this landform type is acres was under irrigation. About two-thirds to three-fourths the "Upper Mesa," a generally westward-sloping desert plain of the total of more than 5 million acre-feet of Colorado southeast of Yuma Mesa. River water imported for irrigation on the mesa from 1922 Dissected piedmont slopes characterized by broad desert through 1966 either went into ground-water storage to pavements cut by numerous washes lie along the margins of build a widespread ground-water mound or induced ground- the hills and mountains. water movement into the valleys west and north of the The undissected piedmont slopes, also near the hills and mesa. Drainage wells were installed in the 1950's and 1960's mountains, are distinguished from the older, dissected pied­ in eastern Yuma Valley and in the 1960's in South Gila mont slopes by the general absence of desert pavement and Valley in order to alleviate drainage problems aggravated by the shallow depth of incision of the most recent washes. by the growth of the ground-water mound. The river terraces and mesas are remnants of an exten­ Irrigation with Colorado River water in Mexicali Valley, sive former valley and delta plain of the Colorado River the northern part of the Colorado delta in , began and its major tributary, the Gila. The surfaces of the ter­ shortly after the turn of the century. By 1955, more than races and mesas lie about 60-80 feet above the present river 500,000 acres in the valley was irrigated. This area re­ valleys except in the extreme western part of the area, quired more water than the 1.5 million acre-feet of Colorado where the terrace surfaces slope west or southwest toward River water guaranteed annually to Mexico under a 1944 the axis of the Salton Trough at gradients steeper than those treaty plus the small supplementary supply pumped from of the river valleys. Yuma Mesa represents the principal private wells. Accordingly, the Mexican Government author­ river terrace in the area. Others are Imperial East Mesa, ized the drilling of several hundred wells to augment the Wellton Mesa, and several distinct smaller terraces that total supply. Pumpage of ground water increased during the extend upstream along both the Gila and the Colorado next decade, so that by 1965 nearly 1 million acre-feet was Rivers. pumped, of which about two-thirds came from Government Windblown sand is extensive in the Yuma area, although wells. Ground-water pumpage is now carefully controlled in only two sizable areas has the sand accumulated to form by the Mexican Government, and the total area irrigated dunes more than 10 feet thick. The larger area, known as with ground water and surface water is restricted to about the Sand Hills or the "," lies northwest of 415,000 acres substantially less than the maximum area Yuma between the Imperial East Mesa and Pilot Knob Mesa; irrigated in the 1950's. the smaller tract of dunes the "Fortuna Dunes" is in the The Yuma area straddles the dividing line between the southeastern part of the area, near the international section and the Salton Trough section of boundary. the Basin and Range physiographic province and is char­ The river valleys (Holocene flood plains of the Colorado acterized geomorphically by low north-northwest-trending and Gila Rivers) were flooded periodically before dams and mountains separated by much more extensive deecrt plains reservoirs were constructed upstream on both the Colorado HI H2 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

and the Gila Rivers. The principal valleys within the area includes fossiliferous silt and clay, subordinate fine sand, of intensive investigation are Yuma Valley, "Bard Valley," hard calcareous claystone, and, locally in the basal part, South Gila Valley, and North Gila Valley. calcareous sandstone or sandy limestone, tuff, and possibly The earth materials of the Yuma area range from dense conglomerate of local derivation. The fine-grained clastic crystalline rocks to unconsolidated alluvium and windblown beds are predominantly greenish to bluish gray and contain sand. These materials are grouped in 10 generalized strati­ small gastropods, pelecypods, and ostracodes, as well as graphy units: (1) Crystalline rocks (pre-Tertiary), (2) several species of Foraminifera which indicate brackish to nonmarine sedimentary rocks (Tertiary) including a new marine environments but are not diagnostic as to age. formation, the Kinter, of Miocene age; (3) volcanic rocks Other evidence, in part from the Parker-Blythe-Cibola area, (Tertiary) (4) older marine sedimentary rocks (Tertiary), indicates a Pliocene age, although a definite assignment (5) Bouse Formation (Pliocene), (6) transition zone (Plio­ within the Pliocene is not yet possible. Except for one small cene), (7) conglomerate of Chocolate Mountains (Tertiary area of exposures 2-3 miles southeast of Imperial Dam, the and Quaternary), (8) older alluvium (Pliocene and Pleisto­ Bouse Formation occurs entirely in the subsurface in the cene), (9) younger alluvium (Quaternary), and (10) wind­ Yuma area. blown sand (Quaternary). Throughout much of the Yuma area, the Bouse Formation The crystalline rocks, which form a large part of the is overlain by a transition zone in which marine strata like mountains and hills and unconformably underlie the Tertiary those of the Bouse alternate or intertongue with nonmarine and Quaternary rocks, comprise a wide variety of meta- strata like those in the overlying older alluvium. The tran­ morphic, plutonic, and dike rocks, of which granite and sition zone reflects the fact that marine or estuarine condi­ quartz monzonite and various kinds of gneiss and schist are tions did not cease abruptly but recurred at intervals for the most abundant. The ages of most of these rocks have some time after the ancestral Colorado River entered the not been established, although all of them appear to ante­ area. date the Laramide orogeny (Late Cretaceous to early The conglomerate of the Chocolate Mountains occurs only Tertiary). in the northern part of the area, on the flanks of the Choco­ The nonmarine sedimentary rocks (Tertiary) consist of late Mountains. This unit, which is composed predomi­ strongly to weakly indurated clastic rocks ranging from nantly of volcanic detritus from nearby exposures of Ter­ mudstone and shale, in part of lacustrine origin, to mega- tiary volcanic rocks, includes strata probably equivalent breccia and boulder conglomerate. For the purpose of this in age to the upper part of the nonmarine sedimentary rocks report all these rocks are grouped in one major unit, al­ (Kinter Formation) but also in part equivalent in age to though detailed mapping in the Laguna Mountains and the lower part of the older alluvium. northernmost Gila Mountains resulted in the delineation of The older alluvium is composed of basin-filling fluvial three mappable units: red beds, breccia and conglomerate, deposits of the Colorado and Gila Rivers and of local ephem­ and the Kinter Formation (chiefly fanglomerate, with sub­ eral streams. The unit is actually a complex of alluvial fills ordinate breccia, arkosic sandstone and mudstone, and separated by unconformities representing degradational tuffaceous beds). Stratigraphic relations with radiometrically cycles that resulted in extensive scouring. It is the most dated volcanic rocks indicate that the red beds and the widely exposed unit in the Yuma area and reaches a maxi­ breccia and conglomerate are pre-Miocene; the Kinter For­ mum thickness of more than 2,000 feet in the southwestern mation is designated Miocene on the basis of a potassium- part of the area. Its age ranges from Pliocene to late Pleis­ argon date of 23 ±2 million years for an interbedded ben- tocene. tonitic ash and of stratigraphic relations with overlying units. The older alluvium comprises a great variety of granular Associated with the nonmarine sedimentary rocks is a materials ranging from clay to cobble and boulder gravel; suite of volcanic rocks that includes an older andesitic se­ sand is predominant at most places. These materials are quence (flows and tuffs), pyroclastic rocks of silicic to classified by primary source as deposits of local origin, intermediate composition ranging from soft pumiceous ash- deposits of the old Colorado and Gila Rivers, and deposits fall tuff to densely welded ash-flow tuff (ignimbrite), basaltic of mixed origin. In addition, relatively thin stream-terrace andesite or basalt of the Chocolate Mountains (a sequence and piedmont deposits cap the older, thicker fills at many of dark-gray flows and flow breccias), flows and vent tuff of places. The deposits of local origin occupy the margins of the Laguna Mountains, and scattered masses of basalt or the area and consist of poorly sorted, obscurely bedded gravel, basaltic andesite of uncertain stratigraphic position and age. sand, silt, and clay which were deposited probably as allu­ Potassium-argon dates for several of the volcanic rocks vial fans. The stream-terrace and piedmont deposits are range from about 25 to 26 million years, indicating a prob­ similar to the deposits of local origin, which they cap near able middle Tertiary age for the unit. the mountains, and are characterized by broad surfaces of The older marine sedimentary rocks consist of more or less so-called desert pavement. The deposits of mixed origin con­ indurated fine sandstone and interbedded gray siltstone and sist of intergradational or intertonguing deposits of local claystone which occur entirely in the subsurface in the origin and old river deposits. The deposits of the old Colo­ Yuma area. Fossils include foraminifers and mollusks indica­ rado and Gila Rivers, which constitute the greatest bulk of tive of a marine environment but not diagnostic as to age. the older alluvium, consist of relatively well sorted sand and The age of these beds and their correlation with units of subordinate silt and clay, at many places containing anasto­ other areas are uncertain, but their stratigraphic position mosing tonguelike and ribbonlike bodies of gravel. The suggests that they probably intertongue with the Kinter gravel includes abundant well-rounded pebbles and cobbles Formation in the upper part of the nonmarine sedimentary of siliceous rocks, chiefly quartzite and chert, which appear rocks. to have been derived from the region and The Bouse Formation, a younger marine unit which prob­ even farther upstream. ably is unconformable on the older marine sedimentary rocks, The younger alluvium comprises all the alluvial deposits GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H3 of the most recent cycle of deposition. These deposits are the conglomerate of the Chocolate Mountains. These units classified in three categories according to the dominant contain some water, but much of it is highly mineralized, agent of deposition: (1) Deposits of the Colorado and Gila and the rocks are too poorly permeable or lie at too great Rivers, (2) alluvial-fan deposits, and (3) wash and sheet- a depth beneath most of the area to be significant sources wash deposits. The river deposits consist predominantly of of ground water. Local exceptions include fresh-water­ sand and silt and underlie the present river flood plains; bearing nonmarine sedimentary rocks, in the northern part locally a basal gravel may be present at depths exceeding of the .area, and a conglomerate in the basal part of the 100 feet. The alluvial-fan deposits, which consist of poorly Bouse Formation, also in the northern part of the area. sorted detritus derived from nearby exposures of granitic (Fresh water is defined herein as water containing not rocks, occur only near the southeastern and northwestern more than 1,800 mg/1 (milligrams per liter) of dissolved corners of the area. The wash deposits are thin, occur in solids or having a specific conductance of not more than channels cut into the older alluvium and prealluvial rocks, 3,000 micromhos.) and consist of sand and gravel and thin lenses of silt. The The units of the second subdivision, which form the upper, sheet-wash deposits are similar to the wash deposits but principal part of the ground-water reservoir, include (1) occupy broader, less well defined areas. the older alluvium, (2) the younger alluvium, and (3) the The windblown sand occurs as dunes, principally in the windblown sand. However, beneath the river valleys and Sand Hills and in the "Fortuna Dunes," and as relatively Yuma Mesa, the upper part of the reservoir is most con­ thin sheets on Yuma Mesa and "Upper Mesa." Small dunes veniently subdivided into three zones, two of which cross occur also in Yuma Valley and "Bard Valley." The wind­ stratigraphic boundaries. In ascending order, these zones blown deposits consist of well-sorted fine to medium sand are (1) the wedge zone (lower, major part of the older which is probably derived from nearby sandy alluvium or, alluvium), (2) the coarse-gravel zone (uppermost gravel for the deposits of the Sand Hills, from old lacustrine or strata of the older alluvium and possibly a basal gravel of marine beaches. the younger alluvium), (3) the upper, fine-grained zone Structurally, the Yuma area is characterized by north- (uppermost strata of the older alluvium beneath Yuma northwest-trending mountains separated by broader basins Mesa, the upper, major part of the younger alluvium be­ filled with Cenozoic deposits possibly as much as 16,000 feet neath the river valleys, and small masses of windblown thick in the "Fortuna basin" west of the southern Gila sand). Outside the river valleys and Yuma Mesa the alluvial Mountains and Butler Mountains. Some of the mountain deposits (almost entirely older alluvium below the water masses, especially in the western Sonoran Desert and east­ table) are not subdivided and are classified instead as older ern Salton Trough, are buried or nearly buried by the alluvium, undivided. Cenozoic deposits. Presumably the mountains and basins are The wedge zone, which extends to depths of about 2,500 separated by faults, but most of the present mountain feet in the south-central and southwestern parts of the fronts are fault-line scarps rather than fault scarps; the area, constitutes the major part of the fresh-water-bearing faults lie basinward and are concealed by alluvial fill. deposits of Pliocene to Holocene age beneath the river Early deformational episodes, which were Laramide and valleys and Yuha Mesa. The average grain size and prob­ probably pre-Laramide (pre-Tertiary), resulted in faulting ably the average porosity and permeability of the wedge (including thrust faulting), folding, and metamorphism. In zone decrease with depth. The lower part of the zone con­ the Sonoran Desert the eastern part of the Yuma area tains more silt and clay than the upper part, but in gen­ structural activity continued into the Tertiary, and by eral, the fine-grained strata are not sufficiently extensive middle Tertiary time the mountains and basins assumed or thick to cause significant hydraulic separation. The upper approximately their present configuration. Subsequent def­ part of the zone locally contains coarse-gravel strata similar ormation has involved only minor warping and normal to those in the overlying coarse-gravel zone. faulting, probably associated with regional subsidence along Except in two small areas, one beneath the city of Yuma the southwest margin, adjacent to the Salton Trough. and the other west of the northern Gila Mountains, the In the Salton Trough in the southwestern part of the water in the wedge zone contains less than 1,800 mg/1 dis­ area, deformation has continued to the present, especially solved solids. In both areas of more highly mineralized water, on and near the faults of the San Andreas system. Move­ the overlying coarse-gravel zone is thin or absent and the ment on these faults has involved large right-lateral com­ wedge zone is thinner and probably less permeable than it ponents as well as apparently sizable vertical displacements. is at most other places. In most of the northern part of the A major fault in this system, herein named the Algodones Yuma area, water in the wedge zone appears to be sub­ fault, has been delineated in the present study from topo­ stantially fresher than that in the overlying coarse-gravel graphic, geophysical, and hydrologic evidence. In the south­ zone. Beneath the southern part of the area the chemical eastern part of the area this fault forms a partial to nearly quality of the water in the wedge zone is virtually indis­ complete barrier to ground-water movement and is a feature tinguishable from that of the water in the coarse-gravel to major hydrologic significance. Other faults, parallel or zone. en echelon to the Algodones fault, have been identified from Relatively little is known about the chemical quality of seismic and temperature data. the water in the older alluvium, undivided. Some of the The ground-water reservoir consists of two major sub­ water is undoubtedly similar to that in the adjacent wedge divisions: (1) poorly water-bearing rocks of Tertiary age, zone. Mineralized water in which the dissolved-solids con­ and (2) water-bearing deposits of Pliocene to Holocene age. tent exceeds 1,800 mg/1 exists west of the northern Gila The first subdivision constitutes the lower part of the reser­ Mountains, beneath "Fortuna Plain" at the southerly inter­ voir and includes (1) the nonmarine sedimentary rocks, (2) national boundary, and possibly between these two places. the volcanic rocks, (3) the older marine sedimentary rocks, The coarse-gravel zone, which is the principal aquifer (4) the Bouse Formation, (5) the transition zone, and (6) beneath the river valleys and Yuma Mesa, is a complex of H4 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

gravel bodies of different ages deposited by the Colorado and Gila Rivers. Transmissivity values exceed 500,000 gpd and Gila Rivers. The zone ranges in thickness from 0 to per foot beneath The Island, north of the area just cited, possibly more than 150 feet; the top lies at an average and they also persist for about 6 miles southward beneath depth of 100 feet beneath the valleys and 170-180 feet Yuma Mesa from the area of maximum transmissivity. beneath Yuma Mesa in the central part of the area. Transmissivities of more than 500,000 gpd per foot occur Under natural conditions, the Colorado and Gila Rivers also beneath the west edge of Yuma Valley and southwest- were the sources of almost all ground-water recharge in ward from a line 3-5 miles southwest of the Algodones the Yuma area, but with the development of irrigation and fault, about along the boundary between southern Yuma the construction of upstream reservoirs on both rivers, Mesa and the "Upper Mesa." irrigation water diverted from the Colorado River became Storage characteristics of the material saturated by the principal source. Local runoff and precipitation are the large ground-water mound built up beneath Yuma Mesa very minor sources of ground-water recharge. after 1947 were estimated on the basis of soil-moisture data The chemical regimen of the Colorado River has been ma­ obtained with a neutron moisture probe lowered into access terially affected by man's control of the river. Before the tubes driven into the zone of saturation. The difference be­ impounding of water in Lake Mead in 1935 the chemical tween the moisture content above the capillary fringe and composition of the water in the lower reaches of the river that below the water table was considered to be a valid was highly variable, both seasonally and annually. Since estimate of the amount of water that would be stored as 1935 the composition has varied much less; during the water levels rose. The storage coefficient at 10 sites in South period 1941-65 the concentration of dissolved solids at Gila Valley averaged 38 percent; at six sites in Yuma Valley, Imperial Dam generally was between 700 and 800 mg/1. 43 percent; and at 10 sites on Yuma Mesa, 28 percent. Stor­ Sulfate was the major dissolved constituent, and calcium age coefficients for the material penetrated by drainage wells was the most abundant cation, although sodium was slightly along the east edge of Yuma Valley as computed by earlier more abundant than calcium when the dissolved-solids con­ investigators ranged from 5.8x10"* to 3.6xlO~3 and averaged centration was highest. 1.2xlO~3 values which indicate confined or artesian con­ Precipitation and local runoff furnish ground-water re­ ditions for at least the periods of the tests. Data for com­ charge of excellent chemical quality. In most places the puting storage coefficients under similar conditions were not overall effect of these sources on the quality of ground water obtained during the present investigation. is negligible; however, in several places, such as along Under natural conditions both the Colorado and the Gila Fortuna Wash near the northwest margin of the Gila Moun­ Rivers were losing streams in the Yuma area. Infiltration tains, fresh ground water derived from storm runoff occurs from these streams was the principal source of ground- as a thin lens or lenses not far below and above the water water recharge. Much of the infiltration replenished the draft table. on ground-water supplies caused by evapotranspiration, but The connate water is likely to be rather highly mineral­ some of the infiltration provided a source for the ground ized; sodium and chloride are the chief ionic constituents. water moving out of the area. Movement of ground water The coarse-gravel zone and the wedge zone are the prin­ through the alluvial section between Pilot Knob and the cipal aquifers in the Yuma area. Subordinate aquifers of Cargo Muchacho Mountains under natural conditions was only local significance include the nonmarine sedimentary about 4,500 acre-feet per year. The movement of ground rocks, the conglomerate in the basal part of the Bouse water westward from the limitrophe (International Bound­ Formation, and a few relatively coarse grained beds in the ary) section of the Colorado River is estimated to have upper, fine-grained zone. Outside the river valleys and Yuma been as much as 110,000 acre-feet per year. As much as Mesa, the older alluvium, undivided, is regarded as the 90,000 acre-feet of water that infiltrated from the Colorado principal single, heterogeneous aquifer. River is estimated to have been discharged by evapotranspi­ Transmissivity values for the principal aquifers were ration in Yuma Valley. estimated on the basis of one or more of the following: The Colorado River continued to be a losing stream until (1) Step-drawdown tests, (2) short-term pumping tests, the early 1940's, at which time the channel near Yuma was (3) specific-capacity data, (4) lithologic logs, (5) electric deepened 5 feet or more by erosion, and ground-water levels and sonic logs, and (6) seismic data. The studies of pre­ rose as a result of irrigation and leakage from the All- vious investigators also were utilized. American Canal. These conditions caused the Colorado above Critical evaluations of the reliability of computed values the limitrophe section to change from a losing to a gaining of transmissivity obtained from pumping tests made during stream. For a distance of 25 miles west of Pilot Knob the the present investigation indicated that three of the values ground-water ridge resulting from leakage of the All- were within 10 percent of true values, 33 within 25 percent, American Canal was 30 feet or more high, with the result 27 within 50 percent, and 10 more than 50 percent. that the direction of ground-water movement south of the Transmissivity values of the wedge zone generally increase canal changed from westward to southward, and the gra­ in a southwestward direction from zero along the relatively dient steepened from that existing under natural conditions. thin east and north margins of the zone to values of more By 1960 many changes in rates of movement had occurred than 500,000 gpd (gallons per day) per foot beyond a north­ and the pattern of movement was more complex than it was westward-trending line about 4 miles southwest of the under natural conditions. In the alluvial section between Algodones fault, where the wedge zone is more than 2,000 Pilot Knob and the Cargo Muchacho Mountains the west­ feet thick. ward flow is estimated to have been only three-eighths of Transmissivity values for the coarse-gravel zone range the flow under natural conditions. The westward movement from zero to about 1,000,000 gpd per foot. Maximum values of ground water to Mexicali Valley adjacent to the limi­ of transmissivity for the coarse-gravel zone occur in the trophe section is estimated to have been 36,000 acre-feet in South Gila Valley, south of the confluence of the Colorado 1960. This estimate is corroborated by an estimate of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H5

20,000 acre-feet of outflow from Yuma Valley opposite the tion to constant-head boundaries. This second model incor­ limitrophe section plus about 15,000 acre-feet for unac­ porated the newly discovered hydrologic-barrier effects of counted depletion of the river in the limitrophe section the Algodones fault and satisfactorily reproduced historical during periods of low flow. In addition to the outflow from changes in water level. Yuma Valley to the limitrophe section, 7,250 acre-feet of In the Yuma area, variations in ground-water tempera­ ground water moved northward to the Colorado River and ture are useful in corroborating vertical movement of water 5,000 acre-feet flowed across the southerly international inferred from other evidence. Also, abnormally high tem­ boundary, making the total ground-water outflow from Yuma peratures at some places furnish supporting evidence for Valley about 33,000 acre-feet. the presence of fault barriers or zones of low permeability. After 1960 the principal changes in ground-water move­ At many places, especially on Yuma Mesa, geothermal gra­ ment were a moderate increase in the size of the ground- dients have been modified greatly from natural conditions, water mound beneath Yuma Mesa and a lowering of water owing to vertical movements of ground water induced by levels in Mexicali Valley. Water levels beneath Yuma Mesa heavy applications of irrigation water or by large-scale continued to rise until 1962, but subsequent to that year, pumping from wells. Faults, such as the Algodones fault and water levels northward and westward from the apex of the the inferred buried faults near the west margins of the mound began a moderate decline, owing to increased pump­ Gila Mountains and the "Yuma Hills," have produced warm ing for drainage near the toe of the mesa in Yuma and anomalies which are caused by upward movement of deep South Gila Valleys. However, water levels continued to rise water near the fault barriers. Upward movement of warm at greater distances eastward and southward from the apex water along the east margin of Yuma Valley has been of the mound. The generally lower water levels in Mexicali accelerated by pumping from drainage wells. Valley resulted from the large-scale pumping for irrigation The chemical quality of ground water in the Yuma area in that valley. Pumping by private interests for irrigation varies markedly, both areally and vertically. Differences in on Yuma Mesa, which began in 1962, caused only a moderate chemical characteristics of the recharge from several sources lowering of water levels through 1966. account for part of these variations, but the most important Average yearly water budgets for the period 1960-63, factors appear to be the chemical changes in the ground inclusive which were prepared for seven subareas designated water that take place as a result of such processes as con­ for the Yuma area, had a net imbalance of 20,000 acre-feet centration by evaporation or evapotranspiration, softening out of a total inflow to the subareas of 1,192,000 acre-feet. by ion exchange, precipitation of insoluble carbonates, sul- The imbalance for individual subareas expressed as a per­ fate reduction, and hardening by ion exchange. Other cent of the inflow to the subarea ranged from zero for the processes probably include re-solution of precipitated salts, Yuma Mesa subarea to about 7 percent for the Reservation oxidation of dissolved organic substances, and mixing of and Bard subarea. Consumptive use in the subareas is waters of different chemical composition. 488,000 acre-feet, or about 40 percent of the total inflow. It is possible to summarize the chemical characteristics A water budget for the entire Yuma area for the 4-year of the ground water in the area by regarding it as chemi­ period 1960-63 shows an imbalance of only 7,000 acre-feet cally altered recent Colorado River water, using a hypo­ an imbalance that is well within the limits of accuracy for thetical-model approach in which the river water is assumed measuring inflow and outflow, each of which exceeds 6 to have been evaporated and subjected to the chemical million acre-feet per year. processes cited above. Most of the chemical characteristics of During the 1950-65 period the average yearly discharge of the ground water can be accounted for by these hypotheses, ground water to the Colorado River is estimated to have although not all the ground water is actually derived from averaged about 21,000 acre-feet in the reach, Imperial Dam recent Colorado River water. Among the various processes, to Yuma, and 17,000 acre-feet in the reach, Yuma to north­ concentration by evaporation or evapotranspiration and sul- erly international boundary. For the 4-year period 1960-63, fate reduction appear to be especially important at most comparable estimates are 45,000 and 27,000 acre-feet, re­ places. spectively. The mineral content of the ground water in the coarse- Two electrical analog models of the hydrologic system of gravel zone in the South Gila Valley and eastern North Gila the delta region were constructed during the present inves­ Valley is greater, on the average, than it is in most other tigation for the purpose of verifying the estimates of places, the sum of determined constituents generally exceed­ hydrologic parameters that had been made as the result of ing 1,800 mg/1. However, information on the preirrigation geologic and hydrologic studies. chemical quality of the water is lacking, so that it is not The first model, built in 1964, simulated a single trans- possible to estimated how much of the present salinity has missive layer connected to a constant-head surface through­ resulted from long-continued irrigation without drainage. out the flood-plain area in the United States by a vertical- Most of the water is of the sodium chloride type, and the hydraulic-conductivity parameter. It was abandoned because proportions of sodium and chloride tend to increase with satisfactory correlation between model responses and his­ increasing dissolved-solids content. Two places, one near the torical changes was not achieved. However, the study did of South Gila Valley, the other near the west end, demonstrate that the model failed to simulate one or more have the most concentrated water, the dissolved-solids con­ significant hydrologic parameters beneath Yuma Mesa. tent exceeding 3,600 mg/1. The water in the wedge zone is Later, a more sophisticated model was constructed. The much fresher than that in the coarse-gravel zone, as it hydrologic system was simulated as a three-dimensional flow generally contains substantially less than 1,800 mg/1 dis­ field idealized as two two-dimensional transmissive layers solved solids. and two layers of solely vertical flow, one of which served In "Bard Valley," "Laguna Valley," and western North as the hydraulic connection between the two two-dimensional Gila Valley the water in the coarse-gravel zone appears to transmissive layers and the other as the hydraulic connec­ contain less than 1,800 mg/1 dissolved solids at most places, H6 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA and the water in the wedge zone is even fresher. The upper, end of the Colorado River basin, in one of the fine-grained zone in these valleys locally contains more highly driest desert regions in North America. The south­ mineralized water, especially where the water table is shallow. western part of the Yuma area is within the Salton Water-quality variation is not well defined in most of Trough, a lowland extension of the Gulf of Cali­ Yuma Valley because of the sparsity of the data. Variations fornia which includes the delta of the Colorado in the upper, fine-grained zone and the coarse-gravel zone River; the northeastern part is in the Sonoran appear to be erratic, although the freshest water commonly Desert, a region of barren, low, generally northwest­ containing less than 900 mg/1 occurs near the Colorado ward-trending ranges separated by extensive desert River. On Yuma Mesa the chemical quality of the ground water basins (fig. 1). The city of Yuma, at the confluence beneath the irrigated area has been affected by infiltrated of the Colorado and Gila Rivers, is 70 airline miles Colorado River water, somewhat concentrated by evapo- north of the mouth of the Colorado at the Gulf of transpiration. Sulfate is the major anion in most of this California. water. Outside the irrigated area the ratio of chloride to sulfate is higher, chloride generally exceeding sulfate in equivalent concentration. The dissolved-solids content of the HISTORY OF WATER-RESOURCES DEVELOPMENT water at most places is less than 1,800 mg/1, except in the area west of the northern Gila Mountains, and beneath the The Yuma area is part of a very arid region city of Yuma at the northwest corner of the mesa, where where crops are entirely dependent on irrigation somewhat brackish water occurs. for their water supply. The dry climate, with its Pumping-test data for five Geological Survey test wells hot summers, mild winters, and practically year­ are presented in an appendix. Possible explanations are long growing season, together with the availability offered for some of the observed anomalies. The probable large differences that may exist between measured drawdown of the Colorado River as a source of water supply, and drawdown in the aquifers are illustrated by the data have encouraged the development of intensive irri­ collected using different pumping equipment. The movement gated agriculture. Since irrigation began, before the of water between strata is offered as an explanation for turn of the century, the acreage under cultivation some of the anomalies. The reasons for some of the other has increased so that, by 1966, a/bout 100,000 acres anomalies are not known. The practical value of a deep- well current meter for determining the rates at which vari­ was being irrigated (fig. 2). ous strata yield water when a well is pumped is shown. Its The first irrigation developments were in the value in connection with other geophysical logs for disclosing river valleys (flood plains of the Colorado and Gila strata that are still sealed with drilling mud is also indi­ Rivers) ; the broad river terrace known as Yuma cated. Mesa (fig. 6) was developed later principally after Soil-moisture data are presented in another appendix. The the end of World War II when citrus orchards relation between counting rate and actual soil moisture of material in place for use with the neutron probe and access were planted extensively on the favorable sandy tubes is difficult to determine for material whose moisture soils. The Colorado River has been the source of content is half or more of the moisture content of the ma­ supply except in the South Gila Valley (fig. 6) and terial when it is saturated. Because of the small variations in small areas in the other valleys and on Yuma in absolute specific gravity of the material for which mois­ Mesa, where ground water has been developed by ture determinations were made, moisture content of satu­ rated material in place was determined on the basis of the means of wells of generally large capacity. bulk density of the material and its absolute specific gravity. The absolute specific gravity of 25 samples of material as YUMA VALLEY determined in the laboratory ranged from 2.66 for a sandy loam to 2.81 for a loamy clay. The absolute specific gravity The first irrigation in Yuma Valley (fig. 6) began for 14 samples of sand ranged from 2.66 to 2.70 and aver­ about 1897. By 1902, four privately owned canal aged 2.68; for five samples of silt, from 2.69 to 2.75 and systems were in operation. In 1904, Congress author­ average- ! 2.72; for six samples classified as clay or clayey ized the Yuma Project, the first Federal irrigation silt, from 2.72 to 2.81 and averaged 2.76. The relation be­ project on the main stem of the Colorado River. At tween counting rate and moisture content for moisture con­ tents of more than 10 percent was interpolated between the that time more than 10,000 acre-feet of water was relation determined for low moisture content and moisture being diverted annually from the Colorado River content when saturated. The soil-moisture studies indicated by pumps and gravity for irrigation. However, the the need for improved methods of constructing access holes, supply was very undependable owing to the large especially to depths greater than 20 feet. Minor differences fluctuations in stage of the river. in the relation between counting rate and soil moisture were found to be due to differences in the construction of the Between 1904 and 1912 about 50,000 acre-feet per access holes and in the material used for casing the holes. year was being pumped from the river to irrigate INTRODUCTION Valley Division (Yuma Valley) lands (fig. 2). In LOCATION OF AREA 1912 the Colorado River siphon was completed and The area investigated is near the downstream thereafter until 1945 water was diverted at Laguna GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H7

117' 116° 115° 114° 113° 112 C

36'

EXPLANATION

Physiographic boundary

35 C

34 £

33 =

32 C

GULF OF CALIFORNIA

FIGURE 1. Map of the lower Colorado River region showing location of the Yuma area.

Dam (pi. 3), and it flowed by gravity to the lands drainage problems as they arose. The Main Drain of the Valley Division of the Yuma Project. (pi. 3) extending southward down the middle of the Continued irrigation resulted in a rise in ground- valley carries the drainage to the southerly inter­ water levels and consequent drainage problems; national boundary where the boundary pumping construction of gravity drainage ditches began in plant (fig. 2) lifts the drainage water 12-15 feet 1916. The system generally was expanded to meet and discharges it into Mexico. H8 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

114-45

32°45' -

Boundary pumping plant

EXPLANATION

Alluvial escarpment Irrigated area 1. Reservation Division 2. The Island Area of shallow bedrock 3. North Gil a Valley Unit 4. South Gila Valley Unit 5. Yitma Mesa Division Fault 6. Yum a Auxiliary Project Dotted where concealed 7. Valley Division

Mountains and hills

32°15

FIGURE 2. Areas irrigated in 1966.

The yearly pumpage of drainage water at the age after 1945 is derived from drainage wells along boundary pumping plant at 5-year intervals is listed the east side of Yuma Valley. The pumpage dis­ in the following table. Much of the increased pump- charges into the drainage system. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H9

Drainage water pumped at boundary pumping plant Yuma Mesa Division of the Gila Project. Under [Amounts rounded to nearest 5,000 acre-feet] this project water diverted at Imperial Dam into Year Amount Year Amount the Gila Gravity Main Canal (pi. 3) is pumped to 1920 ___ _ _. _ 20,000 1945 _ _ _ __ 55,000 the mesa at a point about 9 miles east of Yuma. The 1925 .___ _ 50,000 1950 ______90,000 irrigated acreage increased from about 1,000 acres 1930 _ _ 45,000 1955 -___ _ _ 105,000 1935 __ _ _ . _ 25,000 1960 _ 135,000 in 1944 to about 17,000 acres by 1959, after which 1940 . _ _ 65,000 19fi5-_ . __130,000 it stabilized (table 1). Because the project lands generally were about Between October 1940 and June 1945 diversion of 90 feet above the water table when development water for the Valley Division lands was shifted began, drainage of these lands was not an immedi­ from Laguna Dam to Imperial Dam (pi. 3) with its ate problem. However, the drainage of these lands desilting works and thence into the newly completed was of early concern to the ranchers and farmers of All-American Canal (fig. 2) from which it was the Valley Division, who feared that their existing diverted into the Yuma Main Canal (pi. 3). This drainage facilities would be overtaxed by any sub­ conveyance plan has remained in effect to the pres­ stantial increase of inflow from the mesa. Conse­ ent time. quently, they immediately began to improve and YUMA MESA augment their drainage system. Additional drain­ Only a small acreage was irrigated on Yuma Mesa age wells were drilled near the foot of the mesa prior to 1923. Then about 650 acres, an increase of escarpment to control the rise of water levels in more than 400 acres over that irrigated in 1922, was that area. As a result of this improvement program, irrigated by lifting Colorado River water at the very little, if any, land in the valley was lost to B-lift pumping plant (fig. 2) and distributing it to agriculture because of waterlogging. Several inves­ land east of the plant. This development, known as tigations (p. H16) resulted from the development of the Yuma Auxiliary Project (fig. 2), was authorized the Yuma Mesa Division of the Gila Project (fig. by Congress in 1917. Records of the acreage irri­ 2). Most of the studies attempted to determine the gated and the amount of water diverted under this extent of the adverse effect that the mesa develop­ project are shown in table 1. The B-lift pumping ment had on the valley lands adjacent to the mesa. TABLE 1. Irrigated acreage and water diverted to Complete agreement as to the extent of the effects Yuma, Mesa 1 has not yet been reached. [Diversions in thousands of acre-feet] It is generally agreed that two-thirds to three-

Yuma Yuma Yuma Mesa fourths of the total of more than 5 million acre-feet Auxiliary Auxiliary division of Total Project Project Gila Project of water imported for irrigation of mesa land from Vo1 c ir eai Diver- Diver- Acres Diver­ Acres Diver­ 1922 through 1966 either went into ground-water Acres sions Acres sions sions sions storage to build a widespread ground-water mound 1922 __ 220 1 1943 ___ 1,600 20 200 1 1,800 21 1923 __ 660 7 1944 __ 1,500 17 1,000 15 2,500 32 or induced ground-water movement in the valley 1924 __ 640 5 1945 __ 1,550 20 5,100 55 6,650 75 lands west and north of the mesa. The distribution 1925 540 5 1946 __ 2,100 25 5,500 109 7,600 134 1926 720 3 1947 __ 1,950 33 5,900 118 7,850 151 of unused irrigation water among these three cate­ 1927 880 4 1948 __ 2,050 34 6,300 124 8,350 158 1928 _ _ 1,040 6 1949 __ 2,100 33 6,300 99 8,400 132 gories is also controversial. 1929 _ 1,160 7 1950 __ 2,150 31 7,100 104 9,250 135 1930 __ 1,190 9 1951 __ 2,150 32 8,200 138 10,350 170 OTHER AREAS 1931 __ 1,240 8 1952 __ 2,250 33 10,400 176 12,650 209 1932 _ 1,260 8 1953 __ 2,100 32 14,100 195 16,200 227 The other principal areas where the hydrologic 1933 1,240 9 1954 __ 2,350 37 14,200 235 16,550 272 1934 1,210 10 1955 __ 2,500 35 14,600 214 17,100 249 regimen has changed as a result of development are 1935 ___ 1,220 10 1956 __ 2,600 37 13,500 196 16,100 233 1936 __ 1,210 11 1957 __ 2,850 35 14,700 187 17,550 222 the lands of the Reservation Division, the North 1937 __ 1,240 12 1958 __ 2,900 37 14,200 208 17,100 245 1938 __ 1,260 13 1959 __ 2,950 41 17,200 230 20,150 271 Gila Valley Unit of the Yuma Project, and the South 1939 __ 1,270 13 1960 __ 2,950 42 16,900 253 19,850 295 1940 __ 1,250 14 1961 __ 3,100 42 16,000 248 19,100 290 Gila Valley Unit of the Gila Project (fig. 2). 1941 __ 1,250 14 1962 __ 3,150 45 16,300 282 19,450 327 1942 __ 1,400 15 1963 __ 3,150 42 16,600 275 19,750 317 The Reservation Division of the Yuma Project 1964 __ 3,200 40 17,100 259 20,300 299 1965 17,000 229 20,200 265 generally is that part of the Colorado River flood 1966 3^300 39 16,800 236 20,100 275 plain lying north of Yuma and on the right side of 1 Quantities (rounded) obtained from U.S. Bureau of Reclamation yearly project history reports. the river or on the right side of an abandoned chan­ nel of the river where the channel formed the west­ plant was abandoned in July 1953 when water be­ ern boundary of The Island (fig. 2). Since, the early came available to the project from an extension of 1900's the irrigated acreage has ranged from about the Yuma Mesa Division of the Gila Project. 5,000 to about 12,000 acres and has averaged about A substantial increase in irrigated acreage fol­ 9,000 acres. About 10,960 acres was irrigated in lowed the initial development work done under the 1961.

507-243 O - 74 - 2 H10 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA A system of drains, begun in 1912, keeps water to recharge of leakage from the newly completed levels far enough below the land surface to prevent Gila Gravity Main Canal and in part to lessened waterlogging. Leakage from the All-American outflow to Yuma Mesa because of the growing Canal, beginning about 1939, made necessary the ground-water mound beneath the mesa. construction of additional drains whose principal As the ground-water mound continued to grow, function was to remove this leakage and discharge the historic southward gradient in South Gila Valley it into the river. was gradually decreased until in the 1950's it was The North Gila Valley Unit, now a part of the reversed and became northward. Waterlogging of Yuma Mesa Division of the Gila Project, lies along lands near the mesa was widespread. In 1961 and the left side of the Colorado River north of its con­ 1962, nine large-capacity drainage wells were drilled fluence with the Gila River (fig. 2). This unit, too, near the foot of the mesa to reclaim the land that has had a long history of irrigation with Colorado had become waterlogged and to prevent further River water. Since 1955, it has been served from waterlogging as the result of inflow from the mound a turnout on the Gila Gravity Main Canal; before beneath Yuma Mesa. The wells were drilled to the that time water was diverted from Laguna Dam. base of the coarse gravel zone, which is about 200 About 6,080 acres was irrigated in 1961. feet below land surface. The system was successful Water levels rose because of irrigation, so new and was expanded in later years as the need for drains were constructed to keep the land from be­ more drainage became apparent. Also three supply coming waterlogged. Leakage from the Gila Gravity wells were drilled to depths of about 600 feet to Main Canal, which was completed in 1943, added to obtain water of better quality which was used to the drainage problems of the eastern part of the augment the surface supply. unit. South Gila Valley lies between Yuma and the MEXICALI VALLEY narrows of the Gila River near Dome (fig. 2). It is Irrigation with Colorado River water began in bounded on the north by the Colorado and Gila Mexicali Valley (fig. 2) about 1901. In 1915 about Rivers and on the south by the Yuma Mesa escarp­ 40,000 acres was irrigated out of a total valley area ment. The South Gila Valley Unit is part of the of some 700,000 acres. By 1925 about 200,000 acres Yuma Mesa Division of the Gila Project. Until 1965, was irrigated, but in 1932 the total irrigated area irrigation was dependent largely upon pumping was only 70,000 acres. From this low point the irri­ ground water. An exception was the authorization gated area increased to more than 330,000 acres in under the Warren Act of 1947 to divert surface 1949, and to about 540,000 acres in 1955. water from the Gila Gravity Main Canal onto about Realizing that this amount of land would require 850 acres adjoining the canal. water in excess of the 1.5 million acre-feet of Colo­ The first irrigation well in the valley was drilled rado River water guaranteed to Mexico annually in 1915. By 1925 about 1,000 acres was being irri­ under the treaty of February 3, 1944, the Mexican gated with ground water; by 1943 the acreage had Government in late 1955 authorized the drilling of increased to about 4,500, and by 1948, to almost 281 deep wells for augmenting the surface-water 9,000 acres. The irrigated acreage increased at a supply. In 1957 the Government authorized the slower rate through the fifties and the first half of drilling of an additional 100 irrigation wells. These the sixties, In 1955, 9,700 acres reportedly was irri­ wells were in addition to some 230 privately owned gated with pumped water. irrigation wells which had been drilled by that time. In 1965, surface water from the Colorado River Since 1957, the total number of pumped wells has became available to all the unit. Drainage wells been limited to 495 upon recommendation of the were installed at the same time to keep water levels Ministry of Hydraulic Resources. Notwithstanding from rising to the point where the agricultural lands the increased pumping for irrigation, the total acre­ would become waterlogged. A substantial quantity age irrigated was reduced in the early 1960's from of ground water continued to be pumped for irri­ the 540,000 acres irrigated in 1955 to about 415,000 gation. acres. In contrast to all the other areas, ground-water The early history of pumping for irrigation is not levels in the developed part of South Gila Valley well documented. Most of the wells were drilled by declined from the levels of the early 1920's, which United States interests to furnish a supplemental probably represented natural levels, to the levels of supply to lands normally irrigated with Colorado 1946 and 1947, which were 10-15 feet lower. About River water. As early as 1934 a tract of 800 acres 1947, levels began to rise, probably owing in part near Algodones (fig. 2), at the northeast corner of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Hll Mexicali Valley, was receiving a supplemental sup­ an average annual diversion rate of 5.9 feet (5.9 ply of ground water. acre-ft per acre) for surface water. Paredes (1963) The history of irrigation pumping can be inferred further estimated that land designated as being irri­ from records of well completions. Of more than 140 gated principally by water pumped from private logs of private wells drilled in Mexicali Valley by wells averaged about 60,000 acres, and that land United States drilling firms (made available to the designated as being irrigated principally by water U.S. Geological Survey by Frank E. Leidendeker of pumped from Government wells averaged about Yuma), only the logs of three large-capacity irriga­ 100,000 acres. Based on the average total pumpage tion wells showed drilling dates prior to 1950; all for each year of the period, the average rate at the other logs showed drilling dates from 1950 to which pumped water was diverted was 5.3 feet. The 1957, inclusive, the latter being the year when the average rate of diversion to all the irrigated land well-limiting decree was enacted by the Mexican (415,000 acres) was 5.6 feet per year for the years Government. Because these logs represent about 1961 to 1963, inclusive. half the privately owned irrigation wells in Mexicali In 1964, approximately 49,000 acres were irri­ Valley, the completion rate of these wells probably gated with water pumped from private wells, and is indicative of the completion rate of all the pri­ 107,000 acres with water from Government wells; vately owned irrigation wells. in 1965, figures for these same categories are 54,000 If this is true, and if it is further assumed that and 100,000 acres, respectively (Eduardo Arguelles pumpage was proportional to the number of wells and Eduardo Paredes, written commun., 1966). drilled, then from 1930 (the first year of record of The figures for 1964 and 1965 indicate an average a large-capacity irrigation well, drilled by Mr. Lei- annual rate of pumpage of 4.7 feet from private dendeker's firm) until 1950 the annual pumpage wells and 6.7 feet from Government wells. A similar for irrigation was small relative to the pumpage lesser rate of pumpage from private wells is .indi­ from private wells in 1957 probably ranging from cated by figures furnished by Paredes (1963) ; his a few thousand acre-feet in 1930 to a few tens of data suggest that pumpage from private wells in thousands of acre-feet a year by 1950. From 1950 the 3-year period ending December 1963 averaged to 1956 the pumpage probably increased at an between 3 and 3^ feet annually and that pumpage annual rate of about 25,000 acre-feet to about from Government wells averaged more than 6*72 200,000 acre-feet annually by 1956. With the begin­ feet annually. ning of pumping from Government wells in 1956, The reason for these apparent differences in with­ the total pumpage increased to about 300,000 acre- drawal rates is not known. Part of the difference feet annually by the end of 1956. With the installa­ may be due to the fact that a larger percentage of tion of additional Government wells, the pumpage the pumpage from private wells is basically a sup­ more than doubled from 1956 to 1957, and thereafter plemental supply than is the pumpage from Govern­ continued to increase, so that by 1965 the pumpage ment wells. Part of the difference also may be due amounted to 940,000 acre-feet. (See table below.) to pumping some water from Government wells into Pumpage (1,000 acre-feet) canals and transferring it to other areas to supple­ year Private Government All wells ment supplies on land that is designated as being wells wells irrigated principally with surface water. 1956 _ 200 100 300 1957 _ __ . ^80 M55 635 OBJECTIVES OF PRESENT INVESTIGATION AND 1958 ______X 250 ^10 560 1959 __ _ . *175 M60 635 SCOPE OF REPORT 1960 _ _ _ _ . '230 M70 700 1961 __ X 185 '680 865 This report is one of a series of chapters of Geo­ 1962 __ _ . 845 logical Survey Professional Paper 486, on the water 1963 __ _ _ . 845 1964 _. _ _ . 225 710 935 resources of the lower Colorado River-Salton Sea 1965 _ _ . 255 685 940 area. The broad objectives of the study of the Yuma 1 Figure adjusted on basis of ratios of earlier figures of total pumpage area were to (1) define the geology sufficiently to furnished by Mexican Government in 1962 to figures for total pumpage furnished by Mexican Government in 1966. delineate the ground-water reservoir or aquifer sys­ According to Paredes (1963) land irrigated prin­ tem, (2) determine the sources of the ground water cipally with Colorado River water averaged about and the relations between ground water and surface 256,000 acres during the period 1961 to 1963, in­ water, (3) define the hydrologic characteristics clusive; much of the 1.5 million acre-feet per year (transmissivity and storage coefficient) of the aqui­ of surface water guaranteed to Mexico under the fer system, (4) determine the movement of ground 1944 treaty was applied to this acreage. This implies water in different parts of the area, (5) calculate H12 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA ground-water budgets for both past and present included detailed coverage of the north-central part conditions, and (6) describe the chemical quality of the area: the Laguna Mountains, southeastern of the ground water and relate variations in chemi­ Chocolate Mountains, northern Gila Mountains, cal quality to sources of recharge and to processes southeastern Cargo Muchacho Mountains, and inter­ of chemical change. vening piedmont, mesa, and valley areas. Some of The report is divided into two principal sections: this geology is shown on the geologic map of the The first section describes the geology, with empha­ Laguna Dam lyz-mmute quadrangle (Olmsted, sis on the younger, water-bearing rocks and de­ 1972). The Cenozoic geology of the northwestern posits; the second section describes the various Gila Mountains and adjacent piedmont area was aspects of the ground-water hydrology enumerated also studied in detail by F. L. Doyle in 1963. above. The geology is described in somewhat greater The remainder of the area was covered by a geo­ detail than usual for a report of this type, because logic reconnaissance, relying heavily on photogeo- relatively little previous detailed geologic investiga­ logic techniques, with field checks along variously tion had been done in the area. Basic data consisting spaced traverses, mostly by vehicle. Reconnaissance of well records, well logs, and chemical analyses of of the southeastern part of the area was done chiefly ground water, and detailed descriptions of several by F. J. Frank; that of the northern part, by F. H. pumping tests and of soil-moisture measurements, Olmsted. are given in five appendixes at the end of the report. GEOPHYSICAL EXPLORATION The investigation, which was under the direction Geophysical surveys were made beginning in 1963 of C. C. McDonald, project hydrologist, was started and continuing into 1967 to obtain subsurface in­ in 1961 by G. E. Hendrickson and carried on from formation in support of the geohydrologic investiga­ 1962 to 1968 by the present writers. Other members tion. The work, which was done by the Regional of the Geological Survey who assisted materially in Geophysics Branch of the U.S. Geological Survey the investigation were F. J. Frank, G. R. Vaughan, under the direction of D. R. Mabey, included: (1) R. H. Westphal, and F. L. Doyle. Geophysical work a gravity survey of about 900 square miles (most of was done by the Regional Geophysics Branch of the the area shown on plates 3 and 9), (2) an aeromag- Survey, under the direction of D. R. Mabey. Assist­ netic survey of an area of about 300 square miles ance in well logging, sample analysis, and shallow in Yuma Valley and western Yuma Mesa, (3) nine test drilling was provided by the Hydrologic Labora­ seismic-refraction profiles in the northern part of tory and the Ground-Water Equipment Pool of the the area, and (4) 14 resistivity profiles and lines of Survey, both headquartered at Denver, Colo. electrical soundings at several places throughout the area. In addition, four seismic-reflection profiles METHODS OF INVESTIGATION were made by a commercial firm under contract to The study of the geohydrology of the Yuma area the U.S. Bureau of Reclamation. included geologic mapping, extensive geophysical The gravity and magnetic surveys furnished valu­ exploration and test drilling by the U.S. Geological able information about the gross distribution and Survey and the U.S. Bureau of Reclamation, inven­ thickness of the Cenozoic sediments forming the tory of existing wells and well records, quantitative ground-water reservoir. The seismic and resistivity determinations of aquifer characteristics, calcula­ surveys yielded more detailed information on the tions of ground-water budgets, and determinations thickness and structure of sediments along local of the chemical character and temperature of water profiles. Many of the interpretations of the geology in many wells. Major emphasis was placed on study in this report are based in part on the geophysical of the Cenozoic deposits, which contain virtually all data. the ground water of usable quality, and on the TEST DRILLING delineation of geologic structures that affect the Test drilling by the U.S. Geological Survey and movement of ground water. Toward the end of the the U.S. Bureau of Reclamation provided the pri­ investigation, an electrical analog model was con­ mary basis for the interpretation of the subsurface structed by the Geological Survey which incorpo­ geology and hydrology. For shallow-depth informa­ rated an idealized geohydrologic framework based tion, 134 test holes were bored with a truck- on the results of the several types of studies. The mounted power auger to depths ranging from 4 feet various methods of investigation are summarized in to more than 200 feet (fig. 3). Most of these test the following paragraphs. holes were completed as observation wells with 114- GEOLOGIC MAPPING inch or IVa-inch pipes fitted with well points. Simi­ The geologic mapping, done chiefly in 1962-65, lar shallow wells were installed in the 1940's and GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA HIS

FIGURE 3. Boring a test well with a power auger, ZVz miles south of Somerton, Ariz. later by the U.S. Bureau of Reclamation, particu­ of these wells range from 64 to 1,427 feet. All these larly on Yuma Mesa, where few other well data were test wells were drilled by either the percussion available. In addition, more than 100 wells were (cable-tool) method or the mud-rotary method; drill installed by the Yuma County Water Users' Associa­ cuttings and a few cores were collected for study; tion in the 1950's by jetting pipes into the upper and most of the wells were logged by various wire- part of the coarse-gravel zone in Yuma Valley. line-logging methods. Ten of the U.S. Geological Deeper test drilling was done by private contrac­ Survey test wells and several of the U.S. Bureau of tors for the U.S. Geological Survey (fig. 4) and the Reclamation test wells were test pumped for infor­ U.S. Bureau of Reclamation and by Bureau equip­ mation about transmissivity of the materials and ment. Twelve U.S. Geological Survey test wells were chemical quality and temperature of the water. drilled to depths ranging from 328 to 2,946 feet; STUDIES OF FORMATION SAMPLES one private well and one U.S. Bureau of Reclama­ In addition to megascopic identification of well tion test well were deepened for additional informa­ cuttings made during drilling, several kinds of tion. The U.S. Bureau of Reclamation drilled or had laboratory analyses of formation samples were drilled about 70 test wells from 1957 to 1967. Depths made. Heavy-mineral analyses of alluvial sands and H14 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

FIGURE 4. Drilling of test well LCRP 26 with mud-rotary equipment 1% miles west of Winterhaven, Calif.

X-ray diffraction analyses of clays were made by and spontaneous potential), temperature, fluid- the Hydrologic Laboratory of the Geological Survey resistivity, caliper, contact-caliper (microresistivity- in Denver, Colo. Grain-size analyses were made of caliper), dip, and sonic (acoustic-velocity). Logging samples from several of its test wells by the Bureau was done by three commercial logging companies of Reclamation. Pebble counts and studies of gen­ and by the U.S. Geological Survey and the U.S. eral lithology of alluvial sands and gravels and a Bureau of Reclamation. few petrographic studies of older rocks were made INVENTORY OF EXISTING WELLS AND by the Geological Survey in Yuma. Also, cuttings WELL RECORDS from several oil-test wells were examined at the The bulk of the geologic and hydrologic informa­ Arizona Bureau of Mines office in Tucson, Ariz., by tion about the upper water-yielding zones was pro­ F. J. Frank and F. H. Olmsted. Paleontological vided by records of existing water wells, test wells, studies of cuttings from marine deposits were made and observation wells. These data included descrip­ by Mrs. P. B. Smith, Branch of Paleontology and tions of the wells and their locations, logs, produc­ Stratigraphy of the U.S. Geological Survey, in Menlo tion figures (pumping rates and drawdowns), Park, Calif. chemical quality and temperature of the water, and WIRELINE LOGGING water-level records. Many of these data were ob­ Wireline logs were used extensively to supplement tained from files of the U.S. Bureau of Reclamation, and refine the information obtained from drillers' irrigation districts, and other government agencies; logs, geologists' logs, and sample studies. Logs were other information was obtained from drillers and made of most of the test wells and also of as many private individuals during a field canvass of the private wells and drainage wells as possible. The area. All wells except for a few that had been logs included the following types: Gamma-ray destroyed were inventoried in the field and their (natural gamma radiation), electric (resistivity locations plotted on the latest Geological Survey GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H15 topographic maps. The information thus obtained pumping, or pumping by turbine; and from unused is summarized in appendix A, tables 16-20; the wells and observation wells by airlift pumping, bail­ locations of the wells are shown on plates 13-17. ing, or sampling with a thief sampler. Many of the wells were sampled several times in order to deter­ QUANTITATIVE DETERMINATIONS OF AQUIFER CHARACTERISTICS mine chemical changes occurring with the passage Transmissivity at specific sites was computed on of time. the basis of results of short-term pumping tests of Most of the chemical analyses listed in the present practically all the large-capacity wells in the area. report (appendix C) made in a field laboratory at The tests of private wells commonly were limited Yuma, using rapid analytical methods. A few analy­ to observing rates of change of water level during ses were made in the U.S. Geological Survey's per­ and after pumping periods and to determining spe­ manent water-quality laboratory at Albuquerque, cific capacity (yield per unit of waterlevel draw­ N. Mex., using customary procedures. Most of the down). Collection of data was limited to the pumped earlier analyses were obtained from the files or well because satisfactory observation wells were not publications of the U.S. Geological Survey, the U.S. available. Observation wells were utilized, however, Bureau of Reclamation, other Federal or State for a few of the large drainage wells owned by the agencies, or individuals. Some of these analyses U.S. Bureau of Reclamation or the Yuma County were recomputed from originally reported values in Water Users' Association. order to agree with the format of the U.S. Geological Step-drawdown and recovery tests were made for Survey analyses. all the U.S. Geological Survey test wells that were The analytical data were supplemented by field pumped, for several U.S. Bureau of Reclamation observations made with a conductivity meter and drainage wells, and for a few newly drilled private by electric logs of test holes. irrigation wells. In addition to the tests made dur­ MEASUREMENTS OF GROUND-WATER ing the present investigation, previous pumping TEMPERATURE tests by others were utilized. Especially helpful were Temperature of ground water was among the data pumping tests made by the U.S. Bureau of Reclama­ collected in the routine inventory of well informa­ tion and by the Yuma County Water Users' Associa­ tion. After the study was underway, it became ap­ tion (Jacob, 1960). Where pumping-test data were parent that water temperatures furnished useful lacking, transmissivity was computed on the basis evidence on the sources and movement of the ground of specific capacity or of lithologic logs. water and the nature of the geologic framework Storage coefficients were determined on the basis through which it moves. Accordingly, a special study of soil moisture as indicated by a neutron probe. was made of vertical, and particularly areal, varia­ Soil-moisture profiles which commonly included both tions in temperature, using thermistors as well as the zone of aeration and the zone of saturation were maximum thermometers and a standard mercury obtained at some 30 sites. None of the pumping tests thermometer. during the present investigation provided useful data for computing long-term storage coefficients. ANALOG-MODEL STUDIES As with transmissivity values, the work of earlier Two electrical analog models of the hydrologic investigators was utilized in estimating storage co­ system of the delta region (including both the Yuma efficients. Studies by Jacob (1960) were used as a area and the part of Mexicali Valley where much basis for estimating storage coefficients under arte­ ground water is pumped for irrigation) were con­ sian conditions; these studies were also the basis for structed. The first model, begun in 1964, was a rela­ estimating values for vertical hydraulic conductiv­ tively simple simulation of the hydrologic system. ity and leakage (leakance as defined by Jacob). In 1966 it was replaced by a more complex model CHEMICAL ANALYSES OF GROUND-WATER which took into account the barrier effect of a fault SAMPLES (Algodones fault) that was not recognized as a Variations in the chemical quality of the ground barrier to ground-water movement when the first water were determined primarily by comparisons of model was built. The second model not only repro­ analyses of samples obtained during the present in­ duces in generalized form the present and past vestigation; only a few earlier analyses assembled hydrologic conditions but can be used to predict fu­ from other sources were used. Samples of water ture changes in directions and rates of ground-water were collected from existing wells equipped with movement and changes in water level under various turbine pumps; from test wells by bailing, airlift assumed schemes of ground-water development. H16 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

EARLIER INVESTIGATIONS basin (U.S. Bureau Reclamation, 1953), and the GEOLOGIC STUDIES report on the Lower Colorado River water salvage Previous geologic studies of the Yuma area con­ and phreatophyte control (U.S. Bureau Reclama­ sisted primarily of regional geologic reconnaissances tion, 1963) were especially helpful in the present by Wilson (1933, 1960) in Arizona and by Morton study. (1962) in California; more detailed studies of In 1956, the U.S. Geological Survey, as a result smaller areas such as the study of the Cargo Mu- of a recommendation from the Assistant Commis­ chacho Mountains by Henshaw (1942), or of special sioner of Reclamation to the Secretary of the In­ problems such as the origin of the "Algodones terior, reviewed the problem of high water levels in Dunes" by Norris and Norris (1961) and McCoy, Yuma Valley and studied the need for additional Nokleberg, and Norris (1967); and geophysical information to define and control the problem. The studies such as those by Biehler, Kovach, and Alien results of that study were reported by R. H. Brown (1964) in the Salton Trough, and of private oil and others (1956). companies (unpufc. data) in Yuma Valley and adja­ As a result of the preceding study, in September cent parts of Yuma Mesa in connection with wildcat 1956 the Secretary of the Interior entered into a drilling in search for oil or gas. The earlier geologic contract with the consulting firm of Tipton and study having the most direct application to ground- Kalmbach, Inc., and C. E. Jacob, consultant, which water geology, or geohydrology, is that by R. H. called for an investigation of the ground-water and Brown and others (1956). In a sense, the present drainage conditions in the Yuma Valley and a study report updates and expands the work of Brown and of the relation between these conditions and the others (1956), although some of their geologic inter­ irrigation on Yuma Mesa. The report of this inves­ pretations are modified substantially herein. tigation (Tipton and Kalmbach, Inc., and Jacob, In addition to the reports and data cited above, 1956) was the first attempt to estimate quantita- many papers have dealt with the general region that ively the underground flow of water from the Yuma includes the Yuma area, or have discussed problems Mesa to the adjacent flood plains. that relate to certain aspects of the local geology. In 1960, C. E. Jacob, consultant, completed a Among these are papers describing the geology and study for the Yuma County Water Users' Associa­ geomorphic features of the Salton Trough by J. S. tion (Jacob, 1960) for the purpose of obtaining a Brown (1920, 1923), Kniffen (1932), MacDougal more accurate inventory of water use on Yuma Mesa and others (1914) (a particularly exhaustive treat­ and in Yuma Valley and to better evaluate aquifer ment), McKee (1939), and Sykes (1914, 1937). characteristics. Reports describing the sediments of the Colorado In 1966, C. E. Jacob, at the request of the Com­ River delta include those by Merriam (1965), missioner, United States Section, International Merriam and Bandy (1965), and van Andel (1964). Boundary and Water Commission, made additional The geologic history of the lower Colorado River studies of the ground-water regimen of the Yuma has long been a subject of much interest and specu­ area, which included estimates of the flow of ground lation. A few of the papers discussing this problem water across international boundaries (Jacob, 1966). are those by Longwell (1946, 1954), Lovejoy ACKNOWLEDGMENTS (1963b), Cooley and Davidson (1963), and McKee, Many agencies, groups, and individuals provided Hamblin, and Damon (1968). substantial assistance to the U.S. Geological Survey Other papers describing previous work are cited in the present investigation. The U.S. Bureau of in the section on geology and are listed in the bibli­ Reclamation, Yuma Projects Office, furnished in­ ography. formation from its files, did exploratory drilling, HYDROLOGIC STUDIES contributed financial assistance toward the construc­ Most of the hydrologic studies have been made for tion of an electrical analog model, financed two or by agencies concerned with the management or reflection seismic surveys, and worked closely with use of water. The U.S. Bureau of Reclamation not the writers in all phases of the investigation. Both only has collected a large amount of hydrologic data the United States Section and the Mexican Section during the years but has made many hydrologic of the International Boundary and Water Commis­ studies to appraise the results of its management sion gave freely of information from their files and practices and the probable results of proposed of their general knowledge of the area. The United changes in these practices. The U.S. Bureau of States Section also provided funds to assist in the Reclamation report by Sweet (1952), the report on construction of the analog model. The Yuma County on the water supply of the Lower Colorado River Water Users' Association furnished valuable infor- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H17

mation from its files, such as well logs and water- In the California system, the wells are assigned level records, and the results of hydrologic studies. numbers according to their locations in the land Several water-well drilling companies and drillers, survey based on the San Bernardino base line and notably Hamilton and Hood, Arizona Machine and meridian. A modification of the system used by the Welding Works, Frank H. Leidendeker, and L. P. California Department of Water Resources and by Cromer, provided well logs and other pertinent in­ the California District of the Water Resources Divi­ formation. Many farmers and other landowners gen­ sion of the U.S. Geological Survey is employed in erously permitted access to their lands and wells, which the 40-acre tracts are further subdivided into furnished various kinds of information, and cooper­ 10-acre and 21^-acre tracts. For example, the sec­ ated in the scheduling of pumping tests. Information ond well inventoried in the NE^SW^SW^NE^ such as pumping-test data, well logs, chemical data, sec. 29, T. 16 S., R. 22 E., is given the number and geophysical data was made available from pri­ 16S/22E-29Gca2. The part of the well number pre­ vate consultants, including C. E. Jacob and Asso­ ceding the slash (16S) indicates the township (T. ciates, General Atomic Division of General Dynamics 16 S.); the number following the slash indicates Corp., S. F. Turner and Associates, and Water De­ the range (R. 22 E.) ; the digits following the en velopment Corp. Radiometric dating of several rock dash indicate the section (sec. 29); the letter (G) samples was done by the Geochemistry and Petrol­ following the section number indicates the 40-acre ogy Branch of the U.S. Geological Survey; Geochron tract within the section (SW*4NE^4); and the Laboratories, Inc., of Cambridge, Mass.; and the lowercase letters (ca) indicate the 10-acre and 21/k- Geochronology Laboratories of the University of acre tracts (NE^SW^) according to a subdivision Arizona. similar to that used in the Arizona system (fig. 5, graph B). Within each 2V2-acre tract, the wells are WELL-NUMBERING SYSTEMS numbered consecutively starting with 1. The well-numbering systems used in this report A small area in Arizona west of Yuma and south are based on the rectangular system of land sub­ of the Colorado River is subdivided according to the division used by the U.S. Bureau of Land Manage­ California system. Also, in The Island area north ment. Two systems are used because part of the of Yuma, the California system is used in part of Yuma area is in California and part is in Arizona. what is now Arizona, and the Arizona system is In the Arizona system, the wells are assigned used in part of what is now California. In all these numbers according to their locations in the land areas, State boundaries have been changed since survey based on the Gila and Salt River base line they were originally established. and meridian which divide the State into four quad­ In addition to the U.S. land-net well-location sys­ rants. For assignment of well numbers these quad­ tems just described, the location of each well is rants are designated counterclockwise by the capital described according to a system of grid coordinates letters A, B, C, and D; the letter A being the used by the U.S. Bureau of Reclamation. The Bureau northeast quadrant. All wells in the Yuma area of Reclamation coordinates are based on a zero are in the southwest quadrant the C quadrant. point located at the Southern Pacific Co. railroad For example, the first well inventoried in the bridge across the Colorado River at Yuma. The grid NE^NE^SW^ sec. 35, T. 8 S., R. 22 W., is given utilizes section lines of the U.S. Bureau of Land the number (C-8-22)35caal. The part of the well Management net as mileage increments north or number in parentheses indicates the township and south and east or west of the zero point. For exam­ range in the southwest quadrant (T. 8 S., R. 22 W.), ple, well (C-8-22)35caal has the coordinates 2V2S- the digits following the parentheses indicate the 7V2E, which indicate that the well is half a mile section (sec. 35), and the lowercase letters indicate south of the section line approximately 2 miles south the location within the section (fig. 5, graph A). of the zero point and half a mile east of the section The first letter (c) indicates the 160-acre tract line approximately 7 miles east of the zero point (SW14 sec.), the second (a) the 40-acre tract (fig. 5). Coordinates for each well are given to the (NE^SWi/4 sec.), and the third (a) the 10-acre nearest one-sixteenth of a mile, as measured on tract (NEi/iNEi/iSW^ sec.). These tracts' are the 1:24,000-scale 71/^-minute series quadrangles designated counterclockwise beginning in the north­ of the U.S. Geological Survey published from 1955 east quarter (fig. 5, graph A). Where more than to 1965. In some places these coordinates differ one well is inventoried within a 10-acre tract, the slightly from those assigned earlier by the U.S. wells are distinguished by adding consecutive num­ Bureau of Reclamation using approximate locations bers beginning with 1 after the lowercase letters. shown on older maps. HIS WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Coordinates according 7E 8E to U.S. Bureau of 2S -]2S Reclamation grid system

c j d h -b- b I a I b

Well: (C-8-22) 35caal Coordinates: 2 1/2S.-7 1/2E.

Well'

-c- --d -C -d

3S 3S 7E T.8S., R. 22 W., sec. 35 8E A. Arizona well-numbering system Coordinates according to U.S. , Bureau of 4W 3W Reclamation grid IN i system

D C B A

,____^- - _ _

/ \ E F H Well* ------r 40-acre tract G

I/ M i J Well: 16S/22E-29 Coordinates: 05/8 N.-3 3/8W. _ - -r N P Q R

4W T. 16., R. 22 E., sec. 29 3W B. California well-numbering system

FIGURE 5. Subdivision of land-net sections for assignment of well numbers and locations of wells by grid coordinates. GEOLOGY end of the Colorado River basin, within the United GEOMORPHOLOGY States. The northeastern part of the area lies within REGIONAL SETTING the Sonoran Desert section, the southwestern part The Yuma area includes the upstream part of the within the Salton Trough section of the Basin and delta of the Colorado River, near the downstream Range province, according to the widely adopted GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H19 physiographic (geomorphic) classification of Fen- "plains," and still another, "desert." This local usage neman (1931, 1946). (See fig. 1.) is carried on in the assignment of informal names The Sonoran Desert east of Yuma is character­ to some of the subareas; the terms have no geo­ ized by generally elongate, low, rugged mountains morphic significance. Several subareas beyond the separated by much more extensive desert plains. limits of the principal geohydrologic study were not Many of the mountains trend about north-northwest investigated in detail, and their landforms are (N. 20°-40° W.). The Colorado River flows across described only briefly. the region in an alternating series of narrow valleys or canyons through the mountains and much broader MOUNTAINS AND HILLS alluvial valleys through the desert plains. The Gila The mountains and hills are composed of the River, which is the principal southern tributary of older, more consolidated rocks of the region rocks the Colorado River, flows generally west-southwest of Tertiary and pre-Tertiary age. The higher, more across the mountains and desert plains of the rugged parts of the ranges consist of dense pre- Sonoran Desert to join the Colorado just east of Tertiary crystalline rocks, or, in places, of hard Yuma. volcanic rocks of Tertiary age. The lower, more The southernmost valley in the Yuma area, Yuma rounded hills are exposures of less consolidated vol­ Valley, merges with Mexicali Valley on the west canic and nonmarine sedimentary rocks of Tertiary and southwest, the latter broadens southwestward age. to form the present delta plain of the Colorado Where the mountains are composed of hard crys­ River. The delta plain, and some of the low-lying talline rocks, the topographic contrast between the desert plains to the east, lie within the Salton mountains and the adjacent desert plains and river Trough, a northwestward lowland extension of the valleys generally is abrupt. Slopes of the hard-rock Gulf of California (fig. 1). The lowest part of the exposures are governed by joints and other physical trough is occupied by Salton Sea, a large saline characteristics of the rocks and are ordinarily much lake, the surface of which was about 232 feet below steeper than the slopes in the adjacent unconsoli- mean sea level in 1968. The northeast boundary of dated deposits of the plains and valleys. Slopes in the Salton Trough section, where it adjoins the exposures of metamorphic and plutonic rocks aver­ Sonoran Desert section, is rather vague geomorphic- age about 1,000 feet per mile (11°) and locally ally but may be considered structurally as being exceed 4,000 feet per mile (37°). Geophysical data formed by the Algodones fault, the major fault of indicate that many buried surfaces of the crystalline the San Andreas system in the Yuma area. The rocks are equally steep. Some exposures of hard Salton Trough is bordered on the southwest by the volcanic rocks lava flows and beds of welded Lower California (or Lower Californian) province tuff are even more rugged than those of the crys­ (Fenneman, 1931, 1946). talline rocks; nearly vertical cliffs several hundred feet in height occur at several places in the volcanic CLASSIFICATION OF LANDFORMS rocks of the Chocolate and . Apart from the regional geomorphic classification In contrast, the exposures of slightly to moder­ of Fenneman (1931) just described, the landforms ately consolidated nonmarine sedimentary rocks and of the Yuma area are divided in this report into volcanic rocks of Tertiary age are dissected or seven major types: (1) mountains and hills, (2) dis­ rounded hills of comparatively gentle slope. Instead sected old river deposits, (3) dissected piedmont of the sharp break in slope characteristic of the slopes, (4) undissected piedmont slopes, (5) river margins of the hard-volcanic-rock and crystalline- terraces and mesas, (6) sand dunes, and (7) river rock masses, a gradual transition from foothills to valleys. Each landform type occurs in several sub- piedmont plains occurs where semiconsolidated non- areas shown on the geomorphic map (fig. 6) ; a few marine sedimentary rocks or soft volcanic rocks subareas include more than one type of landform. (tuff and ash) border unconsolidated alluvial de­ Several subareas have no formal geographic desig­ posits. Local relief in exposures of Tertiary sedi­ nation and are given informal names from some mentary rocks or soft volcanic rocks rarely exceeds geographic feature; these informal names are desig­ 400 feet, whereas that in exposures of crystalline nated by quotation marks. The term "mesa" has rocks or hard volanic rocks commonly is 1,000 feet been given to some of the terraces, and to other or more. surfaces some terraced, some not which stand a The principal chain of mountains in the Yuma few feet to several tens of feet above adjacent area comprises the Chocolate, Laguna, Gila, Butler, valleys and plains. Other subareas have been called and (fig. 6). This chain H20 WATER EESOUECES OF LOWEE COLOEADO EIVEE-SALTON SEA AEEA *L4°00' 45' 30' 15'

EXPLANATION 8^^t^^-^^A River valleys Dissected piedmont slopes fe:vV;:-;:^^^:-:-v^::?v->^.^%%: ^^ : ^ ^ ^ : « ^^: ^c. :. .' ^§|;;:'--!^:;--.v.^M^v;y Sand dunes Dissected old river deposits

Eiver terraces and mesas Mountains and hills

Jndissected piedmont slopes 32°15

FIGURE 6. Geomorphic map of the Yuma area. trends about N. 35° W. roughly parallel with sev­ the southeast end of the mountains, adjacent to eral other ranges in the Sonoran Desert farther Laguna and Imperial Dams. In some of the lower east and forms the northeastern bedrock border of parts of the Chocolate Mountains, dissected hills the area of the main geohydrologic investigation. composed of semiconsolidated sedimentary or vol­ The Chocolate Mountains, structurally and topo­ canic rocks of Tertiary age merge on one side with graphically the most complex of the chain, are more rugged exposures of hard volcanic or crystal­ largely a series of southwestward-tilted fault blocks line rocks, and on the other side, with more gently of exposed Tertiary volcanic rocks. The higher dissected exposures of late Tertiary and Quaternary ridges, which reach altitudes of 1,500 feet in the alluvial deposits. southwest part, are capped by flows of basaltic ande- The Laguna Mountains occupy a roughly equidi- site or basalt (fig. 7) ; farther east, the lower ridges mensional area about 6 miles across lying between are of predominantly more silicic pyroclastic rocks. the Colorado and Gila Rivers. The rugged northern Exposures of pre-Tertiary crystalline rocks, not as and eastern parts of the mountains are underlain extensive as in most of the other mountains of the by pre-Tertiary crystalline rocks. The rest of the Yuma area, are relatively low and are chiefly near exposures are chiefly semiconsolidated, coarse- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H21

FIGURE 7. Westward view of a ridge in the southeastern Chocolate Mountains, Calif. The ridge on the skyline is composed of pre-Tertiary cry­ stalline rocks and Tertiary nonmarine conglomerate and breccia, capped by dark basaltic andesite or basalt. Surfaces in foreground and mid­ dle distance are underlain by piedmont gravel deposits of local origin. grained nonmarine sedimentary rocks of Tertiary of gravelly alluvium of local origin, which in turn age. Sugarloaf, a volcanic knob near the west mar­ are bordered by southwestward-sloping alluvial gin of the mountains about 2 miles south of Laguna terraces. Dam, rises to an altitude of 668 feet; the highest The Gila Mountains are fairly straight and point in the eastern exposures of crystalline rocks elongate, trend north-northwest, and are about 27 is the summit designated as Gila City, 1,080 feet miles long by 2-7 miles wide. Toward the south, the above sea level. mountains divide into two ridges about 5 miles The drainage pattern -of the Laguna Mountains apart; farther south, the eastern ridge becomes the is roughly radial. The northwestward-trending Tinajas Altas Mountains, and the western ridge ridges characteristic of the Chocolate Mountains to (Vopoki Ridge) becomes the Butler Mountains the northwest are absent. Along the southwest mar­ (fig. 6). gin of the Laguna Mountains, the dissected hills The Gila Mountains contain some of the most underlain by Tertiary nonmarine sedimentary rocks rugged topography in the Yuma area. Only at the are flanked by only slightly less dissected exposures north end, and in a small area west of Telegraph H22 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Pass, are there significant exposures of Tertiary northeast, they are also separated by substantial nonmarine sedimentary rocks with their character­ gaps in which the alluvial fill attains thicknesses istic smoothly dissected hilly outcrop forms; the ranging from 1,000 to more than 2,000 feet. Except bulk of the range consists of much steeper, more for the Cargo Muchacho Mountains, they are gen­ jagged exposures of pre-Tertiary crystalline rocks erally lower than the mountains to the northeast. (gneiss, schist, and granitic rocks). Local relief is The Cargo Muchacho Mountains are an irregular, greater than 2,000 feet in the southeastern part of deeply embayed mass about 10 miles long in a the mountains, which attain a maximum altitude of northwest direction by about 6 miles wide. Granitic 3,150 feet above sea level. The central and north­ rocks predominate, but there are sizable exposures western parts of the range are not as high; the of metamorphic rocks and associated dikes in the highest summits are about 2,700 feet in the central northern and western parts of the mountains. Sev­ part, south of Telegraph Pass, and 1,500-1,700 feet eral small hills, some of which are capped by basalt northwest of Telegraph Pass. or basaltic andesite, lie as much as 2 miles beyond The Butler Mountains consist of low ridges of the margins of the main mass. The terrain in the pre-Tertiary crystalline rock (granite). The granite main part of the mountains is rugged, like that in outcrops are crudely linear in plan, and oriented exposures of similar rocks elsewhere in the Yuma about N. 30°-50° W. They are nearly buried by area. Highest altitudes are 2,100-2,200 feet about rock waste (local alluvium) that forms the pied­ 1,200 feet above the desert plains at the foot of the mont slope along the southwest flank of the Tinajas mountains. The northeastern part is generally much Altas Mountains to the east (Davis Plain). The lower and less rugged than the rest of the moun­ ridges rise to a maximum of only 400 feet above the tains; the highest summits in that area are less plain, but their slopes are as steep as most of the than 1,200 feet above sea level and some of the slopes in the higher mountains to the north and intervening bedrock exposures are nearly reduced east. to pediments. The Tinajas Altas Mountains are separated from Two small hill masses 1 to 2 miles south of the the southeastern Gila Mountains by a low alluvium- Cargo Muchacho Mountains are named the Ogilby filled gap known as Cipriano Pass. The highest peak Hills from the former settlement of that name on has an altitude of 2,764 feet above sea level about the Southern Pacific Railroad about 2 miles west 1,700 feet above the adjacent desert plains. Except of the hills. The hills are composed of pre-Tertiary for Raven Butte, the mountains are composed en­ crystalline rocks, capped by basalt or basaltic ande­ tirely of buff-weathering, light-gray granite the site which forms extensive talus on the slopes. same as that in the Butler Mountains and the south­ Pilot Knob, so named because of its use as a land­ ern Gila Mountains. Raven Butte, near the north mark during early steamboat navigation on the end of the mountains on their east flank, is a double- lower Colorado River, is a low but rugged hill of crested mass of nearly black basalt or basaltic ande- pre-Tertiary crystalline rocks (chiefly gneiss) rising site, crudely pentagonal in plan, about 1 mile in to an altitude of nearly 900 feet 600-750 feet above diameter, and rising about 700 feet above the the adjacent valleys and desert plains. . "Yuma Hills" is the informal designation applied The Tinajas Altas Mountains derive their name, to a chain of low hills or knobs of pre-Tertiary and Spanish for High Tanks, from the natural tanks Tertiary rocks in and adjacent to Yuma. The Colo­ near the east base of the mountains. The tanks, rado River flows between the northernmost two which are plunge pools beneath usually dry water­ hills, which are exposures of granite fanglomerate falls or cascades, have provided water to wildlife, and breccia of Tertiary age (fig. 12). The remaining and also to men traveling the historic Camino del six outcrops to the south all are coarse-textured Diablo (Devils Road) into Mexico. porphyritic granite or quartz monzonite similar to Southwest of the mountain chain just described that occurring as detritus in the fanglomerate and is another, more crudely alined chain of mountains breccia. The outcrops of granite are about a mile and hills comprising the Cargo Muchacho Moun­ apart and are alined N. 20° W. roughly parallel tains, Ogilby Hills, Pilot Knob, "Yuma Hills," and with the Gila Mountains to the east. The two hills "Boundary Hills." The last two groups of hills are of fanglomerate are slightly east of the axis of this nearly buried by alluvium, and an intervening crys­ trend. All the hills are the summits of a nearly talline-rock mass beneath Yuma Mesa is completely buried ridge which is almost completely engulfed by buried. The hills and mountains in this chain not the alluvium of the Colorado and Gila Rivers. The only are less well alined than the mountains to the southernmost highest hill is about 320 feet above GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H23 sea level and 120 feet above Yuma Mesa; the north­ piedmont surfaces at the west base of the Gila ernmost granite outcrop, known as , Mountains, is the largest area of dissected old river rises to nearly 300 feet above sea level 160 feet deposits. The materials underlying "Upper Mesa" above South Gila Valley to the east and 100 feet are composed of older alluvium of the Colorado and above Yuma Mesa to the west. Gila Rivers and admixed alluvium of local origin. The seemingly anomalous present position of the Near the land surface at many places are reworked Colorado River between the northern two outcrops materials deposited by local runoff after heavy of Tertiary fanglomerate and breccia probably re­ storms and modified by wind erosion and deposition. sults from superposition from a higher level, per­ A poorly formed desert pavement is preserved on haps at a time when the flood plain was the present remnants of some of the older river-formed surfaces Yuma Mesa. At that time, the hills of Tertiary rock but is lacking in most of the mesa. Parts of the much have been buried or nearly so. The river pre­ mesa lie above intervening broad, shallow, stream- sumably exhumed these older rocks as it cut into cut depressions, which are mantled with thin de­ this old flood plain, then backfilled to its present posits of windblown sand and sheet-wash sand and level. At other times as the river cut down, it flowed gravel. north of its present course; young river deposits The general westward slope of the land surface is extend from the northernmost hill of Tertiary rocks interrupted by a northeast-facing escarpment 50-60 about 31/2 miles northward to the edge of the flood feet in height which traverses "Upper Mesa" from plain ("Bard Valley"). "Fortuna Dunes" on the southeast to the edge of The "Boundary Hills" consist of a northwest- Yuma Mesa on the northwest (pi. 1). Southwest of trending small chain of outcrops of pre-Tertiary the escarpment the slope of the dissected surface crystalline rock (iporphyritic granite or quartz mon- is about 40 feet per mile toward the west-south­ zonite) near the southerly international boundary. west somewhat steeper than the average slope of Like the "Yuma Hills," these low hills are the tops the land surface northeast of the escarpment, which of a nearly buried ridge projecting only about 100 is about 30 feet per mile. The drainage from the east feet above the adjacent desert plains. The northern­ is diverted toward the northwest along the foot of most and largest of the hills attains an altitude of the escarpment an obviously anomalous direction 529 feet above sea level just north of the interna­ for the mesa as a whole. This unique feature is the tional boundary; the other hills are in Mexico. trace of the Algodones fault, described in a later East of the area of principal investigation are section (p. H61), an important member of the well- the Middle and Muggins Mountains and the Wellton known San Andreas fault system. Hills. The Middle Mountains are underlain chiefly by "Proving Ground Dome," partly enclosed within volcanic rocks and are low, rising to a maximum of the southern part of "Middle Mountains Plain" in about 500 feet above the adjacent desert plains. The the northeastern part of the Yuma area, is a low Muggins Mountains, a notable exception to the nar­ dome-shaped hill, roughly ellipsoidal in plan, about row, elongate, north-northwest-trending ranges in 4!/2 miles long by 2 miles wide. The summit of the the southwest part of the Sonoran Desert (fig. 6), hill is 562 feet above sea level, about 100 feet above are underlain by pre-Tertiary crystalline rocks, hard "Middle Mountains Plain." "Proving Ground Dome" volcanic rocks (Tertiary?), and nonmarine sedi­ probably is primarily an erosional feature, a rem­ mentary rocks of Tertiary age. The Wellton Hills nant of once more extensive Colorado River allu­ are a small group of northwestward-trending ridges vium which filled the area to a level somewhat higher of gneiss several miles east of the Gila Mountains, than the present summit of the dome. (The altitude rising a maximum of 600 feet above the Lechu- and form of the dome may result in part from guilla Desert. warping, however.) The dome is similar in origin and form to classic desert domes (for example, see DISSECTED OLD RIVER DEPOSITS Sharp, 1957); but, unlike most desert domes, it is Somewhat dissected exposures of predominantly formed on unconsolidated sand, silt, and gravel, old river alluvium are represented by "Upper rather than on consolidated rocks. Desert pavement, Mesa," "Proving Ground Dome," and the central like that on adjacent "Middle Mountains Plain," is part of "Laguna Mesa" (fig. 6). The old river de­ absent; instead, a thin colluvium of pebbly sand and posits are at many places blanketed with thin re­ silt and eolian sand blankets most of the dome. worked deposits left by local ephemeral streams. "Laguna Mesa," which is south of "Proving The informally named "Upper Mesa," a generally Ground Dome," also includes dissected exposures of westward-sloping area between Yuma Mesa and the old river deposits. The mesa is a broad arch sloping H24 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA westward toward the Colorado River flood plain and nonmarine sedimentary rocks along the south­ ("Laguna Valley") and eastward toward Castle west flank of the Chocolate Mountains. Dome Plain from a central area 320-340 feet above "Senator Mesa," on the east side of the Choco­ sea level. late Mountains, comprises several piedmont and terrace levels, all sloping about 70-120 feet per mile DISSECTED PIEDMONT SLOPES toward the east and southeast. The underlying ma­ The third and fourth types of landforms in the terials are alluvial gravel deposits of local deriva­ Yuma area, which occur along the margins of the tion which thin eastward and southeastward, where mountains and hills, are dissected and undissected they overlie relatively fine grained older Colorado piedmont slopes. In places, one type grades into the River alluvium. other, but in general, the dissected piedmont slopes "Middle Mountains Plain" and the western mar­ represent areas where erosion is the dominant gin of "Laguna Mesa" are similar in most respects process today and probably has been dominant for to "Senator Mesa," except that the piedmont sur­ at least the past several thousand years. In contrast, faces and terraces slope westward rather than undissected piedmont slopes represent areas where eastward or southeastward and generally are not either deposition is occurring or a rough balance quite as deeply incised as in "Senator Mesa." Aver­ exists between erosion and deposition. age slopes of "Middle Mountains Plain" range from Many of the dissected piedmont slopes could be more than 100 feet per mile at the foot of Middle classified as dissected pediments under the broad Mountains to about 60 feet per mile near the Colo­ meaning of the term "pediment." However, unlike rado River. classic pediments in desert regions, the surfaces are Plain, a gently sloping desert surface cut chiefly on unconsolidated to semiconsolidated traversed by a network of shallow washes, slopes alluvium rather than on consolidated bedrock. The southwestward at gradients ranging from 100 feet deposits, chiefly coarse grained older alluvium of per mile in the northeast to 45 feet per mile in the local origin, are generally mantled with thin stream- southwest. Dark-brown desert pavement is well de­ terrace and piedmont deposits (gravel). veloped on the surfaces between the present washes, The dissected piedmont slopes occur in "Picacho which are generally incise.d only a few inches to 4 Mesa," "Senator Mesa," Middle Mountains Plain," feet below the pavement surfaces, except in the east­ Castle Dome Plain, "Gila Mesa," and "Ligurta ern part of the plain, where depth of incision is Mesa" and in parts of Pilot Knob Mesa and "Laguna locally as much as 40 feet. Much of Castle Dome Mesa" (fig. 6). In all these subareas, desert pave­ plain is in some respects transitional between the ment is generally conspicuous on the broad gravel relatively undissected and the dissected piedmont surfaces and also conspicuous on the narrow terraces slopes. The chief difference between Castle Dome below the main piedmont levels. Several piedmont Plain and the Lechuguilla Desert farther south is levels are present at most places. The most extensive the absence of dark desert pavement in the latter of these appears to be graded to the level of Yuma area. Mesa. The narrow terraces are not paired, are gen­ "Gila Mesa" and its homolog on the east side of erally adjacent to present washes, and represent the Gila Mountains, "Ligurta Mesa," include some abandoned washes left behind as the ephemeral of the steepest and most deeply dissected piedmont streams cut down to their present levels. slopes in the Yuma area. Slopes of desert pavement "Picacho Mesa," the broad piedmont between the surfaces in the "Ligurta Mesa" area range from Cargo Muchacho Mountains and the Chocolate 160 feet per mile (1°45') near the mountains to Mountains, is drained by subparallel southeast- to about 100 feet per mile (1°05') at the lower ends. south-trending washes, of which Picacho Wash near In "Gila Mesa," slopes are somewhat flatter (55- the center of the area is the largest. The floors of 120 feet per mile). Both areas contain deeply dis­ the washes are incised as much as 80 feet below the sected older alluvial deposits of local origin on adjacent piedmont surfaces near the Colorado River which desert pavement is generally lacking (fig. 9). flood plain ("Bard Valley"), but the depths of in­ Slopes of ridges in these exposures are as much as cision become progressively less toward the north­ 300-350 feet per mile, and near the mountains some west (fig. 8). The average slope of the piedmont of the present washes are incised as much as 150 surface is about 50 to 60 feet per mile. Near its feet below the ridges. north end, "Picacho Mesa" becomes more intricately dissected and merges gradually with low, hilly ex­ UNDISSECTED PIEDMONT SLOPES posures of conglomerate of the Chocolate Mountains The undissected piedmont slopes are distinguished GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H25

FIGURE 8. Dissected piedmont surfaces of reentrant of "Picacho Mesa" in eastern Cargo Muchacho Mountains, Calif. Present wash crosses picture from right to left in foreground. Granitic detritus in this area forms poorly developed desert pavement. from the older, dissected piedmont slopes by the sand and fine gravel that constitute the alluvial-fan general absence of desert pavement and by the very deposits. As mentioned earlier, desert pavement is shallow depths of incision of the most recent washes. either poorly developed or absent; moreover, desert Most of the deposits underlying the undissected varnish has not formed to an appreciable extent on piedmont slopes are classified as alluvial-fan de­ the larger fragments. In part, the absence of var­ posits (younger alluvium) (pi. 3); these deposits nish may reflect the fact that deposition is the are being aggraded slowly in most places, and in dominant process. However, it probably is also a some places, a rough balance appears to exist be­ consequence of the tendency of varnish to form tween aggradation and degradation. very slowly on the light-colored granitic rocks. The subareas representing undissected piedmont Land-surface slopes in the Lechuguilla Desert, slopes are the Lechuguilla Desert, Davis Plain, "For- Davis Plain, and "Fortuna Plain" range from 70 to tuna Plain," and part of Pilot Knob Mesa (fig. 6). 100 feet per mile at the foot of the mountains to The first three subareas are adjacent to the southern about 40 feet per mile at the lower edges of the Gila Mountains and their southerly extensions, the piedmonts substantially flatter than the slopes in Butler and Tinajas Altas Mountains. Light-colored the dissected piedmont areas ("Ligurta Mesa" and fairly coarse grained granitic rock predominates in "Gila Mesa") farther north. Present washes are these mountains and furnishes the coarse granitic poorly defined and entrenched only a few inches to

507-243 O - 74 - 3 H26 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

FIGURE 9. Northern Gila Mountains from Fortuna Wash. Beyond Fortuna Wash in the foreground are dark desert pavement surfaces; the colored exposures in the middle distance, and the somewhat darker smooth exposures near the center of the mountains beyond, are deeply dissected older alluvial deposits (chiefly coarse gravel of local origin). The high, rough exposures are of pre-Tertiary crystalline rocks. a few feet below the general surface of the piedmont RIVER TERRACES AND MESAS areas. In some areas, particularly in the southern The river terraces and mesas are the remnants part of the Lechuguilla Desert and in parts of of former valleys and the delta plain of the Colo­ Davis Plain, a distinctive rhomboidal pattern of rado and Gila Rivers. Yuma Mesa, Wellton Mesa, shallow rills may indicate sheetflooding as the pri­ and Imperial East Mesa are the subareas of this mary geomorphic process. type (fig. 6). All these surfaces are nearly flat and Except for its southeastern part, where it adjoins lie above the present valleys (flood plains) of the "Picacho Mesa," Pilot Knob Mesa consists of a rivers. The old valleys and delta plain were aban­ relatively undissected piedmont slope like the areas doned when the rivers began to cut their present, just described. Also, as in those areas, the detritus narrower valleys. beneath Pilot Knob Mesa'is largely granitic, sheet- Wellton Mesa and northeastern Yuma Mesa lie flooding probably is common, and the present washes respectively 60-70 and 70-80 feet above the adja­ are poorly defined and very shallowly incised. The cent Wellton-Mohawk and South Gila Valleys. Ex­ Southern Pacific Co. has had to protect its railroad tensive river terraces at similar heights occur far­ tracks from washouts and inundation by a continu­ ther upstream on both the Colorado and the Gila ous line of revetments having a zigzag pattern, to Rivers. In places for example at Laguna Dam, concentrate the runoff through culverts. Imperial Dam, and the Gila River narrows between GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H27

the Gila and Laguna Mountains the terraces are The Imperial East Mesa is similarly downwarped cut on pre-Tertiary crystalline rocks or on Tertiary toward the axis of the Salton Trough, although the sedimentary or volcanic rocks. Extensive piedmont direction of tilt may be somewhat different from that surfaces formed by local runoff also are graded to of Yuma Mesa. The East Mesa surface has a west­ this terrace level (fig. 10). ward slope of less than 2 feet per mile substantially flatter than the slope of southwestern Yuma Mesa. The northeast margin of East Mesa is occupied by an old shoreline, either of an ancestral lake or of an arm of the Gulf of California. In the south­ eastern part of the mesa the shoreline is about 160 feet above sea level, but 55 miles northwest of the international boundary it is only 70 feet above sea level (Loeltz and others, 1972). This tilt probably results from the westward (or northwestward) downwarp described above. The west margin of the mesa is occupied by another shoreline that of ancient at about 45 feet above sea level (Stanley, 1962). Unlike the higher, older shore­ line, the Lake Cahuilla shoreline is virtually unde- formed. The lacustrine origin of the 45-foot shoreline is unequivocal, but the origin of the higher shoreline FIGURE 10. Terraces in southern Laguna Mountains. The higher of the is uncertain. Fresh-water shells dated at 37,100 ± two prominent levels appears to be graded to the level of the Yuma Mesa terrace 70 to 80 feet above the present flood plains. 2,000 years before present have been described from this shoreline (Hubbs and others, 1963, p. The time when the streams were at the level 60- 262), but evidence of the barrier across the delta 80 feet above the present flood plains is not indi­ required to contain the lake and exclude the Gulf of cated by direct evidence. However, the terraces may California is lacking (Robison, 1965). Unless sig­ have been formed at the time of the last major nificant warping has occurred in the Yuma area higher sea-level stand during the Sangamon Inter- more recently than indicated by present evidence, glaciation. According to Broecker (1966) and Veeh remnants of this higher shoreline should be found (1966), the last sea-level stand significantly above elsewhere at altitudes similar to those along the the present level occurred about 120,000 years ago. southeastern Imperial East Mesa (140-160 feet Not all the Yuma Mesa represents the terrace above sea level). The widespread tufa "gravel" that just described. In the southwestern part of the occurs in the Yuma Mesa and even on parts of the mesa, one or two much-eroded terraces lie below "Upper Mesa" may be indicative of shorelines, but the main surface of the mesa and 30-50 feet above no other evidence has been found in those areas. adjacent Yuma Valley. These surfaces may be cor­ Since the time the rivers began to cut their pres­ relative with similar levels in the piedmont areas. ent narrower valleys, the older flood-plain surfaces The general slope of Yuma Mesa is much flatter represented by Wellton, Yuma, and Imperial East than that of the "Upper Mesa" to the southeast and Mesas have been modified by erosion and deposition, not greatly different from the slope of the present chiefly by wind but also by water. The southeastern river valleys (flood plains). Northeastern Yuma and eastern parts of Yuma Mesa, adjacent to the Mesa has a southward gradient of about 2 feet per "Upper Mesa," are occupied by thin blankets of mile, but farther southwest the slope changes in windblown sand, and the areas farther west by direction to westward and steepens to about 6-8 broad, wind-scoured depressions. Undrained depres­ feet per mile (pi. 2). The westward slope appears sions as much as 10 feet in depth are common in to be chiefly erosional in origin, although in part it the areas of wind scour and deposition. One par­ results from downwarp along the east margin of ticularly large depression (whose origin may not the Salton Trough. Farther southwest, in Mexico, be entirely wind scour), about 15 feet in depth and westward downwarp causes the mesa surface to 2 miles in width, occurs in the northern part of the intersect the surface of the present river flood plain mesa, just west of the southernmost two outcrops at a point about 18 miles southwest of San Luis, of pre-Tertiary crystalline rocks of the "Yuma Rio Colorado. Hills" (pi. 2). On the Imperial East Mesa, low dunes H28 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA are extensive in places; in other places, sand accu­ transverse ridges are related to an earlier wind mulates around the bases of the larger shrubs, par­ regime, the barchan dunes to a later one. The south­ ticularly the creosote bush (Larrea tridentata) . east, leeward sides of the ridges are linear, steep Notwithstanding the modification of the mesa slip slopes of about 32° inclination the angle of surfaces by wind, traces of old river-formed features repose for the dry fine to medium sand. The bar- remain. On Yuma Mesa, the most noticeable of these chans are on the gentler, windward slopes of the features is a low ridge, perhaps a natural levee or ridge&; these dunes are modified in shape during channel ridge, which trends southwestward in the the summer when the prevailing winds are from the south-central part of the mesa (pi. 2). south-southeast rather than from the north and SAND DUNES west, as they are during the rest of the year (U.S. Weather Bureau unpub. data for Yuma, Ariz.). The Although windblown sand is extensive in the depressions between the transverse ridges are gen­ Yuma area, in only two sizable areas has the sand erally semicircular in plan, with the straight side accumulated to form dunes more than 10 feet thick. on the northwest, and many are scoured free of One of these tracts the Sand Hills, or, as they have sand. been informally designated, the "Algodones Dunes" The northeastern belt consists of low, irregular is on the northeast side of the Imperial East dunes and small barchans. The dunes are much Mesa, chiefly in California. See also Norris and lower than the dunes in the other two belts; they Norris (1961). The other tract informally called range in height from about 5 to 15 feet. They ap­ "Fortuna Dunes," is in Arizona, near the southerly pear to shift and change form more than the other, international boundary (fig. 6). higher dunes, although no measurements are avail­ The "Algodones Dunes" form an elongate north­ able to document this general observation. west-trending belt about 45 miles long by 6 miles The informal name "Fortuna Dunes" is given to wide on the northeast side of the Imperial East an area of windblown sand between "Upper Mesa" Mesa. The surface on which the dunes rest is con­ and "Fortuna Plain," just north of the southerly tinuous with the East Mesa and with the Pilot Knob international boundary. These dunes are merely the Mesa to the northeast; this surface is exposed at northwestern prong of a much more extensive dune several places in the southeastern part of the dunes. area largely in , Mexico. The thicker sand The southeastern part of the "Algodones Dunes" deposits occur as closely spaced small transverse comprises three longitudinal belts: (1) A narrow dunes as much as 30 feet high. The long axes of the southwestern belt generally less than a mile wide, dunes are all uniformly oriented N. 60° E., pre­ (2) a main central belt averaging about 2V£ miles sumably perpendicular to the strongest winds that in width, and (3) a northeastern belt about 2-2 ^ formed them. It is not known whether the dunes are miles wide. Each belt is characterized by a distinc­ moving at present. tive type of dune topography. The southwestern belt is composed of narrow RIVER VALLEYS parallel longitudinal ridges. The higher ridges rise The river valleys are the Holocene flood plains of 60-100 feet above the East Mesa. Their remarkably the Colorado and Gila Rivers. Most of the flood straight southwestern edge has led some observers plains are now farmed and are no longer subject to to believe that they are fault controlled, possibly flooding since dams were constructed upstream and by a branch or parallel branches of the San Andreas levees built along the Colorado River in the Yuma fault system. Loeltz, Robison, Irelan, and Olm- area. The flood plains are bordered by terraces and sted (1972) have shown that the southwest edge other higher desert surfaces into which the rivers of the dunes is adjacent to an old shoreline, of cut down before starting the aggradational cycle either an ancestral lake created by the Colorado that produced the present flood plains. River or an arm of the Gulf of California (p. H27). "Laguna Valley" is the informal name given to The main central belt is composed of high trans­ the flood plain of the Colorado River between La­ verse ridges and intervening depressions having a guna and Imperial Dams. It is the first broad flood remarkably uniform spacing the average distance plain along the river downstream from the Parker- between the ridge crests is about a mile. Smaller Blythe-Cibola area. In its present form it is not a barchan crescent or quasi-barchan dunes are super­ natural feature but is a surface of aggradation imposed on the general form of the transverse caused by Laguna Dam, which was constructed in ridges, which rise 150-300 feet above the depres­ the early 1900's. An estimated 14 feet of aggrada­ sions. According to Norris and Norris (1961), the tion has occurred behind Laguna Dam; the postdam GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H29 fill probably thins upstream toward Imperial Dam. to 125 feet above sea level along the Colorado River Most of "Laguna Valley" is occupied by phreato- west of Yuma an average gradient of about l1/^ phytes and hydrophytes, and much is covered by feet per mile. The reason for the anomalously flat shallow water. Mittry Lake (pi. 3) at the southeast gradient is not fully understood; the presence of edge of the valley is the largest water body. the nearly buried bedrock ridge ("Yuma Hills") The flood plain of the Gila River between the near the downstream end of the valley may be a town of Wellton (pi. 3) and the site of Mohawk 25 contributing factor. miles to the east is usually referred to as the The North Gila Valley is an L-shaped flood-plain Wellton-. The present channel of the area downstream from Laguna Dam, bounded on Gila River follows a somewhat meandering course the east and north by the Laguna Mountains, on the down the valley, which ranges in width from 2 to west by the Colorado River, and on the south by the 4 miles within the area shown in figure 6. The flood Gila River. The northern arm of the L is thus the plain is bounded by higher lands underlain by older, eastern part of the Colorado River flood plain above dissected alluvial deposits. Within the area shown the confluence of the Gila River; the eastern arm is in figure 6, the Wellton-Mohawk Valley slopes west­ the northern part of the lower Gila River flood plain. ward from an altitude of 255 feet above sea level to The northern arm is nearly flat, but the eastern arm 205 feet above sea level in a distance of about 14 slopes westward from 160 feet above sea level to miles an average gradient of about 3*72 feet per 135 feet above sea level at the confluence of the mile. Like most of the other valleys in the Yuma Colorado and Gila Rivers a gradient of 3% fget area, nearly all the area is presently irrigated. per mile. The flood plain of the Gila River between the The South Gila Valley is south of the Gila River North and South Gila Valleys and the Wellton- and of the Colorado River below the mouth of the Mohawk Valley is referred to locally as Dome Valley. Gila River. It extends westward from the Gila Dome Valley is somewhat narrower than Wellton- Mountains to the nearly buried "Yuma Hills." The Mohawk Valley and ranges in width from 3 miles valley is about 12 miles long by 2 miles wide and near its upper end to less than 1 mile at the lower slopes westward at an average gradient of about 3 end, where the Gila River flows between the Gila feet per mile. The valley surface is not perfectly and Laguna Mountains. The average altitude of the flat but consists of a series of low terraces decreas­ flood plain decreases from 205 feet above sea level ing in altitude northward toward the Gila River. at the upper end to 150 feet above sea level at the (Similar terraces occur on the north side of the lower end, in a distance of 15 miles. This gradient Gila River in North Gila Valley.) Old meander 3% feet per mile is slightly steeper than that of scars mark the edge of these terraces, the lowest of the lower end of Wellton-Mohawk Valley to the east. which is 10-15 feet below the southern margin of The part of the valley of the Colorado River in the flood plain. In places the form and outline of California downstream from Laguna Dam is in­ the terraces have been modified greatly by land formally designated "Bard Valley" from the com­ leveling for farming and roadbuilding. munity of Bard in the upper part of the valley The flood plain east of the Colorado River down­ (pi. 3). "Bard Valley" is a broad, flat area, the stream from Yuma is called the Yuma Valley. Yuma southeastern part of which was traversed by a Valley is about 19 miles long by 2-9 miles wide. It meander loop of the Colorado River within historic slopes south-southwestward from 125 feet above sea time. The abandoned meander is now occupied by level west of Yuma to 90 feet above sea level at the two oxbow lakes: Haughtelin Lake (pi. 3) and Bard southerly international boundary an average gra­ Lake about a mile to the east. Until August 1966, dient of 1.8 feet per mile. the meander channel formed the disputed boundary Small, sinuous sand dunes 5-20 feet high are between California and Arizona. The area between scattered throughout the central and eastern parts the present channel of the Colorado River and the of the valley; these dunes have formed on the lee­ abandoned meander is known as The Island. The ward (southeast) side of abandoned meanders. eastern part of The Island and the adjacent area Many of these old meander scars can be discerned to the east is covered by a thin sheet of windblown from the air, even where the land has been farmed sand and a few low dunes (not shown in fig. 6 but intensively for several decades. The soil is sandier shown on pi. 3). and of a lighter color in the old channels than in "Bard Valley" is an unusually flat segment of the the adjacent flood plain. The Yuma Main Drain, the Colorado River flood plain. It slopes southwestward principal surface drain in the valley, occupies an old from about 140 feet above sea level at Laguna Dam river channel along most of its length. H30 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA The present channel of the Colorado River is rocks and older marine sedimentary rocks of Ter­ 15-20 feet below the adjacent flood plain. Much of tiary age are only broadly warped and locally this cutting occurred since the construction of the faulted. upstream dams and the desilting works at Imperial The only fossils diagnostic as to age found within Dam in the 1930's and 1940's, when the sediment the area mapped in the present investigation were load of the river decreased markedly. (See fig. 26.) some bones of Eqwus sp. (a horse) and Odocoileus The terraces along the Gila River in the South and sp. (a deer) reported by Bryan (1923, p. 30-31) North Gila Valleys may reflect the recent degrada­ from a terrace near Ligurta (pi. 3). The bones indi­ tion by the Colorado River below Yuma. cate a Pleistocene age for the enclosing deposits of The Mexican part of the flood plain of the Colo­ older alluvium. Lower Miocene vertebrate fossils rado River downstream from Pilot Knob is gen­ have been reported from a locality about 10 miles erally called the Mexicali Valley. Mexicali Valley east of the mapped area, in the eastern Muggins widens toward the south and west; together with Mountains (Lance and Wood, 1958; Lance, 1960). Yuma Valley, it forms part of the delta of the Colo­ In addition to the scanty fossil data, several radio- rado River. The surface form of the delta is that of metric dates have been obtained for material col­ a large, flat fan having its apex near Pilot Knob lected in the Yuma area and, together with inferred and Yuma. The axis trends west-south westward correlations with units in adjacent regions, have toward the Cucupas Mountains in Baja California; been used to establish the general stratigraphic south of the axis, the surface slopes gradually sequence. toward the Gulf of California; to the north, toward Most of the stratigraphic units (fig. 11 and pis. the Salton Sea. The lowest point on the axis of the 3, 10) are useful subdivisions of the ground-water delta, near the Cucupas Mountains, is about 47 feet reservoir for describing the occurrence and move­ above sea level (Arnal, 1961). At times during the ment of ground water. However, beneath the river Holocene and latest Pleistocene, the Colorado River valleys and Yuma Mesa, the alluvial and minor flowed westward rather than southward and main­ windblown deposits are subdivided into zones that tained large fresh-water lakes about 42-48 feet differ in part from the stratigraphic units, as is above sea level north of the delta axis. explained in the section of the report on occurrence The average land-surface gradient along the east of ground water. The different geohydrologic clas­ side of Mexicali Valley from Pilot Knob to the head sification of these deposits is required because the of tidewater (Gulf of California) is about 2.2 feet boundaries of the water-bearing zones cross the per mile. The river has wandered back and forth stratigraphic boundaries. across the valley frequently in historic time; be­ CRYSTALLINE ROCKS (PRE-TERTIARY) cause of its meandering course, the gradient of the river itself has averaged only about 1 foot per mile Crystalline rocks of pre-Tertiary age form a in this reach. large part of the mountains and underlie the Ter­ tiary and Quaternary rocks throughout the area. STRATIGRAPHY The crystalline rocks comprise a wide variety of CLASSIFICATION OF ROCKS metamorphic and plutonic rocks. For the purposes The geologic materials of the Yuma area range of this report all these rocks are grouped in one from hard, dense crystalline rocks, such as gneiss, unit, as they are uniformly devoid of sizable sup­ schist, and granite, to unconsolidated alluvium and plies of ground water. windblown sand. For the purposes of this report The metamorphic rocks range from weakly meta­ these materials are grouped in 10 generalized strati- morphosed sedimentary and volcanic rocks to graphic units. The inferred stratigraphic relations strongly metamorphosed gneiss and schist. In the of these units are shown in figure 11, the extent of Cargo Muchacho Mountains, Henshaw (1942) di­ their outcrops on plate 3, and their probable subsur­ vided the metamorphic rocks into two formations: face extent and configuration on plate 10. the Vitrefrax Formation, composed of quartzite, The oldest unit the crystalline rocks is sepa­ quartz-sericite schist, kyanite-quartz-sericite schist, rated from the overlying units by a major uncon­ sericite schist, biotite-hornblende schist, and a few formity (nonconformity) ; less significant uncon­ other less extensive types; and the Tumco Forma­ formities are present throughout the Tertiary and tion, composed largely of feldspar-quartz-biotite- Quaternary units. The amount of deformation of hornblende rock, hornblende schist, and metamor­ the various units decreases with decreasing age. phosed arkose. Deposits younger than the nonmarine sedimentary Elsewhere in the Yuma area, the metamorphic O H O W

O f O O

W

B ISI O

"3 O O 00

^D m CO

CRYSTAL­ NONMARINE NONMARINE CONGLOMERATE LINE SEDIMENTARY VOLCANIC ROCKS SEDIMENTARY OF CHOCOLATE OLDER ROCKS ROCKS ROCKS MOUNTAINS ALLUVIUM

CO H32 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

rocks have not been named, although they have been Ironically, the only two radiometric dates, which described in a general way by Wilson (1933) in the are for a coarse porphyritic quartz monzonite in Laguna, Gila, Butler, and Tinaj as Altas Mountains, Yuma, are widely disparate. Wasserburg and Lan- and they have been examined briefly in the Choco­ phere (1965) report a rubidium-strontium age of 73 late Mountains by F. H. Olmsted. The most exten­ million years for the biotite in a sample obtained sive types in all these mountains are various kinds in the Highway 95 cut just east of the railroad over­ of biotite-bearing and hornblende-bearing gneiss, pass in Yuma. However, L. T. Silver (written some of which is migmatitic and highly contorted. commun., 1968) obtained a uranium-lead age of At the north end of the Gila Mountains, crystalline 1,440 million years for crystals of zircon in the same limestone, not known elsewhere in the Yuma area, rock. The zircon age (Precambrian) presumably is intercalated with schist. Gneiss of granitic to indicates the time of original crystallization; the quartz monzonitic composition is abundant in the biotite age (Late Cretaceous) may reflect a Lara­ eastern Laguna Mountains; some of this rock ap­ mide metamorphic event. pears to grade into porphyritic granite and quartz The dated porphyritic quartz monzonite is wide­ monzonite of probable plutonic origin. spread in the Yuma area and makes up almost all In the Chocolate Mountains, a suite of weakly the detritus in some of the breccia and conglomerate metamorphosed rocks includes slate and phyllite ot of Tertiary age described in a later section (p. H33). epiclastic and probable pyroclastic origin, sheared The rock is generally coarse grained, contains ovoid sandstone and arkose, metaconglomerate, sheared to irregular phenocrysts (or porphyroblasts) of tuff breccia, and greenstone derived from mafic lava white to pale-pink microcline as much as 50 mm flows and shallow intrusive bodies. These rocks are (millimeters) in diameter, and smaller grains of similar to the McCoy Mountains Formation of Miller plagioclase, quartz, biotite, and minor accessory min­ (1944) farther north, with which they may be at erals (chiefly magnetite and zircon). In places the least in part correlative. Also present in the Choco­ rock is gneissose, and in ancient (pre-Laramide) late Mountains are several types of schist similar fault and shear zones it is schistose and locally my- to the Orocopia Schist of Miller (1944) in the Oro- lonitic. It is cut by younger plutonic and dike rocks copia Mountains to the northwest. whose ages are unknown. The porphyritic quartz The plutonic rocks include a wide variety of types, monzonite grades into porphyritic granite and has although quartz monzonite and granite are the most been found in almost all wells that penetrate the extensive. Other plutonic rocks include granodiorite, pre-Tertiary crystalline rocks in the Yuma area. quartz diorite, diorite, and gabbro. Dikes of aplite, alaskite, pegmatite, and various fine-grained dark NONMARINE SEDIMENTARY ROCKS (TERTIARY) rocks, of which distinctive dark-green altered dia­ Unconformably overlying the crystalline rocks of base and basalt are most conspicuous, are abundant pre-Tertiary age is a suite of sedimentary rocks and at many places. associated volcanic rocks of Tertiary age. This suite Most of the plutonic rocks clearly intrude meta- comprises several mappable units, all of which ap­ morphic rocks, but in places the relations of the two pear to have been deposited before the Colorado types are gradational. For example, in the Cargo River entered the Yuma area. For convenience, all Muchacho Mountains, some of the granite appears the predominantly nonmarine sedimentary rocks, to grade into meta-arkose, from which it may have except conglomerate of volcanic composition in the been derived (Henshaw, 1942) ; the gradational Chocolate Mountains are included in one major relations of some of the gneiss and the porphyritic unit, the volcanic rocks in another. Marine sedi­ granite and quartz monzonite in the Laguna Moun­ mentary rocks of Tertiary age comprise two addi­ tains were cited above. tional units; the younger marine unit is overlain The ages of most of the metamorphic and plutonic by a transition zone of marine and nonmarine de­ rocks in the Yuma area have not been established, posits of late Tertiary age (fig. 11). All these other although all these rocks appear to be no younger units are discussed in a later section. than the Laramide orogeny, which took place dur­ The nonmarine sedimentary rocks consist of ing the Late Cretaceous and the early Tertiary strongly to weakly indurated clastic rocks ranging (Damon and Mauger, 1966). Some of the youngest from mudstone and shale, in part of lacustrine ori­ plutonic and dike rocks might be of Tertiary age gin, to megabreccia and boulder conglomerate. (Wilson, 1933, p. 185; 1960). For convenience, Fanglomerate is most abundant, at least in the out­ these rocks are grouped with the pre-Tertiary crys­ crop areas. Detailed mapping done during the pres­ talline rocks in this report. ent investigation resulted in the delineation of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H33 several mappable units in the Laguna Mountains, dence indicates that the Muggins Mountains beds southeastern Chocolate Mountains, and northern probably are younger, as discussed on page H37. Gila Mountains. These units, one of which has been named the Kinter Formation, are described briefly BRECCIA AND CONGLOMERATE in the following paragraphs. Exposures in a critical The uppermost red beds in the southern Laguna area in the southeastern Laguna Mountains and Mountains intertongue with a thick sequence of northernmost Gila Mountains are shown on plate 4. generally coarse grained, poorly sorted breccia and conglomerate. These strata are made up of pre­ RED BEDS dominantly angular and subangular fragments of The basal part of the nonmarine sedimentary all sizes up to boulders and blocks many feet across rocks exposed in the Laguna Mountains area is in a semiconsolidated matrix of clayey sand and composed of arkose, conglomerate, mudstone, fine­ silt. Thin interbeds of arkose, sandy siltstone, and grained tuffaceous beds, and bentonitic ash, all re­ felsic tuff occur locally. ferred to herein as red beds from the predominant In the Laguna Mountains the lower part of this color in the exposures near McPhaul Bridge (pi. 4). sequence consists of breccia and conglomerate com­ The coarser beds are red, brownish red, brown, posed entirely of the distinctive pre-Tertiary por- and yellow and contain subangular to rounded frag­ phyritic granite and quartz monzonite and associ­ ments of quartz and feldspar, hornblende, biotite ated dike rocks found in nearby exposures. This and other heavy minerals, and various kinds of monolithologic granite breccia and conglomerate plutonic and metamorphic rocks, including abund­ sequence is obscurely bedded and very coarse ant- slightly metamorphosed volcanic rocks. These blocks as much as 50 feet across have been observed. beds are of fluvial origin; the well-rounded char­ Some of this material appears to have formed as acter of many of the pebbles indicates transport for mudflows, talus, and colluvium, although most of it a considerable distance, probably by a fairly well probably is fanglomerate. Obscure bedding and integrated drainage system. Tongues of coarse faults make estimates of thickness uncertain, but breccia and conglomerate in the upper part of the probably at least 4,000 feet is exposed in the south­ sequence suggest local high relief and rapid erosion ern Laguna Mountains. The granite breccia- toward the close of deposition of the red beds. conglomerate sequence is exposed also in Yuma, The finer beds, generally more abundant in the where the Colorado River has cut its present chan­ lower part of the sequence, are mostly green, pale nel through a low hill of this material (fig. 12). yellow, or gray and locally contain abundant thin The upper part of the breccia-conglomerate se­ seams of gypsum. These finer grained gypsiferous quence is composed of more heterogeneous material sediments probably are of lacustrine origin (no but is otherwise similar to the underlying granite marine fossils have been observed) any may indi­ breccia and conglomerate. The two types intertongue cate the presence of local basins of interior drainage in the southern Laguna Mountains (pi. 4) ; in the in the early stages of deposition of the red-bed se­ southeastern Chocolate Mountains, the heteroge­ quence. Intermittent volcanic activity is reflected by neous type predominates. Typically the heteroge­ the presence of tuffaceous mudstone and a few thin neous breccia and conglomerate has an earthy beds of white bentonitic ash. greenish-gray matrix in which are embedded frag­ In the Yuma area, the red beds are exposed only ments of all sizes as much as many feet across near McPhaul Bridge in the southeastern Laguna composed chiefly of fine-grained varicolored meta- Mountains and at the north end of the Gila Moun­ sedimentary and metavolcanic rocks. The nearest tains (pi. 4). The total exposed thickness in the exposures of similar low-grade metamorphic rocks Laguna Mountains is difficult to estimate because of in the pre-Tertiary crystalline-rock complex are in faulting; probably it is on the order of 2,000-2,500 the Chocolate Mountains near the north edge of feet. The subsurface extent and thickness are largely plate 3. Maximum exposed thickness of heteroge­ unknown; varicolored sandstone, shale, and con­ neous breccia and conglomerate near the southeast glomerate penetrated between depths of 4,937 and end of the Chocolate Mountains is probably more 6,007 feet in oil-test well Colorado Basin Associates than 5,000 feet, although poorly exposed faults of Federal 1 may be at least in part correlative with unknown displacement make this estimate somewhat the red beds exposed near McPhaul Bridge. uncertain. Beds similar to those near McPhaul Bridge are Both the red beds and the overlying breccia and exposed extensively in the Muggins Mountains 10-20 conglomerate have been moderately deformed; bed­ miles to the east, but fossil and radiometric evi­ ding generally dips 30°-60°, most commonly in a H34 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

FIGURE 12. Granite breccia and conglomerate exposed in north bank of Colorado River at Yuma. westerly or southwesterly direction. Good exposures gray arkosic sandstone and gray to pink tuffaceous reveal high-angle reverse, or thrust, faults, as well mudstone and the upper, composed of yellowish- as low to high-angle normal faults. In the southern gray conglomerate (fanglomerate) and some soft Laguna Mountains, pre-Tertiary crystalline rocks arkosic sandstone and mudstone. The type section in places are in contact with the red beds along is described below. high-angle reverse faults. Type section KINTER FORMATION Thickness The name Kinter Formation is proposed in this (feet) report for a sequence of predominantly coarse Top of section concealed by Quaternary alluvium. grained nonmarine sedimentary rocks and minor Upper member: Arkosic sandstone and pebbly sandstone, soft, intercalated beds of tuff and ash exposed principally yellowish-gray (5Y 7/2) ; interbedded pale- in the Laguna Mountains and at the north end of yellowish-brown (10YR 6/2) soft silty sand­ the Gila Mountains. The name is taken from a rail­ stone ______280 road siding of the Southern Pacific Co. at the north Mudstone, sandy, moderately hard, obscurely end of the Gila Mountains, along which the forma­ bedded, pale-brown (5YR 6/2) ; thin interbeds tion is typically exposed. The type section, desig­ of pale-yellowship-brown (10YR 6/2) very fine to fine-grained sandstone. Mudstone has sub- nated A-B-C on plate 4, is in sees. 3, 9, 10, and 11, conchoidal fractures; contains a few poorly pre­ T. 8 S., R. 21 W., Gila and Salt River base line and served small gastropods _ - 120 meridian, directly south of the Wellton-Mohawk Arkosic, tuffaceous sandstone, soft, yellowish-gray Canal, 1.8 miles east to 0.8 of a mile south of (5Y 7/2; 5Y 8/1) to pinkish-gray (SYR 8/1); McPhaul Bridge, and about 7 miles southeast of lenses of pebbly sandstone containing granules and small pebbles of metamorphic and granitic Laguna Dam. The Kinter Formation is divided into rocks and pale-pink pumice; a few interbeds of two unnamed members: the lower, composed of pale-yellowish-brown (10YR 6/2) soft silty coarse unsorted breccia and tongues of brown and sandstone and sandy siltstone 700 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H35

Thickness the upper member, and in most exposures in the (feet) Upper member Continued Laguna Mountains, conglomerate seems to predomi­ Pumice tuff, soft, pale-pink (5RP 8/2) to pinkish- nate over finer grained deposits. The conglomerate gray (5YR 8/1) ______5 (fanglomerate) was deposited on alluvial fans from Arkosic sandstone, soft, yellowish-gray to pinkish- local sources, as indicated by the angularity of most gray; thick, lenticular interbeds of yellowish- of the clasts and their similarity to pre-Tertiary gray to gray conglomerate and pebbly sandstone 120 Conglomerate, obscurely bedded to moderately well rocks presently exposed in the area. The alluvial bedded, yellowish-gray to gray; composed chiefly fans were bounded by flood plains on which were of angular to subrounded clasts, as much as 3 deposited the finer sands and muds. ft across, of gneiss, schist, granite, and scattered Both the upper and the lower members of the pumice tuff; thin, lenticular interbeds of yellow­ Kinter Formation contains beds of ash-fall tuff, ish-gray (5Y 7/2; 5Y 8/1) arkosic sandstone. Lower part traversed by vertical fractures filled some of which have been reworked by streams. The with grayish-brown sandy clay and silt ____ 950 most widespread of these beds is a biotite-bearing Tuffaceous sandstone or sandy tuff, soft, fine- to tuff and altered ash at or near the base of the upper medium-grained, pinkish-gray (5YR 8/1) ; lens member (fig. 13). This bed is only a few feet thick of conglomerate in upper part ______5 and is locally missing, probably because of subse­ Exposed thickness of upper member ______2,180 quent erosion. Lower member: In addition to the extensive outcrops in the La­ Breccia, unsorted, obscurely bedded; contains an­ guna Mountains and northern Gila Mountains, the gular to subangular fragments of metamorphic Kinter Formation is exposed in a narrow belt along and granitic rocks as much as 5 ft in diameter in a light-brown (SYR 5/6) earthy matrix __ 250 the south flank of the hills southeast of Imperial Breccia, earthy, light-brown (5YR 5/6) to pale- Dam and also in the southwestern Chocolate Moun­ olive (10Y 6/2); interbedded gray (N 7) to tains just northeast of "Picacho Mesa." Probable grayish-orange-pink (10R 8/2) sandy tuff or equivalents occur on the east side of the Chocolate tuffaceous sand ______40 Mountains as well, but these last exposures (mapped Breccia, coarse, earthy, greenish-gray (5GY 6/1); crude bedding indicated mainly by alinement of as conglomerate of Chocolate Mountains) consist larger slabs of gneiss and schist -______150 chiefly of conglomerate composed of volcanic detri­ Interval poorly exposed; probably similar to ma­ tus rather than the predominantly metamorphic and terial above and below ______450 granitic clasts typical of the Kinter. Breccia, fine to coarse, earthy, obscurely bedded In the subsurface the Kinter Formation appears and poorly sorted, light-brown (5YR 5/6), pale- to have been penetrated in several test wells where olive (10Y 6/2), and yellowish-gray (5Y 7/2). Larger clasts include tuff as well as metamor­ it underlies fine-grained marine deposits of the phic and granitic rocks ______510 Bouse Formation. The contact probably is an angu­ Fault contact with upper member. lar unconformity, at least near the mountain blocks Exposed thickness of lower member _____ 1,400 on the margins of the basins, as indicated by the Total exposed thickness of Kinter Formation _ 3,580 discordance of several degrees observed in expo­ sures southeast of Imperial Dam and by the rela­ The two members designated in the type section tively mild deformation of the Bouse Formation at can be traced northward into the southern Laguna most places in the subsurface (fig. 15). Metzger Mountains, but the coarse, unsorted breccia char­ (1965) reports a similar angular discordance be­ acteristic of the lower member has not been identi­ tween the Bouse Formation and an underlying Mio­ fied in the central and northwestern parts of these cene (?) fanglomerate in the Parker-Blythe-Cibola mountains. In places in the northern Gila Mountains area. The Miocene (?) fanglomerate appears to be the lower member contains brown and gray arkosic at least in part equivalent to the Kinter Formation. sandstone and gray to pale-pink tuffaceous mud- In the Laguna Mountains the Kinter Formation stone. The sandstone is generally more indurated locally overlies pyroclastic rocks (chiefly silicic ash- than that in the upper member. The coarse, un­ flow tuffs) mapped as volcanic rocks of Tertiary sorted, and virtually unbedded nature of the breccia age (fig. 11 and pis. 3, 4). No angular discordance that constitutes most of the lower member suggests between these two units has been observed, al­ a mudflow origin in a region of strong local relief. though the abundance of clasts of silicic tuff in parts The upper member of the Kinter Formation is of the Kinter suggest at least local unconformity. generally better sorted than the lower member. In On the southwest flank of the Chocolate Mountains, exposures near Dome, east of the type section, con­ just northeast of "Picacho Mesa," the Kinter over­ glomerate makes up the entire exposed thickness of lies basaltic andesite or basalt and contains abund- H36 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

FIGURE 13. Exposure of Kinter Formation in railroad cut along Kinter siding at north end of Gila Mountains. Poorly consolidated fanglomerate overlies thin bed of pale-purplish-gray tuffaceous sand (ts) at base of upper member; unbedded mudflow breccia (br) below the tuffaceous sand at lower right corner of exposure is typical of much of the lower member of the formation. ant clasts of that rock in places. The basaltic ande- high-angle reverse faulting and moderate to steep site or basalt also is part of the main sequence of tilting and folding characteristic of the red beds, Tertiary volcanic rocks (fig. 11). breccia, and conglomerate of the older sedimentary Both the Kinter Formation and the underlying sequence. However, in places in the central Laguna volcanic rocks unconformably overlie the red beds Mountains, the Kinter Formation appears to rest and the breccia-conglomerate sequence. The uncon­ conformably on, or even intertongue with, hetero­ formity has several hundred feet of local relief. The geneous breccia and conglomerate presumed to be angular discordance between the bedding of the part of the older sequence. Evidently, deformation Kinter Formation and that of the red beds is as varied in time and intensity through the Laguna much as 60° in a highly faulted area about 11/2 Mountains. miles north of McPhaul Bridge (pi. 4). The vol­ The age of the Kinter Formation is well estab­ canic rocks and the Kinter Formation have generally lished as Miocene on the basis of radiometric dating been deformed by normal faulting and tilting or and stratigraphic evidence. Biotite from a bed of folding with bedding dips of less than 35°. This bentonitic ash at locality VAW-60:29 near the base comparatively mild deformation contracts with the of the upper member in the southern Laguna Moun- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H37

tains (pi. 4) has been dated by the potassium-argon alluvium of probable Quaternary age and uncon­ method as 23±2 million years (U.S. Geological Sur­ formably overlies crystalline rocks of pre-Tertiary vey, written commun. 1963). (See table 2.) If the age. In the Gila Mountains, similar coarse deposits apparent age is correct, the ash and the enclosing composed of detritus similar to nearby exposed fanglomerate can be assigned an early Miocene age crystalline rocks unconformably rest on the crys­ according to the widely accepted time scales of talline rocks and are overlain unconformably by Holmes (1960) and Kulp (1961). coarse alluvial-fan deposits of probable Quaternary Beds similar to those in the lower member of the age. Kinter Formation and also resembling some of the VOLCANIC ROCKS (TERTIARY) underlying red beds occur in the Muggins Moun­ Volcanism took place intermittently throughout tains 10-20 miles east of the Laguna and northern much of the time the nonmarine sediments of Ter­ Gila Mountains. Lance and Wood (1958) assigned tiary age were accumulating. The volcanic activity an early Miocene age to camel teeth from the Mug­ was most extensive after the deposition of the red gins Mountains beds; in a subsequent paper, Lance beds, breccia, and conglomerate and before that of (1960, p. 156) stated that the fossils are "certainly the Kinter Formation and the unnamed conglomer­ no older than Upper Oligocene or younger than ate of the Chocolate Mountains. The thickest accu­ Middle Miocene." P. E. Damon (written commun., mulation of these volcanic rocks within the area 1968) reports a potassium-argon age of 21.9 ±0.9 mapped (pi. 3) is in the Chocolate Mountains; far­ m.y. (million years) for biotite in a tuff determined ther southeast, in the Laguna Mountains, the vol­ by F. H. Olmsted to be 350-400 feet stratigraphically canic sequence is much thinner. Comparatively thick below the fossiliferous bed; this corresponds to a sections of volcanic rocks occur outside the mapped late Arikaree age according to the Cenozoic mam­ area, in the Muggins Mountains, Castle Dome Moun­ malian chronology of Evernden and James (1964), tains, Middle Mountains, and several other ranges which supports the interpretations of Lance and east and northeast of the Yuma area, but some of Wood (1958) and Lance (1960). these rocks may be older than middle Tertiary. The Bouse Formation, which unconformably over­ lies the Kinter Formation, is considered to be Plio­ OLDER ANDESITE cene (p. H44). The volcanic rocks underlying the The oldest rocks in the main volcanic sequence Kinter in the Chocolate and Laguna Mountains have are exposed chiefly in the easternmost part of the yielded potassium-argon dates ranging from about Chocolate Mountains near the Colorado River and 25 to 26 m.y. (table 2). in the adjacent area across the river in Arizona. All the evidence cited above suggests a Miocene These rocks consist of flows, pumiceous tuff, and age for the Kinter Formation. The probable time some shallow intrusive bodies, agglomerate, and equivalent of the Kinter in the western Salton flow breccia, all apparently of andesitic composition. Trough is the Split Mountain Formation of Tarbet The flows are dull gray to dull red, are cut by closely and Holman (1944), a predominantly nonmarine spaced irregular fractures, and lack pronounced fanglomerate and sandstone containing intercalated flow banding or other primary structures. Most of marine sandstone and shale. Marine beds have not the flows are very fine grained and partly glassy; been definitely identified in the Kinter Formation small phenocrysts of plagioclase, pyroxene, or horn­ in the Yuma area, although in the subsurface the blende are present but not abundant. The tuff is older marine sedimentary rocks underlying the light gray, soft, and pumiceous and contains scat­ Bouse Formation may be at least in part contempo­ tered crystals of biotite, hornblende, pyroxene rary with the Kinter (fig. 11). (mostly augite), and plagioclase, as well as scat­

OTHER NONMARINE SEDIMENTARY ROCKS tered fragments of fine-grained andesite and abun­ dant glass shards. The thickness of this sequence of In addition to the units described above, unnamed andesitic flows and tuffs is difficult to estimate but nonmarine sedimentary rocks of probable Tertiary is probably less than 1,000 feet. age chiefly coarse breccia and conglomerate occur in the east-central Cargo Muchacho Moun­ PYROCLASTIC ROCKS OF SILICIC TO INTERMEDIATE tains and at scattered localities in the Gila Moun­ COMPOSITION tains. The stratigraphic assignment of these de­ Predominantly pyroclastic rocks overlie the older posits is uncertain. In the Cargo Muchacho Moun- andesite in the eastern Chocolate Mountains, in ains, coarse, loosely indurated conglomerate under­ places unconformably. These younger rocks range lies basalt or basaltic andesite of uncertain age and from light-colored soft, pumiceous ash-full tuff to H38 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA red densely welded ash-flow tuff (ignimbrite). Sev­ brecciated, probably from flowage after the lava eral beds of water-laid tuff and tuff breccia also are had begun to solidify. Most of the rock is medium present. A few flows of light- to medium-gray ande- gray to dark brownish gray, is more or less vesicu­ site or dacite occur in the upper part of the sequence lar, and on weathered surfaces is coated with dark- near Picacho Peak. A hard pink trachyte is reported brown desert varnish. It breaks up into small- at Senator Wash about 2 miles northwest of Im­ boulder-sized subangular fragments but on the whole perial Dam (U.S. Bureau of Reclamation, written is very resistant to erosion and forms long, promi­ commun., 1963). Associated with these rocks are nent ridges. widely scattered dikes and, near Picacho Peak, a The rock typically has a groundmass composed circular vent filled with a dull-gray aphanitic rock of tiny laths of plagioclase and pyroxene (chiefly (probably welded tuff). augite) and some brownish glass and opaque grains The softer beds of tuff form valleys, commonly (probably magnetite), and it contains scattered mantled with thin gravel deposits of Quaternary phenocrysts of olivine (partly altered to iddingsite), age; the more resistant beds of welded tuff and the augite, and plagioclase (labradorite). The potassium flows form ridges. The valleys and ridges are gen­ content of 1.4 percent, determined in a potassium- erally oriented northwest, parallel with the strike argon analysis for dating (Geochron Laboratories, of the beds. written commun., 1963), is considerably higher than The tuffs, both welded and nonwelded, are com­ that in most basalt (Nockolds and Alien, 1954) and posed chiefly of glass shards, with scattered crystals suggests that the rock is more likely a basaltic ande­ and small fragments of fine-grained to glassy vol­ site or potassic basalt rather than a normal basalt. canic rocks. The low refractive indices of the glass The flows of basaltic andesite or basalt overlie and the abundance of biotite, sanidine, and quartz in coarse breccia and conglomerate with angular dis­ some of the tuffs indicate probable rhyolitic or cordance and locally rest unconformably on the rhyodacitic (quartz-latitic) composition. Other tuffs older andesitic sequence. At a few places the ba­ contain more plagioclase, little or no sanidine and saltic andesite or basalt is overlain by tuff of silicic quartz, and augite or hornblende rather than biotite to intermediate composition, but most contacts of as the chief ferromagnesian constituent; these rocks these two rocks are faults; their age relations are probably are of andesitic or dacitic composition. therefore uncertain. The maximum exposed thick­ The predominantly pyroclastic sequence appears ness of the basaltic andesite or basalt in the south­ to reach a maximum thickness of about 1,500 feet eastern Chocolate Mountains is about 1,000 feet. in the eastern Chocolate Mountains, although un­ FLOWS AND VENT TUFF OF LAGUN& MOUNTAINS known displacements on poorly exposed faults make Flows and vent tuff of uncertain stratigraphic this estimate somewhat uncertain. A section about position occur at a few scattered localities in the 1,100-1,200 feet thick was observed in upper Sena­ Laguna Mountains. A sizable exposure of very fine tor Wash, but the base is not exposed at this locality. grained rocks of undertermined composition occurs In the Laguna Mountains the older andesite is near the west margin of the mountains, south of missing, and the younger pyroclastic rocks are much Laguna Dam. The concentric, steeply dipping struc­ thinner than they are in the Chocolate Mountains. ture of the rocks in this exposure suggests an The pyroclastic rocks are chiefly welded to non- eroded volcanic neck or plug. The neck or plug welded ash flows locally containing a small amount appears to be capped by remnants of flows that of black vitrophyre in the basal part. The sequence issued from the central part. ranges in thickness from a few feet in the southern Other small remnants of flows or possibly shallow part of the mountains, northwest of McPhaul intrusive bodies occur at several scattered localities Bridge, to nearly 400 feet in the northern part, east in the southern Laguna Mountains. The relations of of Laguna Dam. The pyroclastic rocks overlie these rocks to the other volcanic rocks in the area coarse breccia and conglomerate with angular un­ are not known. conformity and are overlain by the Kinter Forma­ tion without significant angular discordance. BASALT OR BASALTIC ANDESITE OF UNKNOWN AGE Basalt or basaltic andesite of unknown age and BASALTIC ANDESITE OR BASALT OF CHOCOLATE MOUNTAINS stratigraphic position occurs at several localities The most prominent ridges in the southeastern scattered throughout the Yuma area. All the masses Chocolate Mountains are formed of dark basaltic are small, and one was penetrated in U.S. Bureau andesite or basalt (fig. 7). This rock comprises sev­ of Reclamation test well CH-8 about 2 miles north eral distinct flows or flow units, some of which are of Yuma the only known subsurface occurrence of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H39 volcanic rock in the Yuma area. Four of the expo­ TABLE 2. Potassium-argon ages of volcanic rocks in the sures are in the northwestern part of the area: two Yuma area Continued on the east flank of the Cargo Muchacho Mountains, Apparent age Location, description, and stratigraphic position (million one on the west flank of those mountains, and one of sample years) in the Ogilby Hills. A fifth exposure occurs at Eaven Lat 32°56'56" N., long 114°33'12" W., Chocolate Butte on the east flank of the Tinajas Altas Moun­ Mountains, Calif. Sample from a flow of horn­ blende andesite that overlies dated pumiceous tains in the southeastern part of the area. The ex­ andesite tuff (sample COL 2-7:38A). Sample posed bodies are either flat lying or gently tilted. COL 2-7:41A; Univ. Arizona lab. FED 1-67. K-Ar age of hornblende phenocrysts ______24.7±2.1 The overlie crystalline rocks of pre-Tertiary age or, Lat 32°56'37" N., long 114°32'52" W., Chocolate in places, conglomerate of uncertain age. The basalt Mountains, Calif. Sample from a bed of pumi­ ceous andesite (?) tuff that underlies dated horn­ penetrated in the well 2 miles north of Yuma is blende andesite flow (sample COL 2-7:4lA). overlain by possibly a few feet of the Bouse Forma­ Both the flow and the tuff appear to be strati- graphically below the dated felsic tuff and tion and then by alluvium of the Colorado Kiver. welded tuff and probably below the dated basal­ AGE OF VOLCANIC ROCKS tic andesite or basalt. Sample COL 2-7:38A; Geochron lab. BO 514. K-Ar age of biotite ___ 25.9±0.9 The main masses of volcanic rocks in the Choco­ late and Laguna Mountains have been dated with The apparent ages of the volcanic rocks have re­ reasonable certainty by the potassium-argon method. markably little spread and suggest that the entire The results of the determinations for five samples, sequence was erupted within a relatively short time. and for a sixth sample from an ash bed in the over­ The precision of the age determinations is not lying Kinter Formation, are given in table 2. The sufficient to corroborate the inferred stratigraphic samples are listed in approximate stratigraphic or­ sequence. The potassium-argon dates all indicate a der, with the youngest at the top. The stragraphic late Oligocene or early Miocene age for the volcanic position of the basaltic andesite or basalt is uncer­ rocks according to the widely used time scales of tain ; it may be below rather than above most of the Holmes (1960) and Kulp (1961). However, until tuffs of silicic to intermediate composition, but it the problems of interpreting apparent radiometric definitely overlies the older andeside (represented by ages and correlating them with standard Tertiary the lowermost two samples in table 2). sedimentary sequences are worked out more thor­ oughly than they are at present, it seems best to TABLE 2. Potassium-argon ages of volcanic rocks in the Yuma area say only that the main volcanic sequence in the Yuma area is middle Tertiary. Volcanic rocks of Apparent age Location, description, and stratigraphic position (million similar age have been described from many other of sample years) places in the Basin and Range province; Damon and Lat 32°45'58" N., long 114°26'10" W., Laguna Mountains, Ariz. Sample from bed 2-4 ft thick Bikerman (1964, 1965) and Bikerman and Damon composed of pink altered bentonitic ash in lower (1966) have described a middle Tertiary pulse of part of upper member of Kinter Formation. Lo­ cally Kinter Formation overlies breccia and hypabyssal plutonism and volcanism which reached conglomerate of heterogeneous composition. a peak between 25 and 30 million years ago in south­ Sample VAW-60:29; USGS lab, 471-B. K-Ar age of biotite ______23±1.2 eastern Arizona and adjacent areas. Lat 32°49'53" N., long 114°31'39" W., Chocolate The age and correlation of the flows and vent tuff Mountains, Calif. Sample from base of a se­ quence of flows of basaltic andesite or basalt of the Laguna Mountains, and of the scattered that unconformably overlies breccia and con- masses of basalt or basaltic andesite, are uncertain. 'omerate of heterogeneous composition. Sample Stratigraphic relations indicate that these rocks SC2-15:35B; Univ. Arizona lab. (P. E. Damon, written commun., 1970). K-Ar whole-rock age __ 25.1±1.6 also are middle Tertiary. These scattered masses Lat 32°48'13" N., long 114°28'50" W., Laguna Mountains, Ariz. Sample from top of a bed of may be in part correlative with the basaltic andesite pale-purple porous soft vitric crystal tuff at top or basalt of the southeastern Chocolate Mountains, of section at least 200 ft thick composed of vitric but some might be younger. tuff, welded tuff, vitrophyre, and possible flow rock of felsic to intermediate composition. Vol­ OLDER MARINE SEDIMENTARY ROCKS (TERTIARY) canic rocks unconformably overlie granite brec­ cia and conglomerate and are overlain (uncon­ Predominantly fine grained deposits that contain formably?) by fanglomerate of the Kinter invertebrate faunas representing marine and possi­ Formation. Sample 5-15:55A; Univ. Arizona lab. FED 4-65. K-Ar age of biotite ______26.3±1.0 ble brackish-water environments have been pene­ Lat 32°55'15" N., long 114°31'12" W., Chocolate trated in several oil-test wells and water-test wells Mountains, Calif. Sample from a bed of hard grayish-purple slightly welded felsic tuff within in the Yuma area. Data from U.S. Geological Survey a sequence of tuff and welded tuff of felsic to test well LCRP 29 and two oil-test wells indicate intermediate composition. Sample COL 2-35:1A; Geochron lab. FO 448. K-Ar age of sanidine __ 26.2±1.6 that the marine sedimentary rocks in much of the H40 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA area are divisible into two units: (1) An older, more other areas are not known with certainty. The strati- indurated, and probably more deformed sequence, graphic position of these beds suggests that they herein designated the older marine sedimentary probably intertongue with nonmarine beds of the rocks, and (2) a younger, generally finer grained Kinter Formation of Miocene age. sequence which is assigned to the Bouse Formation, Mrs. P. B. Smith (written commun., Oct. 12, a name given by Metzger (1968) to equivalent strata 1969) reports that the planktonic foraminifer in the Parker-Blythe-Cibola area. Sphaeroidinella dehiscens in the sample of older A dip log of one of the oil-test wells Colorado marine sedimentary rocks from well LCRP 29 is Basin Associates Federal 1 in the south-central part now regarded as post-Miocene and is, in fact, con­ of the Yuma Mesa indicates the presence of an sidered to be a guide fossil to the Miocene-Pliocene angular unconformity between the two marine units boundary. The older marine sedimentary rocks and that the older sequence may be essentially con­ therefore would be Pliocene, rather than Miocene. formable on underlying nonmarine rocks. In con­ However, because of the apparent conflict with other trast to the Bouse Formation, which is mostly silt lines of evidence, it seems best to defer assigning a and clay with subordinate thin layers of sand, the definite age to the older marine sedimentary rocks older marine sedimentary rocks contain much more until additional information becomes available. sand and are also more indurated. In test well LCRP On the west side of the Split 29 the greater degree of induration of the older Mountain Formation of Tarbet and Holman (1944) sequence is shown by a caliper log made just after contains a poorly preserved, meager foraminiferal the pilot hole was completed (fig. 14). The log shows fauna of Miocene age in the middle part (Tarbet that the hole remained at or near the diameter of and Holman, 1944), or in the upper part (Durham the drilling bit throughout the thickness of the older and Allison, 1961). The Split Mountain is overlain marine sedimentary rocks, even though the sequence unconformably by the marine Imperial Formation is very sandy; whereas in the Bouse Formation, al­ (Durham and Allison, 1961; Woodard, 1961). Be­ most all the thin strata of sand, and much of the cause of their similar structural and stratigraphic clay and silt as well, washed out or sloughed, en­ relations, the older marine sedimentary rocks and larging the hole. the Bouse Formation of the Yuma area may be cor­ The older marine sedimentary rocks consist of relative, respectively, with the marine part of the more or less indurated light-gray fine-grained sand­ Split Mountain Formation of Tarbet and Holman stone and interbedded medium- to dark-gray silt- (1944) and with the Imperial Formation. However, stone and claystone. The sandy strata make up in both places the faunas are somewhat different in about half the total thickness in all three test wells the presumably equivalent units, and it has not yet (LCRP 29, Colorado Basin Associates Federal 1, proved possible to trace the units from one area to and Yuma Valley Oil and Gas Co. Musgrove 1). the other beneath the intervening Imperial Valley. Beds of ash or tuff are reported in the two oil-test The maximum thickness of the older marine sedi­ wells, and at least one bed of altered soft tuff or mentary rocks in the Yuma area may exceed 1,000 ash was penetrated in the lower part of the section feet. A vertical interval of 1,135 feet was penetrated in well LCRP 29 (fig. 14). in Colorado Basin Associates Federal 1 oil test; Fossils in the older marine sedimentary rocks however, if the average dip of 30° indicated by the include foraminifers and mollusks indicative of a dip log is correct, the stratigraphic thickness in this marine environment but not diagnostic as to age. well is a little less than 1,000 feet. According to an In well LCRP 29, Smith (1968) reports the pres­ interpretation of seismic-reflection data and the ence of two foraminiferal faunas: the older (which record of test well LCRP 29, the thickness may be occurs in what are herein designated the older somewhat greater near that well; it may be greater marine sedimentary rocks) consists of abundant also near well LCRP 25, which, however, did not globigerinids, mainly Globigerinita uvula with few penetrate these rocks. to common Globquaderina hexagona and Sphaer- hoidinella dehiscens, plus a good shelf benthonic BOUSE FORMATION (PLIOCENE) fauna including Planulina sp., Uvigerina sp., Han- The Bouse Formation was named and described zaivayai sp., and Bolivina interjuncta. The younger by Metzger (1968) in the Parker-Blythe-Cibola fauna occurs in the overlying Bouse Formation and area along the Colorado River north of the Yuma indicates much shallower, more restricted waters. area. The younger sequence of marine sedimentary The age of the older marine sedimentary rocks rocks in the Yuma area is assigned to the Bouse on and their correlation with stratigraphic units of the basis of similar lithology and stratigraphic posi- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H41

CALIPER LOG ELECTRIC AND LITHOLOGIC LOGS GAMMA LOG Depth in Hole diameter, Spontaneous potential, Resistivity (18 in.), feet in inches in millivolts in ohms m 2/m Increasing gamma radiation 6 8 10 12 14 16 - 15| + 0 30 1000 Transition zone

1045 ft

1100

1200 Bouse Formation

1300

1320 ft

1400 -1396 ft-

1500

Bit size 10 58 in.

1600

1700

1800

1900

T. P., 1997 ft 2000 6 8 10 12 14 16 Note: Lithologic explanation on plate 6

FIGURE 14. Selected logs of test well LCRP 29 below a depth of 1,000 feet.

507-243 O - 74 - 4 H42 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA tion and of an identical foraminiferal fauna (Smith, and Rosalina columbiense. (P. B. Smith, written 1968). commun., 1969). The faunas are said to indicate The Bouse Formation is widespread in the sub­ brackish to marine environments but are not diag­ surface, but the only known exposure in the Yuma nostic as to age (Metzger, 1968). area is 2 miles southeast of Imperial Dam, just east The sandy limestone or calcareous sandstone of the Colorado River flood plain (pi. 3). The Bouse locally present at the base of the Bouse Formation appears to be more extensive than the older marine is very pale gray to grayish yellow and in places sedimentary rocks and is probably absent only in contains an abundant marine fauna, including corals the mountains, in most of the foothills, and on the as well as mollusks. This calcareous bed is equiva­ tops and upper flanks of buried ridges of pre- lent to the basal limestone described by Metzger Tertiary and early to middle Tertiary rocks (fig. (1968) in the Parker-Blythe-Cibola area. In the 15). Yuma area, this limestone was penetrated in test Although it has been broadly warped and locally wells LCRP 26 and 23, in a private well (C-9- faulted (fig. 15), the Bouse Formation appears to 21)14bdb, and probably in oil-test well Sinclair Oil be substantially less deformed than the nonmarine Co. Kryger 1, but in other wells penetrating the sedimentary rocks and the older marine sedimentary base of the Bouse Formation it is either absent or rocks, and it probably was deposited after the prin­ unrecognized. In gamma-ray logs this basal lime­ cipal mountain masses in the Yuma area had as­ stone is a prominent zone of abnormally low natural sumed approximately their present configuration gamma radiation. In test well LCRP 26 it uncon- but not their present altitude. formably overlies a nonmarine coarse fanglomerate, The thickness of the Bouse ranges from zero the top few feet of which appears to be weathered, where it pinches out or is overlapped by alluvium probably representing a fossil soil zone. The weath­ to a maximum of about 950 feet in Yuma Valley ered zone is characterized by high natural gamma Oil and Gas Co. Musgrove 1 test well near the radiation (probably owing to its clay content), southwest corner of the area. Except at some places which contrasts vividly with the very low gamma in the northeastern part of the area where the con­ radiation of the overlying basal limestone (or cal­ tact with overlying older alluvium is sharp and may careous sandstone) of the Bouse Formation (fig. be an unconformity, the Bouse Formation is over­ 16). In well LCRP 26 the basal limestone is 28 feet lain by a transition zone in which marine clay and thick and is overlain by a bed about 9 feet thick silt are interbedded with nonmarine alluvial de­ that has abnormally high gamma radiation and is posits like those in the older alluvium. probably a tuff or altered tuff (fig. 16). Unfortu­ The Bouse Formation consists predominantly of nately, only a very few cuttings of this bed were silt and clay, with subordinate very fine to fine sand, recovered during drilling, so its exact nature is not hard calcareous claystone, and locally in the basal known, and it could not be dated radiometrically. part calcareous sandstone or sandy limestone, tuff, In test well LCRP 23 the clay, silt, and fine sand and possibly conglomerate of local derivation. In the of the upper part of the Bouse Formation are under­ subsurface the clay and silt are pale-greenish gray lain by conglomerate and arkosic sandstone com­ to bluish gray (dark green to dark blue when wet) ; posed of granitic and metamorphic rocks containing some strata are pink and brown. The very fine to a 3-foot bed of bluish-gray claystone similar to that fine sand is light gray and is well sorted. In the higher in the section. These beds overlie a 6-foot exposures southeast of Imperial Dam the predomi­ stratum of sandy limestone, which in turn rests on nant color of the fine-grained beds is pale-greenish conglomerate (fanglomerate?) much like that above. gray, but pale-yellowish-gray, light-brown, and pink The stratigraphic position of the conglomerate, the beds are conspicuous in the upper part, which is interbed of claystone, and the sandy limestone are transitional into grayish-brown and reddish-brown uncertain; no fossils were collected from these beds. clay and silt characteristic of the overlying older Lithologically, the conglomerate resembles that in alluvium. Organic remains, both plant and animal, the Kinter Formation, which unconformably under­ are abundant in some zones. Small gastropods, pele- lies the Bouse Formation southeast of Imperial Dam cypods, and ostracodes can be seen with the unaided and probably also at test well LCRP 14 at Laguna eye. Plant remains consist of molds of twigs and Dam. However, the presence of the bluish-gray clay- roots, partly filled with brown ferric oxides or hy­ stone in the middle of the section and of the sandy droxides. The microscope reveals also several spe­ limestone at the base suggests that the entire se­ cies of Foraminifera, consisting of Ammonia bec- quence belongs to the Bouse Formation. The con­ carii, Elphidium cf. E. gunteri, Eponidella palmerae, glomerate and sandstone beds may represent beach GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H43

32°45

Inferred subsurface margin of Bouse Formation Well penetrating pre-Bouse rocks '.:::+ 245 beneath alluvium Exposure of Bouse Formation pTc, pre-Tertiary crystalline rocks; Tn, + 245, altitude of top of formation, Tertiary nonmarine sedimentary rocks; in feet above mean sea level TV, Tertiary volcanic rocks .-2950 Mountains and hills Structure contour Well penetrating Bouse Formation Shows altitude of top of Bouse Formation. 2950, altitude of top of formation, in feet Contour interval 500 feet. Datum is above mean sea level. Plus or minus mean sea level Area of shallow bedrock sign after number indicates an estimated altitude, from geophysical data, for well penetrating only the overlying transition Fault offsetting Bouse Formation Alluvial escarpmen t zone Dashed and queried where uncertain 32°15'

FIGURE 15. Inferred extent and configuration of the Bouse Formation. gravels or offshore bars similar to those described The invertebrate fossils in the Bouse Formation by Metzger (1968) in the basal limestone of the are useful as indicators of a marine to brackish- Bouse Formation in the Parker-Blythe-Cibola area water environment, but none so far identified is to the north. diagnostic as to age except within broad limits. H44 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

ACOUSTIC-VELOCITY LITHOLOGIC RESISTIVITY LOG GAMMA LOG Depth LOG LOG in feet Velocity, in feet per second R, in ohms m 2/m (18 in.) Increasing gamma radiation 4000 6000 8000 10,000 12,000 14,000 0 6 12 18 24 30 36 1000 Ib Older alluvium 2a 1033 ft IT 1050

Transition 5 zone

Ib 1100

1115 ft

1150

1200

Bouse Formation

1250

1300

6 1343 ft TcT luffj 1350 1352 ft Basal limestone

1400 Nonmarine sedimentary rocks (fanglomerate)

1450 4000 6000 8000 10,000 12,000 14,000 0 6 12 18 24 30 36 Note: Lithologic explanation on plate 6

FIGURE 16. Selected logs of test well LCRP 26 between depths of 1,000 and 1,450 feet. P. B. Smith (written commun., 1966) reports that within the Pliocene, although a more definite age the foraminifers range from Miocene to Holocene, assignment is not yet possible. Metzger (1968) though none is living on the Pacific coast today. describes a thin tuff within the basal limestone of Metzger (1968) reviews other evidence for the the Bouse Formation between the Parker-Blythe- age of the Bouse and concludes that it belongs Cibola area and Imperial Valley which was dated GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H45 by the potassium-argon method as 8.1 ±4.4 m.y. to moderately indurated conglomerate composed (P. E. Damon, written commun., 1969). This tuff chiefly of volcanic detritus derived from nearby ex­ may be correlative with that just above the basal posures of the volcanic rocks. In places the contact limestone in test well LCRP 26 (fig. 16). of the conglomerate and the older rocks is an angu­ Little additional evidence for the age of the Bouse lar unconformity with a discordance of as much as Formation is available in the Yuma area. As men­ 15°, but in other places the discordance is slight or tioned earlier, the Bouse overlies the Kinter Forma- absent. Small angular unconformities have been (Miocene) with at least local angular discordance; observed within the conglomerate and probably a lower limit of Miocene (probably late Miocene) record uplift of the Chocolate Mountains mass while is therefore reasonably well established. As in the deposition was going on. On the west flank of the Parker-Blythe-Cibola area, none of the distinctive mountains the conglomerate is overlain unconform- well-rounded siliceous gravel characteristic of Colo­ ably by older alluvium (old deposits of the Colorado rado River alluvium occurs within or below the River), but farther west the contact of these two Bouse Formation, so the Bouse antedates the estab­ units may be conformable or gradational. From the lishment of the Colorado River as a through-flowing field relations it appears that the older parts of the stream within the present lower Colorado River conglomerate of the Chocolate Mountains may be region. In the Yuma area, the Bouse Formation is equivalent in age to the upper part of the nonmarine overlain gradationally by alluvium of the Colorado sedimentary rocks (Kinter Formation of Miocene River; Metzger (1968) cites evidence that the age), but that the younger parts are equivalent in earliest deposits of the lower Colorado River are no age to the older alluvium (Pliocene and Pleistocene). younger than late Pliocene. (See fig. 11.) The conglomerate of the Chocolate Mountains is TRANSITION ZONE (PLIOCENE) typically pale pink when viewed from a distance Throughout most of the Yuma area, the Bouse and is composed chiefly of pink and gray fragments Formation appears to be overlain conformably by of ash-flow tuff and welded tuff. Most of the alluvium deposited by the Colorado River and pos­ fragments, which range in size from granules to sibly the Gila River. In much of the area, marine occasional slabs and blocks several feet across, are deposition did not cease abruptly, however, and the subangular or angular. Beds of pale-brown soft marine deposits are overlain by alternating or inter- sandstone are locally conspicuous. The upper part tonguing marine and nonmarine (alluvial) strata. of the unit contains abundant soft brown siltstone. For convenience this interval, which is as much as The conglomerate generally is only mildly de­ several hundred feet thick in the southwestern part formed; the bedding dips less than 5° at most places of the area, is designated the transition zone. The but bedding as steep as 45° has been observed near top of the transition zone is defined by the upper­ normal faults. Small high-angle normal faults are most bed of fossiliferous gray clay or silt, the base abundant, especially in the more indurated parts of by the lowermost bed of recognizable sand or grav­ the unit and where the bedding dips more than elly sand of fluvial origin just above the predomi­ about 4°. nantly fine grained marine beds of the Bouse Forma­ tion. In a few wells, thin beds of bluish- or greenish- OLDER ALLUVIUM (PLIOCENE AND PLEISTOCENE) gray clay have been reported within the alluvium as The older alluvium consists of basin-filling fluvial much as 1,000 feet above the top of the deposits and deltaic sediments deposited by the Colorado and assigned to the transition zone. These beds, gen­ Gila Rivers and by local ephemeral streams. The erally less than 2 feet thick, may indicate later unit does not represent a single cycle of aggrada­ brief recurrences of marine conditions, but more tion but rather is a complex of fills separated by likely they are not beds at all but are boulders of degradational cycles during which extensive scour­ the marine clay reworked into the alluvium by the ing occurred. The degradational and aggradational ancestral Colorado River. Such boulders have baen cycles probably were caused in part by fluctuations observed in exposures of the older alluvium at many in sea level amounting to several hundred feet re­ places. lated to glacial and interglacial stages and in part CONGLOMERATE OF CHOCOLATE MOUNTAINS by both regional and local warping of the land sur­ (TERTIARY AND QUATERNARY) face. Erosion by the river probably occurred during On the flanks of the southern Chocolate Moun­ times of lowered sea level or upwarping; deposition tains, the nonmarine sedimentary rocks and vol­ took place when sea level rose or downwarp oc­ canic rocks of Tertiary age are overlain by a slightly curred. The southwestern part of the Yuma area, H46 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA on the margin of the Sal ton Trough, subsided con­ AGE AND CORRELATION tinually under the load of the fluvial and deltaic The age of the older alluvium ranges from Plio­ deposits so that not all the deposits of the aggrada- cene to late Pleistocene, according to several lines tional episodes were removed during the ensuing of evidence. The underlying Bouse Formation is degradational episodes. Farther northeast and adja­ considered Pliocene (p. H44), and the overlying cent to the mountain blocks, however, many if not younger alluvium is Holocene and possibly latest most of the earlier fills were removed and replaced Pleistocene. Recent studies of the erosional history by later fills. of the Grand Canyon, summarized in McKee, Wilson, Although different alluvial fills separated by un­ Breed, and Breed (1967), show that the canyon was conformities have been identified in outcrop areas, cut to nearly its present depth by the middle Pleis­ subsurface delineation of all the fills has not been tocene. This seems to require an inauguration of possible with present data. Accordingly, all the the canyon cutting well before the beginning of the alluvial and deltaic deposits older than the most Pleistocene and would imply that the Colorado River recent fill are grouped in one unit designated as had entered the downstream region including the older alluvium. The older alluvium occupies the Yuma area at least as early as some time in the stratigraphic interval between the transition zone Pliocene. The Gila River may not have entered the (or the Bouse Formation where the transition zone Yuma area until long after the advent of the Colo­ is absent) and the younger alluvium (the most re­ rado River, but the scanty evidence is inconclusive cent fill). as to the history of the ancestral Gila River down­ DISTRIBUTION AND THICKNESS stream from the Phoenix basin (M. E. Cooley, writ­ The older alluvium is the most widely exposed stratigraphic unit in the Yuma area. It is exposed ten commun., 1969). Three samples of carbonized wood from the upper in mesas, stream terraces, and piedmont areas and part of the older alluvium in the Yuma area have underlies the younger alluvium of the present flood been analyzed by the radiocarbon (C14) method. plains of the Colorado and Gila Rivers and the The results are listed below: young alluvial fans in the southeastern part of the area (pi. 3). At some places the older alluvium is Age in years before present concealed by a blanket of windblown sand. Expo­ (C-10-23)31bbbl. U.S. Geological Survey test well sures of older alluvium commonly are dissected, and LCRP 1. Lignite from a depth of 472-474 ft. USGS lab. W-1428 ______>42,000 many are characterized by desert pavement that (C-10-24)12ccc2. U.S. Bureau of Reclamation formed on poorly sorted gravelly deposits (pi. 3). drainage well YVI-28. Carbonized wood from a depth of 128-130 ft. Geochron lab. GXO-661__ >33,600 On the flanks of some of the mountains, coarse older 16S/23E-10Rcc. U.S. Geological Survey test well alluvium of local origin forms low hills and dis­ LCRP 23. Carbonized wood from a depth of sected uplands similar to some of the exposures of 224-234 ft. USGS lab. W-1538 ______>36,000 coarse nonmarine sedimentary rocks of Tertiary All three samples are older than the limits of the age (fig. 9). radiocarbon method of measurement, and the differ­ The thickness of the older alluvium ranges from ences in the minimum ages shown are not signifi­ zero to as much as 2,500 feet in the southwestern cant. The unconformably overlying younger allu­ part of the area, near San Luis, Ariz.; if the under­ vium has yielded radiocarbon ages of less than lying transition zone is included, the maximum 10,000 years in the Parker-Blythe-Cibola area thickness is about 3,400 feet (fig. 15 and pi. 10). (Metzger and others, 1972). Thus, the radiocarbon This thickness is much greater than that attained evidence indicates that the upper part of the older by equivalent deposits north of the Yuma area; alluvium can be no younger late Pleistocene. Metzger, Loeltz, and Irelan report that the maximum The older alluvium of the Yuma area probably is depth to the base of the older alluvium in the correlative with the older alluvium of the Parker- Parker-Blythe-Cibola area is about 600 feet. The Blythe-Cibola area (Metzger and others, 1973). great thickness in the Yuma area, and the much Deposits near Gila Bend 120 miles east of Yuma, greater thickness of equivalent deposits of the Colo­ called older alluvial fill by Heindl and Armstrong rado River in Imperial Valley, indicate subsidence (1963), probably are correlative with the older during deposition. The oldest alluvial deposits (at alluvium in the Yuma area. In the Imperial Valley the base of the transition zone), which are now more region, units equivalent or partly equivalent to the than 3,000 feet below sea level near San Luis (fig. older alluvium of the Yuma area include the Palm 15), must have been deposited above or at least not Spring Formation, the Canebrake Conglomerate of far below sea level by the ancestral Colorado River. Dibblee (1954), and the Borrego Formation of Tar- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H47 bet and Holman (1944); the Ocotillo Conglomer­ of silty or clayey sand (fig. 17). Scour and fill are ate and the Brawley Formation (both of Dibblee, common, and individual strata are poorly defined 1954) may be equivalent to the uppermost part of and lenticular. The composition of the gravel is the older alluvium. closely related to the kinds of older rocks in the drainage area. Farther from the source, the deposits CLASSIFICATION OF DEPOSITS BY SOURCE become finer grained and better sorted and the The older alluvium comprises a great variety of gravel more rounded. granular materials ranging from clay to cobble and Most of the older alluvium of local origin probably boulder gravel. On the geologic map (pi. 3) these was deposited as alluvial fans. The oldest exposed materials are classified according to their primary local deposits are comparatively thick masses of source into deposits of local origin, deposits of the coarse ill-sorted gravel which characteristically form old Colorado and Gila Rivers, and deposits of mixed low hills and dissected uplands mantled with a origin. In addition, many of the areas adjacent to blanket of coarse colluvium (fig. 9). the mountains are mantled with relatively thin sheets and ribbonlike bodies of gravelly deposits left STREAM-TERRACE AND PIEDMONT DEPOSITS behind as these areas were dissected. These deposits* Except for the scattered low hills and dissected referred to as stream-terrace and piedmont deposits, uplands mentioned above, the older fills in the older are included with the older deposits of local origin alluvium are capped by relatively thin stream- on the geologic map; their extent is indicated in a terrace and piedmont deposits left behind as the general way by the pattern representing desert older deposits were progressively dissected by local pavement, which is characteristic of the exposures streams and sheetfloods. The stream-terrace and (Pi. 3). piedmont deposits consist largely of ill-sorted gravel associated with much sand, silt, and clay. At most DEPOSITS OF LOCAL ORIGIN places they overlie similar older fill from which The deposits of local origin occupy the margins they are often difficult to distinguish. According to of the area, adjacent to the mountains and expo­ F. L. Doyle (written commun., 1963), who inten­ sures of older rocks, and were laid down by ephem sively studied the piedmont area at the northwest eral streams and sheetfloods. Because most of the corner of the Gila Mountains, the gravelly pied­ materials were deposited as flood-swollen, muddy mont deposits represent the bedloads of ephemeral masses of debris from nearby sources, they are streams that dissected the older rocks and alluvial obscurely bedded and poorly sorted. Typically they fills. consist of angular to subangular gravel in a matrix As their name implies, the stream-terrace and piedmont deposits occur in two principal environ­ ments which, however, tend to intergrade. The stream-terrace deposits are found at different levels along the larger washes and also along abandoned washes, where they reach a maximum thickness of more than 50 feet. The terraces are not paired and are most extensive on the concave sides of large bends. The deposits undoubtedly are analogous to those now accumulating in the larger washes. The piedmont deposits underlie extensive piedmont sur­ faces formed by a combination of sheetfloods and shifting ephemeral streams. These deposits are less than 10 feet thick at most places. Most exposures of stream-terrace and piedmont deposits are characterized by an armor of closely spaced pebbles or small cobbles which is called "desert pavement." In many places these stones form a mosaic so that little sand or silt is visible. The stones are generally coated with a dark stain called "desert varnish," which gives the pavement FIGURE 17. Poorly sorted gravelly deposits of local origin exposed in a dark aspect, like asphalt. Not all pavement is dark, west bank of Fortuna Wash 0.4 of a mile north of U.S^ Interstate Highway 8. however. Pebbles and cobbles of the lighter colored H48 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA granitic and quartzose rocks commonly lack a good the flanks of the Chocolate Mountains (fig. 18) and coating of desert varnish (fig. 8). the almost-buried "Yuma Hills." Most desert pavement contains a layer of silty DEPOSITS OF THE OLD COLORADO AND GILA RIVERS sand and silt 2-4 inches thick just below the armor The greatest bulk of the older alluvium in the of pebbles and cobbles. The layer is impoverished in Yuma area consists of deposits of the old Colorado gravel and nearly everywhere contains some clay as and Gila Rivers. These deposits are noticeably dif­ a binder. It is underlain by a darker mixture of ferent from those of local origin. They are better silty sand and gravel in a zone as much as 8 inches sorted and stratified and less heterogeneous on a thick. The darker third layer contains seams of cal­ small scale than the local deposits; the river gravel cium carbonate (caliche) and may represent the is much more rounded than the local gravel and B soil horizon. Owing to their clay arid silt content, contains types of rocks derived from the middle and the second and third layers are not very permeable, upper parts of the Colorado River drainage basin. and the dense mosaic of stones in the top layer does In contrast with the local deposits, which are ex­ not allow water to penetrate rapidly from the sur­ tremely variable, both areally and vertically, the face. Infiltration rates from precipitation are low, river deposits contain some beds or zones that can and much of the water runs off pavement surfaces be traced for several miles. during storms. Infiltration rates are higher in the Sand is the most abundant material in the old areas of light-colored granitic and quartzose pave­ river deposits. The river sand is much better sorted ment, which have thinner silty and clayey sub­ than the local sand and is more commonly cross- strata. bedded (fig. 19). Also, the grains of river sand are The desert varnish on desert pavement consists generally more rounded than those of local sand. of oxides of manganese and iron brought to the sur­ River sand is typically gray to pinkish gray, where­ face by capillary action assisted by acid secretions as local sand is yellowish to reddish brown. of lichens (Laudermilk, 1931). Hunt (1954) cites Crude analyses of several samples of fine to archeological evidence that most coatings of desert medium river sand from the older alluvium near varnish are at least 2,000 years old, although Engel Yuma indicate the following approximate composi­ and Sharp (1958) state that varnish is not neces­ tion: Quartz, 65-75 percent; feldspar (not differ­ sarily an indicator of antiquity. If Hunt's conclu­ entiated), 10-20 percent; rock fragments, 5-15 per­ sions (1954) are correct, the widespread presence cent; calcite and dolomite (in part as cement), 2-5 of varnish on even the lower stream terraces and on percent; and heavy minerals, 1-8 percent. The bedrock exposures attests to the general slowness quartz is clear to translucent, mostly subrounded to of the processes of weathering and erosion in the subangular but occasionally rounded; feldspar is region. white, pink, or grayish-yellow and subangular to DEPOSITS OF MIXED ORIGIN subrounded; rock fragments are chiefly small, angu­ Where the deposits of local origin intertongue or lar to subrounded, and composed of chert, quartzite, grade laterally into old deposits of the Colorado and granitic, metamorphic, and volcanic rocks. Most of Gila Rivers, the materials are classified on the geo­ the river sand is feldspathic, according to the classi­ logic map (pi. 3) as deposits of mixed origin. Much fication of Krumbein and Sloss (1951). of this unit consists of river deposits that have been Results of heavy-mineral analyses of alluvial sand reworked by local ephemeral streams and sheetfloods (chiefly older alluvium but including some younger and mixed with deposits of local origin. At many alluvium) are summarized -in table 3. Most of the places, good exposures reveal a broad zone of dis­ samples represent river deposits; the two samples tinctive buff silt and fine sand which grades away from well (C-8-23)33cdd (test well LCRP 13) rep­ from the mountains into well-sorted fine to medium resent local sand and are quite different in composi­ river sand, and toward the mountains into ill-sorted tion from the other samples. Amphiboles (chiefly gravelly deposits of local origin. From this relation­ green hornblende), pyroxenes (chiefly augite), and ship it is inferred that the old Colorado and Gila opaque minerals (magnetite, ilmenite, and pyrite) Rivers were bordered by broad flood plains into typically compose about three-fourths of the total; which discharged, during brief periods, local runoff garnet and zircon are the other important heavy carrying detritus from the adjacent hills and moun­ minerals. No significant variation in heavy-mineral tains. However, at some places the flood-plain silt composition with depth has been noted, with the and fine sand abut directly against older rocks and possible exception that the orthorhombic pyroxenes contain very little coarse detritus of strictly local (hypersthene and enstatite) are scarce or absent derivation. This relationship has been observed on below depths of about 350 feet in the Yuma Mesa. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H49

FIGURE 18. View in southeastern Chocolate Mountains, Calif., showing predominantly fine-grained older alluvium abutting basaltic andesite or basalt of Tertiary age.

Other investigators in the region have reported River gravel is exposed at many places through­ similar conclusions. R. W. Thompson (written out the Yuma area. Along the southeast margin of commun., 1963) states that amphiboles, pyroxenes, "Picacho Mesa" a gravel tongue can be traced for and opaque minerals compose more than 80 percent a distance of about 10 miles. Similar tongues occur of the heavy-mineral total in sand of the lower farther north as much as 560 feet above sea level Colorado River delta and Gulf of California; epi- and also in the "Upper Mesa" as much as 580 feet dote, titanite, garnet, and zircon also are present above sea level. The highest known occurrences of in significant amounts. Imbrie and van Andel (1964) river gravel in the Yuma area are at 740 feet above describe the north end of the Gulf of California as sea level on the southwest flanks of the Chocolate an amphibole-augite-garnet heavy-mineral province Mountains. in which the Colorado River is the probable source In the subsurface, river gravel occurs throughout of the sediments. the entire thickness of older alluvium and underly­ After sand, gravel probably is the most abundant ing transition zone to depths as great as 3,400 feet material in the deposits of the old Colorado and Gila near the southwest corner of the area, although the Rivers, especially in the upper several hundred feet coarse cobble-gravel strata probably extend no of these deposits. Some of the gravel is coarse and deeper than about 750 feet (pi. 6). The uppermost contains many rounded cobbles and small boulders. coarse-gravel strata beneath the river valleys and H50 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA 80 feet below sea level at the southwest corner of the area (pi. 7). Corresponding depths below valley surfaces are about 70 feet in eastern South Gila Valley, 100 feet at Laguna Dam, and 170 feet at the southwest corner of the area. The increasing depth toward the southwest results chiefly from southwestward gradation of the uppermost coarse- gravel strata into finer deposits, so that the top of the coarse-gravel zone is at a lower horizon in the southwest than in the northeast. Areas where the coarse-gravel zone does not ap­ pear to be present include the southeast margin of northern Yuma Mesa, "Picacho Mesa" and adja­ cent parts of "Bard Valley," most of the "Upper Mesa," and the northwest corner of Yuma Mesa and the adjacent northeast corner of Yuma Valley (pi. 7). The older alluvium of these areas is pre­ dominantly sandy, with only minor, apparently dis­ continuous streaks of fine gravel. The river gravel differs markedly in several re­ FIGURE 19. Crossbedded coarse sand and fine gravel in exposure of older spects from the local gravel of the older alluvium. alluvium 6 miles west of Yuma. The more resistant sand laminae in Unlike local gravel, in which bedding is indistinct these old deposits of the Colorado River have a slightly higher content of calcareous cementing material than the rest of the sand. and crossbedding rare, river gravel commonly is crossbedded; foreset bedding dips about 20°-30° Yuma Mesa constitute the principal aquifer in the and is conspicuous in many exposures. Cementation, Yuma area and are referred to collectively as the generally calcium carbonate, is a widespread char­ coarse-gravel zone (p. H67). Brown and others acteristic of the river gravel, both in exposures and (1956), who named the coarse-gravel zone, described in the subsurface. Compared to the local gravel, the it as a widespread blanketlike deposit underlying river gravel is better sorted, and the clasts are more at least part of their "upper terrace" ("Picacho rounded and include a large proportion of hard, Mesa" and "Upper Mesa"), as well as the interven­ siliceous rocks (fig. 20). Gray and tan quartzite are ing Yuma Mesa and river valleys. However, detailed generally the most abundant types of siliceous rocks; studies by both the U.S. Bureau of Reclamation other types include red and brown jasper, gray and (J. W. Julian, written and oral commun., 1967) black chert, and a distinctive crosslaminated tan and the U.S. Geological Survey have shown that and maroon quartzite very similar to some of the the coarse river gravel in the older alluvium occurs Tapeats Sandstone of Cambrian age in the Grand as a complex of several gravel bodies of different Canyon. Except for a few pebbles of brown jasper, ages, although it has not yet proved possible to these hard siliceous rocks are completely absent in determine the boundaries of all these bodies. The the gravel of entirely local origin. top and bottom of the coarse-gravel zone are there­ In places the river gravel contains as much as fore at different horizons and altitudes from place 80 percent siliceous rocks, but the usual proportion to place (pi. 7). Some of the irregularities in the is 30-60 percent (table 4). Other types of rocks zone are shown also in the geologic sections of the include a variety of felsic plutonic (granitic) rocks; area (pis. 5, 6, 8). The coarse-gravel bodies, includ­ felsic to intermediate volcanic rocks (including ing those below the coarse-gravel zone, probably abundant hard red welded tuff) ; various kinds of were deposited during the glacial stages of the schist, gneiss, and fine-grained metamorphic rocks; Pleistocene, when the Colorado River was swollen vein quartz; pegmatite, aplite, and other dike rocks; by glacial melt water from the Rocky Mountains, and in places some limestone and dolomite. Worn, and each gravel body fills a trench or valley scoured rounded fragments of silicified wood (probably in older fills. desert iron-wood) also occur locally. Like the sili­ The top of the coarse-gravel zone slopes generally ceous rocks, some of the plutonic, metamorphic, and southwestward from altitudes of about 90 feet above volcanic rocks, especially the most resistant, well- sea level at the east end of South Gila Valley and rounded clasts, probably came from regions far 40 feet above sea level at Laguna Dam to about upstream from Yuma, but others probably were con- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H51

TABLE 3. Summary of heavy-mineral analyses of alluvial sand (deposits of the Colorado River of the Yuma area) [Analyses by U.S. Geol. Survey. Hydrologic Laboratory]

Range in Percentage of total heavy minerals 1 Well samples samples Amphiboles Pyroxenes Opaques Garnet Zircon (feet) i (C-10-23)31bbbl ,_ ._ 3 195-955 0.1 14 21 9 7 (C-10-23)15aab _ __ _ _ 2 400-851 32 18 16 9V2 12 (C-10-23)5ddd _____ 14 0-500 44 34 11 5 IVa (C-8-22)35ccb __ _ 10 85-600 40 34 16 4 2 16S/22E-23Caa 2 100-248 28 16 28 10 8 (C-ll-24)23bcb _ _ 7 39-1,038 33 21 16 12 7 (C-8-23)33cdd 2 _ _ _ 2 705-1,080 12 2V2 22 20 11 (C-7-22)14bcd ______3 77 209 30 14 33 9 1/2 5 (C-10-25)35bbd _ __ _ 10 51 2,823 30 18 23 9 5 Average for eight wells __ 34 21 20 8V2 6

1 Other heavy minerals present in significant amounts include epidote, biotite, tourmalne, apatite, and titanite. 2 Samples from (C 8-23)33cdd not included in averages; probably represent deposits of local origin.

Most of the samples appear to be river gravel, although in some of the samples the angularity of the clasts and the relatively low percentage of quartzite and chert suggest local origin. Possibly the most significant parameter in the gravel analyses is the percentage of black chert. Recent studies of the south-central Yuma area by the U.S. Bureau of Reclamation (J. W. Julian and Earl Burnett, oral commun., 1966-67) have shown that the deeper, older gravel strata in the older alluvium have a noticeably higher concentration of black chert than the shallower, younger gravel strata. The figures in table 4 tend to substantiate that conclusion, although admittedly the data are too few to indicate more than a general trend. The source or sources of the black chert have not yet been identified with certainty; M. E. Cooley (oral commun., 1967) reports that similar black chert in the Grand-Glen Canyon region was probably de­ rived originally from the Mescal Limestone (upper

FIGURE 20. Well-rounded to subrounded Colorado River gravel in an ex­ unit of the Precambrian Apache Group) of central posure of older alluvium southwest of Pilot Knob. Pebbles and cobbles Arizona, from which it was deposited in the Shina- are chiefly quartzite and chert in a matrix of lime-cemented coarse rump Member and other conglomeratic sandstone sand. Steel tape (extended to a little more than a foot) gives scale. units of the Chinle Formation (Upper Triassic), and whence reworked later by the Colorado River. tributed from local sources. Welded tuff derived M. E. Cooley (written commun., 1969) reports also from the local Tertiary volcanic sequence is locally that no black chert has been observed in the terrace abundant, and some of the granitic clasts undoubt­ gravel of the Gila River between Hyder and Phoe­ edly had local sources. nix, Ariz., although black chert is present in the A few of the most significant characteristics of Mescal Limestone in the canyon of the Salt River, the gravel penetrated in test wells and deep private a tributary of the Gila near Phoenix. The paleo- wells are summarized in table 4. Each sample con­ geographic significance of the relative abundance of sisted of 100 pebbles and small cobbles selected at black chert in the river gravel of different ages and random from the bulk sample obtained from the different sources may be a fruitful subject for depth interval indicated. Clasts ranged in size from future investigation. about 1/2 inch to 4 inches; most were in the range Although generally less abundant in the older of 1-2 inches. Identifications were made by hand alluvium than sand and gravel, clay and silt strata lens. are locally conspicuous, especially below depths of H52 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

TABLE 4. Selected data from analyses of gravel from wells meability, indicate the presence of much sand and in older and younger alluviums silt. Brown and others (1956, p. 20) report that [Analyses by F. J. Frank. Average roundness (Wadell, 1932; Krumbein particle-size analyses of samples from U.S. Bureau and Sloss, 1951) derived by assigning the following roundness va ues to each of four categories described by visual inspection: Well rounded, of Reclamation observation wells drilled on Yuma 0.875; subrounded, 0.625; subangular, 0.375; angular, 0.125] Mesa showed that pure clay is uncommon; particle- Percentage size analysis of a representative bed described by Well Depth of Average sample roundness Quartzite Black the driller as "silty clay with sand streaks" or "silty (feet) and chert chert sand with clay streaks" might show about 55 per­ (C 7 22)14bcd _ _ 111 125 0.70 52 C) cent clay, 30 percent silt, and 15 percent sand. 177-183 .60 36 o (C-8-22)15bdd _ 109-120 .54 45 6 The clay and silt strata of the older alluvium are 135 .70 43 2 typically brown to gray, in contrast with the 145-150 .53 41 10 260-280 .50 34 15 greenish- to bluish-gray marine clay and silt of the 285-290 .43 47 21 underlying transition zone and Bouse Formation. A 415-420 .40 42 11 (C-8-22)19ccc 225-235 .44 37 (') nonmarine origin for the fine-grained strata of the 355-375 .47 41 9 older alluvium is suggested by the abundance of 390-400 .58 36 16 440-465 .49 30 12 fossil twigs, roots, and root fillings, the scarcity or (C-8-22)33cbb _ 109-120 .58 35 5 absence of marine fossils, the close association with (C-8-22)35caal _ 89 .60 43 0 122 .59 22 2 coarser strata of obviously fluvial origin, and the 548-556 .56 32 11 similarity to flood-plain clay and silt at the top of (C-8-22)35ccb _ 150-185 .70 56 0 190-240 .68 50 0 the younger alluvium. Slack-water deposition on 240-245 .54 45 3 broad flood plans is the most likely origin. 273-300 .42 54 20 415-425 .38 43 13 Little work has been done on the determination 495-515 .36 55 20 of the mineral composition of the clay and silt in 560-570 .37 51 15 (C-10-23)llccb _ 131-163 .68 59 12 the Yuma area. Two samples of clay and silt from 332-336 .66 56 11 U.S. Geological Survey test well (C-10-23)31bbbl (C-10-23)15aab __ (?) 2 .44 72 27 615-670 .61 72 22 (LCRP 1) were analyzed by X-ray diffraction in 730-754 .55 59 23 the Hydrologic Laboratory of the U.S. Geological 754-798 .48 62 19 848-856 .49 57 22 Survey at Denver, Colo., with the following results: (C-10-23)31bbbl __ 137-150 .66 39 3 Approximate mineral content 178-190 .60 41 7 (percent) 395-407 .49 56 28 115-120 ft 7S5-7S6 ft 545-560 .49 62 26 Clay minerals: (C-ll-24)23bcb 186-196 .72 38 9 Illite ______- 7.5 6.3 211-226 .62 46 10 Kaolinite ______--. 7.5 4.9 370-379 .74 87 25 Montmorillonite __ -. 45.0 51.8 381-394 .77 79 26 Mixed-layer _. 15.0 7.0 398-410 .75 77 14 Quartz ______. 13 13 472-490 .74 80 30 Calcite _-______-____ . 9 10 523-540 .70 70 20 Dolomite ______-_-____- Trace 5 627-630 .74 76 27 Potassium feldspar ______2 682-685 .64 64 17 850-866 .69 65 24 Montmorillonite, the dominant clay mineral in 987-990 .60 62 18 1,004-1,006 .59 57 11 both samples, is common in arid environments, 16S/23E-10Rcc 110-155 .56 28 6 especially where source rocks include volcanic ash 224-264 .58 43 13 334-364 .47 26 13 or tuff. Montmorillonite has the property of expand­ 495-515 .45 51 8 ing its crystal structure to accommodate variable 1 Black chert not differentiated in count. amounts of water, and a body of it moistened with 2 Roundness probably too low; many pebbles in sample were broken by drill. water tends to thus swell and become impermeable. Montmorillonite has a considerable capacity for 1,000-1,500 feet in the southern part of the area base (cation) exchange. (pi. 6) and in the uppermost deposits, above the Seismic-reflection data indicate that some of the coarse-gravel zone (pis. 5 and 8). These fine-grained deeper beds of clay and silt extend several miles strata can be identified readily on electric logs by laterally. Extensiveness is suggested also by some­ their low resistivity and on gamma logs by their what uncertain correlation of several of the thicker relatively high natural gamma radiation. The high fine-grained beds between wells (C-ll-25)llab and gamma intensity of most beds suggests a substantial (C-10-25)35cab, which are about 2 miles apart clay content, although most samples from wells, (pl. 6). together with evidence of at least moderate per­ Some of the clay and silt strata in the uppermost GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H53 part of the older alluvium beneath Yuma Mesa can deposits of the most recent major cycle of deposition. be traced several miles in wells and good exposures. These deposits underlie the present river flood One prominent bed 5-15 feet thick of fine sandy silt plains, the washes, and the alluvial fans. At these and clay is exposed in the escarpment along the places, aggradation has been the dominant process northern and western edges of Yuma Mesa, where during the last several thousand years, although it extends, with some interruptions, more than 15 locally degradation seems to have occurred most miles. recently. Soils on the younger alluvium are imma­ Two fine-grained beds in the top part of the older ture and lack the profile development characteristic alluvium have been identified in wells beneath siz­ of the exposures of older alluvium. able areas of eastern Yuma Valley and western The younger alluvium has been classified in three Yuma Mesa. The lower bed, informally designated categories according to the dominant agent of depo­ clay A (fig. 21 and pi. 5), is not far above the sition : (1) Deposits of the Colorado and Gila Rivers, coarse-gravel zone beneath Yuma Valley and adja­ (2) alluvial-fan deposits, and (3) wash and sheet- cent parts of Yuma Mesa. This bed ranges in thick­ wash deposits (fig. 11). Each of these three cate­ ness from a few inches to about 35 feet. Parts of gories or subunits is described briefly below. clay A appear to grade laterally into coarser ma­ terials at different places, so it is difficult if not DEPOSITS OF THE COLORADO AND GILA RIVERS impossible to trace a single horizon far enough to The deposits of the Colorado and Gila Rivers determine the precise attitude of the bedding be­ underlie the present river flood plains. Until Hoover neath a large area. In general, however, the middle Dam and other large dams were constructed on of the bed seems to have approximately the same both the Colorado and the Gila Rivers, floods added slope toward the southwest as the present surface increments of predominantly fine-grained deposits of Yuma Valley. to the flood plains. The rivers continually shifted Southeast of Somerton, where clay A is thickest their courses across the flood plains in meandering and least sandy, its middle part lies about at sea channels. In Yuma Valley the sites of many of the level (pi. 5, geologic section E-E' and fig. 21). In old meanders are marked by long, narrow, arcuate places along the margins of the bed the clay and or sinuous sand dunes which accumulated on the silt grade laterally into pebbly clay and other ill- leeward sides of the channels. sorted gravelly deposits which, like the clay and The river deposits consist predominantly of sand silt, are characterized by high gamma radiation. and silt. Pebbly sand and silt are abundant in places, Clay A underlies an area of at least 33 square miles. especially in the lower part, and beds of clay and Clay B is the informal designation applied to silty clay, which are rarely more than a few feet another, higher fine-grained bed that occurs beneath thick, are locally extensive. One extensive bed of western Yuma Mesa at an average altitude of silt and clay lies immediately beneath the flood plains about 100 feet above sea level (fig. 22 and pi. 5). of the Colorado and Gila Rivers. It is not present Clay B is even more extensive than clay A, under­ everywhere, having been replaced by scour and fill lying an area of at least 42 square miles, and it of sand along channels occupied by the rivers dur­ probably extended farther west before it was re­ ing relatively recent times, probably within the last moved by erosion when Yuma Valley was cut (fig. few hundred years. In northern and central Yuma 22). Clay B is 10-15 feet thick at most places; more Valley the silt and clay range in thickness from a than half the thickness is clay and silty clay, the few feet to as much as 30 feet (pi. 5). Deposition on remainder is silt, fine sand, and scattered pebbles. the flood plain during times of overbank flow is the Toward the northwest the bed is difficult to dis­ most likely origin. tinguish from other strata of clay and silt above The river sand of the younger alluvium is gen­ and below; possibly clay B underlies much of he erally similar to that of the older alluvium, except city of Yuma. Like clay A, clay B grades laterally that it is commonly looser. Van Andel (1964, p. into pebbly clay and other heterogeneous gravelly 236) gives the following composition for a sand deposits, particularly toward the southwest (fig. from the Colorado River near Yuma: Quartz, 73.3 22). Along its southeastern margin, clay B may percent; feldspar (chiefly potassium feldspar), 18.8 abut older deposits that are exposed in the "Upper percent; and rock fragments, 7.9 percent. Mesa" farther southeast. A gravel occurs at the base of the younger allu­ vium of the Colorado River at depths of about YOUNGER ALLUVIUM (QUATERNARY) 100-130 feet in the Parker-Blythe-Cibola area 30- The younger alluvium comprises all the alluvial 100 miles north of Yuma, where it has been dated H54 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

114°45'

32°45'

AMERICAN CANAL

UNITED STATES """MEXICO

EXPLANATION

Subsurface margin of clay A Well used for control Dashed where doubtful or Solid circle denotes well having gamma log; open poorly controlled circle, well having only driller's log. Upper number 32°30' indicates altitude of top; lower number, altitude of bottom of clay A, in feet related to mean-sea-level. Letter symbols designate: S, sandy clay; VS, very Area underlain by clay A sandy clay; G, gravel and clay; M.clay missing or not identifiable; (?), clay not distinguishable from beds above and below Bedrock outcrop

FIGURE 21. Extent and altitude of top and bottom of clay A beneath Yuma Valley and northwest margin of Yuma Mesa. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H55

114°30' 32°45'

/ YUMA \

^inRU3v;^;|:|if::ffl.:ilii:iif|l||i

EXPLANATION

Subsurface margin of clay B Dashed where doubtful or poorly controlled

Area underlain by clay B

Bedrock outcrop

Well used for control Solid circle denotes well having gamma log; open circle, well having only driller's log. Upper number indicates altitude of top; lower number, altitude of bottom of -clay B,in feet above mean -sea -level. Letter symbols designate: S, sandy clay; VS, very 32°15' I- sandy clay; G, gravel and clay; M, clay missing or not identifiable; (l),clay not distinguishable from beds above and below

FIGURE 22. Extent and altitude of top and bottom of clay B beneath Yuma Mesa. H56 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA by the radiocarbon method as less than 10,000 years aggradation (perhaps by sheetfloods) has been old (Metzger and others, 1973). This gravel prob­ dominant most recently. ably was the first material deposited during the WASH AND SHEET-WASH DEPOSITS most recent aggradation by the Colorado River as The wash deposits occur in washes and channels sea levels rose with the retreat of the last glaciers cut into the older alluvium and prealluvial rocks. of the Wisconsin stage. Two samples of carboniz.ed The deposits are generally thin and consist of sa"nd wood from overlying fine-grained younger alluvium and gravel and thin, lenticular beds of silt. In many in the same area gave radiocarbon ages of 5,380 and washes, degradation rather than aggradation is the 6,250 years (Metzger and others, 1973). dominant process at present, and even the most The basal gravel of the younger alluvium of the recent wash deposits have been subject to extensive Colorado and Gila Rivers has not been dated or scour during floods. positively identified in the Yuma area; accordingly, The sheet-wash deposits are similar to the wash the younger alluvium and older alluvium are not deposits but occupy broader, less well defined areas. differentiated in the geologic sections (pis. 5, 6, 8). They also resemble the alluvial-fan deposits. How­ If present in Yuma Valley, this gravel must occur ever, instead of forming fairly thick wedges like in the western part; no significant gravel strata the alluvial-fan deposits, the sheet-wash deposits overlie clay A of the older alluvium in eastern are thin blankets on older rocks and deposits, and Yuma Valley, which is at a depth of 80-90 feet are probably formed by sheetfloods and thin mud- below the land surface (pis. 5 and 8). In South flows. Their most extensive development is in the Gila Valley, likewise, a basal gravel of the younger "Laguna Mesa" north of the Laguna Mountains, alluvium has not been definitely identified; if pres­ where they consist of sand and silt reworked from ent, such a gravel must be nested in gravel of the the underlying older alluvium. older alluvium which extends southwest of the val­ ley, beneath Yuma Mesa (coarse-gravel zone on WINDBLOWN SAND (QUATERNARY) pi. 8). The thickest and most extensive deposits of wind­ blown sand are the Sand Hills ("Algodones Dunes") ALLUVIAL-FAN DEPOSITS on the East Mesa of Imperial Valley, northwest of Although surfaces somewhat similar to alluvial the Yuma area, proper. The less extensive "For- fans are common in the Yuma area, true young tuna Dunes" occur on the "Upper Mesa" and "For- alluvial fans that is, thick accumulations of young tuna Plain" in the southeastern part of the Yuma deposits having fan-shaped aggradational sur­ area (fig. 6). These two dune areas are alined faces occur only in the southeastern part of the northwest and may once have been part of a con­ area, adjacent to the Tinajas Altas and Butler tinuous belt before the Colorado River formed what Mountains and at the northwest corner of the is now the Yuma Mesa and, later, the Yuma and area, on the west flank of the Cargo Muchacho Mexicali Valleys. The belt appears to extend south­ Mountains. In both these areas the deposits consist eastward into Mexico, where dunes are large and of poorly sorted granitic detritus derived from the extensive. The "Algodones Dunes" and "Fortuna exposures of granitic rocks in the mountains. U.S. Dunes" are described earlier, in the section "Geo- Bureau of Reclamation test well CH-28YM on the morphology" (p. H28). southerly international boundary about 30 miles Other, smaller dunes, as well as thin sheets of east of San Luis, Rio Colorado, Mexico, penetrated windblown sand, occur at many places throughout 310 feet of ill-sorted arkosic sand and silt with thin the area. One small area of low dunes and sand interbeds of calcareous clay, overlying older allu­ sheets is on the east side of The Island in Bard vium consisting of interbedded river deposits and Valley, 3-4 miles northeast of Yuma. These deposits local deposits, probably also of alluvial-fan origin. are adjacent to a meander channel of the Colorado (See log of well (C-13-20)2abdl in appendix B.) River that was cut off within historic time. In Yuma The scattered shallow exposures in this area reveal Valley, long sinuous or arcuate dunes are wide­ granitic (arkosic) sand and fine gravel (chiefly spread; they occur on the leeward sides of aban­ angular clasts of granite, felsic dike rocks, quartz, doned meanders. Most of these dunes (or perhaps and feldspar), and interbedded silt and clay. The more properly, sand ridges) are less than 20 feet fan surfaces are characterized by a network of high and 500 feet wide. Some are long in proportion broad, shallow channels having a dendritic pattern to their width; one ridge just east of Somerton is where degradation has been the dominant recent more than a mile long. On Yuma Mesa, the wind­ process, and a distinctive rhomboidal pattern where blown sand occurs in somewhat discontinuous thin GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H57 sheets rather than in discrete dunes; most of this what more northwesterly than the mountains of the sand is on the inner margin of the Yuma Mesa, adja­ Sonoran Desert and their inferred bounding faults, cent to the "Upper Mesa." Other small masses of although the two trends appear to converge to the windblown sand occur on the north flank of the southeast, in Mexico. Laguna Mountains and in scattered windrows on The Salton Trough has sunk rapidly during Ceno­ the "Upper Mesa." zoic time and has accumulated as much as 20,000 The windblown deposits consist almost entirely feet of fill (Biehler and others, 1964). Much of this of well-sorted fine to medium sand which is probably fill in the southern part of the trough consists of derived from nearby sandy alluvium or, with the alluvial and deltaic deposits of the Colorado River. "Algodones Dunes," from old lacustrine or marine PRE-TERTIARY STRUCTURAL FEATURES beaches. The sand grains are subrounded to The structural features of the Yuma area may be rounded, include many frosted grains, and are com­ classified according to the time of their principal posed chiefly of quartz, with subordinate feldspar, development. Some deformation has affected only rock fragments, and heavy minerals. the pre-Tertiary crystalline rocks; other features STRUCTURE probably had their maximum development during REGIONAL STRUCTURAL PATTERNS Tertiary time; and still others such as the faults of The Yuma area lies at the southwest edge of the the San Andreas system have been active through­ Sonoran Desert section and the northeast edge of out late Tertiary and Quaternary time, although the Salton Trough section of the Basin and Range most of these faults originally formed earlier. province of Fenneman (1931, 1946). (See fig. 1.) The structural features that affect only the crys­ The structural features of these two physiographic talline rocks of pre-Teriary age did not all originate sections are somewhat different, both in pattern at the same time, but no attempt was made in the and in time of most actve development. present study to decipher the sequence of the older The Sonoran Desert east of Yuma is characterized deformational episodes. The pre-Tertiary struc­ by subparallel, narrow, low but rugged mountain tural features include old faults, metamorphic folia­ ranges trending generally north-northwest, sepa­ tion and lineation, and joint systems. Most of the rated by much more extensive desert plains under­ old faults are mineralized and filled with dikes and lain by Cenozoic fill. The mountains probably owe quartz veins. their configuration at least in part to block fault­ The last major deformation affecting only the ing (Davis, 1903; Gilbert, 1928; Gilluly, 1946; crystalline rocks was the Laramide orogeny, which Thornbury, 1965), although most of the marginal occurred at the end of the Cretaceous period and faults are concealed by the Cenozoic fill of the extended, in its waning phases, into the early Ter­ plains and must be inferred from geophysical and tiary (Damon and Mauger, 1966). The Laramide other indirect evidence (pi. 9). Some of the moun­ orogeny resulted in extensive folding, reverse and tain masses, especially those adjacent to the Salton normal faulting, igneous intrusion and extrusion, Trough, are buried or nearly buried by fill. The and recrystallization of many of the older rocks. mountains and basins assumed approximately their The rubidium-strontium date of 73 million years present configuration by middle Tertiary time; sub­ reported by Wasserburg and Lanphere (1965) for sequent deformation has involved only broad-scale biotite in a porphyritic quartz monzonite at Yuma warping and minor normal faulting, probably asso­ probably indicates a Laramide metamorphic event. ciated with regional subsidence along the southwest Abundant evidence of Laramide plutonism and margin of the Sonoran Desert. volcanism farther east in southern Arizona has been The Salton Trough, by contrast, has been tec- reported (Richard and Courtright, 1960; Creasey tonically active to the present time, especially west and Kistler, 1962; Lootens, 1966; Bikerman and of the Yuma area, where movement on faults is still Damon, 1966). going on. The faults are part of the well-known San Laramide and pre-Laramide structural features Andreas system. Along this major fault system, are expressed topographically where rocks of dif­ aggregate right slip (blocks southwest of the fault ferent resistance to erosion are juxtaposed along displaced northwestward relative to blocks northeast faults, where faulting has formed easily eroded of the fault) in southern California has amounted crushed or sheared rocks, and where extensive and to about 160 miles since earliest Miocene time, ac­ conspicuous joint systems and metamorphic folia­ cording to Crowell (1962). The faults of the San tion have controlled patterns of erosion. The south­ Andreas system in the Salton Trough trend some­ eastern Laguna Mountains afford good examples of

507-243 O - 74 - 5 H58 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA the effects of probable Laramide faults on topog­ sequence of volcanic rocks is probably repeated raphy. Joint systems and foliation have profoundly several times from northeast to southwest, although affected the topography of the Gila, Butler, and the actual throw on the faults and even some of Tinajas Altas Mountains. their positions are uncertain. At some of the faults The present outlines of some of the ranges and near Senator Wash Dam and Imperial Dam, nearly basins in the Yuma area may be related to faulting horizontal slickensides record strike-slip movement and domal uplift that began during the Laramide where the faults cut welded tuff or other hard vol­ orogeny and continued, at intervals, throughout canic rocks. The fault pattern in part of the expo­ much of the Tertiary, but present evidence on this sures of basaltic andesite or basalt farther west question is inconclusive. Farther north, in the Great indicate left-lateral displacement on north-north­ Basin section of the Basin and Range province, the westward-trending faults; intervening tension faults block faulting that resulted in the present pattern and fractures trend west-northwestward. The pre­ of the basins and ranges is generally regarded as dominant trend of faults in the southeastern Choco­ post-Laramide (Gilbert, 1928; Nolan, 1943; Mackin, late Mountains is northwest, but another important 1960). However, some students of the basin^range set has a north-south trend. problem have questioned this interpretation; Love- In the Cargo Muchacho Mountains to the west, joy (1963a) has ascribed the product of so-called the exposed faults strike northwest to west. Hen- basin-range faulting of classical theory to normal shaw (1942) suggests that the range may be an erosional processes acting on Laramide structures. elevated block between two now-buried strike-slip Later workers have generally agreed with the inter­ faults which are approximately parallel to the San pretation of Gilluly (1946) that the faulting in Andreas fault system (northwest). In the north- southern Arizona (Ajo area) began earlier than it central part of the mountains, Henshaw (1942) did farther north. In the Yuma area the outlines of mapped a thrust fault on which the upper plate was the present basins and ranges resulted chiefly from thrust from the south. Most of the other faults Tertiary faulting, accompanied by domal uplift and within the range are normal faults, however. The basin subsidence, but some faults, particularly in quaquaversal attitude of several flows of basalt on the southeastern part of the area, date from the the margins of the mountains suggests domal up­ Laramide orogeny. Some of the Laramide faults lift as well as faulting. thus became the loci of later activity. In the Laguna Mountains, the straight northeast BASIN AND RANGE STRUCTURAL FEATURES margin of the exposures of crystalline rocks, and (TERTIARY) seismic-refraction data as well suggests a high- The so-called Basin and Range structural fea­ angle fault trending about N. 60° W., downthrown tures, as apart from Laramide and earlier structural to the northeast. South of this probable fault is a features, are not well understood in the Yuma area. set of normal (?) faults trending about northward; Except for parts of the Chocolate Mountains and the youngest rocks affected are middle Tertiary possibly the southern part of the Tinajas Altas volcanic and sedimentary rocks. Mountains, the present form of the mountains and In the southeastern part of the Laguna Mountains intervening basins seems to be only indirectly re­ is a set of concentric arcuate faults bending from lated to faulting, uplift of the mountain blocks, and an easterly strike on the west to northeasterly subsidence of the basins. The present mountain farther east. These faults- are roughly parallel to fronts are in most places erosional in origin. The the foliation and joints in the pre-Tertiary gneiss faults that may determine the general pattern of and probably developed before Tertiary time. At the basins and ranges are mostly buried beneath least one of the faults extends westward across alluvium and lie basinward from the mountain exposures of early to middle Tertiary sedimentary fronts, although a few faults within the G'ila rocks (pi. 4). Where the fault planes are clearly Mountains have helped to determine the general exposed they dip about 50°-80° north to northwest. outline of those mountains. Direction of net slip is generally unknown, but on The clearest evidence of Basin and Range block two of the more southerly faults, pre-Tertiary gneiss faulting in the Yuma area is found in the south­ is thrust over Tertiary nonmarine sedimentary eastern Chocolate Mountains, where middle Tertiary rocks (red beds). Similar faults may extend be­ volcanic rocks are offset by antithetical faults, with neath the alluvium between the Laguna and the southwesterly to westerly tilting of the fault blocks Gila Mountains. In the southeastern Laguna Moun­ and steep northeasterly dips of fault planes. The tains are several small northwestward-trending GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H59 normal faults. The throw on these faults is gen­ and perpendicular to the margins. This pattern sug­ erally no more than 100 feet. gests that the margins of the mountains, which are Bedding in the nonmarine sedimentary rocks in fairly straight in most places, may be controlled at the Laguna Mountains dips generally west to south­ least indirectly by faults parallel or nearly parallel west at angles ranging from a few degrees to more to the exposed faults. The western edge of the than 40°. The older part of the sequence, the red Tinaj as Altas Mountains near the Mexican border beds, dips west to north in an arcuate pattern; the is controlled in large part by such a fault (pi. 3). attitudes of the bedding are generally similar to Farther northwest the parallel ridges of the Butler those of the foliation in the adjacent pre-Tertiary Mountains may result from en echelon faults trend­ gneiss, but the dips are flatter. Evidently middle ing about N. 50°-60° W. (pi. 9). Tertiary deformation in this area had a pattern Between the Cargo Muchacho Mountains and the governed in large part by Laramide or older struc­ Chocolate Mountains, and farther south, between tures and merely accentuated these structural fea­ the "Yuma Hills" and the Laguna and Northern tures in the pre-Tertiary rocks. Gila Mountains, is a basin informally designated The Kinter Formation and the volcanic rocks in the "Picacho-Bard basin." The depth to the pre- the southern part of the mountains overlie the older Tertiary crystalline rocks along the axis of the nonmarine sequence with marked angular discord­ basin increases southward from about 1,500 feet to ance ; dips of the Kinter are gentle toward the west about 3,500 feet, according to an interpretation of and northwest where it fills an old valley trending gravity data. The presence of a few outliers of west-northwest cut into the older rocks. In the crystalline rocks near the margins of the basin and northern part of the mountains the beds of the the complexity of the gravity and magnetic patterns Kinter Formation have low, irregular dips and suggest that the bedrock surface has considerable strikes indicating broad folding and warping. local relief. In the southwestern part of the Laguna Moun­ South of the Gila River the trough west of the tains, alluvium of local origin unconformably over­ Gila Mountains essentially a continuation of the lying the Kinter Formation is very gently deformed. "Picacho-Bard basin" called the "Fortuna basin" Bedding dips westward to southwestward at angles deepens rapidly and attains a depth estimated from ranging from 1° or less to as much as 4° not much gravity data to be about 16,000 feet. (See pi. 9.) As more than the probable initial dips. indicated by the log of well (C-9-22)28cbb (test The easterly to northeasterly trending fault pat­ well LCRP 25), only the upper one-eighth of the tern of the southeastern Laguna Mountains con­ basin-filling deposits consists of alluvium of the tinues southward into the northern Gila Moun­ Colorado and Gila Rivers; the lower seven-eighths tains. A steep normal fault having a throw of more probably is composed of marine and nonmarine de­ than 2,000 feet extends northeastward across the posits older than the Colorado River (Bouse Forma­ northern Gila Mountains, the Kinter Formation on tion and older units). the northwest being faulted against pre-Tertiary Farther south, the "Fortuna basin" does not ap­ crystalline rocks on the southeast along the eastern pear to be quite as deep. Estimates from gravity part of its exposed length (pi. 4). Aeromagnetic data and electrical soundings indicate that the base­ data suggest that this fault continues southwest- ment (pre-Tertiary crystalline rocks) surface is ward beneath the alluvium of the South Gila Valley. 10,000-13,000 feet below the land surface in the mid­ The Kinter Formation is titled about 15°-30° dle of the basin just north of the southerly in­ toward the northwest along the northern margin ternational boundary. Information from test well of the Gila Mountains; foliation in the metamorphic (C-13-20) 2 abdl (USER CH-28YM) and from a rocks south of the fault dips southward to southeast­ profile of electrical soundings indicates that only ward at about 40°-50°. the upper 1,200 or 1,300 feet of the overlying fill is In the central and southern parts of the Gila alluvium; the bulk of the basin-filling deposits prob­ Mountains several large faults near the margins of ably are semiconsolidated marine and nonmarine the range trend northwest to west-northwest. Prob­ sedimentary rocks of Tertiary age (pi. 10). ably other parallel faults exist farther out from the On the west side of the trough formed by the margins, where they are now buried by alluvium. "Picacho-Bard basin" and the "Fortuna basin", is The foliation and prominent joints in the crystal­ an irregular chain of basement highs composed of, line rocks in this area dip 30°-60° southeast to from north to south, the Cargo Muchacho Moun­ south-southeast; another joint set dips northwest. tains (described earlier), the "Yuma Hills," a These trends are athwart the long axis of the range buried ridge south of the "Yuma Hills" referred to H60 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA informally as the "Mesa basement high," and a and younger alluviums. Farther west, within 2 or 3 southeast-trending basement high culminating in miles of Pilot Knob, the crystalline basement is the row of low hills, known as the "Boundary Hills," shallower and is overlain only by the older and straddling the southerly international boundary younger alluviums or, in places, the transition zone (fig. 6). and Bouse Formation. The north-northwesterly alinement of outcrops of Gravity and magnetic data indicate a deep basin the "Yuma Hills" and various kinds of geophysical between the "Boundary Hills" and San Luis which data indicate that these hills are the summits of a is given the informal name "San Luis basin." (See nearly buried ridge approximately parallel to the pi. 9.) The axis of the "San Luis basin" trends west- Gila Mountains and other ranges of the Sonoran northwest along the southerly international bound­ Desert farther east. The "Yuma Hills" basement ary. Estimates indicate that the depth to basement ridge probably is bounded on both sides by faults in the middle of the basin is about 13,500 feet. Oil- whose precise location and attitude can be only a test well (C-10-24)24cbb (Colorado Basin Associ­ matter of speculation at present. ates Federal 1) on the north side of the basin The "Mesa basement high" is separated from the bottomed in Tertiary nonmarine sedimentary rocks "Yuma Hills" to the north by a saddle in which the at a depth of 6,007 feet (pi. 10). basement surface is estimated on the basis of geo­ LATE TERTIARY AND QUATERNARY STRUCTURAL physical data to be at a depth between 1,000 and FEATURES 1,500 feet. Shallow test drilling by the U.S. Bureau The older and younger alluvium, the underlying of Reclamation and the U.S. Geological Survey, and transition zone, and the Bouse Formation, which geophysical exploration by the Geological Survey, range in age from late Tertiary (Pliocene) to Qua­ have established that the highest part of the buried ternary (Holocene), are substantially less deformed basement ridge, which is oriented northwest, is less than the pre-Bouse rocks, from which they are than 100 feet below the surface of Yuma Mesa; well separated by significant angular unconformities. (C-9-23) 33cdd (USER CH-20YM) penetrated Nevertheless, except for the younger alluvium and porphyritic quartz monzonite at a depth of only 47 possibly the upper parts of the older alluvium, these feet. The "Mesa basement high" is bounded on both late Tertiary and Quaternary units are affected by northeast and southwest sides by faults (pis. 9, broad-scale warping and local faulting. 10). The large fault on the southwest is the Algo- Deformation of the older alluvium on the flanks dones fault which is described on pages H61-H63; of the mountains consists chiefly of slight tilting the other faults probably are parallel or en echelon with dips as much as 6° away from the mountains, to the Algodones fault. and, locally, of small-scale high-angle normal fault­ Geophysical data suggest that southeast of the ing. Uplift of the mountains in post-older alluvial "Mesa basement high" and on the southwest side time is indicated by the presence of Colorado River of the Algodones fault, the surface of the crystalline deposits as high as 740 feet above sea level on the rocks slopes steeply southward into a broad saddle flanks of the southeastern Chocolate Mountains and and thence rises southeastward to the line of low about 580 feet above sea level on the west flank of outcrops straddling the southerly international the northern Gila Mountains. Even greater uplift boundary the "Boundary Hills." The "Boundary since the deposition of the Bouse Formation is indi­ Hills" are composed of the same porphyritic quartz cated by the presence of basal limestone and tuff of monzonite as that penetrated in test wells on the the Bouse at an altitude of about 1,000 feet above "Mesa basement high" and exposed in the "Yuma sea level in a gap in the Chocolate Mountains 10 Hills" farther north. miles beyond the north edge of plate 3 (Metzger, Between the "Yuma Hills" and Pilot Knob is a 1968). basement trough oriented north-northeast referred In the subsurface, a measure of the maximum to informally as the "Yuma trough." Geophysical deformation since the late Tertiary is provided by data, supplemented by information from test wells the configuration of the top of the Bouse Formation 16S/22E-29Gca2 (USGS LCRP 26) and (C-8- (fig. 15). The Bouse, being marine, presumably was 23)32caal (Sinclair Oil Co. Kryger 1) and from nearly horizontal at the time of deposition; the water well 16S/21E-36Fca, show that the basement basal beds of the overlying transition zone are the surface is deepest in the eastern part of the trough, earliest deposits of the Colorado River, which must where the sedimentary fill includes the Tertiary have been laid down not far above sea level. The nonmarine sedimentary rocks below the less de­ maximum dip of the top of the Bouse Formation is formed Bouse Formation, transition zone, and older about 9°-10°. These deposits have been down warped GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H61 in the basins such as "Fortuna basin" and differ­ dones Dunes"). On the basis of this evdence and of entially upwarped along the margins of the moun­ further evidence from seismic data (Kovach and tain blocks (pi. 10). The top of the Bouse Forma­ others, 1962), the fault appears to extend beneath tion is more than 3,000 feet below sea level in the the Sand Hills to a point on the Colorado River southwest corner of the Yuma area, near San Luis south of Pilot Knob; the exact location is uncertain. (fig. 15 and pi. 10). This probably reflects broad- The fault just described (or possibly a parallel scale downwarp or subsidence in the Colorado delta fault) appears to continue southeastward across the region as well as more local downwarp or down Yuma area from a point on the Colorado River about faulting in the basins. At least part of the down­ a mile south of Morelos Dam to the southerly inter­ warp results from differential compaction in the national boundary 26 miles east of the Colorado fine-grained deposits. Farther west, in the central River at San Luis (pis. 3 and 9). It is herein named part of the Salton Trough, probably nonmarine de­ the Algodones fault from the village of Algodones posits (possibly of the Colorado River?) have been just northeast of the trace of the fault in the north­ penetrated in oil-test wells at depths exceeding eastern corner of Baja California, Mexico. The evi­ 13,000 feet (Muffler and Doe, 1968), which indicates dence for the Algodones fault is summarized: much greater downwarp or subsidence there. 1. Anomalous topography on the "Upper Mesa." Structural activity has generally occurred more The existence of the Algodones fault was recently in the Salton Trough than it has farther first inferred from a topographic anomaly on northeast, in most of the Yuma area. The trough the "Upper Mesa," in the southeast part of is crossed at acute angles by northwest-trending the area of investigation. The anomaly con­ faults of the well-known San Andreas system. sists of a northwestward trending drainage Many members of this system are well delineated system approximately perpendicular to the by seismic and gravity data in the delta region normal, consequent streams draining south- (Biehler and others, 1964). One of these faults and westward from the Gila Mountains. The in­ several other probably related faults that cross the ferred fault trace is along this system, at the Yuma area are described in the following section. foot of an eroded northeast-facing alluvial escarpment. The mesa surface southwest of ALGODONES FAULT AND RELATED FAULTS the fault is 30-60 feet higher than the surface The San Andreas fault system is a major crustal to the northeast and slopes toward the west- feature along the northeast margin of the Pacific southwest at about 30-40 feet per mile (pi. Ocean. The Gulf of California a southern exten­ 1). Lineaments apparent on vertical aerial sion of the Salton Trough was probably formed photographs suggest that the fault has a by oblique rifting across the system (Hamilton, branching pattern in the central part of the 1961) and probably also by ocean-floor spreading "Upper Mesa." (Larson and others, 1968). Displacements on the 2. Offset of the water table and ground-water bar­ faults have been right lateral and, in southern Cali­ rier effect. Test wells in the "Upper Mesa" fornia, may have amounted to as much as 160 miles indicate an abrupt offset in the water table since early Miocene time (Crowell, 1962). An earler along the inferred fault trace. Water levels date has been postulated for some of the faults by northeast of the fault are more than 30 feet Hill (1965), who believes that possibly several higher than those southwest of the fault near hundred miles of right slip has occurred since the the northwest edge of the "Upper Mesa" and Cretaceous. about 7 or 8 feet higher near the southerly One of the main branches of the San Andreas international boundary (pi. 1). Measurements system extends along the northeast side of Coach- in private irrigation wells and government ella Valley southeastward to the northeast shore of observation wells indicate that the water-table Salton Sea. Alien (195T) calls this branch the offset continues about 3 miles northwestward Banning-Mission Creek fault; Dibblee (1954) con­ beneath Yuma Mesa, although this part of the siders it the San Andreas, itself. Southeast of Salton fault trace is concealed. Sea the trace of the fault is concealed by unaffected The water-table offset results from the func­ alluvium and windblown sand, so its precise trend tion of the fault as a barrier to ground-water is not known. Biehler (unpub. Ph. D. thesis, 1964; movement. The barrier effects of faults in allu­ oral commun., 1967) interprets a strong alinement vial materials are well known and are com­ of gravity lows as indicating the trace of the fault monly attributed to: (a) Pulverization of earth where it is concealed by the Sand Hills ("Algo- materials along the fault, (b) offset of bedding H62 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

so that impermeable beds are juxtaposed 10.) The faults inferred to be parallel to the against permeable beds, (c) rotation of flat 6r Algodones fault near the "Mesa basement elongate clasts parallel to the fault, thereby high" (pis. 9 and 10) all were determined decreasing permeability normal to the fault from seismic-reflection data. plane, and (d) deposition of minerals along the 6. Seismic-refraction data. A seismic-refraction fault surface (Davis and De Wiest, 1966, p. profile extending southward from the crest of 396). The first and fourth factors listed above the "Mesa basement high" revealed that the are probably most significant at the Algodones basement surface is downthrown 350 feet fault. Electrical-analog data, described on page toward the south or southwest along a steeply H108, indicate that observed changes in water dipping fault in alinement with the projected level on both sides of the fault are best mod­ extension of the ground-water barrier to the eled by assuming that the transmissivity of southeast. This fault is interpreted as being the fault barrier is less than one-thousandth the main Algodones fault (pi. 10). of that of the alluvial deposits on either side. 7. Ground-water-temperature anomalies. The configuration of the water table-water- Although the Algodones fault is concealed be­ level contours on both sides of the fault are neath Yuma Mesa and Yuma Valley, its posi­ nearly perpendicular to the fault trace also tion throughout much of its extent across supports the conclusion that very little ground these features is revealed by an elongate body water moves across the fault. of anomalously warm ground water, mostly 3. Magnetic gradients. A steep magnetic gradient on the northeast side of the inferred fault along the southwest side of the buried "Mesa trace (fig. 47). Similar temperature anoma­ basement high" suggests a fault or series of lies farther southwest probably reflect parallel step faults on which the basement is down- or en echelon faults. The elevated temperatures thrown to the southwest. The zone of steep of these anomalies are probably the result of gradient extends across Yuma Valley to the upward movement of deep warm water in­ northwest and indicates that the inferred fault duced by the barrier effects of the faults. or fa-ult zone crosses the Colorado River some­ However, the effect of the buried basement where between IVa and 4 miles south of Pilot ridge at the "Mesa basement high" may in Knob. part account for the temperature anomaly 4. Gravity patterns. Gravity data generally cor­ along the Algodones fault. roborate the magnetic data. Also, the gravity In addition to the methods of investigation de­ data indicate a very steep gradient on the scribed above, attempts were made to delineate the northeast flank of the "Boundary Hills" base­ Algodones fault beneath Yuma Mesa by use of ment high, which suggests downthrow of the resistivity profiles and electrical soundings. Unfor­ basement surface toward "Fortuna basin" tunately, the resistivity surveys did not provide the along a fault about in the position of the fault expected information as to the location and nature inferred from topographic and hydrologic evi­ of the fault or fault zone. Information on the atti­ dence. tude and width of the fault, and on whether the 5. Seismic-reflection data. Seismic-reflection pro­ barrier effect results primarily from pulverized files made by a commercial firm under contract material (gouge) or from cemented material, must to the U.S. Bureau of Reclamation revealed await detailed exploration by test drilling or exca­ several faults including what is interpreted vation. herein as the main Algodones fault. The faults Likewise, unambiguous information on the direc­ offset reflecting horizons such as the top and tion and amount of movement on the Algodones bottom of the Bouse Formation and the top of fault is not yet available. Analogy with other, bet­ the transition zone, and locally are associated ter known faults in the San Andreas system sug­ with steep dips of the reflecting horizons gests chiefly right-lateral movement; this inference (Snodgrass, 1965,1966). On a profile along the is substantiated to some extent by gravity and mag­ limitrophe section of the Colorado River, the netic patterns. However, vertical components of top of the Bouse Formation was determined movement also are indicated by some of the evi­ to be downthrown 500 feet to the south or dence summarized above. Northwestward from the southwest along a fault that is probably the vicinity of the "Mesa basement high" the southwest main Algodones fault about 21/2 miles south side is downthrown, but to the southeast, across the of Pilot Knob (Snodgrass, 1966). (See pi. "Upper Mesa," the throw is opposite. Such reversals GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H63 in throw along the strike are common along other sidered as being composed of two parts, which are faults in the San Andreas system which have had discussed separately below. predominantly strike-slip movements. The last significant movement on the Algodones MAJOR SUBDIVISIONS OF THE RESERVOIR fault can be dated approximately by geology and The ground-water reservoir consists of two major topography. The fault is exposed on the "Upper subdivisions: (1) Poorly water-bearing rocks of Mesa" but is concealed beneath apparently unaf- Tertiary age and (2) water-bearing deposits of ected alluvial deposits in both the Yuma Mesa and Pliocene to Holocene age. The first subdivision con­ Yuma Valley. The uppermost coarse-gravel strata stitutes the lower part of the reservoir and includes of the older alluvium (coarse-gravel zone) are not the following stratigraphic units: (1) The nonma- offset, at least vertically, beneath western Yuma rine sedimentary rocks, (2) the volcanic rocks, (3) Mesa and eastern Yuma Valley (pis. 5 and 8). The the older marine sedimentary rocks, (4) the Bouse age of the Yuma Mesa surface is late Pleistocene Formation, (5) the transition zone, and (6) the perhaps Sangamon (p. H27) and the presumably conglomerate of the Chocolate Mountains. The vol­ unaffected gravel strata are somewhat older. The canic rocks and the conglomerate of the Chocolate age of the "Upper Mesa" surface, which is offset, Mountains appear to be of very minor subsurface has not been established but almost certainly is extent within the area of principal hydrologic in­ older than latest Pleistocene. It is therefore inferred vestigation and are not considered further in this that significant movement on the Algodones fault section of the report. The stratigraphic units of the ceased before the latest Pleistocene. Movement on second subdivision include: (1) The older alluvium, the parallel or en echelon faults probably ceased (2) the younger alluvium, and (3) the windblown even earlier; this is indicated by the lack of topo­ sand. These units contain most of the fresh ground graphic expression of these faults on the "Upper water. For convenience, the water-bearing deposits Mesa" and from the apparent absence of significant of the second subdivision are further subdivided hydrologic effects (other than thermal effects) into water-bearing zones that cross stratigraphic caused by these faults. By contrast, many faults of boundaries, as discussed on pages H66-H69. the San Andreas system crossing the Salton Trough DEFINITION OF FRESH WATER farther west are still active, which indicates the more recent deformation of that region as compared In describing the fresh-water part of the ground- to the Sonoran Desert. water reservoir, the term "fresh water" requires definition. Fresh water is an imprecise term prob­ GROUND-WATER HYDROLOGY ably best defined as water that has a sufficiently THE GROUND-WATER RESERVOIR low mineral content to be acceptable for ordinary The limits of the ground-water reservoir in the uses. The Office of Saline Water defines fresh water Yuma area are considered as being formed by the as that containing not more than 3,000 mg/1 of dis­ crystalline rocks of pre-Tertiary age. These rocks solved solids. In many reports of the U.S. Geological include many types, but all are dense and contain Survey, fresh water is defined as that containing only small quantities of water in open fractures and not more than 1,000 mg/1 of dissolved solids a use­ weathered zones within a few tens of feet of the ful limit in most parts of the United States where land surface and possibly to greater depths in faults such water is widely available. However, in the and shear zones. In the arid environment of Yuma, Yuma area, as in many other desert areas, more most of the small quantity of water in the crystal­ highly mineralized water is used extensively; not line rocks near the mountains and hills occurs far many wells yield water containing less than 1,000 above the regional water table as small, discontinu­ mg/1 dissolved solids. On the other hand, water con­ ous perched bodies. taining as much as 3,000 mg/1 dissolved solids is The ground-water reservoir is therefore composed injurious to some of the local salt-sensitive crops of the Cenozoic basin-fill deposits overlying the pre- and is not considered acceptable for general domes­ Tertiary crystalline rocks. The general configuration tic use. Accordingly, a limit of 1,800 mg/1 probably of the basins was discussed in the preceding section is applicable to local conditions and is used in this on structure. The thickness of fill in the deepest report. This limit corresponds approximately to a parts of some of the basins probably exceeds 16,000 specific conductance of 3,000 micromhos per centi­ but only the upper 2,000-2,500 feet at these places meter (hereinafter abbreviated to micromhos), is composed of fresh-water-bearing alluvial deposits. which is used as the upper limit for fresh water in For this reason, the ground-water reservoir is con­ the interpretation of electric logs of wells. H64 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

POORLY WATER-BEARING ROCKS rine sedimentary rocks, (2) the older marine sedi­ OF TERTIARY AGE mentary rocks, (3) the Bouse Formation, and (4) Within the area of principal geohydrologic inves­ the transition zone. Inferences as to the subsurface tigation, the lower part of the ground-water reser­ extent and configuration of these units (pi. 10) are voir the poorly water-bearing rocks of Tertiary based primarily on records of 31 test wells and water age includes, in ascending order: (1) The nonma- wells (table 5) and on geophysical data. In parts of

TABLE 5. Depths of Tertiary and pre-Tertiary horizons in wells

Depth, in feet, to top of Name of Altitude W(5ll well or of land Total Older Non Remarks owner surface depth Transition Bouse marine marine Crystalline (feeit) (feet) zone Formation sedimentary sedimentary rocks rocks rockc (C-7-22) 14bcd _ USGS LCRP 14_ 155.1 505 __ 209 __ 471 (C-8-21) 16bca _ Tanner Paving 195 396 ______207(?) ____ Co. (C-8-22) 15bdd _ USER CH-6 __ 140.5 501 __ 422 __ 497 ____ 15dab _ Gila Valley Oil 145 2,140 __ 422 __ 482 _ ___ & Gas Co Kamrath 1. 35caal __ USER CH-704 150.8 1,997 794(?) 1,045 1,396 ______Top of transition USGS LCRP zone may be at 29. 885 ft. (C-8-23) 2lcaa __ Yuma School 175 404 ______280(?) ____ District 1. 2lcac _ Abe Marcus Pool- 175 478 ______300(?) 470 "Granite" at bottom. 32caal __ Sinclair Oil Co. 120 1,400 __ 972(?) __ 1,243 1,398 Do. Kryger 1. SScdd . Stardust Hotel 197 1,090 ____ 1,085 Porphyritic quartz USGS LCRP monzonite at 13. bottom. 35caa ___ S & W Ranches _ 141 191 190 "Granite" at bottom. (C-9-21) 13ccb B. Palon 423 603 563 14bac _ do ______395 1,085 700 _ _ _ -_ 1,082 Do. (C-9-22) 28cbb _ USGS LCRP 25- 204.6 2,318 2,101 ______"292 (C-9-23) 2cda __ Yuma County 212 306 Do. Fairgrounds. 19bcd _ Colorado Basin 110 3,277 __ 1,431 Drilled 1,846 ft Associates into granitic Elliott 1. basement. 29aab _ Old oil test 118 730 730 Reported in Ko- vach, Press, and Alien (1962). 32bad _ USER CH-21YM 188.0 285 ______267 Cored porphyritic quartz mon­ zonite. 33cbd _ USGS AH 195 90 90 33cdd _ USER CH-20YM 196.0 64 47 Do. 33dab _ USGS AH 196 79 79 (C-9-24) 8baa __ USGS LCRP 28_ 118.7 2,466 1,927 ______(C-10-23) 31aaa ___ M. P. Stewart 181 3,660 1,748(?) 2,515(?) (?) ______Co. Federal 1. (C-10-24) 24cbb __ Colorado Basin 170 6,007 2,367 3,112 3,802 4,937(?) ____ Top of nonma- Assoc. Fed­ rine sedimen­ eral 1. tary rocks may be at 4,302 ft. (C-10-25) 35bbd ___ USGS LCRP 17_ 94 2,946 2,514 ______(C-ll-25) llab __ Yuma Valley Oil 90 4,868 2,525 3,395 4,350 __ & Gas Co. Musgrove 1. (C-13-20) 2abdl __ USER CH-28YM 577.5 1,427 1,285 ______16S/21E 36Fca __ Arizona Public 117 978 (?) ___. ______Bottom in allu­ Service Co. vium or transi­ tion zone. 16S/22E 23Caa __ USER CH-8RD _ 128.5 360 __ 328(?) ______Basalt 342-360 ft. 29Gca2 __ USGS LCRP 26_ 125.4 1,777 1,033 1,115 __ 1,380 35Hac __ San Carlos Hotel 145 173 ______173 "Granite" boulder at bottom. 16S/23E lORcc __ USGS LCRP 23_ 143.8 715 __ 548 __ 687 703(?) May be breccia at bottom. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H65 the area these wells are far apart (pi. 3), and by no of the northern part of the area. These deposits are means all the wells penetrate the units below the very coarse grained in places but are slightly to transition zone. Interpretations shown in figure 15 moderately indurated and therefore are generally and plate 10 are therefore in part uncertain and less porous and permeable than the alluvial deposits generalized. The poorly water-bearing rocks are in the upper part of the ground-water reservoir. relatively unimportant in the hydrology of the area, Even the coarser phases, like the fanglomerate of and each of the units listed above is discussed only the Kinter Formation, do not appear to be potentially briefly. very productive. In test wells (C-7-22) 14bcd (USGS LCRP 14) and 16S/22E-29Gca2 (USGS LCRP 26) NONMARINE SEDIMENTARY ROCKS in the northern part of the area, the productivity The nonmarine sedimentary rocks of Tertiary age of the fanglomerate was much less than that of the occupy the basal part of the ground-water reservoir alluvium. throughout much of the Yuma area. In the south­ western part of the area, on the north flank of the OLDER MARINE SEDIMENTARY ROCKS "San Luis basin," varicolored sandstone and con­ The older marine sedimentary rocks have been_ glomerate of the nonmarine sedimentary rocks were penetrated in three test wells (table 5), where bore­ penetrated in oil-test well (C-10-24)24cbb (Colo­ hole geophysical logs and drilling characteristics rado Basin Associates Federal 1) from a depth of indicate that these rocks are moderately indurated 4,937 feet to the bottom of the well at 6,007 feet; and therefore probably less porous and permeable some nonmarine strata, possibly interbedded with than the overlying Bouse Formation, transition marine strata (older marine sedimentary rocks) zone, and water-bearing deposits of Pliocene to Holo- occur as high as 4,302 feet in this well (table 5). cene age. Like the nonmarine sedimentary rocks, the The electric log indicates very brackish-water extent of the older marine sedimentary rocks is not probably exceeding 15,000 micromhos specific con­ well known, but their absence below the Bouse For­ ductance throughout this interval. mation in several test wells in the northern part of Farther north, in the "Yuma trough" and the area suggests that they are less extensive than "Picacho-Bard basin," several test wells penetrated the Bouse Formation. coarse fanglomerate and breccia of the nonmarine Although no samples of ground water from the sedimentary rocks. Electric logs and pumped water older marine sedimentary rocks were obtained for samples indicate much fresher water than that in chemical analysis, electric logs of the three wells well (C-10-24)24cbb the specific conductance of penetrating the unit indicate brackish water (spe­ most of this northern water is substantially less cific conductance 3,000-15,000 micromhos) unfit for than 3,000 micromhos. However, at test well (C-7- most uses. 22) 14bcd (USGS LCRP 14) at Laguna Dam, analysis BOUSE FORMATION of a sample of water from fanglomerate (probably The Bouse Formation appears to be widespread the Kinter Formation) indicated 3,420 mg/1 dis­ (fig. 15 and pi. 10), although it has not actually solved solids and 5,610 micromhos specific conduct­ been penetrated by wells in the southern and south­ ance, which is too mineralized for most uses eastern parts of the area, where its subsurface (appendix C, analysis 206b). extent and configuration are inferred from geophysi­ The extent and thickness of the nonmarine sedi­ cal data. The unit consists chiefly of clay and silt mentary rocks beneath "Fortuna basin" in the having small hydraulic conductivity, but the inter- southeastern part of the area are unknown (no bedded very fine to fine sand probably would yield wells in this basin are deep enough to penetrate small amounts of somewhat mineralized water to these rocks); however, the nonmarine sedimentary wells. In places the basal part of the Bouse Forma­ rocks probably are present in at least part of the tion contains sandy limestone or limy sandstone, basin. On the southerly international boundary, deep conglomerate, and tuff; a conglomerate penetrated electrical soundings and an electric log of test well by test well 16S/23E-10Rcc (USGS LCRP 23) in (C-13-20)2abdl (USER CH-28YM) indicated the "Picacho-Bard basin" yielded large quantities brackish to saline water in all the Tertiary deposits of fresh water (1,180 mg/1 dissolved solids) when below the base of the older alluvium at depths of that well was test pumped,.but such coarse-grained 1,200-1,300 feet. productive strata have not been recorded elsewhere In summary, the nonmarine sedimentary rocks in the Yuma area. probably contain brackish water in the southern part In the "Picacho-Bard basin" and the "Yuma of the Yuma area but contain fresh water in much trough" the predominantly clay and silt of the H66 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Bouse Formation form an aquiclude between the beneath the northwest corner of Yuma Mesa and the underlying nonmarine sedimentary rocks (which north-central part of "Bard Valley." However, at contain fresh to somewhat brackish water) and the most places beneath the river valleys and Yuma overlying water-bearing deposits of Pliocene to Mesa, the zones are useful subdivisions of the upper Holocene age, which constitute the upper, main part part of the ground-water reservoir. The wedge zone, of the ground-water reservoir. Farther south, the the coarse-gravel zone, and the upper, fine-grained Bouse is underlain by the older marine sedimentary zone correspond respectively to the lower sandy allu­ rocks, and both units contain brackish water. vium, the coarse-gravel zone, and the sandy and silty TRANSITION ZONE alluvium of Brown and others (1956, p. 15-22). The transition zone overlies the Bouse Formation Later writers have used classifications similar to throughout most of the Yuma area but is missing that of Brown and others (1956), and it seems de­ in the northeast and perhaps elsewhere along the sirable to continue with this classification in the margins of the Bouse embayment (fig. 15), where present report. the Bouse Formation is overlain by the older allu­ Outside the river valleys and Yuma Mesa, where vium. The transition zone is as much as several the coarse-gravel zone is generally absent or un­ hundred feet thick in the "San Luis basin" in the recognized, the water-bearing deposits of Pliocene southwestern part of the area, where it is pene­ to Holocene age, which are almost entirely the older trated by several test wells (table 5). Electric logs alluvium below the water table, are not subdivided of wells (C-10-24)24cbb and (C-ll-25) llab indi­ and are classified instead as older alluvium, undi­ cate that the specific conductance of the water in vided. The older alluvium, undivided, is stratigraph- the zone increases from about 3,000 micromhos near ically equivalent to the wedge zone and hydraulically the top to more than 8,000 micromhos near the base. continuous with it.

Although the transition zone locally contains fresher WEDGE ZONE water (less than 3,000 micromhos in some test The wedge zone constitutes the major part of the wells) the unit is unimportant hydrologically be­ water-bearing deposits of Pliocene to Holocene age cause of the generally small hydraulic conductivity beneath the river valleys and Yuma Mesa. Through­ inferred from the abundance of clay and silt and out most of its extent the wedge zone overlies the from the slight to moderate induration of the transition zone or the Bouse Formation and under­ coarser strata. lies the coarse-gravel zone; laterally, beneath "Pi- WATER-BEARING DEPOSITS OF PLIOCENE TO HOLOCENE AGE cacho Mesa" and "Upper Mesa," the wedge zone is The upper, principal part of the ground-water adjacent to the older alluvium, undivided, to which reservoir the water-bearing deposits of Pliocene to it is largely equivalent. The zone extends to depths Holocene age includes the following stratigraphic of about 2,500 feet in the "San Luis basin" and the units: (1) The older alluvium, (2) the younger allu­ northern "Fortuna basin" but wedges out beneath vium, and (3) the windblown sand. However, be­ the coarse-gravel zone against the Laguna and Gila neath the river valleys and Yuma Mesa the areas Mountains to the northeast and also against the of most intensive present and probable future water buried and nearly buried "Mesa basement high" and development the upper part of the reservoir is "Yuma Hills" farther southwest, hence its name. more conviently subdivided into three zones, two The top of the wedge zone ranges from about sea of which cross stratigraphic boundaries, as shown level (depth 160 ft) near Laguna Dam and eastern below: South Gila Valley to nearly 200 feet below sea level Zones Stratigraphic units (depth nearly 300 ft) in southern Yuma Valley. Upper, fine-grained zone _Windblown sand (small dunes However, where strata of coarse gravel are abun­ in valleys, sheets of sand on Yuma Mesa). dant in the upper part of the wedge zone, as they Younger alluvium (upper, ma­ are at many places, the boundary between the wedge jor part). Older alluvium (uppermost zone and the overlying coarse-gravel zone is vague strata beneath Ynma Mesa). and arbitrary and is not shown at a definite horizon Coarse-gravel zone ______Younger alluvium (basal grav­ el). in the geologic sections of the area. (See pis. 5, 6, 8.) Older alluvium (uppermost) Scanty information indicates that the average coarse-gravel strata). Wedge zone - __ Older alluvium (lower, major grain size and probably the average porosity and part). hydraulic conductivity of the wedge zone decrease These zones are not everywhere well defined; for with depth. Clay and silt appear to be more abun­ example, the coarse-gravel zone is thin or absent dant below depths of 1,000-1,500 feet than they are GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H67 at shallower depths, especially in the "San Luis shows little vertical variation in concentration and basin." However, except possibly for the lower chemical characteristics, but it is virtually indis­ 1,000 feet or so, fine-grained strata do not appear tinguishable from the water in the overlying coarse- to be sufficiently extensive or thick to cause sig­ gravel zone. (See pi. 11.) However, this condition nificant hydraulic separation. Thus, on a large scale, may change when water from irrigation to the the wedge zone is considered to be a single hetero­ north moves farther southward, largely through the geneous hydrologic unit. coarse-gravel zone. The chemical characteristics of the water in the Scattered sample and electric-log data suggest wedge zone are not known in detail, owing to the that the freshest water in the wedge zone occurs small number and irregular spacing of wells from beneath a strip along the Colorado River. This water which samples haye been collected (pi. 11). How­ is considerably fresher than the present Colorado ever, electric logs of several test wells supplement River; four samples had dissolved solids concentra­ the chemical data and help to provide reasonably tions ranging from 451 to 624 mg/1 (pi. 11). reliable estimates of the extent and general char­ Elsewhere, except in the two areas of brackish acter of fresh water in the zone. water described earlier, the concentration of dis­ Except for two small areas, the water in the solved solids in wedge-zone water generally ranges wedge zone is fresh, as defined in this report. The from about 700 to 1,500 mg/1. At most places below two areas where the concentration of dissolved a depth of 500 feet, the concentration generally is solids exceeds 1,800 mg/1 (and the specific conduct­ less than 1,200 mg/1. ance exceeds 3,000 micromhos) are roughly the city Expressed in chemical equivalents, wedge-zone of Yuma at the northwest corner of Yuma Mesa and water characteristically contains considerably less a strip along the west flank of the northern Gila magnesium than calcium, and much of the water Mountains (pi. 11). In these areas the overlying contains less sulfate than bicarbonate (pi. 11). Ex­ coarse-gravel zone is thin or absent and the deposits cept for one sample (242c), for which the analysis of the wedge zone are relatively thin and probably represents a mixture of water from the coarse- less permeable than they are at most other places. gravel zone and the uppermost part of the wedge The body of somewhat brackish water along the zone, the equivalent concentration of chloride ex­ west flank of the northern Gila Mountains, which is ceeds that of sulfate. The equivalent concentrations much more extensive farther south, in the older of sodium and chloride are generally about equal, alluvium, undivided, may represent contamination although a few wells have yielded water in which from deeper water in the Bouse Formation and non- calcium seems to have replaced sodium by base marine sedimentary rocks of Tertiary age which exchange, so that the chloride substantially exceeds has risen along faults. the sodium. Electric logs and a few chemical analyses indicate In general, the water in the wedge zone has a that in the northern part of the Yuma area the smaller range in concentration and chemical char­ water in the wedge zone becomes fresher with depth. acteristics than that in the overlying coarse-gravel The wedge-zone water in this part of the area ap­ zone, and probably much less than that in the upper, pears to be substantially fresher than that in the fine-grained zone. overlying coarse-gravel zone, except for the two occurrences of brackish water described above. The COARSE-GRAVEL ZONE decrease in dissolved-solids content with depth prob­ The most permeable deposits in the Yuma area, ably indicates that some of the more concentrated and the ones that are tapped by nearly all the pro­ water in the coarse-gravel zone has moved down­ ducing wells, are the coarse-gravel strata in the ward into the upper part of the wedge zone. upper part of the older alluvium and locally, perhaps, Farther south, beneath central and southern Yuma at the base of the younger alluvium. These strata Mesa and Yuma Valley, vertical variations in con­ are herein referred to collectively as the coarse- centration and chemical characteristics of water in gravel zone, which is the principal aquifer beneath most of the wedge zone appear to be relatively small. the river valleys and Yuma Mesa. This zone, to However, several electric logs in that part of the which Wilcox and Scofield (1952) applied the term area indicate a gradual downward increase in spe­ "deep aquifer," has long been recognized as the cific conductance of the water below depths of primary source of ground water pumped in the 1,500-2,000 feet, where clay and silt are more abun­ Yuma area. Brown and others (1956) suggested dant in the zone. South of the irrigated area on that "deep aquifer" is not an appropriate designa­ Yuma Mesa, the water in the wedge zone not only tion because of the presence of much deeper fresh- H68 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA water-bearing deposits; instead, they used both tion of dissolved solids than that in the wedge zone. "coarse-gravel zone" and "coarse-gravel aquifer." (See pi. 11.) In much of the coarse-gravel-zone water Usage of the term "coarse-gravel zone" is contin­ the concentration of sulfate (expressed in chemical ued in the present report. equivalents) exceeds that of chloride, whereas in As described in the section, "Geology" (p. H50), the wedge-zone water, chloride exceeds sulfate in the coarse-gravel zone consists of a complex of equivalent concentration except for one analysis, and gravel bodies of different ages deposited by the Colo­ that analysis represents a strong admixture of rado and Gila Rivers; the top and bottom of the coarse-gravel-zone water. The higher sulfate con­ zone are at different altitudes and stratigraphic centrations probably indicate that river water horizons from place to place (pi. 7).' Delineation of (chiefly, but not entirely, the Colorado River) is a the zone is necessarily arbitrary at many places; the more recent source of the water in the coarse-gravel upper part of the underlying wedge zone locally zone, and that sulfate reduction (explained in the contains similar coarse gravel. The coarse-gravel section "Chemical Quality," p. H127) has not gen­ zone generally ranges in thickness from 0 to more erally proceeded as far as it has in wedge-zone water. than 100 feet (or more than 150 ft, depending on The water in the coarse-gravel zone is highly vari­ which horizon is identified as the bottom). The zone able in proportions of the major dissolved constitu­ generally dips southwestward at an angle somewhat ents, and the variations are not necessarily correla­ steeper than the slopes of the valley surfaces and tive with the variations in concentration of dissolved Yuma Mesa; in the central part of the area the solids (pi. 11). Because the coarse-gravel zone is the depth to the top averages about 100 feet beneath overwhelmingly predominant source of ground water the valleys and about 170-180 feet beneath Yuma pumped in the Yuma area, a more detailed descrip­ Mesa. tion of the variations in the chemical characteristics Somewhat saline water, in which the sum of de­ of the water in the zone, and suggested explanations termined constituents exceeds 1,800 mg/1, occurs for the variations are given in the section, "Chemi­ in the coarse-gravel zone beneath most of South cal Quality." Gila Valley, eastern North Gila Valley, northwestern UPPER, FINE-GRAINED ZONE Yuma Mesa, a U-shaped area in northern Yuma The upper, fine-grained zone includes most of the Valley, and scattered other areas of small extent younger alluvium, the uppermost deposits of the (pi. 11). At all these places except the northwest older alluvium, and the relatively minor deposits of corner of Yuma Mesa (city of Yuma) and the east windblown sand beneath the river valleys and Yuma end of South Gila Valley, the water in the under­ Mesa. Although little water is pumped from these lying wedge zone is fresh. fine-grained deposits, the upper, fine-grained zone Elsewhere, the concentration of dissolved solids is significant hydrologically because most of the of the ground water in the coarse-gravel zone ranges ground-water recharge and discharge within the from about 900 to 1,500 mg/1, although scattered Yuma area take place through it and because the wells of small capacity have yielded water contain­ water table beneath the irrigated areas lies within ing as little as 418 mg/1 dissolved solids (pi. 11). it. As in the wedge zone, much of the fresher water in The upper, fine-grained zone generally ranges in the coarse-gravel zone is near the Colorado River thickness from about 70 to 240 feet and averages and presumably results from local recharge of river about 100 feet beneath the valleys and 170-180 water. The scattered occurrences of fresher water feet beneath Yuma Mesa. Sand and silt are the most at sites away from the river probably are due to abundant materials in the zone, although beds of local anomalous conditions such as excessive sulfate silty and sandy clay and sandy gravel are extensive reduction. in places. Beneath most of Yuma Mesa the water in the Because much ground water moves vertically coarse-gravel zone has a smaller range in concen­ through the upper, fine-grained zone, a special effort tration of dissolved solids than it has beneath the was made to determine the thickness and lateral valleys: most analyses from the mesa range in con­ extent of fine-grained beds that might impede or centration from 900 to 1,400 mg/1. As mentioned restrict vertical movement. Studies of geologic logs earlier, the water in the coarse-gravel zone in the and gamma logs of numerous test wells and obser­ southern part of the mesa is chemically about the vation wells in Yuma Valley and on Yuma Mesa same as that in the underlying wedge zone. were supplemented by careful examination of expo­ The water in the coarse-gravel zone is more vari­ sures along the escarpment along the northern and able in chemical character as well as in concentra­ western edges of Yuma Mesa. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H69 Clay beds A and B of the older alluvium (p. H53) variable in chemical characteristics and concentra­ are two of the more extensive iine-grained beds tion of dissolved solids. The variations probably are mapped in the subsurface study, and other beds of related to several factors, among which are depth clay and silt in both the older and younger alluviums of the water table, proximity of canals, laterals, or in the upper, fine-grained zone may be extensive surface drains, irrigation regimen, and upward or enough to be hydrologically significant. No attempt downward movement of water reflecting areal pat­ was made to trace these individual beds as was done terns of ground-water circulation. Not nearly with clays A and B. Instead, the aggregate thick­ enough wells tapping the upper zone are available ness of clay, silty clay, and clayey silt in the upper to document adequately the pattern of chemical 100 feet beneath three areas Yuma Mesa, Yuma variation; wide differences exist between wells less Valley, and South Gila Valley was computed from than a mile apart. Where the water table is shallow, well-log data (pi. 12). Because the thickness of the the dissolved solids are concentrated by evapotrans- upper zone considered in each area is 100 feet, the piration, and brackish water, generally high in aggregate thickness of the fine-grained materials is sodium chloride, is the result. At some other places, also equivalent to their percentage in this inter­ where infiltration of canal water occurs, the shal­ val. The well-log data consist of drillers' or geolo­ low ground water is almost identical to the water in gists' logs of many wells, supplemented by gamma the canal (Colorado River water). logs or other borehole geophysical logs. Using the gamma logs, the drillers' or geologists' logs were OLDER ALLUVIUM, UNDIVIDED modified so that the thickness of the clay-bearing Outside the river valleys and Yuma Mesa, the strata could be computed more precisely than would coarse-gravel zone appears to be largely absent, and have been possible otherwise. the older alluvium forms a single water-bearing The computations indicate that the average thick­ unit which is stratigraphically equivalent to the ness of clay-bearing strata in the top 100 feet be­ adjacent wedge zone and hydraulically continuous neath the river valleys and Yuma Mesa is only with it. This unit, called older alluvium, undivided, about 15 feet; however, the range is from 0 to more consists chiefly of slightly to moderately indurated than 50 feet (pi. 12). The clayey deposits are thick­ sand, silt, and a minor amount of gravel and clay est in South Gila Valley (pi. 12). Somewhat lesser of river origin, interbedded or mixed with deposits thicknesses occur beneath northern Yuma Mesa, of local origin. Near the mountains, poorly sorted west-central Yuma Mesa (in the vicinity of the apex gravelly deposits of local origin predominate. As in of the large ground-water mound caused by irriga­ the wedge zone, the permeability and porosity of tion), south-central Yuma Valley, and several other the deposits probably decrease with depth, owing to scattered localities. Beneath much of the Yuma area, compaction and cementation. However, because of the aggregate thickness of the fine-grained clayey the considerable thickness as much as 2,000 feet deposits in the top 100 feet is less than 10 feet. beneath part of the "Upper Mesa" the older allu­ Most of the clayey strata in the upper, fine-grained vium, undivided, stores and transmits substantial zone contain a considerable amount of silt and sand. amounts of water. In "Fortuna Plain" and Davis Consequently, the permeability of these strata is not Plain in the southeastern part of the Yuma area, sufficiently low to cause extensive perching of ground the older alluvium is overlain by younger alluvial- water, even where these fine-grained strata, such as fan deposits, but these fan deposits are largely if clays A and B described earlier, are thick and ex­ not entirely above the water table and are not con­ tensive. However, although true perching is rare or sidered further here. absent, the fine-grained strata inhibit vertical move­ Relatively little is known about the chemical ment of ground water, so that sizable differences in quality of the water in the older alluvium, undi­ water levels exist at different depths where upward vided. Beneath the "Upper Mesa," three analyses or downward movement occurs. One of the best ex­ indicate that the water is similar to that in the amples is in the west-central Yuma Mesa. In this wedge zone beneath Yuma Mesa (pi. 11). Farther area, which has been irrigated for about 50 years east, beneath "Gila Mesa," the water is brackish and which is the apex of the ground-water mound and probably contaminated by deeper water rising beneath Yuma Mesa, the water table locally is more along fault barriers. The southern limits of the than 35 feet higher than the piezometric level for brackish water are not known. The electric log of the top of the coarse-gravel zone. U.S. Bureau of Reclamation test well CH-28YM on Scattered chemical analyses suggest that the "Fortuna Plain" at the southerly international water in the upper, fine-grained zone is exceedingly boundary indicated water having a specific con- H70 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA ductance slightly exceeding 3,000 micromhos the in the flood plain probably resulted in increased limit for fresh water in the Yuma area. However, salinity at shallow depth. The rest of the ground there are no data to show whether or not the brack­ water moved slowly southward and southwestward ish water at test well CH-28YM extends all the way into Mexico to areas of discharge in the Colorado north to the body of brackish water beneath "Gila delta around the head of the Gulf of California. The Mesa." underground flow was a very small fraction of the flow in the river itself. ORIGIN OF GROUND WATER AND SOURCES OF RECHARGE After the construction of Hoover Dam, Imperial Almost all the ground water in the upper part of Dam, and other upstream dams, the Colorado River the ground-water reservoir in the Yuma area is in­ cut down, so that its channel now lies 10-20 feet filtrated river water; precipitation and local runoff below the adjacent flood plain from Laguna Dam to are very minor sources of ground-water recharge. the southerly international boundary. The downcut- ting resulted from the clearer water in the river The more highly mineralized water in the older rocks of the lower part of the reservoir may include some after its normal load of sediment was largely trapped connate water which was not completely flushed out. by the dams. At the same time, irrigation has main­ tained a high water table beneath the flood plain, Patterns of ground-water recharge have changed, hence the lowered river channel now acts primarily both in geologic time and in historic time, so that as a drain rather than as a source of ground-water the configuration of the water table and the chemical recharge. However, some recharge from the river character of the ground water are in a state of still occurs, during occasional high flows, and also flux. The relative importance and the chemical char­ at other times along reaches where significant quan­ acteristics of each of the various sources of ground- tities of ground water are pumped from adjacent water recharge are described in the following para­ graphs. wells, such as along the limitrophe section between Pilot Knob and the southerly international boundary. COLORADO RIVER The chemical composition of ground-water re­ Under natural conditions the Colorado River was charge from the Colorado River has been materially the predominant source of ground-water recharge affected by control of the river by the upstream in the Yuma area, and it still is by way of diver­ dams. Before the impounding of water in Lake Mead sions for irrigation. Water-level contours for 1925 behind Hoover Dam, beginning in 1935, the chemical (fig. 29) indicate that the Colorado River at that composition of the river water in the lower reaches time was a source of ground-water recharge during was highly variable, both seasonally and annually. low flows as well as high flows. The water table Concentrations of dissolved solids were relatively sloped away from the channel so that the river low during seasons and years of high flow and rela­ formed a ground-water ridge, and water moved tively high during periods of low flow. Because of away from the channel on both sides. Evapotrans- their longer duration, periods of low flow and high piration, in large part by the phreatophytes grow­ concentration may have affected the chemical quality ing on the flood plain, maintained the lower water of ground-water recharge more than periods of high levels away from the river. Considerable quantities flow and low concentration. of ground-water recharge occurred during floods, As shown by the summary below, the chemical when most of the flood plain was covered with slow- characteristics of Colorado River water at Yuma moving sheets of water. were very similar to those at Grand Canyon during Discharge of ground water by evapotranspiratfon the two years of parallel sampling, 1927 and 1928. Constituent concentrations in Colorado River water prior to closure of Hoover Dam in 1935 Grand Canyon Yuma Year Constituent Minimum Weighted average Maximum Minimum Weighted average Maximum 1927 238 569 1,450 287 612 1,300 1927 Bicarbonate _ _ _ _ _ - - 121 162 289 133 169 256 1927 Sulfate ______66 235 597 75 238 579 1927 Chloride ______18 53 248 25 73 278 1928 Dissolved solids 233 491 1,180 285 513 1,180 1928 Bicarbonate _ _ 126 162 240 132 163 234 1928 Sulfate 66 187 525 79 195 557 1928 Chloride ______10 48 165 23 55 157 L934 Dissolved solids 437 960 1,890 1934 Bicarbonate _ 145 206 280 1934 Sulfate ______131 392 827 1934 Chloride ______51 136 310 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H71 Concentrations were not determined at Yuma dur­ Ground water beneath South Gila Valley moved ing 1934, the minimum annual flow year of record southward beneath eastern Yuma Mesa, eastern of the Colorado River prior to construction of Glen "Upper Mesa," and "Fortuna Plain"; therefore, Canyon Dam, but were probably similar to those under natural conditions, much of the ground water listed for Grand Canyon. Thus, the pre-Hoover Dam beneath the eastern part of the Yuma area was. de­ records indicate that the usual flow of the Colorado rived from the Gila River. River water in the Yuma area contained less than Unfortunately, no analytical records describe the 1,000 mg/1 dissolved solids, with sulfate the major natural variation of the chemical quality of the Gila anion and with concentrations of bicarbonate exceed­ River before the construction of upstream dams and ing chloride except during periods of low flow. Dur­ the diversions for irrigation. Recent analytical rec­ ing flood flows, bicarbonate was the major anion. ords for the major tributaries above Phoenix indi­ Sulfate always exceeded the chloride, regardless of cate considerable differences in chemical character­ flow. istics among these tributaries, which are the former During the 25-year period 1941-65, the composi­ major sources of inflow to the lower Gila River. The tion of Colorado River water downstream from Lake natural chemical characteristics of water in the Mead, although still somewhat variable on a year-to- lower Gila River probably were quite variable, de­ year basis, did not depart much from a character­ pending on the proportions of inflow from each of istic concentration pattern. Thus, although the con­ the major tributaries at any particular time. centration of dissolved solids at Imperial Dam fluc­ The Gila River flowed at the mouth during the tuated between 600 and 900 mg/1, it was generally winter of 1966 as the result of release of low-salinity between 700 and 800 mg/1. The chloride concentra­ water from the new Painted Rock Reservoir, about tion fluctuated between 70 and 140 mg/1. Sulfate, 100 miles east of Yuma. The water was stored as a always the major dissolved constituent, usually result of flooding on the Salt and Verde Rivers (two ranged from 260 to 370 mg/1 and amounted to about of the major tributaries) when runoff in December three-sevenths of the dissolved solids. The calcium 1965 filled the storage reservoirs. Analyses of sam­ concentration, ranging from 80 to 115 mg/1, was ples taken at various points from Painted Rock Dam generally about three times the magnesium concen­ downstream to Dome (12 miles upstream from the tration and was also usually a little greater than mouth) during release of the stored water showed the sodium concentration when the dissolved solids that it flowed down the river without great change concentration was lowest (about 700 mg/1), and in composition. Similarity in chemical composition somewhat less than the sodium concentration when of this water to that produced from wells at many the dissolved solids concentration was highest locations on Yuma Mesa supports the hypothesis about 900 mg/1). No consistent relation existed be­ that much of the original ground water beneath the tween the concentrations of any of the cations and mesa was derived from flood flows of the Gila River. anions, although the equivalent concentration of IRRIGATION sodium was generally about twice the equivalent concentration of the chloride. Irrigation with diverted Colorado River water is now the source of almost all ground-water recharge GILA RIVER in the Yuma area. The principal exception until 1965 Under natural conditions the Gila River was peren­ was the South Gila Valley which was irrigated with nial to its mouth near Yuma, except during pro­ ground water and therefore received much recircu- longed dry periods, when flow ceased during some lated ground water as well as some water from adja­ months (Wells and others, 1954, p. 707-709). Regu­ cent areas irrigated with Colorado River water. lation of the river began in 1911 with the construc­ Water applied in excess of crop requirements and tion of Roosevelt Dam on the Salt River, a major the amount evaporated from the soil penetrates to tributary near Phoenix. Thereafter, as irrigation the water table. In addition, leakage occurs from increased east of the Yuma area, especially near the canals and distribution system; a considerable Phoenix, the flow at the mouth generally decreased; proportion of this leakage also reaches the water after the late 1920's, only occasional floods produced table. Much of the ground water derived from irri­ flow near Yuma. gation is discharged by surface drains or, in recent Water-level data for 1925 indicate the Gila River years, by drainage wells. Since the early 1920's, but was a significant source of ground-water recharge especially since the late 1940's irrigation with Colo­ to South Gila Valley at that time; by inference, the rado River water on Yuma Mesa has resulted in the recharge under natural conditions was even greater. formation of a ground-water mound of considerable H72 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA size. Because of the sandy soils of low water-holding 200 to 300 micromhos. Feth found that most of the capacity and the need to reduce salt accumulation samples having higher specific conductance came in the soil zone, the amount of irrigation water from locations where dry fallout might include dusts applied has been several times as much as the stirred up from the surface of desert play as. These amount evaporated and transpired, so that ground- more concentrated samples probably are not repre­ water recharge from this source has been sub­ sentative of bulk precipitation in the Yuma area stantial. because playas are absent. Otherwise, Feth's results As discussed in the quality of water section of appear applicable. It appears reasonable to assume, this report, there has been a significant change in therefore, that the average mineral content of rain­ the quality of water obtained from domestic wells fall in the Yuma area has less than 100 micromhos in the part of the Yuma Mesa irrigated with Colo­ specific conductance and contains 60 mg/1 or less rado River water. Older analytical data indicate that dissolved solids. Several of Feth's analytical results formerly the quality of the water obtained from representing samples collected near the Yuma area, wells in this area was of rather uniform character are given in table 6. with sodium and chloride the principal ionic con­ LOCAL RUNOFF stituents and with much less sulfate than chloride Even the small amount of precipitation in the being present. Domestic wells in the area now gen­ local mountains is enough to produce local runoff, erally yield water more like Colorado River water, especially during periods of intense storm rainfall. with sulfate exceeding chloride, except that there The mean annual runoff in the mountains near Yuma apparently has been considerable softening as the may exceed 1 inch (Hely and Peck, 1964, pi. 5). water infiltrated from the land surface. Apparently However, because of rapid infiltration in the sandy surface application of large volumes of imported and gravelly washes, most of this locally generated Colorado River water has resulted in a downward runoff does not reach the Colorado and Gila Rivers. displacement of the original water accompanied by A major part of the infiltrated water is later evapo­ softening of the displacing water. rated and transpired, but a minor part eventually LOCAL PRECIPITATION reaches the water table. Chemical-quality and water- In the Yuma area, as in most desert regions, pre­ level data from wells near Fortuna Wash show that cipitation is too scanty to allow deep penetration of local runoff has reached the water table and has moisture at most places. The mean annual precipita­ also formed perched or semiperched bodies of ground tion in Yuma for the period 1931-60 was only 3 water. Although no data have been gathered else­ inches, and in the adjacent mountains, 4-6 inches where, the large washes like Picacho Wash and Un­ (Hely and Peck, 1964, pi. 3). Even during relatively named Wash north of Yuma are likely sources of wet years and during periods of intensive rainfall, local ground-water recharge. However, the flat little or no water penetrates below the soil zone. water-table gradients adjacent to the mountains Moisture measurements by the neutron-meter indicate that the total quantity of recharge from method made during the present study showed that local runoff is very small. the materials between the top few feet and the water Evidence that local runoff, particularly in the table are nearly dry outside of the irrigated areas; mountains, is low in mineral content is afforded by moisture contents of less than 5 percent far below a number of analyses of samples collected from both field capacity were recorded at most places. Deep natural and artificial tanks and one spring in moun­ penetration of precipitation, therefore, is a negligi­ tainous areas near the Yuma area. An analysis of ble source of ground water recharge in the Yuma a sample from Little Picacho Wash, in California, area, except possibly in irrigated areas where the and another from the Gila River near Texas Hill, soil is wet before rains occur. Ariz., taken after a rain also show low mineral con­ The addition from precipitation to the mineral tents. (See table 6.) content of ground water in the Yuma area is almost HYDROLOGIC CHARACTERISTICS OF AQUIFERS certainly negligible. Investigations by Feth (1967) DEFINITION OF TERMS have shown that the dissolved mineral content of The term "aquifer" commonly is applied to a bulk precipitation (rainwater and incorporated dry water-bearing formation or rock unit that is capa­ fallout from the atmosphere) in the ble of yielding appreciable quantities of water to region is generally very low; the specific conductance wells. The term is flexible, in that it may denote a of most samples is less than 100 micromhos, al­ single bed, or it may refer to a relatively thick though in a few samples of fallout it ranged from sequence of beds. The latter usage is especially GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H73

TABLE 6. Miscellaneous chemical analyses [Values in milligrams per liter, except for specific conductance]

Hardness as _ CaCOa ~ Is 8 1 I spo­ ts 8 cine ~ ~ 1 ,-. ** ^" *^ ,-, « *° c o> con- Sample source Date £ g ft£ £ -gw« 6 ~S £~ 2~ Iw fE *c ductance' 33 ~ ""' £ G ~ o>o> *8 - .2 (micro- B £ & & 22-2 2 § 3 mhos .2* «§ 1§ ||S2 S 1 S 1 | 8 at25°C a "3 _S ^ o .a -3 25-c .a -3 § w o £ W fc « W 3 fa fc PUS Bulk precipitation-3-Slashes Ranch, Mar. 17, to 0.2 10.0 1.0 4.6 3.8 10 13 4.8 ___ 8.7 51 29 21 111 lat 33°17' N.. long 114°43' W. Apr. 18, In California.) (Data from Feth, 1965. 1967, table 1.) Bulk precipitation-3-Slashes Ranch Apr. 4 to 18 1.7 12.0 11 94 16 16 _ __ 2.5 124 50 0 259 Data from Feth, 1967, table 1. ) Nov 23. 1965. Bulk precipitation Singers, lat Mar. 17, 1965. 1.0 4.8 0.0 1.0 .8 8 4.0 .8 ___ 1.5 26 12 5 44 33°03' N , long 114°43' W. (In to Mar. 21, California.) (Data from Feth, 1966. 1967, table 1.) ______99 33° 00' N., long 115° 04' W. (In Apr. 4, California.) (Data from Feth, 1965. 1967 table 1.) Bulk precipitation-Glamis (In Cali- Apr. 4, 1965, .3 8.8 .5 1.0 1.8 2 8.0 3.8 ___ 12 37 24 22 72 fornia.) (Data from Feth, 1967, to Jan. 20. table 1.) 1966. Owl Head Dam, , Aug. 11, 1965 11 45 4.7 ___ 8.7 152 6 14 .30 166 132 8 295 Ariz. Budweiser Spring, Kofa Mountains, Jan. 14, 1965 25 25 5.7 ___ 14 102 17 9.5 .3 ___ 148 86 2.5 216 Ariz. High tank No. 7. Kofa Mountains, Jan. 14, 1965 12 38 3.6 ___ 11 106 22 16 .3 __ _ 156 110 23 253 Ariz. Charley Died tank, Kofa Mountains, Feb. 3, 1965 14 23 4.3 ___ 19 70 35 16 .2 ___ 146 75 18 219 Ariz. Horse tank. Castle Dome Moun- Dec. 13, 1964 1 20 2.4 60 0 232 tains, Ariz. Horse tank __ _ _ _ Sept. 15, 1965 16 17 .9 35 124 0 14 _ 145 46 0 238 Frenchman tank, , Mar. 5, 1965 7 22 0 ___ 12 64 12 10 .2 1.3 97 55 2.5 143 Ariz. Black tank. , Jan. 12, 1965 5 30 4.6 ___ 15 120 7 14 .3 ___ 136 94 0 236 Ariz. Arch tank. Castle Dome Mountains, Mar. 23, 1965 6 26 .7 ___ 8.7 56 19 9.5 .2 8.8 107 68 22 166 Ariz. Bandy tank. Castle Dome Moun- Mar. 23, 1965 1 34 5.6 ___ 13 110 19 18 .2 ___ 146 108 18 242 tains, Ariz. Saguaro tank, Castle Dome Moun- Feb. 17, 1965 7 38 1.9 ___ 14 80 27 16 .2 15 162 103 32 246 tains, Ariz. Ladder tank, Castle Dome Moun- Dec. 14, 1964 11 38 3.2 14 72 42 26 170 108 49 297 tains. Ariz. Burnt Wagon tank, Castle Dome July 15, 1965 6 3T 2.8 ___ 6.9 116 9 10 .1 ___ 130 104 9 226 Mountains, Ariz Salton tanks. Castle Dome Moun- Feb. 18, 1965 6 29 2.S ___ 7.1 65 13 6.5 26 ___ 122 82 28 190 tains. Ariz. Carrizo tank. Chocolate Mountains, Feb. 5, 1962 11 32 1 5 66 30 70 119 84 30 223 Calif. Little Pichacho Wash., near Burro Jan. 31, 1962 27 31 4 73 177 63 31 317 96 0 513 Wash., in Calif. Gila River near Texas Hill, Ariz., Aug. 15, 1963 7 30 4.4 ___ 26 86 34 30 .3 __.._ 175 93 22 291 after rain, barely flowing. Gila River near Dome, Ariz. Flood Feb. 28. 1966 11 68 18 ___ 185 180 98 281 .3 ___ 751 244 96 1,390 water being released from Painted Rock reservoir. Gila River near Dome, Ariz. Flood Mar. 18, 1966 10 70 16 191 186 115 272 _ 767 240 88 1,360 water being released from Painted Rock reservoir. Well in nonmarine sedimentary Apr. 24, 1963 1 964 651 5,450 29 792 11,400 _ 19,300 5,080 5,060 31,300 rocks at North end of Gila Moun­ tains. Ariz. Mine shaft near well at North end Apr. 24, 1963 25 230 264 6,680 696 367 10,800 18,700 1,660 1,090 31,300 of Gila Mountains, Ariz. applicable to alluvial deposits in the Yuma area alluvium, undivided, is regarded as the principal where individual permeable beds are lenticular or single, heterogeneous aquifer. Further studies using vaguely bounded and are not generally separated more data than are presently available may indicate by extensive relatively impermeable beds. that the older alluvium, undivided, and the wedge The principal aquifers in the Yuma area are the zone actually comprise several distinct aquifers and coarse-gravel zone and the wedge zone; subordinate interbedded relatively impermeable beds. aquifers of only local significance include the non- Because what is considered to be an appreciable marine sedimentary rocks, conglomerate in the basal water supply varies widely from place to place, aqui­ part of the Bouse Formation, and a few relatively fer is a relative term which depends in large part coarse grained beds in the upper, fine-grained zone. on the conditions that must be met. The adjectives Outside the river valleys and Yuma Mesa, the older excellent, good, fair, or poor are commonly used to

507-243 O - 74 - 6 H74 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA denote the degree to which the supply is satisfac­ aquifer composed of many different strata ranging tory. However, these general terms are inadequate from clay or silt to sand or gravel may have a hori­ for quantitative appraisal of an aquifer or aquifer zontal hydraulic conductivity that is hundreds or system, or for comparing one supply with another. even thousands of times larger than the vertical For these purposes, more specific terms are re­ conductivity. Values of horizontal hydraulic con­ quired. ductivity commonly range from a fraction of a The principal characteristics of an aquifer that gallon per day per square foot for clay and silt to permit a quantitative analysis of its response to 10,000 gallons per day per square foot for well- changes in supply or withdrawal are designated by sorted gravel. two terms: "transmissivity" and "storage coeffi­ Determinations of hydraulic conductivity are cient." among the principal objectives of an appraisal of a The term "transmissivity," which is equivalent ground-water system. Reasonably close estimates of to the term "coefficient of transmissibility" intro­ hydraulic conductivity can be obtained by proper duced by Theis (1935), has been used by an increas­ sampling and laboratory procedures. However, the ing number of hydrologists in recent years because results thus obtained apply only to the samples it is a more appropriate word than transmissibility analyzed. It is seldom feasible to obtain a sufficient for the property that is described. In units com­ number of samples to adequately define hydraulic monly used by the U.S. Geological Survey, trans­ conductivity throughout a ground-water system. missivity may be expressed as the rate of flow of Rather, the average horizontal hydraulic conduc­ water in gallons per day through a vertical strip tivity is computed on the basis of a known trans­ 1 foot wide of the entire saturated thickness of the missivity and a known thickness of saturated ma­ aquifer under a unit hydraulic gradient at the pre­ terial. vailing temperature of the water. In some applica­ Vertical hydraulic conductivity can be computed tions it may be visualized more easily by expressing from adequate pumping-test data for a leaky arte­ the width of the aquifer cross section in miles and sian system. It also can be computed for areas in the hydraulic gradient in feet per mile. which most of the flow is vertical, if data on vertical Hydraulic conductivity (formerly coefficient of gradients, changes in water level with changes in permeability) is the term that expresses the flow rate of recharge or discharge, and storage coeffi­ of water in gallons per day that will occur through cients are known or can be estimated with reason­ a 1-square-foot cross section of the aquifer under able accuracy. The costs of obtaining the data a unit hydraulic gradient at a water temperature necessary to compute vertical hydraulic conduc­ of 60°F (15.6°C). If the flow is that occurring at tivity often exceed the available funds, and thus in the prevailing temperature of the water, the term many investigations this parameter is not well de­ is referred to as the field hydraulic conductivity. fined. The inability to adequately define the vertical Thus, the field hydraulic conductivity is related to hydraulic conductivity will not of itself prevent a the transmissivity by the formula satisfactory appraisal of the total quantities of Pm = T water involved in recharge, storage, and discharge. in which P is the field hydraulic conductivity, ra is However, its absence will lessen the precision with the saturated thickness of the aquifer in feet, and which the response of the system to stresses placed T is the transmissivity. on it by changes in rates of recharge or discharge Under certain conditions, especially in alluvial ma­ can be predicted. terial, it is necessary to differentiate between the In the Yuma area, values of vertical hydraulic horizontal and vertical hydraulic conductivity. Gen­ conductivity had been computed for limited areas erally, the horizontal hydraulic conductivity of a by Jacob (1960). Most of the values were for the particular bed is substantially greater than the ver­ alluvial material above the coarse-gravel zone be­ tical hydraulic conductivity because of the size sort­ neath the irrigated area of the Yuma Mesa and for ing and the alinement of platy and ellipsoidal grains the alluvial material both above and below the that occur during the deposition of alluvial mate­ coarse-gravel zone for limited areas of the flood rials. The difference between average horizontal and plain in Yuma Valley and the South Gila Valley that average vertical hydraulic conductivity increases border the Yuma Mesa. These values were used as markedly with thickness if an aquifer is composed guidelines for determining values to be used in the of a large number of thin beds whose conductivities electrical analog model of the Yuma area. cover a wide range, such as is common in the allu­ Transmissivity generally is determined from vial deposits of the Yuma area. Thus, an alluvial pumping or aquifer tests for areas where adequate GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H75 data are available. However, the areas for which ing with regional transmissivity values it was de­ aquifer-test data are inadequate generally are much cided that, for the time and funds available, more more widespread than the areas for which the data representative information could be obtained by are adequate. For the areas where aquifer-test data making short-term pumping testa of practically all are inadequate but the specific capacities of wells the large capacity wells, even though some of the of known construction can be computed, the trans- procedures might yield questionable data in some missivity for the materials tapped by the wells can instances, than by making more detailed and much be estimated on the basis of the theoretical relation more expensive and time-consuming tests at only a between specific capacity and transmissivity that limited number of sites. Consequently, advantage exists under a given set of conditions (Theis and was taken of almost all opportunities to make pump­ others, 1963). ing tests on existing large-capacity wells for which If data on specific capacity are lacking, transmis­ adequate tests had not been made. In most places, sivity can be estimated for those areas where litho- the procedure was limited to obtaining data on the logic logs or good drillers' logs are available if the rate of recovery of water level in the pumped well relation between hydraulic conductivity and median after it had been pumped at a constant rate for a grain size is known. Such a relation has been estab­ known period of time. Although the reliability of lished for alluvial material in the Arkansas River this procedure was unpredictable it generally pro­ Valley, Ark., (Bedinger and Emmett, 1963). vided useful information for computing transmis­ To the extent that the relation found for the allu­ sivity for the material tapped by the well. When it vial materials of the Arkansas River Valley are was possible to obtain rate-of-drawdown data also, applicable to the materials of the area being investi­ the transmissivity computed from that data was gated or that a new relation can be established, compared with the value computed from the recov­ possibly on the basis of pumping tests or laboratory ery data. A substantial difference between the two analyses, the transmissivity can be computed by values was considered an indication that one or summing the products of the various hydraulic con­ both was unreliable. Other measures of transmis­ ductivities and the thicknesses of the strata to sivity, such as specific capacity, were considered in which they apply. checking the reasonableness of the values computed Transmissivity can also be computed if the width from drawdown or recovery data. of a vertical section through which ground water Step-drawdown tests were made for most of the is moving at a known rate and the hydraulic gradi­ test wells that were drilled and for a few other wells ent normal to that section are known or can be esti­ where it was practical to do so. Step-drawdown tests mated with reasonable accuracy. permit the separation of the observed drawdown All the above methods were used in varying de­ into two components, one due to well losses and the grees during the current investigation for estimat­ other due to formation losses. A transmissivity com­ ing transmissivity. puted on the basis of the specific capacity from TRANSMISSIVITY which well losses have been excluded is likely to be closer to the true transmissivity than is a value DETERMINATIONS BY PREVIOUS INVESTIGATORS that is based on the assumption that the well loss Prior to the present investigation, Jacob (1966) is average for the area. analyzed the results of interference tests for 10 The Thiem method for computing the transmis­ deep drainage wells along the eastern side of Yuma sivity was used for several of the large drainage Valley. Transmissivities obtained as a result of wells for which observation wells were available for these tests are shown in figure 23. He also analyzed computing the hydraulic gradient toward the the results of step-drawdown tests on six of these pumped well. All the pumping tests, except those wells to determine the characteristics of the wells which were analyzed by the Thiem method, in­ themselves. Step-drawdown tests also were made on volved the use of the nonequilibrium formula of 10 other wells, of which three were in the Yuma Theis (1935) or modifications thereof. The nonequi­ Valley, three in the South Gila Valley, and four on librium formula is based on the following assump­ the Yuma Mesa. The location of these tests and the tions: (1) The aquifer is isotropic and homogenous, transmissivities, where considered reliable by Jacob, (2) the aquifer is of infinite areal extent, (3) the are also shown in figure 23. well taps the full thickness of the aquifer, (4) the well has an infinitesimal diameter, and (5) the re­ DETERMINATIONS DURING PRESENT INVESTIGATION lease of water from storage with decline of head is In planning the phase of the investigation deal­ instantaneous. H76 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA 114°45' 30'

32°45'

30'

.460 Pumping-test site Circle shows well-site location; number shows transmissivity of materials tested, in thousands of gallons per day per foot

Mountains and hills

Area of shallow bedrock

32°15'

FIGURE 23. Transmissivities computed from pumping tests made prior to the present investigation. It was realized that the actual conditions differed meaningful results can be obtained if the tests are substantially from the ideal conditions that were made and the results are analyzed in a way that assumed in deriving the nonequilibrium formula. minimizes the effects of any conditions that differ Nevertheless, the results of previous pumping tests substantially from ideal conditions. Accordingly, throughout the country have demonstrated that pumping tests utilizing the nonequilibrium formula GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H77

114°45' 30'

32°45' - 18cbd 18ddd 13bdd2, /21ddd /22caa

,28cbb Well for which pumping test(s) were made and well number

Mountains and hills

Area of shallow bedrock

Alluvial escarpment

Fault Dotted where concealed

32°15'

FIGURK 24. Wells for which pumping tests were made during present investigation. were made on practically all large-capacity wells on ously precluded obtaining meaningful results (fig. which pumping tests had not been made previous 24). Because of this practice, some of the pumping to the present investigation and for which satisfac­ tests yielded data that were not satisfactory for tory arrangements for a pumping test could be made, analyses by the nonequilibrium formula. unless the geologic and hydrologic conditions obvi­ Table 7 lists the results of the pumping tests that H78 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA were made during the present investigation. Each tapped by the well, or at least a general knowledge of the values of transmissivity is designated as as to what percentage of the transmissivity of the being considered an excellent, good, fair, or poor fully saturated section is represented by the com­ indicator of the transmissivity of the material puted value. A good understanding of the various tapped by the well. The classification takes into kinds of water-bearing material and their positions account the construction of the well, the possibility in the geologic framework in which the ground water of leakage between strata tapped by the well either occurs is necessary for this evaluation and was at­ within the well casing or the gravel envelope out­ tained during the present investigation. This knowl­ side the casing, the storage capacity of the well edge together with pumping-test data and drillers' casing and the gravel envelope relative to the rate logs of wells permitted the compilation of maps at which the well had been discharging, and other showing transmissivity (fig. 25 and others not factors that might tend to invalidate the results. shown), which were used as a basis for construct­ The degree to which changes in water level with ing the analog model of the Yuma area and for time conformed with theory also was used to judge computing rates of ground-water movements. the reliability of the transmissivity. Another cri­ STORAGE COEFFICIENT terion was the ratio between the transmissivity and An important characteristic of an aquifer is its the specific capacity of the well, a method mentioned ability to store or to release water in response to earlier in this report. For most of the wells that changes in head. This characteristic commonly is were tested, ratios of 2,000-3,000 were considered designated by a dimensionless number called the reasonable. Lower ratios were indicated when the storage coefficient (formerly coefficient of storage), drawdown used to compute specific capacity did not which has been defined as the volume of water that include well losses, when the specific capacity was is released from or taken into storage per unit sur­ considerably higher than it would be at the end of face area of an aquifer per unit change in the com­ a 1-day pumping period, or when effective well diam­ ponent of head normal to that surface (Ferris and eters were considerably more than 24 inches. others, 1962, p. 74). Another criterion for evaluating the reliability of The changes in storage that result from changes the indicated values of transmissivity was whether in head when water is confined, that is, when it the hydraulic conductivity as computed by dividing occurs under artesian conditions, are due almost the indicated transmissivity by the thickness of entirely to compressibility of the water and the strata tapped by the well greatly exceeded the aquifer. Storage coefficients under artesian condi­ probable maximum hydraulic conductivity of the tions, therefore, are small, generally ranging from material tapped by the well. In the Yuma area the about 0.00001 to 0.01. average maximum hydraulic conductivity of allu­ The changes in storage that result from changes vial material several tens of feet thick probably is in head when water is unconfined, that is, when it not more than 10,000 gallons per day per square occurs under water-table conditions, are dependent foot. Thus, computed values of transmissivity that almost wholly on the drainage characteristics of the indicated hydraulic conductivities two or more times aquifer material. larger than the above figure were considered un­ The volume of water involved in gravity drainage reliable. ordinarily is many hundreds or even thousands of A classification of excellent for the reliability of times greater than the volume attributable to com­ the transmissivity was made where, taking into pressibility of the aquifer materials and of the water account all the aforementioned criteria, the com­ in the saturated zone; therefore, the volume of puted transmissivity was thought to differ from the water resulting from compressibility can be ignored. true value by less than 10 percent; good, if the The volume of water involved in gravity drainage difference was likely to be as much as 25 percent; divided by the volume through which the water table fair, if as much as 50 percent; and poor, if more moves, has been defined as the specific yield. Under than 50 percent. Of the 73 evaluations of reliability dewatering and unconfined conditions the storage of the computed values of transmissivity, three are coefficient therefore is sensibly equal to the specific classified as excellent; 33 as good; 28 as fair, and yield. When water is going into storage, that is, nine as poor. when the water table is rising, the storage coeffi­ To adequately evaluate the transmissivity of the cients may exceed the specific yield if the material full thickness of saturated material at a particular in which the water is being stored contains less mois­ well site, one must also have knowledge of the hy­ ture than it can retain against gravity drainage. The draulic conductivity of all water-bearing strata not upper limit of the storage coefficient in the latter con- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H79

TABLE 7. Results of pumping tests Type of test: D, drawdown; R, recovery; SD, step-drawdown. Aquifers tested: B, Bouse Formation; C, coarse-gravel zone; N, nonmarine sedimentary rocksffi O, older alluvium, undivided; W, wedge zone.

(T)Transmissivity, Depth interval feetDrawdown,in Conform- U ance of test Reliability Aquifers tested, in Date of crt Well Owner or name feet below test inYield,gpm gpdftinper data to of T tested Remarks land- S || theoretical surface O 300,000 __ do _____ do _____ C, W Only parts of aquifers tested. lORcc __ USGS LCRP 23 _ 634-694 1-21-63 D 1,230 22 56 260,000 B See page H209 for additional data. 1-21-63 R 1,230 22 56 4,600,000 Poor B 120-548 4- 6-65 R 650 4 160 240,000 C, W 31Dbc __ Dover and Webb_ 100-144 4-30-63 R 3,000 21 140 420,000 C (C- 7-22) 14bcd ___ USGS LCRP 14 _ 470-490 R 290 46 63 110,000 do N Only part of aquifer tested. 118-128 \ Poor 152-162 / R 600 9 67 790,000 Poor C (C- 8-21) 19dad __ F. J. Hartman _ 115-165 9-11-62 R 2,600 28 93 230,000 C 30cdc do 120-140 10 9 62 R 2,050 11 190 1,800,000 Fair ______C Gravel re- 150 feet. Only part of aquifer tested. (C- 8-22) 13bdd2 __ S. Sturges _____ 109-128 4- 9-64 R 1,325 53 25 65,000 C In tight gravel. Only part of aquifer tested. IScbd 110-160 10-16-62 R 4,400 9 490 610,000 do _ _ do C 18ddd do 100-155 10-17-62 R 4,600 24 190 800,000 C 370-390 ) Only parts of 19ccc USER CH702 395-435 } 11-13-63 R 1,060 35 30 68,000 W aquifer tested 455-463 ' 21ddd __ B. Church _____ 105-150 10-10-62 R 2,820 16 180 390,000 do do C 22caa do 100-165 10- 5 62 R 3,200 15 210 430,000 Excellent _ __ do _____ C 22cdal __ _ _do _ .. __ <136 10- 4-62 R 3,200 16 200 320,000 - do _' C T may be low by about 25 percent be­ cause well % mile distant was shut off 10 minutes prior to re­ covery test. Only part of aquifer tested. 22cda2 do 100-152 10- 4-62 R 2,600 10 260 380,000 Fair do C 25bad __ F. J. Hartman _ 100-114 9-20-62 R 2,600 14 190 400,000 do do C Only part of aquifer tested. 26adb __ S & W (?) 10- 8-62 R 2,400 20 120 290,000 Good _____ Good ___ C 28aaa ___ B. Church ______105-150 10-10-62 R 2,600 18 140 350,000 Excellent __ __ do _____ C 30cab ___ C. Lord ______115-170 10- 4-62 R 3,100 12 260 380,000 do do C SOddd - do 130 160 10- 9-62 R 1,450 8 180 360,000 do C Do. 34aaa ___ W. R. Whitman _ 93-177 10- 9-62 R 2,560 26 98 960,000 Excellent __ __ do _____ C 34add ___ USER CH750 __ 500-600 10- 7-64 R 2,700 60 45 150,000 Fair Fair W 35caal _ USER CH704 __ 435-445 I 480-490 } 12-24-63 R 1,100 24 46 340,000 do do W Do. 507-570 ' 99-170 1- 7-64 R 1,620 8 200 1,100,000 Good Good _ C 35caa2 _ USER CH751 __ 484-585 10-13-64 R 2,750 65 42 190,000 Fair Fair W Do. 35cca ___ Arizona Western 180-248 9 30 62 R 690 30 23 230,000 do do C College. 36cad USER CH752 ___ 520-621 10 1 64 R 2,600 82 32 200,000 do do W Do. \ U o £ o ) K. Easter day __ 120-145 11- 6-62 R 2,900 22 130 600,000 Poor do C 12cdb do _ 115-171 11 8 62 R 4,500 27 170 480,000 do do C 25acb Gunther and 115-175 10- 5-62 R 2,230 20 110 260,000 C Shirley. 25dab do 115-175 10- 5-62 R 2,400 17 140 300,000 Excel1 ent _ Excellent __ C 26bac ___ G. Ogram _ _ 142-180 10-10-62 R 1,960 22 89 180,000 do do C Only part of aquifer tested. 27ada ___ USER CH701 ___ 84- 88 \ 125 160 / D 1,250 20 62 330,000 C 12- 3-63 R 1,300 19 68 230,000 Excellent _ Excellent __ C 27dddl Carter 135-158 10- 8-62 R 1,725 35 49 120,000 Fair C Do. (C- 8-24) 22ccd __ McLaren Produce 117-142 7-15-30 D 2,850 39 58 300,000 Good ___ _ Good _____ C Do. Co. (C- 9-22) 28cbb __ USGS LCRP 25 _ 862-2,002 1-19-65 SD, R 600 11 54 200,000 Poor W See page H213 for additional test data. Upper 500 feet of aquifer not included in test. (C- 9-23) 17abcl YCWUA 3 130-170 4-29-63 D 4,700 42 110 230,000 do C 20cdd ___ YCWUA 5 130-203 \ Only upner 27 213-240 / D 6,300 35 180 250,000 do C, W feet of wedge zone included in test. oo o o oow tO H> l_i1 |_11 o tx5 tO to to to or ib. CO

to co to to to co co co too" i-1 cro. CO cnts o'eo » ? cr ? S- Sf ;ra.s> o" cr f a- 01 » g"S- i 1 i i i 1 1 1 i i 1 1 1 i i i 1 1 1

2.M cj CH d 8-1 co"C CO co' d d «!d C ' ' O 03 W 2M CO 1, ^ O»Tl 0 td 0°P o co- WOO t"1 ^ t "§ ^ red Fi i }rc o o r? re HH > d"0 S) s- a^ to B i-H H "di? ^) SE p -q H 1 ^K i?^" to! o I «-< td *'i i i ! *g.i ! i i i td i H col-1 m toi-i t-> H'T? H cn i- tOA 01 00 °° IS3c> O A O ^ s ? f ?f O9 S cO tO CO O5 tO -» tO5OO5 I-1 to t o J no 0 O to OOOOO 05 tO 0 05 tO 0 OCO to o H r r s T T T TT fT h- » M CO tO CO Ji. Ja. H" M f °>r I 1 III 1 1 ^ 05^ co en O5 O5 O5 £ 5 en gbs cn en en en to i-1 w co to 10 to C/J CO _ CG^_, IT! D » c3?° 0 S)0 d » Type of test » » H Js- « CO eo i » t * *-* *^ en -_, 15 en ^) "CTJOT co"o § §D OS § § o to o> *^ o Yield, in gpm o s3=> o o o o o 8 S O OT cg" oo1-1 i-"^ l-i |_i H" I-1 CO 0 g to )_t 1 i 1 » tO f Drawdown, in feet o Specific capacity, to en en to o to t.D 0 I i o o o o o in gpm per ft

CO to M |_ih-" h-" 0-3 "en t £ "° "OS 7-»V» CO O5 totocnto 000 00 oo-;> o 2 § §2 p § o o o p p oowo go o.p ooo Transmissivity ( T ) , o oo "oo in gpd per ft § §§ 000 00 0 0 ° i I o oo oo fill fill 1 p hd i 1 1 O i i Hg >*1O S1 H «1 w O 1 » 1 Oil XV B o i 5- oil n £' e§ 5. x ^' > 1 0.* S"0 o^ O- a,&i n «'§.o. ^ o S. 3 f 0 1 i 00 S1 ' JT H 1 i II S 3 1 1 1 rt- 1 cf O 1 1 i 1 i ! ! i i 1 1 1 ! i i < 1 ^3 ? hj i O !jlp ^ o £ 010 S» 0 (0TO » D o ' ? 0- 0, 010 E5'S I 0 i-! ft,O. °' * a, a, a. 5- o 0 O o Si O I » § o o ""§- ?: 1 1 i 1 1 . 1 i "SS 1 1 1 i 1 1 ii1 1 1ii ' 1 i H 1 1 II II 1 i p p 0 0 p 3°° 3° ^000 0 * 3

0 o £*! " -H.S? !il llSl^i ° 2S-S.^ ff d H£ £,3\ g'oP-^rf^o S s-8 "> S-toM, 1-1" srs.'aSjglS jrS.* ?S:*;Ue-3 ! ,°-

32°45' ?

Line of equal transmissivity, in thousands of gallons per day per foot

32°15'

FIGURE 25. Transmissivity of alluvium. dition is the porosity of the material. Under water the aquifer material increase and (or) sorting im­ table conditions, the storage coefficient for clay and proves, the storage coefficient commonly increases. silt commonly ranges from almost zero to a few him- For clean sand and gravel, it frequently ranges dredths. Generally, as grain size, and sphericity of between 0.2 and 0.4 H82 WATER RESOURCES OP LOWER COLORADO RIVER-SALTON SEA AREA By definition, the storage coefficient is not a func­ of water that will go into storage as the water table tion of time. It represents the ultimate change in rises. storage, regardless of the time necessary to achieve This approach was used for estimating storage the change. In practice, the ultimate change, is characteristics of the material saturated by the rarely, if ever, reached. Rather, it is approached large ground-water mound that built up beneath within widely varying limits depending on the time Yuma Mesa after 1947. The details of the investiga­ since the change in head occurred and the physical tion of moisture content by means of the neutron properties of the water-bearing material. In a clean probe are given in appendix E. sand or gravel almost all the gravity drainage may Storage coefficients for artesian conditions were be completed in a few hours or a few days, whereas not computed from any of the pumping tests that in silt or clay, an appreciable part of the ultimate were made during the present investigation because drainage may occur after weeks and months. the conditions for the pumping tests were not ade­ Storage coefficients used in conjunction with quate for obtaining valid results. Artesian storage transmissivities enable one to determine for a given coefficients for drainage wells along the eastern change in the ground-water supply in a given area boundary of Yuma Valley, as computed by Jacob the relative amounts of ground water that will be (1960, appendix E, table E-l) ranged from 5.8X10'4 involved in storage changes and those that will be to 3.6 XlO"3 and averaged 1.2x10 3. innvolved in movement of ground water toward or In the Yuma area, the quantities of water that away from the area. In other words, using these two are involved in changes in storage under artesian characteristics one is able to determine the change conditions are very small relative to the quantities in position and change in shape of the water or involved under water-table conditions. Thus, only a piezometric surface that results from a given change general knowledge of the storage coefficient under in the supply of ground water. artesian conditions is needed to account for or pre­ Storage coefficients can be determined from pump­ dict the principal changes in ground-water move­ ing tests. Pumping tests are probably the most ment or storage resulting from stresses imposed on practical way for obtaining storage coefficients if the system. artesian conditions exist, but many times they may MOVEMENT OF GROUND WATER be less practical than other methods where water- As in surface flow, ground water moves in the table conditions prevail. The failure of short-term direction of decreasing head, but its rate of move­ pumping tests to provide valid data for computing ment through granular materials, such as those in a storage coefficient is due in most places to the slow the Yuma area, is only a small fraction of the rate rate at which many water-bearing materials drain. of movement of surface water, and its path of move­ The mathematical formulas used in this analysis ment is much more complex. of pumping tests assume an instantaneous change During the present study, water-level maps were in storage with a change in head. Although this prepared to show the direction of movement of idealization is approached under artesian conditions, ground water under natural conditions and at se­ it is not approached under water-table conditions. lected times during the historical development of Most storage coefficients computed from data ob­ the water resources of the area. Because the Colo­ tained during pumping tests of unconfmed aquifers rado River and the ground-water system are con­ are likely to be substantially less than the true stor­ nected hydraulically, important controls for prepar­ age coefficient unless the test is extended for sev­ ing the water-level maps were the mean annual eral days and adjustments for the protracted drain­ stages of the river (fig. 26). age are made. In most tests, therefore, it is A river-profile map and a series of topographic impractical to meet all the conditions that are neces­ maps of the Colorado River flood plain were pub­ sary to obtain valid data. A more practical approach lished in 1927 by the U.S. Geological Survey from for determining storage coefficients under water- surveys made in 1902. These maps together with the table conditions in the Yuma area appears to be the early records of river stage at Yuma were used to use of a neutron moisture probe in conjunction with estimate mean annual river stages under natural access tubes driven to depths of several feet below conditions and also during the period of water- the water table. The average difference between the resources development until the rapid degradation moisture content of material above the capillary of the river channel in the early 1940's. After 1940, zone and that of material below the water table is considerable information regarding the river profile then considered a reliable indicator of the amount was inferred from river-channel-cross-section sur- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H83

1935

- 120

115

110 1940 1945 1950 1955 1960 1965 1970

105

100 Morelos Dam

95 1940 1945 1950 1955 1960 1965 1970

85 I I

80

Southerly International Boundary

75 1940 1945 1950 1955 I960 1965 1970

FIGURE 26. Mean annual stages of Colorado River at Yuma, Ariz. H84 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA veys that were made periodically at selected sites The irrigation of land with surface water in by the U.S. Section of the International Boundary Mexicali Valley, without provisions for drainage, and Water Commission. caused water levels to rise above the levels that Before 1942 the mean annual stage of the Colorado existed under natural conditions. By 1939, several River at Yuma ranged from 120 to 125 feet above places had been noted in which irrigated lands had mean sea level; during the next few years the stage become so waterlogged that farming was no longer dropped about 5 feet, then continued to drop, but feasible. at a lesser rate, to a stage of about 113 feet in 1966 Although the configuration of the water-level sur­ (fig. 26). Although the lowering of stage was due in face in Mexicali Valley in 1939 was similar to its part to decreased flow of the river, the principal configuration under natural conditions, its south- cause of the rapid lowering in the 1940's probably westward slope had decreased somewhat because its was the erosion of the channel by the clearer water eastern boundary was hinged to the Colorado River that resulted from upriver storage. and did not rise as did water levels beneath the irri­ Stages were also dropping at the Morelps gaging gated lands farther westward from the river. station and at the southerly international boundary, For these reasons a somewhat lesser rate of infil­ undoubtedly for the same reasons as at Yuma (fig. tration of Colorado River water to the ground-water 26). In the 1960's a stage of about 74 feet indicated system, both beneath Yuma Valley and Mexicali no measurable streamflow at the southerly interna­ Valley, is indicated by this map (fig. 28) than tional boundary. existed under natural conditions. The map shows DIRECTION OF MOVEMENT UNDER that as late as 1939 the Colorado River was a source NATURAL CONDITIONS of recharge to the ground-water body, although Adequate water-level data are not available for ground-water levels had risen as much as 5 feet as determining directly the configuration of the ground- a result of irrigation with surface water. Under water surface beneath Yuma Valley or Mexicali natural conditions, then, the movement of ground Valley under natural conditions. The earliest year water easterly from the river to the Yuma Valley for which sufficient data are available for drawing and westerly to Mexicali Valley was substantially a water-level map for Yuma Valley is 1911. Although greater than that indicated by the 1939 data. the valley had been irrigated with Colorado River In 1939 there was also a southward movement of water for several decades priod to 1911, the effects water beneath Yuma Mesa and across the southerly of irrigation on the configuration of the ground- international boundary (fig. 28). The available data water surface probably was small, partly because for later years indicate that neither the direction under natural conditions Yuma Valley had been sub­ nor the rate of movement across the southerly in­ ject to periodic flooding by the river and partly be­ ternational boundary was greatly different from cause only one-eighth of the valley land was being what it probably had been under natural conditions. irrigated. Therefore, ground-water levels in Yuma Therefore, the movement of ground water across Valley in 1911 probably were similar to those under this boundary as shown by the 1939 water-level data natural conditions. is a good indication of the movement under natural The inferred configuration of the water table in conditions. Yuma Valley in 1911 is based on widely scattered The westward movement of ground water through water-level data and estimated river stages (fig. 27). the alluvium between Pilot Knob and the Cargo Mu- The water-level contours indicate that in 1911 and chacho Mountains as shown in 1939 probably also by inference, also under natural conditions, the is a good indication of the direction and rate move­ Colorado River was a source of recharge to the ment under natural conditions. However, after 1939, ground-water body underlying Yuma Valley. leakage from the All-American Canal greatly The earliest year for which similar information changed the ground-water gradients in this area. is available for any part of Mexicali Valley is 1939. (Compare figs. 28 and 30.) Water-level data for 1939 for that part of Mexicali In summary, the water-level data, for the delta Valley lying north of the Alamo Canal, together with area in 1939 also indicate the direction of ground- water-level data for 1958 for that part of Mexicali water movement under natural conditions. However, Valley lying south of the Alamo Canal, were used as the rates of movement from the Colorado River to a basis for drawing a water-level map showing the the ground-water system adjacent to the limitrophe probable configuration of ground-water levels in section, as shown by gradients in figure 28, are less Mexicali Valley in 1939 (fig. 28). than under natural conditions. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H85

32°45'

-AMERICAN CANAL

UNITE£_STATES_ _ ""MEXICO / Morelos / Dam

EXPLANATION

Water-level contour Shoivs altitude of water level. Contain interval 5 feet: datum is mean sea level

Bedrock outcrop

32°30' Alluvial escarpment

FIGURE 27. Average water-level contours in 1911 in Yuma Valley. ffi 00 Oi 115°00' 45' \ 1 t^v 32°45' /

/ ALL- AMERICAN\ CANAL o STATES ___\_ _ - d / UNITED » o M TO O*=d f o ^ H

O Of o o 30' - o

H O EXPLANATION ss 92 TO Water-level contour H Shows altitude of water level. A £ u 11 u j i Dashed where approximately Area °f shall°W bedr°ck located. Contour interval 5 and Alluvial escarpment

Dotted where concealed o i i i i i 32°15'

FIGURE 28. Average water-level contours in 1939 in the delta region. Data for Mexicali Valley provided by the Mexican Section, International Boundary and Water Commission. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H87

RATE OF MOVEMENT UNDER international boundary, a distance of about 15 miles. NATURAL CONDITIONS The gradient in the northern third of this section It is impractical to determine the rate of move­ was less than that in the southern two-thirds of the ment of ground water by direct measurement. How­ section (fig. 28). The westward gradient across the ever, an average rate of movement can be computed northern third of the section is estimated to have if the total quantity of ground water passing across been about 4 feet per mile, and that across the a known section in a given period of time is known, southern two-thirds to have been about 5 feet per or if the transmissivity of the material through mile. which the water moves, the width normal to the The transmissivity is estimated to average about direction of movement, and the hydraulic gradient 800,000 gpd per ft for the northern third of the causing the movement are known. alluvial section and about 1,000,000 gpd per ft for Rates of movement under natural conditions at the remainder of the section. Using the foregoing selected sections necessarily must be computed or values, the flow of ground water westward into estimated by the latter method because there are Mexicali Valley from the limitrophe section of the no data on quantities that pased a known section Colorado River in 1939 is estimated to have been during a given period of time. about 66 mgd or about 74,000 acre-feet per year. ALLUVIAL SECTION BETWEEN PILOT KNOB AND Under natural conditions the outflow was larger CARGO MUCHACHO MOUNTAINS because by 1939 water levels in Mexicali Valley had On the basis of transmissivity values shown in risen as a result of irrigation, thereby decreasing figure 25, the transmissivity of the alluvial material the hydraulic gradient from the river. The extent through which ground water moved westward be­ to which the gradient was decreased is not known tween Pilot Knob and the Cargo Muchacho Moun­ precisely, but if water levels in Mexicali Valley had tains is about 200,000 gpd per ft. The gradient prob­ risen 5-15 feet above their levels under natural ably was about 4 feet per mile in 1939 (fig. 28), and conditions the westward flow of ground water in the width of the section is about 5 miles. The rate 1939 may have been only about three-fourths of the of movement under natural conditions based on the flow under natural conditions. On this basis the foregoing estimates then was about 4 mgd (million movement of ground water westward from the limi­ gallons per day) or about 4,500 acre-feet per year. trophe section of the Colorado River under natural conditions may have been almost 100,000 acre-feet LIMITROPHE SECTION OF COLORADO RIVER a year. Computations of the rate of ground-water move­ YUMA VALLEY ment westward into Mexicali Valley from the limi­ The movement of ground water from the Colorado trophe section of the Colorado River (the reach of River to Yuma Valley is postulated on the basis of the river forming the international boundary) river-stage records and early records of water level under natural conditions are based on an average in Yuma Valley, plus the fact that such movement transmissivity value for the alluvium as determined was necessary in order to meet the evapotranspira- during this study, and the estimated gradients that tion requirements of the natural vegetation in Yuma caused the movement. As stated in the foregoing Valley. section, the earliest date for which data on water Under natural conditions Yuma Valley supported levels in Mexico are available to the present study a rather heavy growth of water-loving vegetation is 1939, at which time ground-water levels had risen over most of the valley. Mesquite was the dominant in some areas as a result of irrigation. Using the species, although willow, cottonwood, and arrowweed gradients of 1939, therefore, will tend to make the also thrived. The Colorado River annually overflowed estimates of ground-water movement under natural its banks in early summer. In years of average or conditions somewhat too low. below-average floods most of the overflow was car­ The gradients under which the ground water ried in the abandoned channels and sloughs that moved westward from the Colorado River probably trended southward through the valley. In years of can be estimated within the limits warranted by the above-average floods however, the overflow spread data by assuming that most of the water moved over much of the valley. across a north-south alluvial section that originates The average annual rate of use of water by the at the northerly international boundary about 6 natural vegetation is not known. However, an esti­ miles west of Pilot Knob, or near where the 90-foot mate can be made using as a basis the present rates contour crosses the northerly international bound­ of use by these plants in the flood plain of the river. ary, and that extends southward to the southerly The average density of the mesquite in the flood H88 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA plain of the Colorado River in the reach between the reach from Pilot Knob to the southerly interna­ Davis Dam and the southerly international boundary tional boundary (limitrophe section) is estimated in as mapped by the U.S. Bureau of Reclamation in a similar manner. 1962 was about 50 percent, and the average annual The gradients eastward from the river in this rate of use was about 2 feet; the density of arrow- reach were much less uniform than the southward weed was slightly less than 60 percent, and its gradients in the reach between Yuma and Pilot annual rate of use was slightly less than 3 feet; tules Knob. However, gradients along flow lines some dis­ used slightly more than 8 feet per year (U.S. Bureau tance from the river, yet before points where sub­ of Reclamation, 1963, p. 26, 33). stantial discharge occurred, appear to have aver­ It seems probable therefore that the average rate aged about 5 feet per mile. The section normal to of use by mesquite in Yuma Valley under natural these gradients is about 15 miles long, and the conditions was about 2 feet per year, and the rate transmissivity of the section is estimated to be of use by the other vegetation was slightly higher. 900,000 gpd per ft. On this basis the eastward flow The area of Yuma Valley is slightly more than of ground water from the Colorado River in the 60,000 acres, so the total evapotranspiration prob­ reach between Pilot Knob and the southerly inter­ ably was between 100,000 and 150,000 acre-feet national boundary was 68 mgd or about 76,000 acre- annually. feet per year. Owing to the almost yearly flooding of large parts Thus, in 1911, and also under natural conditions, of Yuma Valley by the Colorado River, a substantial the total ground-water flow from the Colorado River part of the transpiration requirements of the natural to Yuma Valley in the reach bordering the valley vegetation was supplied by the soil moisture result­ was about 86,000 acre-feet per year. This inflow plus ing from the infiltration of the flood waters; the the inflow from Yuma Mesa of ground-water origi­ remainder, however, was supplied with ground water nating in South Gila Valley was discharged by evapo­ having a more remote source. The only remote transpiration in Yuma Valley. sources of any significance were the Colorado and The inflow to Yuma Valley from South Gila Valley Gila Rivers. is estimated on the basis of water-level contours in Water-level contours in 1911 (fig. 27), which 1925 (fig. 29) and the transmissivities shown in probably are fairly representative of the slopes and figure 25. Water-level contours in 1925 are more directions of ground-water movement that existed typical of natural conditions than are those in 1939, under natural conditions, show that ground water especially in South Gila Valley, because pumping moved to Yuma Valley both from the Colorado River for irrigation was just beginning in 1925. The flow where it bordered the valley and from the Colorado line that divides the ground water into segments and Gila Rivers in the South Gila Valley. that discharge to Yuma Valley from those that do The quantity of the discharge originating along not, is about 3 miles east of Yuma in the vicinity of the reach of the Colorado River from Yuma to the the 120-foot water-level contour. Using the gradients west edge of the flood plain where the river abruptly and transmissivities west of this line, the discharge changes its direction from westward to southward to Yuma Valley is computed to have been about is computed on the basis of the average ground- 5,000 acre-feet per year in 1925, and by inference, water gradient southward, the length of the section, also under natural conditions. and the average transmissivity. The gradient is se­ In summary, under natural conditions, the total lected sufficiently far from the river and from the amount of ground water that originated near the areas of substantial ground-water discharge to mini­ Colorado and Gila Rivers and that was discharged mize the effect of vertical components of flow, and in Yuma Valley is estimated to have been about also the decrease in gradient that occurs in the area 90,000 acre-feet per year. This estimate is about of discharge as more and more of the initial inflow six-tenths the maximum and about nine-tenths the is discharged. estimated minimum total transpiration of the natu­ The gradient is estimated to have averaged 3 feet ral vegetation. In view of the almost yearly flooding per mile normal to a section 5 miles wide west of of parts of Yuma Valley by the Colorado River, Yuma for which the transmissivity is estimated to which undoubtedly supplied some of the transpira­ be 600,000 gpd per ft. This gradient makes the in­ tion requirement of the natural vegetation, the above flows to the north end of Yuma Valley from the estimated of ground-water inflow from the Colorado Colorado River before it turns southward about 9.0 River appears reasonable, although somewhat high. mgd or about 10,000 acre-feet per year. DIRECTION OF MOVEMENT IN 1960 The quantity of the discharge originating along The configuration of the ground-water surface GEOHYDEOLOGY OF THE YUMA AEEA, AEIZONA AND CALIFOENIA H89

114°45 114-15'

32°45

95 Water-level contour Shows altitude of water level. Dashed where Area of shallow bedrock approximately located. Contour interval 1, 2, and 5 feet; datum is mean sea level Alluvial escarpment

Fault Mountains and hills Dotted where concealed

32°15'

FIGURE 29. Average water-level contours in 1925. changed considerably between 1939 and 1960 (and Yuma Mesa that had formed by 1960. The influ­ also, by inference, between the time of natural con­ ence of the mound extends in all directions: east­ ditions and 1960; see figs. 28 and 30). A significant ward toward the Gila Mountains, southward toward change is the large ground-water mound beneath Mexico, northward into South Gila Valley, and west-

507-243 O - 74 - 7 114'15'

M 32°45' -

M 03 O

M w O ^ t" O * M

O f O d o a< M P CQ > f H O

90 CQ Water-level contour M Shoivs altitude of water level. Area of shallow bedrock Dashed where approximately ______located. Contour interval 5 and Alluvial escarpment M 10 feet; datum is mean sea level Fault Dotted where concealed

. Average water-level contours in 1960 in the delta region. Data for Mexicali Valley provided by the Mexican Section, International Boundary and Water Commission. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H91 ward into Yuma Valley. The very steep gradients Leakage from the All-American Canal is the prin­ westward toward Yuma Valley result in large part cipal cause lux the changes in the direction and rate from the lowering of head by drainage wells in of movement of ground water relative to the course Yuma Valley along the toe of the mesa. A more of the Colorado River. Leakage from the Ail-Ameri­ detailed discussion relative to the build up of the can Canal and the Coachella Cai;al branch of'the mound is given in the section on the analog model. canal obviously had built a sizable mound beneath (See p. H109.) these canals by 1960. For a distance of 25 miles Also significant is the change in the character of west of Pilot Knob, the height of the mound aver­ the Colorado River upstream from the limitrophe aged 30 feet or more. The net result is that in a section. Under natural conditions and as late as the 30-mile reach the direction of ground-water move­ early 1940's, the Colorado River was a losing stream. ment south of the All-American Canal had been The mean annual stage of the river was higher than changed from westward, or practically parallel to the mean annual water levels on either side of the the United States-Mexico boundary which existed river. under natural conditions and until some years fol­ However, during the early 1940's the river chan­ lowing the completion of the All-American Canal, nel was eroded 5 feet or more in the Yuma area to southward and at a gradient that was steeper (fig. 26). This degradation of the river channel, plus than was the westward gradient before completion rising ground-water levels as the result of irriga­ of the All-American Canal. tion and leakage from the Ail-American Canal, all RATE OF MOVEMENT IN 1960 tended to raise ground-water levels upstream from Many of the same difficulties mentioned in the the limitrophe section above the mean stage of the discussion of rates of movement under natural con­ Colorado River, thereby making the river a gaining ditions also arise in making estimates of rates of stream in the reach above the limitrophe section. ground-water movement after development of water Marked changes also occurred in the limitrophe resources by man. By 1960, many changes in rates section area. Movement of ground water was still of movement had occurred, and the pattern of move­ westward from the Colorado River into Mexico, but ment was more complex than under natural condi­ the direction of the movement in the northern part tions. Much of the complexity is due to the fact that of the limitrophe section, principally as the result many of the changes noted by 1960 were interim of leakage from the Ail-American Canal, had changes, which did not represent the ultimate re­ changed from westward to southward. sponse of the ground-water system to the develop­ A marked change in the direction of the contours ment that had occurred. in Yuma Valley near the Colorado River also oc­ curred between 1939 and 1960. Under natural con­ ALLUVIAL SECTION BETWEEN PILOT KNOB AND ditions, and as late as the early 1940's, the mean CARGO MUCHACHO MOUNTAINS stage of the river was above the adjacent ground- The rate of movement westerly through the allu­ water levels in Yuma Valley. vial section between Pilot Knob and Cargo Muchacho In 1960, however, and for some 10 years prior Mountains is difficult to estimate, principally because thereto, ground-water levels in western Yuma Valley of lack of knowledge of the westward gradient. Only were higher than the adjacent mean river stages. two control points are available for defining the As a result, ground water moved from Yuma Valley gradient. One indicates that the altitude of the water toward the river. To what extent the ground water level in well 16S/22E-2Hac which is less than half discharged into the river rather than moved west­ a mile west of the All-American Canal, was about ward beneath the river is not known, but consider­ 135 feet. The other indicates that the altitude of ing the westward gradient from the river to Mexi- the water level in a well 8 miles west was 123 feet. cali Valley and the substantial thickness of pre­ Thus a westward gradient of 11/2 feet per mile is dominantly fine-grained materials beneath the chan­ indicated. nel and above the coarse-gravel zone, which greatly If this figure is accepted as a reasonable value of inhibits interchange between the ground-water body the gradient, then the westward flow through the and the river, it is doubtful that a large percentage section in 1960 probably was only three-eighths of of the outflow from Yuma Valley westward to the flow under natural conditions, or somewhat less Mexicali Valley was intercepted by the Colorado than 2,000 acre-feet per year. River. LIMITROPHE SECTION OF COLORADO RIVER An estimate of the outflow from Yuma Valley is In 1960, the movement of ground water in the made in a later section of this report. (See p. H103.) 2-mile reach downstream from the northerly inter- H92 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA national boundary was toward the Colorado River The streamflow depletion in 1960 and thereafter, both from Mexicali Valley and Yuma Valley (fig. therefore, probably is best estimated by noting the 30). The eastward movement of ground water to losses that occurred in years when the flows were the river was due principally, if not entirely, to the near to and less than the 1960 flow. discharge of part of the leakage from the All- Estimates of loss between the northerly inter­ American Canal. South of this reach, or beginning national boundary and the southerly international at a point about where the 100-foot water-level con­ boundary were computed by adding to the flow re­ tour crosses the river, to a point about 5 miles down­ corded at the northerly international boundary the stream, or where the 95-foot contour crosses the wasteway water from the Yuma project, then sub­ river, there was a westward gradient of about 3 feet tracting (1) the diversions to Mexico made at per mile almost directly away from the river. Morelos Dam, (2) the pumpage in the limitrophe Using an average transmissivity of 80,000 gpd section of the river, and (3) the flow at the south­ per ft and the foregoing data, the westward flow is erly international boundary. indicated to have been 12 mgd, or 13,500 acre-feet Years of relatively low flow of the Colorado River per year. and rates of depletion in the limitrophe section of Southward from this reach to the southerly inter­ the river since 1950 are as follows: national boundary, the contours are so irregular that Flow at Loss between northerly northerly and southerly it is difficult to determine the many gradients that Year international international boundary boundaries are implied. Undoubtedly, much of the irregularity (acre-feet) (acre-feet) 1956 ______1,640,000 9,000 is caused by pumping of ground water for irrigating 1960 ______2,338,000 47,000 land west of the Colorado River. 1961 ______1,672,000 31,000 However, in a gross sense, the contours in this 1962 ______1,811,000 35,000 1963 ______1,834,000 72,000 reach leave the river at an angle of about 45°; the straight-line distance of the river reach is about Average (rounded)- 1,860,000 39,000 9 miles; and the contour difference is 20 feet. Using From the foregoing, it appears that for a flow of an average transmissivity of 1 mgd per ft and the about 1.9 million acre-feet per year at the northerly foregoing data, the rate of movement of ground international boundary, the computed loss in the water southwestward into Mexicali Valley from the limitrophe section averages about 39,000 acre-feet. point where the 95-foot water-level contour crosses This loss is only about 2 percent of some of the the river to the southerly international boundary is measured flows, which is within the probable limits 20 mgd, or about 22,500 acre-feet per year. The total of error of the data. westward movement of ground water into Mexicali Another evaluation can be made by computing the Valley adjacent to the limitrophe section, thus, was losses in the limitrophe section from Morelos gaging about 36,000 acre-feet in 1960. station to the southerly international boundary. The data on which the foregoing estimate is based Morelos gaging station is about 1.7 miles south of the are very meager. The principal value of the estimate northerly international boundary and about 0.5 mile is that it shows the order of magnitude of the move­ south of Morelos Dam (fig. 30). The advantage of ment of ground water westward from the Colorado this evaluation is that the magnitude of the flows are River to Mexicali Valley in 1960. Some support for much smaller than the flows at the northerly inter­ the reasonableness of the foregoing estimate is national boundary and the diversions to Mexico obtained by examining its value relative to estimated from Morelos Dam which were used in the preced­ outflow from Yuma Valley in the limitrophe section ing analysis. and estimates of streamflow depletion and other According to water-level data for 1960 (fig. 30), losses in the limitrophe section. the losses indicated for the reach between Morelos The outflow from Yuma Valley in the limitrophe gaging station and the southerly international section is estimated to have been about 20,000 acre- boundary should be a good indication of the net loss feet in 1960 (p. H95). Estimates of streamflow de­ in the entire limitrophe section because northward pletion in the limitrophe section vary widely, de­ from Morelos gaging station the Colorado River is pending on the magnitude of the flow and its relation a gaining stream. to preceding flows and also the points between which Estimates of loss were obtained by adding to the the losses or gains are computed. Streamflow in the measured flow at Morelos gaging station the inflows limitrophe section in 1960 was small relative to his­ from Eleven-Mile and Twenty-One-Mile wasteways, torical flows but somewhat larger than flows after which are S1/^ and lY 1/-? miles respectively down­ 1960. stream from Morelos Dam, and subtracting there- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H93

from the pumpage from the limitrophe section and and Water Commission (not shown) were used to the flow at southerly international boundary. determine the location of the divide for the ground- Years of relatively low flow and rates of unac­ water recharge due to local irrigation. The contours counted depletion since 1950 are as follows: were based on water-level altitudes in more than 200 Unaccounted depletion, shallow wells and on the altitude of the water sur­ Moreios (japing station Flow at Moreios to southerly interna­ face in the drains. The ground-water divide that Year gaging station tional boundary (acre-feet) (acre-feet) separates the area from which the outflow was prin­ 1956 ______242,000 6,000 cipally northward coincided roughly with an easterly 1960 ______540,000 18,000 1961 ______177,000 20,000 prolongation of the northerly international boundary. 1962 ______313,000 23,000 Most of the land north of the divide, about 2,500 1963 ______176,000 10,000 acres, was irrigated. Average (rounded). 290,000 15,000 Based on reports of the Yuma County Water The yearly inflows from the wasteways were Users' Association the diversion of water to land about 25,000 acre-feet, and pumpage from the river irrigated in Yuma Valley, including losses from generally was about 4,000 acre-feet. The average laterals, averaged 6.5 feet for the years 1955 to unaccounted depletion of the gross flow therefore is 1960, inclusive. Estimates of consumptive use for about 5 percent of the average maximum flow. Five crops was assumed to have been 3.6 feet, the same percent is outside the probable limits of error of the value as used throughout this study for crops grown data, and therefore the indicated unaccounted deple­ in the flood plain. The recharge to ground water tion by the latter method is considered the more from irrigation thus averaged about 2.9 acre-feet per reliable of the two estimates. Therefore, the loss of acre per year for lands that were irrigated. The out­ Colorado River water in the limitrophe section in flow from Yuma Valley northward of an imaginary 1960 and thereafter probably averages about 15,000 extension of the northerly international boundary acre-feet yearly. therefore was about 7,300 acre-feet. The outflow of 20,000 acre-feet from Yuma Valley The area between the river, the ground-water di­ plus the unaccounted depletion of the riverflow of vide, and the northerly and southerly international about 15,000 acre-feet suggests that in 1960 the out­ boundaries which contributed to the outflow was flow westward to Mexico opposite the limitrophe sec­ 15,000 acres. Of this acreage, 3,100 acres supported tion of the Colorado River was about 35,000 acre- the growth of phreatophytes, and 11,900 acres sup­ feet minus evaporation losses from the free water ported irrigated crops. The recharge from irriga­ surface of the river. The latter probably is less than tion, therefore, was 34,500 acre-feet per year, from 2,000 acre-feet at low stages of the river. which must be deducted the consumptive use by This estimate of slightly less than 35,000 acre-feet phreatophytes and pumpage for irrigation. The lat­ per year, which is based largely on excess irrigation ter two items are 8,200 and 13,000 acre-feet, respec­ water and infiltration of river water, compares tively, based on data in the U.S. Bureau of Reclama­ favorably with the estimate of 36,000 acre-feet per tion (1963, p. 28 and 34) study. The net outflow year, which was based wholly on ground-water from Yuma Valley to the limitrophe section as a parameters in Mexicali Valley. result of local recharge from irrigation not diverted YUMA VALLEY to drains, therefore, was about 13,000 acre-feet in Ground-water outflow from Yuma Valley can be 1960. analyzed as the sum of the flows that cross its north­ Outflow also occurred in the deeper aquifers. Con­ ern, western, and southern boundaries. An estimate tours based on water levels in wells penetrating the of the ground-water outflow northward and west­ top of the coarse-gravel zone are considered to be ward from Yuma Valley is made on the basis that representative of the head in the coarse-gravel zone part of the outflow is ground-water recharge from and the underlying wedge zone. Therefore, the con­ irrigated land lying between the northern and west­ tours are useful for estimating gradients and for ern boundaries of Yuma Valley and the ground- selecting width of sections through which water is water divide southerly and easterly from these transmitted to or across the limitrophe section. boundaries, less the use of ground water by phreato- Using the information shown in figure 31 and phytes and the pumpage of ground water from be­ transmissivity values shown in figure 25 the flow to neath these lands for irrigation, and that part is or across the limitrophe section through the coarse- ground water moving westerly at depth. gravel zone and the wedge zone is computed to have Detailed water-level contour maps compiled by the been about 6,400 acre-feet in 1960. The combined United States section of the International Boundary outflow of ground water from Yuma Valley to the H94 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

32°45'

UNITED STATES """MEXICO

EXPLANATION

Water-level contour Shows altitude of water level. Contour interval 5 feet; datum is mean sea level

Bedrock outcrop 32°30' Alluvial escarpment

FIGURE 31. Average water-level contours for upper part of coarse-gravel zone in 1960 in the Yuma Valley. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H95

limitrophe section in 1960, therefore, is the above stable or continue to rise and water levels in Mexi­ quantity plus the 13,000 acre-feet of local recharge cali Valley continue to decline, the outflow from the from irrigation not diverted to drains, or about United States will increase. 20,000 acre-feet. Water levels in the United States may be lowered The outflow across the southerly international by improving the irrigation efficiency to the point boundary based on a transmissivity of 1 mgd per ft, where only sufficient water is diverted for irriga­ a width of section of 1% miles, and a gradient of tion to satisfy evapotranspiration needs and to carry about 3 feet per mile is about 6,000 acre-feet per away the salts contained in the irrigation water. year. Water levels also may be lowered by pumping. The total outflow from the valley in 1960 thus was The marked increased pumpage of ground water for the 20,000 acre-feet to the limitrophe section, plus drainage beginning in 1961 illustrates the effective­ the outflow northward of 7,300 acre-feet, plus the ness of this method for lowering water levels. Pump­ outflow across the southerly international boundary ing of ground water by private interests for the of 6,000 acre-feet, a total of about 33,000 acre-feet. irrigation of land on Yuma Mesa outside designated irrigation districts, which began in 1962, also has MOVEMENT AFTER 1960 Both the direction and rate of movement of resulted in lower water levels. As of 1968 the pump- ground water continued to change after 1960. In age and consequent lowering has been only moderate, general, the changes followed the pattern that was but if the present rapid pace of developing new land established prior to 1960. A comparison of water- for pumping irrigation is maintained for only a few level contours as of December 1965 (fig. 32), with more years sufficient land will be developed in the the water-level contours as of December 1960 (fig. southern part of Yuma Mesa to require the pump­ 30), illustrates the changes that occurred. ing of more ground water than presently is entering The principal changes were: a moderate increase the area. Additional ground water will be diverted in the size of the ground-water mound beneath the to the area because of the lowering of water levels, Yuma Mesa and a lowering of water levels in Mexi- but if a ground-water sink is maintained, the chemi­ cali Valley. Water levels beneath Yuma Mesa con­ cal quality of the pumped ground water eventually tinued to rise until 1962. After 1962, owing to will deteriorate because of the continued reuse of increased pumpage for drainage near the toe of the much of the water. mesa in Yuma and South Gila Valleys, water levels The extent to which the outflow of ground water northward and westward from the apex of the from the United States eventually will be influenced ground-water mound began a moderate decline. by the control of water levels is likely to be governed However, at greater distances eastward and south­ not only by economic factors but also by interna­ ward from the apex, water levels continued to rise. tional political considerations. More details on the areas and amounts of change of WATER BUDGETS water level beneath Yuma Mesa are given in the Water budgets provide an accounting for the section on the analog model (p. H107). water resources of an area during a specific period The other principal change is the generally lower of time. The budget may be for either the surface- water levels in Mexicali Valley, which resulted from water system or the ground-water system or both, pumpage for irrigation. These lower water levels depending on the objective of the analysis. together with generally unchanged levels for most In the present study, the movement of ground of Yuma Valley resulted in an increased westward water is of principal concern. Therefore, the budg­ component of the water-level contours crossing the ets presented emphasize the disposition of the limitrophe section of the Colorado River. The in­ ground-water supply rather than the surface-water creased westward component plus an increased supply. The budget period was selected as the calen­ ground-water gradient away from the river imply dar years 1960-63, inclusive, because better-than- an increased outflow of ground water from the average data are available for most of the budget United States. More details about the lowering of items during this period. The budget years also oc­ water levels in Mexicali Valley is given in the sec­ curred near the end of a long period of continuous tion on the analog model (p. H107). growth of the ground-water mound beneath Yuma Movement of ground water in future years will Mesa. depend on the changes in recharge to and discharge In order to obtain a better understanding of the from the ground-water system. As long as ground- complex movement of the ground water, the Yuma water levels in the United States remain relatively area is divided into subareas, mainly on the basis w CD Oi

32°45' - H » » H ALL-AMERICAN CANAL w OUTH,\3 GILA VALLEY O UNDERSTATES _ L22? a - - - 'MEXICO £0 O H

O sO O o EXPLANATION

Water-level contour H Shows altitude of water level. P Da.shed where approximately located. Contour interval .5 and 10 feet; datum is mean sea level 3

Mountains and hills H

Area of shallow bedrock

Alluvial escarpment

Fault Dotted where concealed

FIGURE 32. Average water-level contours in December 1965 in the delta region. Data for Mexicali Valley provided by the International Boundary and Water Commission. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H97

114° 45' 30' .'IS

32°45' -

EXPLANATION

Subsurface-water inflow or outflow Mountains and hills

Surface-water inflow or outflow Area of shallow bedrock

Consumptive use Alluvial escarpment

U+62 Fault Ground-water storage Dotted where concealed gain ( -I- ) or depletion ( ) Numbers show quantities in 1,000 acre-feet

FIGURE 33. Water budgets for subareas, 1960-63, inclusive. of the principal irrigation districts (fig. 33). These that valley and that the Yuma Mesa subarea in this subareas correspond to some of the subareas de­ section of the report includes also the "Upper Mesa," scribed in the section "Geomorphology" with the "Fortuna Plain," and "Fortuna Dunes" subareas of exception that The Island area of "Bard Valley" is the geomorphic classification. herein made a subarea separate from the rest of Values for surface inflow and outflow items were H98 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA determined from records published either by the TABLE 8. Diversions, consumptive use, and ground-water recharge for Yuma Mesa U.S. Geological Survey, or from operational records [Quantities in 1,000 acre-feet] maintained by the U.S. Bureau of Reclamation or Calendar Consumptive Groun d-water the irrigation districts. Unmeasured runoff, esti­ year Diversions 1 use recharge mated to average less than 1,000 acre-feet per year, 1941 14 6 8 1942 15 7 8 was not considered large enough to be distributed 1943 21 8 13 among the various subareas. Values for subsurface 1944 32 14 18 1945 75 38 37 inflow and outflow items were computed on the basis 1946 134 50 84 of transmissivity, width of section, and hydraulic 1947 151 47 104 1948 158 50 108 gradient, as indicated by the map of the Yuma area 1949 132 52 80 showing transmissivity (fig. 25) and maps compiled 1950 135 56 79 1951 170 62 108 quarterly by the U.S. Bureau of Reclamation show­ 1952 209 72 137 ing water-level contours. The estimated average 1953 227 84 143 1954 272 95 177 yearly recharge to ground water resulting from pre­ 1955 249 90 159 cipitation was negligible and therefore was not in­ 1956 233 77 156 1957 222 72 150 cluded in any of the budgets. 1958 245 74 171 Estimates of leakage from the principal canals 1959 271 81 190 1960 295 78 217 were in part based on unaccounted-for differences in 1961 290 77 213 flow between gaging stations and in part on trans­ 1962 327 79 248 1963 317 78 239 missivity, hydraulic gradients, and length of canal. 1964 299 82 217 Ground-water storage change was considered sig­ 1965 265 82 183 nificant only for Yuma Mesa subarea. The change 1966 275 82 193 was computed on the basis of increase in volume of 1 Based on crop reports of the U.S. Bureau of Reclamation. the ground-water mound multiplied by storage co­ estimates as long as the imbalances are less than the efficients of 31 per cent for the volume underlying probable error and the imbalances do not tend to be Yuma Mesa and 18 percent for the volume underly­ in the same direction. None of the imbalances are ing the "Upper Mesa" and "Fortuna Plain." Volume thought to be unreasonable in view of the uncertain­ changes were determined from water-level contour ties of many of the items to which they pertain. maps for year end 1959 and 1963. Average annual budgets for the period 1960-63, Values for consumptive use in the flood-plain inclusive, for the subareas of the Yuma area are areas, except where noted in a particular budget, given in the following sections. were computed by multiplying the average net irri­ "LACUNA VALLEY" SUBAREA gated acreage for the years 1960-63 as listed in U.S. The "Laguna Valley" subarea consists of the Colo­ Bureau of Reclamation records by 3.6 feet and by rado River flood plain between Laguna and Imperial multiplying the remaining area by an average con­ Dams (fig. 33). Most of the subarea is covered by sumptive use rate of 2.5 feet. natural vegetation or shallow lakes and marshes Consumptive use on Yuma Mesa was assumed to (Mittry Lake is the principal water area) ; cropland be the average of the annual consumptive use values is restricted to a small area immediately upstream for the years 1960-63 as shown in table 8. The con­ from Laguna Dam. The water budget follows: (Acre-feet)_____ sumptive use values were based on irrigated acreage Inflow, subsurface water: of crop and noncropland and the following annual Leakage from Ail-American Canal 1 __ 13,000 Leakage from Gila Gravity Main rates of use: (1) Alfalfa hay, 7 feet, (2) unhar- Canal 2 ______10,000 vested fields, 2.6 feet, (3) citrus and others, 3.9 feet, Leakage beneath Imperial Dam 3 ____ 10,000 Total ______33,000 (4) urban and suburban, 2.5 feet, and (5) farm­ Consumptive use: steads and ditches, 2.5 feet. Crops, 80 acres ______300 Natural vegetation ______22,000 Budgets for the individual subareas are based on Evaporation from free water surface the principle that inflow less consumptive use equals other than river and canals 6 __ 7,100 change in storage plus outflow. Because of practical Total ______29,400 limitations on the accuracy of flow measurements Inflow less consumptive use __ _ _ 3,600 Change in storage ______-__Negligible and of limited knowledge about values to be used Outflow, subsurface water: for computing indirect estimates and estimates of To North Gila Valley subarea6 ______700 To Colorado River 7 ______2,900 consumptive use an equality is rarely achieved. This Change in storage plus outflow ___ _ _ 3,600 fact, of itself, does not lessen the reliability of the Imbalance 0 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H99

1 Estimated on basis of 3-mile length of canal and average rate of leakage of 4,300 acre-feet per year per mile of canal, the average rate Outflow: of leakage computed from U.S. Geological Survey measurements of canal Surface water: flows. Araz Drain 4,600 3 Estimated on basis of 5-mile length of canal and average rate of Reservation Central Main Drain 46,600 leakage of 2,000 acre-feet per year per mile of canal. 3 Unaccounted-for pickup in flow of river between Imperial Dam and gaging station 0.6 of a mile below dam is about 11 cubic feet per second Total surface water _____ 51,200 or about 8,000 acre-feet per year. This pickup probably is due to leak­ Subsurface water: age beneath the dam; an additional 1,000 to 2,000 acre-feet of leakage To The Island subarea* ______14,000 probably is still subsurface inflow 0.6 of a mile downstream from the dam, based on an estimated maximum coefficient of transmissivity of To Colorado River 5 ______22,000 500,000 gpd per ft, IV2 mile width of section, and hydraulic gradient of 2 feet per mile. Total subsurface water 36,000 1 Estimated on basis of acreages of natural vegetation and rates of use by various species as computed from data in U.S. Bureau of Reclama­ Change in storage plus outflow _ 87,200 tion (1963) study. 3 Areas of open water as determined from U.S. Geo'oprical Survey topographic map Laguna Dam 7.5-minute series multiplied by a net Imbalance: Inflow less consumptive use exceeds annual rate of 6.2 feet. change in storage plus outflow _ 10,800 6 Computed on basis of transmissivity of 0.3 mgd per ft, hydraulic gradient of 2 feet per mile, and 1 mile width of section. 1 Water pumped from river for irrigation at estimated rate of 6 feet 7 Computed to balance budget. on 600 acres. - Based on average rate of leakage for the period 1958-64, inclusive, The network of observation wells does not extend of about 4,300 acre-feet per year per mile length of All-American Canal bordering the subarea as computed from U.S. Geological Survey meas­ into the "Laguna Valley" subarea nor are the inflow urements of canal flows, multiplied by the 13-mile length of canal border­ ing the subarea. and outflow of the Colorado River known. The avail­ " Based on rate of leakage of 2,000 acre-feet per year per mile length of canal. able data therefore are insufficient for obtaining a 4 Computed on basis of transmissivity of 0.9 mgd per ft, hydraulic gradient of 4 feet per mile, and 3 mile length of section across northern check as to whether or not estimates of inflow less part of The Island subarea boundary plus transmissivity of 0.7 mgd per ft, hydraulic gradient of 2 feet per mile, and 1% mile length of section consumptive use equal estimates of change in storage at southwestern boundary. 5 In reach between Laguna Dam and The Island subarea, outflow is plus outflow. Rather, the budget was balanced by compupted as 6,000 acre-feet per year based on transmissivity at 0.6 mgd per ft, hydraulic gradient of 3 feet oer mile, and length of reach of 3 assuming that the amount needed to balance the miles; in reach between Yuma and All-American Canal, outflow is com­ puted as 16,000 acre-feet per year based on transmissivity of 0.6 mgd budget was subsurface inflow to the Colorado River. per ft, hydraulic gradient of 6 feet per mile, and length of reach of 4 The reasonableness of the various estimates there­ miles. fore depends to a large extent on the reasonableness Minor items of inflow and outflow that were not of similar types of estimates in other subareas where included in the budget are: (1) Ground-water re­ data or estimates for all budget items were avail­ charge from the tributary area west of the subarea, able, because the basis for the estimates, other than (2) unmeasured runoff to the subarea from the the subsurface inflow to the Colorado River, is the tributary area, and (3) subsurface outflow through same. the alluvial section between the Cargo Muchacho Mountains and Pilot Knob. RESERVATION AND BARD SUBAREA The latter item is estimated to be about equal to The Reservation and Bard subarea includes all the two minor inflow items, so the omission of these "Bard Valley" except for The Island, which is as­ minor items has no appreciable effect on the budget. signed to a separate subarea. More than half the A substantial part of the imbalance of 10,800 acre- subarea is in cropland, irrigated with water diverted feet probably is due to an overestimate of the or pumped from the Colorado River (a small tract amount of water diverted for irrigation of district in the northeastern part of the subarea is irrigated lands. Beginning in 1965, measurement procedures with ground water). The water budget follows: were improved, with the result that the average Acre-feet yearly diversion rate per acre irrigated apparently Inflow : Surface water: dropped 0.5 of a foot. An overestimate of 0.5 of a Diversions to district lands ____ 95,100 foot would account for about half of the imbalance. Diversions to other lands 1 _____ 3,600 The remaining imbalance is of the same magnitude Total surface water ______98,700 but of opposite sense to the imbalance for The Island Subsurface water: Leakage from All-Amprican Canal 2 56,000 subarea. (See p. H100.) Part of the imbalance may Leakage from Yuma Main Canal 3 _ 5,000 be due to the use of the same rate of consumptive Total subsurface water ______61,000 use for nonirrigated land (2.5 feet per year) for both Total inflow ______159,700 subareas. The average depth to water in the Reser­ Consumptive use: vation and Bard subarea is several feet less than the Irrigated cropland in district, 10,800 acres at 3.6 feet ______38,900 average depth to water in the flood-plain subareas, Other irrigated cropland, 630 acres at whereas the depth to water in The Island subarea is 3.6 feet ______2,300 Other land in subarea, 8,190 acres at several feet greater. 2.5 feet ______20,500 Rates of consumptive use commonly decrease as Total ______61,700 the depth to water increases. Thus it is reasonable Inflow less consumptive use ______98,000 to infer that the consumptive use estimate for non- Change in storage ______Negligible irrigated land is somewhat too low for the Reserva- H100 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA tion and Bard subarea and somewhat too high for Consumptive use: Irrigated cropland, 7,100 acres at 3.6 The Island subarea. feet ______25,600 Other land in subarea, 4,300 acres at 2.5 THE ISLAND SUI5AREA feet ______10,800 The Island subarea is that part of "Bard Valley" Total ______36,400 south of an abandoned meander loop of the Colorado Inflow less consumptive use ______91,600 River (fig. 33). The subarea is outside the estab­ Change in storage ______Negligible lished irrigation district and the cropland (less than Outflow: half of the total land area) is irrigated mainly with Surface water: Laguna Canal Wasteway 7,700 ground-water supplies. The water budget follows: Levee Canal Wasteway ______15,500 Acre-feet North Gila Main Canal Wasteway _ 8,300 Bruce Church Wasteway _ ___ _ 9,400 Inflow: North Gila Drain No. 1______7,300 Surface water: North Gila Drain No. 3______600 Diversions from river for irrigation _____ 2,200 Bruce Church Drain ______700 Subsurface water: Inflow from Reservation and Bard Total surface water ______49,500 subarea 1 ______14,000 Subsurface water: Inflow from North Gila subarea _ 7,000 To The Island subarea 3 ______7,000 Total subsurface water ______21,000 To Colorado River 4 ______23,000 Total inflow ______23,200 To South Gila Valley subarea 5 __ 14,000 Consumptive use: Total subsurface water ______44,000 Irrigated cropland, 3,100 acres at 3.6 feet ______11,200 Change in storage plus outflow ______93,500 Other land in subarea, 5,470 acres at 2.5 Imbalance: Amount by which inflow less consumptive feet ______13,700 use is less than change in storage plus outflow 1,900 Total ______24,900 1 Inflow across southwest corner of subarea computed on basis of transmissivity of 1 mgd per ft, hydraulic gradient of 6 feet per mile, Inflow less consumptive use ______1,700 and length of section of 1% miles. 3 Computed as average of 16,000 acre-feet per year based on average Change in storage ______Negligible rate of leakage of 2,000 acre-feet per year per mile length of canal as indicated by measurements of flows and diversions. Outflow, subsurface water to Colorado River 2 ___ 4,000 :) Computed on basis of transmissivity of 1.0 mgd r>er ft, hydraulic gradient of 4 feet per mile, and length of section of l 1,^ miles. Change in storage plus outflow ______4,000 1 Computed on basis of transmissivity of 0.6 mgd per ft, hydraulic gradient of 5 feet per mile, and 6-mile length of reach less 7,000 acre- Imbalance: Amount by which inflow less consumptive feet to The Island subarea, plus outflow across southwest corner of use is less than change in storage plus outflow ___ 5,700 subarea of 10,000 acre-feet. 5 Computed on basis of transmissivity of 0.5 mgd per ft, hydraulic 1 See footnote 4 of budget for Reservation and Bard subarea. gradient of 8 feet per mile, and length of section of 3 miles. 3 Computed on basis of transmissivity of 0.7 mgd per ft, hydraulic gradient of 2 feet per mile, and 2V« mile length of reach east of Yuma. The imbalance of 1,900 acre-feet per year is con­ Much of the imbalance probably is due to an over­ sidered insignificant. estimate of consumptive use on land that is not irri­ gated (p. H99). SOUTH GILA VALLEY SUBAREA The South Gila Valley subarea, which lies south of NORTH GILA VALLEY SUBAREA the Gila and Colorado Rivers and north of Yuma The North Gila Valley subarea, an L-shaped area Mesa, was until 1965 irrigated principally with east of the Colorado River and north of the Gila ground water. A minor part was irrigated with River, is chiefly in cropland which is irrigated with surface water diverted from the Gila Gravity Main Colorado River water except for the eastern arm of Canal under Warren Act contracts. About two- the subarea, which is now (1968) irrigated in large thirds of the total area of nearly 15,000 acres is in part with ground water. The water budget follows: irrigated cropland. The water budget follows: Acre-feet Acre-feet Inflow : Inflow: Surface water (Gila Gravity Main Canal): Surface water (Gila Gravity Main Canal): Diversions at North Gila Main Diversions for irrigation, (Warren Canal turnout ______88,400 Act contracts) ______5,100 Diversions at other points (Warren Automatic canal spills ______- 1,000 Act contracts) ______11,600 Total surface water ______6,100 Automatic canal spills ______1,000 Subsurface water: Total surface water ______101,000 Leakage from Gila Gravity Main Subsurface water: Canal 1 ______12,000 From South Gila Valley subarea 1 __ 10,000 Leakage from Wellton-Mohawk From "Laguna Valley" subarea and Main Outlet Drain 2 ______3,000 tributary areas eastward _____ 1,000 Inflow from Dome Valley 3 _____ 1,000 Leakage from Gila Gravity Main Inflow from North Gila Valley sub- Canal 2 ______16,000 area 4 ______14,000 Inflow from Yuma Mesa subarea B _ 57,000 Total subsurface water ______27,000 Total subsurface water ______87,000 Total inflow ______128,000 Total inflow ______93,100 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H101

Consumptive use tion exists is not known, but on the basis of obser­ Irrigated cropland,8 9,850 acres at 3.6 feet ______35,500 vations in the field and general ground-water condi­ Other land in subarea, 4,850 acres at 2.5 tions, at least half the leakage, or 4,000 acre-feet feet ______12,100 per year, is estimated to be inflow to the South Gila Total ______47,600 Inflow less consumptive use ______45,500 subarea. The rest of the inflow as measured at-the Change in storage 7 ______2,000 station 8 miles above the drain outlet is considered Outflow: a through flow, or return flow to the Colorado River Surface water: Deep Pump Outflow Canal No. 1 _ 17,000 via the Gila River, and as such need not be consid­ Deep Pump Outflow Canal No. 2 __ 13,000 ered in the budget of the subarea. Total surface water ______30,000 The imbalance of less than 1,500 acre-feet is con­ Subsurface water: To North Gila Valley 8 ______10,000 sidered negligible in view of the uncertainty regard­ To Colorado River 9 ______9,000 ing true values for many of the budget items. Total subsurface water ______19,000 Change in storage plus outflow ______47,000 YUMA MESA SUBAREA Imbalance: Amount by which inflow less consumptive The Yuma Mesa subarea includes the "Upper use is less than change in storage plus outflow _ 1,500 Mesa" and "Fortuna Plain" as well as Yuma Mesa. 1 Based on 2,000 acre-feet per year per mile length of canal and 6-mile length of canal in subarea. This subarea is underlain by most of the ground- - See discussion following budget. 3 Computed on basis that transmissivity does not exceed 1 mgd per ft., water mound which has developed from irrigation hydraulic gradient of 2 feet per mile; and % mile-width of section. 4 Computed on basis of transmissivity of 0.5 mgd per ft., hydrau'ic of citrus orchards on Yuma Mesa, mostly since the gradient of 8 feet uer mile, and 3-mile length of section. 3 See discussion following budget for Yuma Mesa subarea. p. H101. mid 1940's. The water budget for the subarea 9 9,420 acres in district plus 430 acres outside district. 7 Computed from water-level maps for December 1959 and December follows: 1963, assuming a specific yield of 20 percent. Acre-feet 8 Computed on basis of transmissivity of 1 mgd per ft., hydraulic gradient of 6 feet per mile, and width of section of 1M; miles. Inflow: 9 Computed on basis of transmissivity of 0.7 mgd per ft., hydraulic Surface water: gradient of 4 feet per mile, and width of section of 3 miles. Diversions for irrigation 307,000 City of Yuma (diversions in excess The budget item "Leakage from Wellton-Mohawk of sewage returns) ______4,000 Main Outlet Drain" requires some additional expla­ 311,000 Consumptive use: nation. Flow in this drain, or conveyance channel, Crops 1 ______78,000 began in February 1961. Therefore, for practical Lawns ______2,000 purposes, the drain was in operation for 3 of the 80,000 4 years of the budget period, 1960-63. The flow in Inflow less consumptive use 231,000 the drain is measured at a point 8 miles above its Change in storage 2 ____ 47,000 Outflow, subsurface: outlet to the Gila River. Except at the measure­ To South Gila Valley 8 ______57,000 ment sections, the drain is unlined. Leakage from To Yuma Valley 3 ______97,000 Across international boundary east of the drain during the budget period could not be com­ San Luis ______30,000 puted because measurements were first made near Total ______184,000 the drain outlet beginning in October 1965, at which Change in storage plus outflow _ 231,000 time the Main Outlet Drain Extension to Morelos Imbalance ______0 1 Average of values shown in table 8. Dam was completed. A comparison of flows between - Computed from map showing changes in water level, December 1959 to December 1963 and using coefficient of storage of 0.18 for changes the two stations shows that in each of the years beneath "Upper Mesa," 0.31 for changes beneath nonirrigated land of Yuma Mesa, and one-half of the foregoing coefficient for changes beneath 1966, 1967, and 1968 the flow near the outlet to the irrigated land. Gila River is about 9,500 acre-feet less than the " See discussion following budget. corresponding flow at the station where the flow The outflow from the ground-water mound to the was measured during the budget period. Allowing South Gila Valley subarea and to the Yuma Valley that some of the indicated loss represents evapora­ subarea was computed by determining the percent­ tion and that the loss may be somewhat more than age of the ground-water recharge that moves toward during the budget period because of a slightly each of these subareas and to the area east and higher stage due to the construction of the drain southeast of the mound. A contour map showing the extension, a seepage loss of 8,000 acre-feet per year, head in the coarse-gravel zone beneath the irrigated or about 1,000 acre-feet per year per mile of chan­ area of the Yuma Mesa as of December 1962 was nel is indicated. To the extent that the leakage does used for establishing the position of the ground- not discharge to the Gila River, whose channel gen­ water divides of the mound. erally is within half a mile of and north of the Although only a few data were available for con­ drain, the seepage is an inflow item to the South trols as early as December 1962, by making use of Gila subarea. The extent to which the above condi­ all the data on water levels in both shallow and deep H102 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

wells over a period of years, and of more complete ing the final stages of the verification procedures. data in deeps wells in later years, it was possible to Although historical changes were verified to a bet­ draw contours showing the head in the coarse- ter degree by using those coefficients than the larger gravel zone and also the ground-water divides. Then coefficients of 0.25 for the material underlying the by assuming that the yearly rate of ground-water "Upper Mesa" and 0.35 for that underlying Yuma recharge per acre irrigated was uniform for blocks Mesa, the possibility that an excellent verification of several thousand acres or more, the yearly re­ by using the larger coefficients and adjusting other charge that was diverted to the various subareas parameters could be obtained was not fully explored was computed by determining the percentages of because of a lack of both time and funds. The larger the total irrigated areas that lay between specific storage coefficients would increase the estimate of divides. On the above basis it was found that about ground-water storage an additional 10,000 acre-feet 25 percent of the irrigated acreage, and therefore per year. An increase of this magnitude would sig­ of the recharge, or about 57,700 acre-feet, was nificantly reduce the imbalance of the Yuma Valley within the divide diverting recharge to the South subarea, the algebraic sum of the imbalance of all Gila Valley subarea. Of this amount, some 500 acre- the subareas (p. H105), and would change only the feet went into storage beneath the mesa, leaving character of the imbalance for the whole Yuma area. 57,000 (rounded) acre-feet as outflow to the South The above observations suggest that the estimate Gila Valley subarea. About 45 percent of the irri­ of yearly increase of ground-water storage beneath gated acreage, and thus 45 percent of the recharge, the Yuma Mesa subarea as computed for the budget or 104,000 acre-feet, was in the sector where re­ may be too low by 10,000 acre-feet. Further studies charge was diverted westward toward the Yuma of the storage characteristics of the materials under­ Valley subarea. Of this amount, about 7,000 acre- lying the Yuma Mesa subarea are needed in order feet went into storage beneath the mesa leaving to more reliably estimate the quantities of ground 97,000 acre-feet as outflow to the Yuma Valley water represented by a given change in volume of subarea. saturated material. About 30 percent of the irrigated land was in the Outflow from the Yuma Mesa subarea also would sector in which water moves eastward and south­ be lessened if the average yearly recharge were not ward from the mound. Of the 69,000 acre-feet of as large as is shown in the budget. Some justifica­ recharge to this sector, about 40,000 acre-feet went tion for the possibility that the estimate of average into storage beneath the mesa, and 29,000 acre-feet yearly recharge is too high may be had from the moved as outflow southward toward the interna­ fact that the estimated yearly recharge during the tional boundary. 4-year budget period was the highest of record, that A small eastward or westward shift of the di­ it exceeded the average of the 4 preceding years by vides causes a pronounced change in the relative 62,000 acre-feet, and the average of the 3 following quantities of recharge that are diverted to the Yuma years by 31,000 acre-feet, whereas the average irri­ Valley subarea and to the subarea eastward and gated acreages for these periods were only 1,800 southward of the divide, but the shift causes only acres less and 7,000 acres more, respectively, than a relatively small change in the recharge that is the average acreage for the budget period. Average diverted northward to the South Gila Valley sub- rate of ground-water recharge during the budget area. Although shifting the ground-water divides period was 11.7 feet per year, whereas for the peri­ slightly westward would reduce the outflow to Yuma ods preceding and following the budget period the Valley and thus would reduce the rather large im­ rates were 9.4 and 9.8 feet per year, respectively. balance for that subarea, it would increase the Part of the 2-foot lower rate of ground-water re­ recharge to the eastern and southern sector a simi­ charge following the budget period undoubtedly was lar amount. A balance presently exists between the due to a request by the U.S. Bureau of Reclamation recharge estimated on the basis of the ground-water to irrigation districts in the Yuma area to conserve divides and the recharge based on outflow and stor­ water by diverting less water for irrigation. age estimates in this sector, so any westward shift The indicated 2.2 foot per year higher ground- of the divides should be governed by the extent to water recharge rate during the budget period than which the outflow and storage estimates for the the recharge rate preceding the budget period is eastern sector might be too low. not as easily explained. The storage coefficients used for the budget may YUMA VALLEY SUBAREA be too low. The coefficients used for the budget are The Yuma Valley subarea includes about 62,000 those that were simulated by the analog model dur­ acres, of which more than three-fourths is irrigated GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H103 cropland. Except for a narrow strip adjacent to the shown in figure 34. A flow net was used to facilitate Colorado River, which is outside the irrigation dis­ computations of the amounts of flow toward various trict and is irrigated chiefly with ground-water segments of the limitrophe section. supplies, the subarea is irrigated with Colorado The flow toward the limitrophe section as given River water by way of the Yuma Main Canal. The for the budget contains some duplication to the water budget for the subarea follows: extent that the flow in the coarse-gravel zone in­ Acre-feet cludes some of the excess irrigation water that Inflow: Surface water: originated between the Colorado River and the shal­ Diversions for irrigation from low ground-water divide east of the river. The Yuma Main Canal ______341,000 Diversions for irrigation by pump­ amount of duplication is thought to be small, prob­ ing from river, 1390 acres at 6 ably less than 5,000 acre-feet. feet ______8,000 Subsurface water: The subsurface flow across the southerly interna­ Inflow from Yuma Mesa ______97,000 tional boundary is the product of the transmissivity, Total inflow ______446,000 width of Yuma Valley between the river and Yuma Consumptive use: Irrigated cropland, 45,270 acres of dis­ Mesa, and the hydraulic gradient as shown in or trict land and 2,220 acres of nondis- computed from figure 34. trict land at 3.6 feet ______171,000 Other land in subarea, 14,810 acres at The budget imbalance of 20,000 acre-feet is quite 2.5 feet ______37,000 large relative to the budget items, being almost Total ______208,000 5 percent of the total inflow, about 10 percent of the Inflow less consumptive use ______238,000 estimated consumptive use, and about 10 percent Change in storage _____-______-______-_-Negligible Outflow: of the estimated outflow. A significant part of the Surface water: imbalance may be due to an overestimate of the Cooper Canal Wasteway ______2,000 Eleven Mile Wasteway ______16,000 subsurface inflow from Yuma Mesa as was explained Twenty-One Mile Wasteway ____ 8,000 in the discussion of the budget for the Yuma Mesa East Main Canal Wasteway ____ 12,000 Main Drain ______135,000 subarea. Other causes of the imbalance are possible Subsurface water 1 ______45,000 overestimates of the surface-water inflow and under­ Change in storage plus outflow ______218.000 estimates of the consumptive use, or the subsurface Imbalance: Amount by which inflow less consumptive outflow. It seems quite unlikely, however, that the use is more than change in storage plus outflow __ 20,000 latter item is underestimated by much more than 1 5,000 acre-feet across southerly international boundary (p. H103); 13,000 acre-feet to limitrophe section, resulting from net excess irriga­ 5,000 acre-feet. Because of a lack of knowledge as tion (p. H93): 20,000 acre-feet to limitrophe section in main aquifers (p. H103) : 7,000 acre-feet to Colorado River between Yuma and northerly to which estimates cause the imbalance, no adjust­ international boundary (p. H93). ments of the estimates shown have been made to The estimates of subsurface outflow to the limi­ reduce the imbalance. trophe section and across the southerly international boundary were computed on the following basis. It SUMMARY OF SUBAREA BUDGETS was assumed that the head in the top of the coarse- The water budgets for all the subareas are sum­ gravel zone in the western half of Yuma Valley is marized in table 9. The algebraic sum of the imbal­ the same as the head in the underlying wedge zone. ances of 19,000 acre-feet apparently is due in large This assumption is based on limited evidence of part to the imbalance for the Yuma Valley subarea, little or no measurable differences of head with the probable causes of which are discussed in the depth that was obtained during the present study. section on the budget of the Yuma Mesa subarea The head near the top of the coarse-gravel zone was (p. H102). The interrelations of the budgets for the computed from water-level measurements in the various subareas and the principal items of these network of observation wells constructed and mea­ budgets are shown in figure 33. sured periodically by the Yuma County Water Users' YUMA AREA Association. Water levels as of December 1962 (fig. A water budget for the entire Yuma area for the 34) are assumed to be good indicators of average period 1960-63, inclusive, was also prepared. With heads for the period 1960-63, inclusive. the exception of consumptive use by evaporation The rate of ground-water movement toward the from free water surfaces, the consumptive use limitrophe section was computed as the product of values are the sum of the respective values given the transmissivity, width of section, and hydraulic in the budgets of the subareas. Consumptive use by gradient. The transmissivity was that indicated in evaporation (total evaporation less precipitation) in­ figure 25; the other parameters of width and hydrau­ cludes evaporation from the Colorado River and the lic gradient were determined from the information Ail-American Canal in addition to evaporation within H104 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

114°45'

32°45'

Water-level contour Sliou's altitude of water level. Contoitt interval .5 feet: datum IK mean sea level

32°30 r

FIGURE 34. Average water-level contours for upper part of coarse-gravel zone in 1962 in the Yuma Valley. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H105

TABLE 9. Summary of ground-water budgets of Yuma subareas, 1960-63 [Quantities in acre-feet per year] Imbalance, Column 2 Change Column 5 column 4 Subarea Inflow Consumptive minus in Outflow plus minus use column 3 storage column 6 column 7 1 2 3 3 5 6 7 8 "Laguna Valley" _ _ 33,000 29,400 3,600 0 3,600 3,600 0 Reservation and Bard - - 159,700 61,700 98,000 0 87,200 87,200 10,800 The Island 23,200 24,900 -1,700 0 4,000 4,000 -5,700 North Gila Valley 126,400 36,400 90,000 0 93,500 93,500 -3,500 South Gila Valley 93,100 47,600 45,500 -2,000 49,000 47,000 -1,500 Yuma Mesa 311,000 80,000 231,000 47 000 184,000 231,000 0 Yuma Valley __ _ 446,000 208,000 238,000 0 218,000 218,000 20,000 _ _ 1,192,000 488,000 704,000 45,000 639,000 684,000 20,000 1 Column totals are rounded to nearest 1,000 acre-feet per year. The rounded column totals therefore do not necessarily check by row. the subareas. Change in subsurface (ground water) The outflow item "surface-water deliveries to storage is that indicated in the budgets of the sub^ Mexico" under footnote 5 consists of the same flows areas. The other items of inflow and outflow are as those used in the administration of the Mexican based on surface-water measurements or are esti­ Water Treaty of 1944, namely "the sum of the Colo­ mated as explained in the footnotes pertaining to rado River at the northerly boundary, the drainage individual items. The boundaries of the budget area and waste waters which enter the limitrophe section are quite evident except in the limitrophe section of and the southerly boundary from the United States, the river where the boundary is the left or easterly less the small (about 5,000 acre-feet annually) use edge of the river. within the United States in the limitrophe section." Water budget for Yuma area., 1960-63, inclusive The drainage and waste waters that are included in [Mean annual quantities in 1,000 acre-feet] the computations are those measured at Cooper, Inflow: Eleven-Mile, Twenty-One Mile, and East Main Canal Measured: Surface 1 ______6,719 Unmeasured: Wasteways, and at the boundary pumping plant of Surface 3 ______2 the Yuma Main Drain. Subsurface 3 ______11 The small imbalance of 7,000 acre-feet has no sig­ Total inflow ______6,732 Consumptive use: nificance because of the uncertainty of the true Irrigated cropland ______363 values of many of the budget items. Natural vegetation and evaporation from other lands ______118 The budget compares favorably with a longer Evaporation from free water surfaces _ 16 term (1951-66), slightly different, and less detailed Total ______497 budget which was prepared for Hely (1969). Inflow less consumptive use ______6,235 Change in storage (subsurface) 4 ______45 Outflow: GROUND-WATER DISCHARGE TO THE COLORADO Measured: Surface 5 ______6,115 RIVER BETWEEN IMPERIAL DAM AND THE Unmeasured: Subsurface 8 ______68 Total ______6,183 NORTHERLY INTERNATIONAL BOUNDARY Change in storage plus outflow ______6,228 The water budgets for the various subareas of the Imbalance: Inflow less consumptive use exceeds change in storage plus outflow ______7 Yuma area for the period 1960-63 indicate that 1 Sum of the average flows of the Colorado River at Imperial Dam, ground water generally was being discharged to the the Gila River near Dome, and the Wellton-Mohawk Main Outlet Drain - Estimate of average annual runoff from precipitation. Colorado River. The average yearly quantities of 3 Includes 10,000 acre-feet underflow below Imperial Dam; and 1,000 acre-feet underflow at the gap where the Gi'a River enters the area. ground water discharged to the Colorado River or to * Increase in storage beneath Yuma Mesa subarea of 47,000 acre-feet les_s decrease in storage in South Gila Valley subarea of 2,000 acre-feet. the Gila River from each of the subareas between 5 Sum of: flows of All-American Canal above Pilot Knob Power Plant and Wasteway less flows through Pilot Knob Power Plant and Wasteway Imperial Dam and the northerly international (3,634,000 acre-feet); diversion to Wellton-Mohawk Irrigation District (399,000 acre-feet); and surface-water deliveries to Mexico (2,082,000 acre- boundary are listed in table 10. feet ). " Sum of ground-water flow across southerly international boundary Of the 72,000 acre-feet of ground-water discharge of 35,000 acre-feet, and ground-water flow across limitrophe section from Yuma Va'ley of 33,000 acre-feet. to the river, about 45,000 acre-feet is indicated to The flows used to compute the average measured enter the river upstream from Yuma and 27,000 inflow are published flows except the flow of the acre-feet downstream. Colorado River at Imperial Dam in 1960. The pub­ Surface-water records also indicate that ground lished flow for 1960 is adjusted downward 100,000 water is being discharged to the river. However, be­ acre-feet to compensate for an overstatement of pub­ cause of the large volume of surface water relative lished flows at Imperial Dam prior to 1961 (Loeltz to the discharge of ground water to the river, which and McDonald, 1969, p. 67-69). is computed as the difference between surface inflow

507-243 O - 74 - H106 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

TABLE 10. Ground-water discharge to the Colorado or Gila For the period of record the yearly ground-water Rivers between Imperial Dam and northerly international boundary, 1960-63 inflow less evaporation of river water (4,000 acre- Average yearly quantity feet) and water diverted for irrigation (6,000 acre- Subarea (acre-feet) feet) ranges between 11,000 and 40,000 acre-feet Laguna Valley _____ 3,000 Reservation and Bard: and averages 28,000 acre-feet. Adding 10,000 acre- Eastern boundary _ 6,000 feet because of annual evaporation of river water Southern boundary 16,000 The Island ______4,000 and diversions for irrigation indicates an average North Gila Valley _____ 23,000 annual inflow or discharge of ground water to the South Gila Valley __ 9,000 Yuma Valley: river of 38,000 acre-feet. This discharge of ground Northern boundary 7,000 water to the Colorado River in the reach between 68,000 Imperial Dam and Yuma computed on the basis of Plus: Estimated leakage from All- American Canal to river between Res­ surface-water inflows and outflows thus averages ervation and Bard subarea boundary only about 7,000 acre-feet less than the discharge of and northerly international boundary 1 4,000 72,000 45,000 acre-feet indicated by the water budgets of 1 Estimated on basis that only the leakage from about 1 mile of the the various subareas (p. H105). Because of the un­ 2-mile length of canal at rate of 4,300 acre-feet per year per mile reaches the river. certainty of the true values of many of the items in and outflow, the errors inherent in surface-water all the budgets the difference of 7,000 acre-feet be­ measurements may be the principal influence on the tween the two estimates is insignificant. yearly differences of ground-water inflow indicated The difference by which the flow at the northerly by surface-water measurements. Sufficient surface- international boundary exceeds the sum of the flow water data are published so that computations can at Yuma and the other return flows is a measure of be made as to the indicated discharge of ground the discharge of ground water to the river in the water to the Colorado River for the reach Imperial reach, if to the difference is added about 2,000 acre- Dam to Yuma for the period 1961-65, inclusive, and feet for average annual evaporation from the river for the reach Yuma to northerly international and about 2,000 acre-feet because of pumpage from boundary for the period 1950-66. the river for irrigation. Table 12 shows a wide The first computation involves the flow of the Colo­ range in these annual differences from an indi­ rado River, the Gila River, and 12 or more other cated loss of 85,000 acre-feet in 1952 to a gain of inflows. The second involves the flow of the Colo­ 74,000 acre-feet in 1954. It is quite apparent that rado River and four other inflows. As many as four the yearly differences are dominated to a large ex- different agencies supply data for computing flows. TABLE 12. Flow of the Colorado River at Yuma and at northerly international boundary, and differences between The yearly difference for the period 1961-65, sum of all surface-water-inflow items in the reach and inclusive, by which the flow of the Colorado River at flow of Colorado River at northerly international boundary Yuma exceeded the sum of the flow of the Colorado [All quantities in 1,000 acre-feet]

River at Imperial Dam and all the known surface- Gaging station at Surface- Surface- water water water inflows to the river in the reach between outflow outflow Calendar exceeds is less than Imperial Dam and Yuma, including the flow of the year Yuma Northerly surface- surface- international water water Gila River, are shown in table 11. boundary inflow inflow TABLE 11. Flow of the Colorado River at Imperial Dam 1950 3,464 4,456 43 and at Yuma and differences between sum of all surface- 1951 2,764 3,639 48 water inflow items in the reach and flow of Colorado 1952 9,192 10,146 85 River at Yuma 1953 4,095 5,224 44 [All quantities in 1,000 acre-feet] 1954 3,196 4,346 74 1955 2,118 3,058 17 Surface-water Gaging station at outflow 1956 881 1,638 30 exceeds 1957 1,167 2,853 2 1958 2,951 5,908 68 year Imperial inflow ! Dam Yuma 1959 933 3,051 25 1960 702 2,338 66 1961 _ _ __ 437 683 38 1961 683 1,672 25 1962 _ _ _ 510 860 32 1962 860 1,811 28 1963 _ _ 575 924 40 1963 924 1,834 42 1964 _ _ _ 440 712 20 1964 712 1,502 51 1965 _ 297 560 11 1965 560 1,524 31 Average _ _ 28 1966 428 1,420 34 Total 510 203 1 After adjusting published return flows to Gila River from Wellton- Mohawk Outlet Drain downward 4,000 acre-feet per year to compensate NOTE. Surface-water outflow exceeds surface-water inflow: for estimated seepage loss in 8-mile unlined channel between measuring For period of record 307 point and river that does not reach Colorado River. Yearly average 18 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H107

tent by errors of measurement. However, they also computed on the basis of ground-water parameters are influenced somewhat by the amount of flow in agree as well as can be expected in view of the un­ the preceding year. Generally, the ground-water certainties of the values of the items used to obtain discharge for a given year should be less than the the estimates. ground-water discharge for the preceding year when ANALOG-MODEL STUDIES the stream discharge for the given year is substan­ Because of the complex nature of the hydrologic tially larger than the stream discharge for the pre­ system in the Yuma area and the continuing and ceding year. A large annual increase of stream dis­ varied development of the system, the use of mathe­ charge for a given year ordinarily implies an in­ matical formulas for directly computing the re­ crease of river stage. An increase of river stage in sponse of the system to this development becomes an area of ground-water discharge to the river de­ impractical. The electrical-analog method, however, creases the gradient from the ground-water reser­ is well adapted for solving the complex mathematics voir to the river and consequently the ground-water of the partial differential equations involved in de­ discharge to the river. Similar reasoning shows that scribing the hydrologic system. The construction ground-water discharge to the river should increase of an electrical analog model of the Yuma area that in a year in which the stream discharge, and presum­ would simulate responses of the actual system to ably the stream stage, is lower than in the preceding stresses imposed on it therefore was one of the year. The average annual amount by which the objectives of the present investigation. discharge at the northerly international boundary An initial attempt in 1964 to simulate observed exceeds the sum of the measured inflows for the changes of water level beneath Yuma Mesa by means years listed in table 12 is 18,000 acre-feet. of a one-layer model was not successful enough to The average annual discharge of ground water to warrant further work on the model. The model was the river is an additional 4,000 acre-feet because of useful, however, in demonstrating that some of the evaporation and pumpage, or 22,000 acre-feet for parameters of transmissivity, storage, and boundary the 17-year period 1950-66. For the period of the effects in the southern and southeastern part of water budgets of the various subareas 1960-63 the Yuma Mesa that were being simulated by the model discharge of ground water to the river is indicated to be about 44,000 acre-feet. were incorrect. In 1966, the barrier effect of the Algodones fault to the southward movement of The true value probably is somewhere between ground water beneath Yuma Mesa was first recog­ these two values unless consistent errors of measure­ nized as the result of drilling exploratory wells on ment are involved. Even in years of relatively low both sides of the fault. Discovery of this highly ef­ flow, the flow at the northerly international bound­ fective barrier appeared to provide the boundary ary is between 1.5 million and 3 million acre-feet, so parameter that would permit reasonable agreement a consistent error of only 1 percent would cause the computed discharge of ground water to the river to between observed changes in water level and those be in error 15,000-30,000 acre-feet. The indicated indicated by an electrical analog model using values mean annual difference even for a 10-year or longer similar to those assumed for the initial study. period therefore, may be reliable only to plus or The United States Section of the International minus 10,000-20,000 acre-feet. Boundary and Water Commission, and the U.S. Bu­ As a basis for comparison, the average annual dis­ reau of Reclamation were very much interested in charge to the Colorado River in the reach Yuma to obtaining a model that might be used in predicting the northerly international boundary as indicated by the effect of future water development on the move­ the water budgets of the various subareas was about ment of ground water across international bounda­ 27,000 acre-feet for the period 1960-63 (p. H105). ries. As a consequence, both agencies cooperated This estimate is based on the ground-water parame­ with the Geological Survey in building a more repre­ ters of transmissivity, hydraulic gradient, and sentative electrical analog model of the Yuma area width of section. It is 17,000 acre-feet less than the and in providing additional hydrologic data, prin­ estimate for the same period computed from surface- cipally from exploratory drilling in the southeastern water measurements and 5,000 acre-feet more than part of the "Upper Mesa" and "Fortuna Plain." the estimate computed from surface-water measure­ Also, these two agencies provided funds for addi­ ments for the period 1950-66. tional geophysical exploration. In general, the estimates of ground-water dis­ MODEL CHARACTERISTICS charge to the Colorado River computed on the basis The analog model includes the Yuma area and con­ of surface-water measurements and the estimates tiguous parts of Sonora and Baja California, Mexi- H108 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA co; a total area of some 2,000 square miles. The southern boundary is arbitrarily modeled as being actual hydrologic system is simulated as a three- about 15 miles south of San Luis, Mexico, and is a dimensional flow field idealized as two two-dimen­ constant-head boundary so as to yield or receive sional transmissive layers and two layers of solely water in response to changes in ground-water vertical flow. gradients. The upper transmissive layer generally corres­ Also modelel as constant-head boundaries are ponds to the coarse-gravel zone, but where that zone the Ail-American Canal and the Colorado River. is missing, such as beneath the "Upper Mesa" and Their hydraulic connection with the upper trans­ "Fortuna Plain," it includes the upper part of the missive layer is a parameter representing the older alluvium, undivided. Beneath' southwestern hydraulic radius, the permeability of the deposits Yuma Mesa and southern Yuma Valley the upper underlying the river or canal, and the distance transmissive layer includes all the alluvial deposits through which the water moves in the interchange in which most wells have been completed or are process. Values for this parameter were selected by likely to be completed. Thus, in those areas the trial and error until reasonable agreement between upper transmissive layer includes the uppermost interflow rates computed from model response and part of the wedge zone as well as the coarse-gravel best estimates of historical rates were obtained. For zone. computational purposes, both the Ail-American Overlying the materials modeled as the upper Canal and the river are divided into two segments, transmissive layer are much finer grained materials one end of each terminating near Pilot Knob. corresponding to the upper, fine-grained zone. In In the lower transmissive layer the Algodones Yuma and South Gila Valleys these finer materials fault is modeled as a partial barrier to the move­ are modeled as a confining layer which allows ver­ ment of water throughout its length, whereas in the tical flow to or from the upper transmissive layer upper transmissive layer, the fault's barrier effect according to the hydraulic gradient between the con­ was modeled only southeast of the apex of the stant-head surface assumed in these valleys and the ground-water mound. This difference in the two head in the upper transmissive layer and the vertical layers was modeled because barrier effects of the hydraulic conductivity of the confining material. fault were not recognizable during the present in­ Elsewhere in the modeled area the upper confining vestigation in wells bottoming in the coarse-gravel layer is lumped with the upper transmissive layer. zone (principal part of upper transmissive layer) The lower transmissive layer is hydraulically con­ northwest of the apex of the ground-water mound. nected to the upper transmissive layer and is mod­ eled as a single transmissive layer. Beneath the TRANSMISSIVITY VALUES river valleys and Yuma Mesa the lower transmissive Ranges in transmissivity for the upper and lower layer includes most of the wedge zone, and beneath transmissive layers as finally modeled are shown in the "Upper Mesa" and "Fortuna Plain" it includes figures 35 and 36. The transmissivity values were the lower, major, part of the older alluvium, undi­ adapted by the analog-model-unit laboratory from vided. The average head loss resulting from vertical more detailed maps submitted to the laboratory from flow between the upper and lower transmissive lay­ the project office, which showed respective trans­ ers at any site is simulated by a parameter repre­ missivity values for the upper and the lower trans­ senting the average vertical hydraulic conductivity missive layers. These estimates were based on the and average flow distances between the two layers. results of pumping tests, specific capacity of wells, Wherever practicable, the model boundaries (part­ drillers' logs, lithologic logs, borehole geophysical ly shown in fig. 35) approximate natural hydrologic logs, and probable thickness and permeability of boundaries. The eastern boundary of the model sediments as interpreted from all the geologic, geo­ coincides with the Gila Mountains and their south­ physical, and hydrologic studies in the area. Verifica­ ern continuation the Butler Mountains; the north­ tion studies of the model showed that increasing the ern boundary generally follows the Cargo Muchacho original estimates 25 percent resulted in an im­ Mountains and a marked decrease in transmissivity proved correlation between model response and in the alluvium about 9 miles north of the northerly observed changes of water level. This increase, international boundary; the western boundary is therefore, was incorporated into the model and is modeled as being about 30 miles west of Pilot Knob included in the values shown in figures 35 and 36, along a line that approximates the increasing clay and in figure 25, which shows the sum of the trans­ content and consequent decreasing permeability of missivity values that were the basis for transmissivi­ the deposits in Imperial and Mexicali Valleys; the ty values simulated by the analog model. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H109

STORAGE-COEFFICIENT VALUES boundaries as indicated by the model response is at a The storage coefficients for the upper transmissive maximum rate. layer that were actually modeled are shown in figure STRESSES APPLIED TO THE MODELED SYSTEM 37. They were arrived at in the following manner. Recharge to the system was computed on the basis A first estimate of the storage coefficient for the of imports to Yuma Mesa minus consumptive use, nonirrigated areas of Yuma Mesa was 35 percent, and was apportioned areally according to the acre­ based on soil-moisture studies with the neutron age irrigated during specific periods (table 13). Dis- moisture probe (p. H219). Geologic studies indicated that the foregoing value was too large for the "Up­ TABLE 13. Design stresses for analog model of Yuma area per Mesa" and "Fortuna Plain," so a value of 25 [Quantities in 1,000 acre-feet] percent was used for those areas. Subsequent verifi­ Yearly Period rate Period Accumulated cation studies, however, indicated that the smaller Recharge values shown in figure 37 resulted in model re­ 1925-42 ___ . 95 95 sponses that correlated with observed changes much 1943-47 __ . 51 256 351 better than did the original estimates. 1948-52 102 512 863 1953-57 _ _ . 147 785 1,648 A storage coefficient of 20 percent was originally 1958-62 ___ . 208 1,039 2,687 assumed for all the flood-plain land in Mexico and 1963-64 _ __ . 228 456 3,143 1965-66 _ . for land in the United States north and west of Pilot 188 376 3,519 Knob. Verification studies indicated that a value of Drainage-well pumpage 18 percent as shown in figure 37 was as valid as the 1948-52 19 95 95 1953-57 36 182 277 original 20 percent estimate. Construction of the 1958-62 80 400 677 model therefore was not modified to incorporate a 1963-64 114 228 905 1965-66 126 251 1,156 simulation of the somewhat higher original value. The storage coefficient for the upper transmissive charge of ground water by pumps in the United layer beneath Yuma Valley is 5X10'4, an artesian States from the coarse-gravel zone began in 1948 coefficient. In this area, the changes in water level and was apportioned according to the location of the are assumed to be small because of the extensive principal drainage wells along the western and network of drains in most of the area. The specific northern margins of Yuma Mesa and the pumpage value to be assigned to the storage coefficient is not for specific periods (table 1). Pumpage in Mexicali critical because storage in the upper transmissive Valley was determined on the basis of the stress that layer beneath the flood plain in the United States has had to be imposed on the system to cause historical little effect on the response of the system. declines in head in the coarse-gravel zone underlying A storage coefficient of 0.31 was modeled for the the Mexicali Valley well field. (See last column of flood-plain area north and northwest of Yuma Mesa. table 14.) In addition, a constant head was modeled for North TABLE 14. Effective yearend declines of water level, in feet, and South Gila Valley subareas. Modification of the in Mexicali Valley at a site 12 miles west of the middle model in the flood plain north of Yuma Mesa proba­ of the limitrophe section of the Colorado River bly would better simulate actual conditions. How­ Average addi- Period Average decline tional decline ever, the modifications were not essential to the prin­ ending during irriga- due to draw- Decline since Effective year- cipal objectives of the study and therefore they were December tion season down at wells December 1952 end decline not fully explored. 1952 __ 0 0 0 0 1957 __ 1 3 -2 2 One modification, which involved using a constant 1962 __ 2 6 7 15 head and artesian storage coefficient for the entire 1964 __ 3 7 11 21 flood plain north and northwest of Yuma Mesa, gave 1966 __ 3 7 15 25 poorer correlations between model response and The average decline of water levels since Decem­ historical changes than did the present model with ber 1952 and the seasonal decline were based on the supposedly less realistic values. water-level maps obtained by the United States A value of 5xlO~4 was modeled for the storage co­ Section of the International Boundary and Water efficient throughout the lower transmissive layer. Commission from the Mexican Section of the Com­ Hydrologic data were not available for making an mission. The average additional decline due to estimate of this parameter, so a reasonable value drawdown at wells was estimated to be about one- that would result in the shortest travel time for fourth of the average drawdown at the well sites. pressure waves was selected. Under this design, the Points of stress were distributed uniformly through­ movement of ground water across international out the Mexicali Valley well field. H110 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA O M 32°45' - O W

ALL-AMERICAN CANAL O UNITEDS _ f ^ TvTpYTf.O O

aH

M EXPLANATION

Transmissivity boundary line Number is transmissivity, in thousand gallons per day per foot. o Adjacent areas connected by inter­ a; mediate transmissivity values except across that part of Algo- dones fault where transmissivity is 250 gallons per day per foot o o

Mountains and hills oi

Area of shallow bedrock I2 I > Alluvial escarpment

Fault Dotted where concealed 32°15

FIGURB 36. Transmissivity of the lower transmissive layer simulated in the analog model in the delta region. H112 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

114M5' 30'

32°45' =

" ' MEXICO

Storage coefficient boundary line Shows boundaries of areas of storage coefficients simulated in the analog model. Number within boundary is storage coefficient Alluvial escarpment International boundary line Shows location of international boundary as sim­ Fault ulated by analog model. Line is storage coeffi­ Dotted where concealed cient boundary line i?) limitrophe section of Colorado River

Mountains and hills

FIGURE 37. Storage coefficients of the upper transmissive layer simulated in the analog model.

The resultant pumpage figures therefore were not Valley. Recharge to the upper transmissive layer indicative of the actual pumpage in Mexicali Valley resulting from diversion of surface water for irriga­ because the stresses imposed on the model were only tion is a stress that would need to be imposed before part of the stresses that were operative in Mexicali a meaningful net pumpage figure could be expected. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H113 However, the objectives of the model study that is, with caution, can be used to predict the effect of an evaluation of the changes in the rate of movement other stresses that might be imposed on it. After of ground water across international boundaries, the model is modified to obtain more realistic stor­ especially the limitrophe section of the Colorado age coefficients in the flood plain north of Yuma River during a given time period can be computed Mesa and after other small adjustments to lessen satisfactorily from transmissivity values and observed discrepancies between model response and changes in gradients across international bounda­ historical changes are made, it should be a useful ries as shown by the analog model without regard to tool for predicting the changes in head that will net pumpage in Mexicali Valley. The magnitude of result from future development of the ground- the rate of ground-water movement across interna­ water resources of the area under any proposed tional boundaries at a given time can be computed plan. The changes in head can be readily converted from transmissivity values shown in figure 25 and to changes in gradient, which together with the hydraulic gradients computed from water-level con­ transmissivity values can be used to compute tour maps of a given date, provided the gradients are changes in the direction and rate of ground-water adjusted for changes as indicated by the analog movement. model that have occurred or will occur between the TEMPERATURE OF GROUND WATER date of the water-level contour map and the time The temperature of ground water often provides at which the rate of movement is desired. clues to the sources of ground-water recharge, the VERIFICATION STUDIES direction and rate of ground-water movement, and Verification of the analog model involves a com­ the characteristics of the geologic framework that parison of the model responses with historical re­ constitutes the ground-water reservoir. In the Yuma sponses. The respective responses for selected time area, variations in temperature with place and depth intervals and the corresponding actual observed or have been particularly useful in corroborating ver­ estimated changes in water level are shown in figures tical ground-water movement inferred from other 38-43. evidence. In addition, local high-temperature anoma­ The configuration of the change in water-level lies furnish supporting evidence for the presence of contours as inferred from field data and the response faults affecting water-bearing materials and also of the analog model are seen to be good in a general for the presence of zones of low hydraulic conduc­ sense, although the changes in water level as deter­ tivity in the alluvial deposits. mined from field data generally exceed the changes VARIATIONS IN TEMPERATURE WITH TIME in water level computed on the basis of the model Temperature of the ground water in the Yuma response. Differences are at a maximum for the area fluctuates seasonally above depths of 30-60 heavily irrigated areas of the Yuma Mesa because feet. The amplitude of the fluctuation decreases with the changes computed from field data include ver­ depth. At a depth of 4 feet, the seasonal range is tical head losses between the bottom of a well and about 12°-14°C substantially less than the 20°C the top of the coarse-gravel zone, whereas the model (36°F) range in average monthly air temperature response excludes these losses. Differences of 30 feet at Yuma (Sellers, 1960). At a depth of 10 feet in and more between water levels in shallow wells and well (C-9-24)llccc, a representative observation water levels in wells tapping the coarse-gravel zone well of the Yuma County Water Users' Association beneath the principal recharge areas on the Yuma in central Yuma Valley, the difference in tempera­ Mesa have been observed. However, with increasing ture from May to November 1967 amounted to a distance from the irrigated areas, the differences in little more than 6°C. At depths greater than 55 feet, head between water levels in shallow wells and the seasonal differences for the same period were those in wells that tap the coarse-gravel zone de­ less than 0.2°C, and even these small differences crease rapidly, so that at distances of a mile or more probably were at least in part instrumental or ob­ the differences are negligible. servational error (fig. 44). The historical changes and the changes indicated Trends in temperature that are not seasonal may by the model response for the periods 1957-62 and be significant where heavy pumping or application 1962-66 also agree reasonably well. of irrigation water have altered local patterns of RELIABILITY OF THE ANALOG MODEL ground-water movement. An example of this type of In view of the model's ability to duplicate reason­ change is provided by the record of well (C-9-23) ably well both the series of overall changes and the 20bdc, a U.S. Bureau of Reclamation drainage well intermediate changes that have occurred, the model, in eastern Yuma Valley (fig. 45). The temperature H114 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

32°45' =

UNITED STATER ll^ -^ -5 ^- - ^7PT~ Algpdones, v*^- MEXICO >x /MorelosDam SOUTH GILA VALLEY _____

EXPLANATION

______I /f ______Line of equal change in water level Alluvial escarpment Number indicates rise (+), in feet Fault Dotted where concealed Mountains and hills

32°15

FIGURE 38.-"-Changes in water level, 1925 to December 1957, as indicated by field measurements or as estimated. of the water pumped from this well, which is per­ February 1968, 14 months later. Except for about forated in the coarse-gravel zone, has decreased at a week in early December 1966, the well was pumped a diminishing rate from 28.9°C in late November continuously during this period. The decrease in tem­ 1966 when the pump was started to 27.8°C in early perature probably resulted from increasing leakage GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H115 114°45' 30'

32°45

Line of equal change in head Number indicates increase (+), in head, in feet

32°15'

FIGURE 39. Changes in head in the upper transmissive layer, 1925 to December 1957, as indicated by responses of the ana'og model. of cooler water from the upper, fine-grained zone gravel zone and into the upper zone. The water in into the coarse-gravel zone as the pumping contin­ the wedge zone in this area is substantially warmer ued. Before the pumping began, the vertical com­ than that in the overlying zones. Thus, the tempera­ ponent of ground-water movement was entirely up­ ture record furnishes corroborative evidence that ward, from the wedge zone through the coarse- the drainage well is fulfilling its designed function, H116 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

114°45' 114°15'

32°45'

Line of equal change in water level Number indicates rise (+),infeet

Mountains and hills

Area of shallow bedrock

Alluvial escarpment

Fault Dotted where concealed

32°15'

FIGURK 40. Changes in water level, December 1957 to December 1962, as indicated by field measurements. which is to lower the water table by causing down­ VERTICAL VARIATIONS IN TEMPERATURE ward leakage from the upper, fine-grained zone into In dense rocks, where porosity is small and little the coarse-gravel zone. ground-water movement occurs, the temperature GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H117

114M5'

32°45' -

-UNITED_STATES_- MEXICO

Line of equal change in head Alluvial escarpment Number indicates increase (+) or decrease ( ) in head, in feet Fault Dotted where concealed

Mountains and hills

Area of shallow bedrock

FIGURH 41. Changes in head in the upper transmissive layer, December 1957 to December 1962, as indicated by responses of the analog mode'.. generally increases with depth. However, geothermal Gradients are relatively large in fine-grained de­ gradients are modified greatly or even reversed by posits of small to moderate permeability like those significant circulation of ground water, such as penetrated by U.C. Geological Survey test well occurs in most of the Yuma area. (C-8-23)33cdd (LCRP 13) in Yuma (fig. 46). In H118 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

114°45' 30'

32°45'

30'

EXPLANATION

Line of equal change in head Alluvial escarpment Number indicates increase (+) or decrease ( ) _____...... in head, in feet Fault _/57v Dotted where concealed

Mountains and hills

0 5 10 MILES I I I I I I I Area of shallow bedrock

32°15'

FIGURE 42. Changes in water level, December 1962 to December 1966, as indicated by field measurements. this well, the average gradient between depths of (about 100 ft) cited by Gutenberg (1959) as an 80 and 730 feet is 1.3°C per 100 feet not greatly average for many oil fields. different from the value of 1.0°C per 30 meters Gradients are usually smaller in permeable de- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H119

114M5' 30' 114 8 15'

32°45'

30'

Line of equal change in head Alluvial escarpment Number indicates increase (+) or decrease ( ) _____...... *^~*» ^ *' in head, in feet Fault _^->. Dotted where concealed

Mountains and hills

Area of shallow bedrock 0 5 I I I I I I

32°15'

FIGURE 43. Changes in head in the upper transmissive layer, December 1962 to December 1966, as indicated by responses of the analog model. posits where ground-water circulation is more rapid Geological Survey test well (C-ll-24)23bcb (LCRP and where few beds of clay and silt are present to 10), which penetrated mostly permeable sand and impede vertical movement. For example, in U.S. gravel, the range in temperature from the water H120 WATER RESOURCES OF LOWER COLORADO RIVER^SALTON SEA AREA

Water level 7.16 ft 5-5-6?x Water level 8.15 ft -Water level 7.28 ft 11-3-67 2-3-68 10

February 3, 1968 November 3, 1967 20

30

40

50

60

70

80

Measurements made with two Whitney thermi­ stors, both of which were calibrated with a mercury thermometer. Readings made at 90 depth intervals of 2 feet, starting at a depth of 10 feet below measuring point (8.75 ft be­ low land surface)

100 Date Thermistor Readings to nearest °F °C 5-5-67 USBR 61401 0.1 0.06 11-3-67 USGS W-276594 .1 .06 110 2-3-68 USBR 61401 .05 .03

120

130 20 21 22 23 24 25 26 27 28 TEMPERATURE OF WATER, IN DEGREES CELSIUS

FIGURE 44. Temperature profiles in well (C-9-24)llccc for May and November 1956 and February 1968. table at a depth of about 80 feet to the bottom of Reversed geothermal gradients occur seasonally the well at a depth of more than 1,000 feet is no within about 30 feet of the land surface, owing to more than 0.3°C. summer warming of the shallow water. However, GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H121

29 ;Pump off about 1 week; turned on again Dec. 12 ~Pump on Nov. 27

<0 u.2 28

27 Nov. j Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May 1966 1967 1968

FIGURE 45. Change in temperature of water pumped from well (0 9 23)20 bdc (USER drainage well YV 13) from November 1966 to February 1968. the reversed gradients locally extend to greater advection from various sources. depths and persist throughout the year, as, for Temperatures representative of the coarse-gravel example, at well (C-9-24)llccc cited earlier (fig. zone or, where that zone is missing, of materials at 44). These perennial reversed gradients indicate equivalent depths below the water table (about either that the deeper water has a cooler, more dis­ 100-150 ft) were measured in nearly 500 wells tant source than the shallower water, or that the (appendix A). In roughly one-third of these wells ground at the well site is warmer on the average chiefly irrigation and drainage wells the tempera­ than that in most of the surrounding area. The tures were measured at the discharge pipe with a latter situation commonly occurs where the well is mercury thermometer while the wells were pumping. in a bare, uncultivated, or paved area bordered by In the rest of the wells the temperatures were mea­ irrigated fields or orchards. sured with a thermistor or a maximum thermometer At many places, particularly in the irrigated part inside the casings at depths corresponding to the of Yuma Mesa and along the line of drainage wells middle of the coarse-gravel zone. In some places, in northeastern Yuma Valley, the geothermal gra­ particularly on the "Upper Mesa" and "Fortuna dients have been altered greatly from natural con­ Plain," temperatures at depths about 100-150 feet ditions, owing to vertical movement of ground water below the water table were estimated by extrapola­ induced by heavy applications of irrigation water tion from water-table temperatures. Geothermal and by large-scale pumping from wells. Some of the gradients observed in the nearest wells having such observed conditions are described in the next section. data were used. The configuration of the tempera­ ture lines is uncertain beneath most of the "Upper AREAL VARIATIONS IN TEMPERATURE Mesa" because of the paucity of reliable data (fig. The most useful and informative temperature 47). data proved to be the areal variations in tempera­ The coolest water in the coarse-gravel zone occurs ture of the water in the coarse-gravel zone (fig. 47). beneath the river valleys. At most places in the The zone is sufficiently deep so that seasonal fluc­ valleys the temperature ranges from about 21 °C to tuations in temperature are negligible, yet shallow 23°C; a few areas underlain by somewhat warmer enough so that the temperature of the water would water are considered to be warm anomalies, as ex­ not be much different from the mean annual air plained farther on. The usual temperatures are temperature were it not affected by conduction or slightly higher than the mean annual air tempera-

507-243 O - 74 - 9 H122 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA perature at Yuma (northwestern Yuma Mesa) for the period 1893-1957 was 22.4°C, as compared with 20.7 °C for the Yuma Valley station for 1906-53 (Sellers, 1960). Beneath parts of Yuma Mesa, deep Water table. infiltration of irrigation water probably has cooled the water in the coarse-gravel zone to a temperature 100 below what it was naturally. The close correspond­ ence of the boundaries of the cooler water and the boundaries of the irrigated area at many places sup­ ports this inference. (Compare figs. 2 and 47). 200 In general, the warmest water in the Yuma area occurs beneath "Upper Mesa" and contiguous parts Temperature measured of "Fortuna Plain" and "Gila Mesa." The coarse- with a WIDCO logger gravel zone is absent in most of those areas, but at using a thermistor sensor equivalent depths below the water table the tem­ 300 peratures (which are largely extrapolated from temperatures at the water table and therefore some­ what uncertain) range from about 25°C along the northwest edge of "Upper Mesa" to more than 36°C at several places (fig. 47). In large part, these higher 400 temperatures are a consequence of the fact that the water table is deeper beneath "Upper Mesa," "For­ tuna Plain," and "Gila Mesa" than it is elsewhere in the Yuma area. The geothermal gradient in un- saturated material is generally greater than that in 500 saturated material, so that depth to water has a pronounced effect on temperatures below the water table; the average geothermal gradient for dry ma­ terials beneath "Upper Mesa" is about 2.8°C per

600 100 feet. After taking into account the effects of the vari­ able depths of the water table and of recharge from irrigation, as described above, a number of warm anomalies can be delineated throughout the area 700 (fig. 47). Most of these anomalies appear to be re­ lated to faults or fault zones such as the northwest­ ward bulge of warm water beneath central Yuma Mesa and east-central Yuma Valley which is chiefly on the northeast side of the buried trace of the 800 20 25 30 35 Algodones fault. Some anomalies may reflect hot zones in the pre-Tertiary crystalline rocks that are TEMPERATURE OF WATER, IN DEGREES CELSIUS not related to faulting, but these possible sources of FIGURE 46. Temperature profile in well (C-8-23)33cdd (LCRP 13) for heat cannot be evaluated with the available data. March 12, 1863. Other anomalies related to faults or suspected faults ture at the Yuma Valley weather station in northern are those west of the northern Gila Mountains, in Yuma Valley, which was 20.7°C for period 1906-53 north-central "Bard Valley," along the west edge of (Sellers, 1960). Yuma Mesa in Yuma, on Yuma Mesa about a mile With certain exceptions, discussed later, the water west of the west edge of the "Upper Mesa," and on in the coarse-gravel zone beneath Yuma Mesa is southern Yuma Mesa 1-3 miles north of the south­ 2°-3°C warmer than that beneath the adjacent erly international boundary. The warm water in valleys. The higher temperatures beneath the mesa these areas probably has resulted from upward probably result from the greater average depth of movement from the wedge zone into the coarse- the water table and the somewhat higher mean gravel zone induced by the partial damming effect annual air temperature; the mean annual air tem­ of the faults. Where the anomaly is related to the GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H123

114°45' 30'

32°45

28 Line of equal temperature of water, Alluvial escarpment in degrees Celsius Dashed where approximately located Dotted where concealed

Warm anomaly

Mountains and hills

Area of shallow bedrock Coarse-gravel zone absent

FIGURE 47. Temperature of ground water in coarse-gravel zone or at equivalent depth below the water table, 1965-68. Algodones fault, the temperature data indicate that of the buried bedrock ridge may also account for the barrier effect of the fault extends farther north­ the northwestern part of the anomaly. west than can be demonstrated unequivocally from Not all the warm anomalies are caused entirely or water-level and geologic data. However, the effect even partly by faults acting as ground-water bar- H124 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA riers. Alluvium that is less transmissive than that the interpretation of the second factor the chemi- in surrounding areas may account for the two call changes is facilitated by the fact that the anomalies in western "Upper Mesa," for the broad relatively shallow ground water beneath the irri­ anomaly at the northwest corner of Yuma Mesa in gated areas is derived mainly from recent recharge Yuma, and possibly for the southwest-trending band from the Colorado River by way of diversions for of slightly warmer water in south-central Yuma irrigation. The following discussion considers the Valley (fig. 47). processes of chemical change that produce the types Another major anomaly is the elongate, some­ of ground water observed beneath the irrigated what irregular band of warm water that extends areas, starting with the Colorado River as the recent along the west margin of northern Yuma Mesa and source of ground-water recharge. the east margin of the adjacent Yuma Valley. Two thermal maxima occur within the band: a northern CHEMICAL CHANGES IN GROUND WATER DERIVED one in the southwest part of Yuma, where the maxi­ FROM THE RECENT COLORADO RIVER mum temperature exceeds 30 °C and a southern one An appraisal of ground water beneath the irri­ just south of the first major westward bend in the gated areas as chemically altered recent Colorado escarpment along the west edge of Yuma Mesa River water requires consideration of the chemical south of Yuma, where the maximum temperature processes capable of altering the river water to is a little less than 29°C (fig. 47). observed types of ground water, and also the estab­ The higher temperatures in this band result from lishment of criteria for recognition of the altered the upward movement of ground water from the river water. In the approach used, recent Colorado wedge zone through the coarse-gravel zone and into River water is assumed to have been evaporated and the upper, fine-grained zone, from which it is dis­ subjected to specified chemical changes while it evap­ charged by evapotranspiration or by surface drains. orated. Hypothetical chemical analyses computed This movement has taken place since irrigation from a 25-year weighted-average analysis of Colo­ began on Yuma Mesa and the associated ground- rado River water, and from two single-year weighted water mound began to form. However, the northern averages, then serve as examples that suggest how thermal maximum, in Yuma, probably results also ground water represented by actual analyses might from natural upward movement caused by a con­ have been derived (table 15). cealed fault barrier, as mentioned earlier. The assumption that the recent Colorado River Pumping of drainage wells along the east margin (indicated by the chemical-quality records at Im­ of Yuma Valley has accelerated the upward move­ perial Dam for 1941-65) is the source of ground- ment by providing additional discharge from the water recharge is most nearly valid for the rela­ coarse-gravel zone with a consequent lowering of tively shallow ground water in the upper, fine­ head in that zone, but the pumping has also induced grained zone and the coarse-gravel zone beneath the downward leakage into the upper part of the coarse- irrigated areas of the valleys and Yuma Mesa. gravel zone. The downward movement of relatively Deeper, older ground water beneath those areas and cool irrigation water from the upper, fine-grained ground water outside the irrigated areas were de­ zone has lowered the temperature in the coarse- rived from the Colorado River before regulation by gravel zone adjacent to the drainage wells, as illus­ upstream reservoirs and from the Gila River when trated by the record for well (C-9-23)20bdc (fig. it was still a live stream near Yuma. These sources 45) and by less-abundant data for some of the other of recharge may have differed substantially in wells. chemical character from recent Colorado River water. The same chemical processes as those occur­ CHEMICAL QUALITY OF GROUND WATER ring in the younger ground water probably were Chemical analyses of ground water in the Yuma operative in the older ground water, although the area indicate marked differences from place to place actual changes would have been different from those in the percentage and concentration of the six ionic described below. constituents that make up the bulk of the dissolved The chemical-change processes probably operative solids. (See appendix C; pi. 11). The chemical char­ in ground water in the Yuma area include: (1) Con­ acter of the ground water depends on (1) the chemi­ centration by evapotranspiration, (2) softening, (3) cal character of the source of recharge and (2) the carbonate precipitation, (4) sulfate reduction, (5) chemical changes that have occurred since the water hardening, (6) re-solution of precipitated salts, (7) entered the ground. Separation of the effects of oxidation of dissolved organic substances, and (8) these two factors is ordinarily difficult. However, mixing of waters of different chemical composition. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H125

TABLE 15. Hypothetical analyses of ground water resulting fr om specified chemical changes in Colorado River water

Relative Concen- Cal- Magne- Sodium Bicar- Sulfate Chloride Sum Hardness !Specific volume con- No. Description factor (Ca) (Mg) potas- (HCOs) Non- < luctance Percent sium Total carbon­ (micro- sodium (Na+K) ate imhos at 25°C) Milligrams per liter

Unchanged Colorado River water

1 _ _] 1941-65 1,000 1 94 28 110 165 309 93 730 350 214 1,120 40.6 2 1950 1,000 1 84 27 90 163 265 77 625 320 187 985 38.0 3 __ _ U956 1,000 1 106 34 142 173 375 128 872 404 262 1,340 43.4 Concentrated by evaporation, no other change

_ -1941-65 667 1.5 141 42 165 248 464 140 1,090 525 321 1,680 40.6 5 _ 500 2.0 188 56 220 330 618 186 1,460 700 428 2,240 40.6 6 __ _ . __ 1941-65 333 3.0 282 84 330 495 927 279 2,190 1,050 642 3,360 40.6 7 - - 250 4.0 376 112 440 660 1,236 372 2,920 1,400 856 4,480 40.6 8 - _ ___1950 250 4.0 336 108 360 652 1,060 308 2,500 1,280 748 3,940 38.0 9 . __ _ 1956 250 4.0 424 136 568 692 1,500 512 3,490 1,616 1,048 5.360 43.4

Concentration by evaporation with 50 percent softening

10 - - - 667 1.5 117 35 205 248 464 140 1,080 437 234 1,680 50.5 11 _ 1941-65 500 2.0 141 42 300 330 618 186 1,450 524 254 2,240 55.4 12 _ _ . 333 3.0 188 56 491 495 927 279 2,190 699 292 3,360 60.4 13 250 4.0 234 70 681 660 1,236 372 2,920 873 332 4,480 62.9 14 _ . _ _ 1950 250 4.0 210 68 583 652 1,060 308 2,560 803 269 3,940 61.2 15 250 4.0 264 85 846 692 1,500 512 3,550 1,010 442 5,430 64.6

Concentration by evaporation, precipitation of insoluble carbonates at 380 mg/1 HCOs

16 1941-65 333 3 255 76 330 380 927 279 2,060 951 640 3,180 43.0 17 250 4 313 93 440 380 1,236 372 2,640 1,160 853 4,040 45.1 18 1941-65 200 5 370 110 550 380 1,545 465 3,230 1,380 1,070 4,900 46.5 19 - _ _ 1950 200 5 328 106 450 380 1,325 385 2,780 1,250 942 4,250 43.8 20 _ 1956 200 5 424 136 710 380 1,875 640 3,980 1,620 1,310 6,020 48.8 Concentration by evaporation, bicarbonate ceiling 3SO mg/1, 25 percent sulfate reduction

21 ___ .. _ __ _ .1941-65 667 1.5 141 42 165 339 393 140 1,050 525 248 1,680 40.6 22 _ _ -. _ __ _1941-65 500 2.0 155 46 220 380 464 186 1,260 576 266 2,010 45.3 23 - . __ 1941-65 333 3.0 160 48 330 380 585 279 1,590 596 284 2,500 54.7 24 _ . __ _ 1941-65 250 4.0 162 48 440 380 696 372 1,910 603 292 2,970 61.3 25 __ -1941-65 200 5.0 161 48 550 380 795 465 2,210 598 286 3,420 66.7 26 __ _ 125 8 0 142 42 880 380 1,040 744 3,040 528 216 4,650 78.4 97 100 10.0 126 37 1,100 380 1,190 930 3,570 468 157 5,450 83.6 28 _ 1950 100 10.0 134 43 900 380 1,030 770 3,070 510 199 4,700 79.3 9Q 1956 100 10.0 135 43 1,420 380 1,430 1,280 4,500 515 204 6,860 85.7 As above but 33-1/3 percent sulfate reduction

30 _ - _ 1941-65 667 1.5 141 42 165 371 367 140 1,040 524 220 1,680 40.6 31 _ -. _ 1941-65 500 2.0 141 42 220 380 412 186 1,190 524 212 1,910 47.7 32 _ . 333 3.0 133 40 330 380 489 279 1,460 496 184 2,310 59.2 33 _ _ - __ _ 1941-65 250 4.0 121 36 440 380 548 372 1,710 443 138 2,680 68.1 34 _ . _ _ 1941-65 200 5.0 106 32 550 380 600 465 1,940 395 84 3,030 75.2 35 _ __ . _ 1941-65 125 8.0 57 17 880 380 736 744 2,620 212 0 4,040 90.0 36 _ _ - 1941-65 100 10.0 17 5 1,100 380 800 930 3,040 62 0 4,680 97.5 37 _ _ . _ _ 1950 100 10.0 48 16 900 380 720 770 2,640 188 0 4,090 91.2 38 . _ _ . _ 1956 100 10.0 18 6 1,420 380 1,000 1,280 3,910 68 0 6,010 97.8

As above but 40 percent sulfate reduction

39 __ ... 667 1.5 137 41 165 380 346 140 1,020 510 198 1,660 41.3 1941-65 500 2.0 129 39 220 380 371 186 1,140 482 170 1,830 49 8 41 _ _ . _ 1941-65 333 3.0 113 34 330 380 416 279 1,360 420 108 2,170 63.1 42 _ _ . _ 1941-65 250 4.0 92 27 440 380 445 372 1,570 342 30 2,470 73.9 43 _ . _ 1941 65 200 5.0 70 21 550 380 470 465 1,770 270 0 2,770 82.1 44 ___ . 1941 65 125 8.0 0 0 880 380 533 744 2,350 5 0 3,650 100.0 45 __ . _ _ 1941-65 100 10.0 0 0 1,100 609 560 930 2,900 0 0 4,560 100.0 46 _ __ . 1950 200 5.0 78 25 450 380 405 385 1,530 296 0 2,430 76.8 47 _ 1950 125 8.0 24 8 720 380 458 616 2,020 90 0 3,160 94.5 48 _ _ _ .. _ 1950 100 10.0 0 0 900 442 490 770 2,380 0 0 3,730 100.0 49 _ _ . _ _ 1956 200 5.0 71 23 710 380 580 640 2,210 273 0 3,460 85.0 50 _ . _ _ 1956 125 8.0 0 0 1,136 431 648 1,024 3,020 0 0 4.710 100.0 51 _ 1956 100 10.0 0 0 1,420 648 690 1,280 3,740 0 0 5,880 100.0 Concentration by evaporation, bicarbonate ceiling 380 mg/1, 40 percent sulfate reduction, hardening equivalent to sulfate equivalents increase resulting from evaporation

52 _ _ . 1941-65 667 1.5 147 44 147 380 346 140 1,010 548 237 1,660 36.9 53 _ . 1941-65 500 2.0 147 44 190 380 371 186 1,130 546 234 1,830 43 1 54 _ _ . 1941-65 333 3.0 142 42 279 380 416 279 1,350 530 219 2,170 53i4 55 1941-65 250 4.0 130 39 375 380 445 372 1,550 484 172 2,470 62.8 56 __ _ 1941-65 200 5.0 115 34 473 380 470 465 1,750 428 116 2,770 70.6 C7 1941-65 125 8.0 63 19 773 380 533 744 2,320 233 0 3,650 87.8 58 __ . _ 1941-65 100 10 0 20 6 980 380 560 930 2,690 74 0 4,200 96.7 59 _ __ . _ -1950 200 5.0 116 37 383 380 405 385 1,520 442 130 2,430 65.3 1950 125 8.0 76 25 628 380 458 616 1,990 292 0 3,160 82.4 61 _ __ . _ 1950 100 10.0 61 20 769 380 490 770 2,300 234 0 3,630 87.7 62 _ . _ 1956 200 5.0 127 41 612 380 580 640 2,190 486 174 3,460 73.3 63 _ . _ 1956 125 8.0 63 20 1,006 380 648 1,024 2,950 242 0 4,630 90.0 64 .._ _ __ 1956 100 10.0 19 6 1,270 380 690 1,280 3,460 73 0 5,400 97.4 H126 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

TABLE 15. Hypothetical analyses of ground water resulting from specified chemical changes in Colorado River water Continued Relative Conven- Cel- Magne- Sodium Bicar- Sulfate Chloride Sum Hardness Specific volume tration No. Description factor (Ca) (Mg) potas- (HCOa) Non- ductance Percent sium Total carbon- (micro- sodium (Ns+R) ate mhos at 26° C) Milligrams per liter Concentration by vaporation, bicarbonate ceiling 380 mg/1, 40 percent snlfate reduction, hardening until sodium equivalent concentration is reduced to chloride equivalent concentration 65 ______1941-66 667 1.5 180 54 91 380 346 140 1,000 672 360 1,660 22.8 66 ______.______-1941-65 500 2.0 187 56 121 380 371 186 1,110 698 386 1,830 27.3 67 ______.______1941-65 333 3.0 200 60 181 380 416 279 1,330 744 432 2.170 34.6 68 ______.______1941-65 250 4.0 208 62 241 380 445 372 1,520 774 463 2,470 40.4 69 ______1941-65 200 5.0 215 64 302 380 470 465 1,710 800 489 2,770 45.0 70 ______1941-65 125 8.0 233 70 483 380 533 744 2,250 869 558 3,650 54.8 71 ___ __.______1941-65 100 10.0 240 72 603 380 560 930 2,600 894 582 4,200 59.6 72 ______. 1950 200 5.0 192 62 250 380 405 385 1,480 723 421 2,430 42.6 73 _ ____ -._ __ __ 1950 125 8.0 206 66 400 380 458 616 1,940 788 476 3,160 524 74 ______. 1950 100 10.0 215 69 499 380 490 770 2,230 821 510 3,630 56.9 75 ______. ______1956 200 5.0 239 77 415 880 580 640 2,140 914 603 3,460 49.7 76 ______.______-1956 125 8.0 258 83 664 380 648 1,024 2,870 986 674 4,630 59.4 77 _ ____ .. 1956 100 10.0 269 87 830 380 690 1,280 3,350 1,030 718 5,400 63.9 1 Weighted average. The last three processes are not readily demon­ centration by evapotranspiration. Such concentra­ strated from analytical evidence and are not readily tion is indicated wherever all constituents in a well demonstrated from analytical evidence and are not water are nearly the same multiple of river-water considered further here. concentrations. If concentration by evapotranspira­ Several combinations of the fir^t five processes, tion is the only chemical change occurring, dissolved carried out to varying degrees, are listed in table ionic concentrations increase by the same multiple, 15, beginning with the weighted-average chemical but the percent sodium, which depends on the ratio analysis of the Colorado River at Imperial Dam for of sodium concentration to total cation concentra­ the period 1941-65. In addition, the effects of mod­ tion, both expressed in equivalents, does not increase. erate annual variations in the chemical character Thus, approximately equally increased ionic concen­ of the river water are shown by listing the calcu­ trations in ground water compared to concentra­ lated analyses of substantially evaporated ground tions of Colorado River water, and unchanged or water derived from the weighted-average river nearly unchanged sodium percentage, are indicative water for 1950, when the concentration of dissolved of evapotranspirative change. solids was low, and the analyses for 1956, when the Bicarbonate concentrations greater than 500 mg/1 dissolved-solids concentration of the river was high. are extremely rare in Yuma area ground water and Several series of hypothetical chemical analyses few analyses show bicarbonate concentrations as are given as illustrations of specified chemical proc­ great as 450 mg/1. These limits probably indicate esses, assuming that each process has operated con­ the level at which calcium carbonate precipitation tinuously, and that the ground water it represents begins. Recent Colorado River water has contained was sampled at specified evaporative volume reduc­ from 150 to about 175 mg/1 bicarbonate, which sug­ tions. Generally each series is ended when the speci­ gests that evapotranspiration by itself seldom ac­ fied chemical process results in hypothetical analyses counts for more than a threefold increase in ground- with one or more ionic concentrations greater or water concentrations as compared to river-water less than those commonly observed in the many concentrations. In order to allow for all possible actual analyses of ground water from the irrigated strictly evapotranspirative effects and not go be­ areas. A few series are carried beyond these end yond probable natural-process limits, the hypotheti­ points to illustrate particular hypothetical analyses. cal analyses were computed for as much as a four­ CONCENTRATION BY EVAPOTRANSPIRATION fold concentration by evapotranspiration but no Evaporation is loss of water to the atmosphere further. across an air-water interface. Transpiration is loss SOFTENING of water from plants by permeation through a cell Softening, the replacement of the hardness-caus­ membrane. In both processes (commonly lumped to­ ing constituents calcium and magnesium by a chem­ gether as evapotranspiration) a more concentrated ically equivalent amount of sodium, commonly oc­ residual solution remains. Because of the prevailing curs wherever hard water, such as Colorado River high temperatures and low humidity and the pres­ water, seeps through beds containing a large num­ ence of phreatophytes in the river valleys of the ber of clay-mineral particles. Softening is a Yuma area, probably very little water infiltrates particle-surface reaction between ions chemically from the Colorado River without considerable con­ attached to the clay-mineral particles and the ions GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H127 dissolved in the water. Although it can continue so other ceilings were considered and carried through long as dissolved calcium and magnesium ions in the the evaporation sequence, model analyses are given water are available for replacement, softening rare­ in table 15 only for the arbitrarily selected bicar­ ly removes all these constituents from the water. In bonate ceiling of 380 mg/1. the calculated analyses, softening is assumed to have Precipitation of insoluble carbonates with or with­ resulted in replacement of half the increases in cal­ out concentration by evaporation is best indicated by cium and magnesium resulting from a 50 percent an increase in percent sodium because, as calcium evaporation. However, softening may occur where and magnesium are lost by precipitation and sodium there is little or no evaporation. is not, the relative amount of sodium increases. For Softening and carbonate precipitation the next the same reason, the ratio of chloride to bicarbo­ change considered both result in reduction in calci­ nate increases. um and magnesium concentrations in water, but they Softening (described in the previous section) also are almost mutually exclusive and probably can­ results in an increase in percent sodium but not in not go on simultaneously. They can be distinguished an increase in the ratio of chloride to bicarbonate. by the fact that carbonate precipitation results in Also, as the loss of dissolved solids caused by pre­ decreases in calcium, magnesium, and bicarbonate, cipitation of insoluble carbonates is often consid­ whereas softening results in decreases in calcium erable, and as there is always a small increase in and magnesium but not of bicarbonate. dissolved-solids content resulting from softening, Softening is always accompanied by an increase the two processes can ordinarily be separated by in percent sodium. Because the equivalent weight of inspection of the chemical analyses. sodium is somewhat greater than that of calcium and substantially greater than that of magnesium, SULFATE REDUCTION there is usually a somewhat greater increase in Most analyses of ground water from the irrigated dissolved-solids concentration in water which is areas indicated lower ratios of sulfate to chloride both concentrated by evaporation and softened than than those characteristic of recent Colorado River in water which is merely concentrated by evapora­ water. High-sulf ate water is rare; even the analyses tion. representing the greatest concentration by evapo- CARBONATE PRECIPITATION transpiration do not indicate sulfate concentrations Water containing appreciable quantities of bi­ nearly high enough for precipitation of calcium sul­ carbonate and either of the alkaline earth ions cal­ fate to occur. Also, although hydrogen sulfide was cium or magnesium precipitates the corresponding not determined in the chemical analyses, hydrogen alkaline earth carbonate when sufficiently evapo­ sulfide odor was reported when many wells were rated. Water containing both alkaline earths, such fumped. For these reasons, sulfate reduction is as Colorado River water, can precipitate mixed salts. probably a major process occurring in Yuma area The carbonate precipitation is indicated in pipes and ground water. boilers by the formation of scale. Carbonate precipi­ Sulfate reduction is an incompletely understood tation is indicated wherever decreases in calcium and process, which probably occurs in several ways under magnesium concentrations, in equivalents, are different conditions. Some may occur wherever or­ equalled by decreases in bicarbonates, in equivalents. ganic matter is in long-continued anaerobic contact However, because of temperature, pressure, and with water containing sulfate. The process is more combination effects caused by other dissolved ions, likely associated with the natural metabolic proc­ the actual bicarbonate-concentration level at which esses of a widely distributed group of sulfate- insoluble carbonate precipitation begins is not reducing bacteria. These bacteria derive energy from readily predictable. oxidation of organic compounds and in the process Analyses from frequently sampled wells suggest obtain oxygen from the sulfate ions in water. Sul­ that individual ceilings on bicarbonate concentration fate reduction by the bacteria probably involves a do exist, depending in some manner on well environ­ series of steps in which polysaccharides and other ment, and that the concentration levels at which complex organic compounds are depolymerized, hy- calcium and magnesism carbonate loss becomes an drolized, and oxidized simultaneously with the re­ important control on dissolved-solids concentration duction of sulfate ion to sulfide ion or hydrogen may range from less than 200 mg/1 to more than sulfide. 450 mg/1. But after precipitation begins, the differ­ Starting with cellulose, the organic substance ent bicarbonate-ceiling levels apparently have little (polysaccharide) making up most of the cell walls effect on the general pattern of chemical change of plants, the complete process can be represented occurring with evaporation. Therefore, although by the following steps: H128 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA 1. Depolymerization of the cellulose to the monomer Moderate: Sulfate reduction nearly the same as that (sugar): shown by the 25-percent model analysis series. (CellToOjx * X'C6H1005 Considerable: Sulfate reduction nearly the same as 2. Hydrolysis of the monomer to methane and that shown by the 33-percent model-analysis carbon dioxide: series. C6H1005+H20 -* 3CHt+3C02 Substantial: Sulfate reduction nearly the same as 3. Reduction of sulfate ion to give bisulfide ion that shown by the 40-percent model-analysis or hydrogen sulfide: series. (a) S04+CH4 -» HS+HC03+H20 High: Apparent sulfate reduction considerably more (b) S04+2CH4 -> H2S+C03+H20 than 50 percent as indicated by sulfate concen­ Other reactions have been written in which hy­ trations less than 300 mg/1 but greater than drogen is an intermediate decomposition product 100 mg/1. which reduces the sulfate. Very high: Sulfate concentrations less than 100 An important point in considering sulfate reduc­ mg/1 with chloride concentrations equal to or tion is that for each chemical equivalent of sulfate greater than usual Colorado River concentrations. ion reduced, one chemical equivalent of carbonate or The rate of sulfate reduction apparently is not bicarbonate is formed. These newly formed ions often much less than 25 percent, because reduction must be allowed for in constructing model analyses at lesser rates would result in the presence of more of reduced waters. Generally the bicarbonate con­ sulfate relative to chloride than is indicated by any centration is controlled as explained previously. of the analyses of more concentrated ground water. Although sulfate reduction undoubtedly takes A 50-percent reduction rate would result in a sulfate place, its extent is variable and uncertain. Hypo­ level unchanged as chloride increases during evapo­ thetical analyses resembling a considerable number ration. A reduction rate greater than 50 percent of Yuma area ground-water analyses are produced would result in decreased sulfate concentrations as by imposing sulfate reduction at three rates in which chloride concentrations increase. 25 percent, 33 Vs percent, and 40 percent of the sul­ In computing hypothetical analyses produced by fate disappear each time the river water is evapo­ sulfate reduction the calcium and magnesium con­ rated by one half, with the reduction process being centrations are also lowered as the sulfate is re­ continued until the original volume is reduced by duced in amounts sufficient to maintain cation-anion nine-tenths. Some actual analyses indicate even balance, with the bicarbonate concentration main­ greater sulfate reduction. Thus, some show chloride tained at 380 mg/1. Comparison of hypothetical concentrations similar to those in recent river water analyses so produced with actual Yuma area ground- analyses but show sulfate concentrations much less water analyses indicates many close resemblances than those in the river water. Other analyses indi­ up to about a fivefold evaporative concentration. cate chloride concentrations substantially greater Beyond that concentration the quantities of dis­ than those in recent river water and sulfate con­ solved calcium and magnesium remaining in the centrations somewhat less than those of the river water begin to be so lowered that the model analyses water. Although either of these water types might become softer than most Yuma area ground water. be explained by imposing large sulfate reduction This difficulty disappears if. hardening, explained in rates on recently infiltrated river water, an environ­ the next section, is also assumed. ment that could produce rapid reduction on the HARDENING large amounts of water pumped by some wells does Hardening, the reverse of softening, is a base- not seem very likely. Thus it appears that the low- exchange process in which sodium ions dissolved in sulfate water may have been produced by slow sul­ water are replaced by calcium and magnesium ions fate reduction acting over a long period and may not attached to clay-mineral particles present in water­ be related to recent river water. bearing materials. Montmorillonite, which consti­ By comparing the sulfate and chloride concentra- tutes more than half the clay minerals in two sam­ trations in the Yuma area ground water with con- ples of older alluvium (p. H52), is noted for having trations that would have occurred if the original the highest cation-exchange capacity of any of the water was average Colorado River water, the appar­ common clay minerals (Robinson, 1962). Hardening, ent sulfate reduction in the ground water can be like softening, probably depends on clay-mineral described as follows: particle saturation. For this reason the hardening Slight: Sulfate reduction somewhat less than that reaction is likely to go to different completeness in shown by the 25-percent model analysis series. different aquifer locations. Hardening is a hypothesis GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H129 helpful in accounting for the presence of moderately and more individualistic chemical patterns as con­ high concentrations of calcium and magnesium in centration increases. ground water in which sulfate reduction appears to A general conclusion is that a dissolved solids have been considerable. Hardening is strongly sug­ value (or specific conductance) by itself is not a very gested by so-called calcium or magnesium chloride good guide as to how much the original volume may water. have been reduced by evaporation. For example, dia­ Two rates of hardening are considered in the gram 17 represents a reduction to one-fourth the series of hypothetical analyses (table 15). Sulfate original volume with 2,640 mg/1 dissolved solids. In reduction is assumed to be concurrent with evapo­ contrast, diagram 59 represents a volume reduction ration, but the sulfate concentration increases if the to one-tenth the original volume and 2,600 mg/1 dis­ reduction rate is less than 50 percent. In the first solved solids. series of analyses computed so as to allow for hard­ SUBDIVISION OF YUMA AREA FOR DESCRIPTION ening, the hardening is made chemically equivalent OF QUALITY OF WATER to the increase in sulfate concentration. The second series of analyses is calculated so that hardening Almost all information on chemical quality of occurs until sodium concentration is reduced to ground water in the Yuma area is limited to the equivalence with chloride concentration. Both series central part of the area, which includes the river of hypothetical analyses simulate some actual valleys, Yuma Mesa, and the northern parts of ground-water analyses, but the second series repro­ "Upper Mesa" and "Gila Mesa." In order to facili­ duces more actual analyses than the first. tate detailed description of differences in water quality, this central part is divided into four sub- SUMMARY OF HYPOTHETICAL ANALYSES areas which are further subdivided into a total of To summarize, the table of hypothetical analyses 19 sectors (fig. 49). In the descriptions of the sec­ represents the quality of the ground water that tors, references are made to place names not shown would be obtained from wells assuming that the in figure 49; these places are shown on the standard water infiltrated from the recent Colorado River U.S. Geological Survey ly^-mmute series topo­ and was evaporated to the degree indicated and sub­ graphic maps of the Yuma area. The four subareas jected to the particular chemical processes described. correspond in a general way to some of the subareas Limits on concentration or process rates used in described in the geomorphology section of the report preparing the table were chosen for descriptive pur­ (p. HIS) and together constitute the part of the poses and are not meant to imply that other limits Yuma area investigated most intensively. A brief or rates do not occur. Because of chemical consid­ generalized description of the chemical characteris­ erations, some of the processes are terminated after tics of the ground water in each of the water-bearing less concentration by evaporation than others. Thus units is given in the section on occurrence of ground the evaporation process and the combination of water. The present discussion is more detailed and evaporation and softening are terminated at the first is concerned chiefly with water-quality differences step and produce bicarbonate concentrations above in the coarse-gravel zone and, to a lesser degree, in 500 mg/1, because that level represents about the the upper, fine-grained zone and wedge zone. maximum observed in Yuma area ground water. Selected chemical analyses of ground-water sam­ To facilitate visual comparison of the model analy­ ples collected from wells in the Yuma area are given ses with analyses indicated in other figures in the in appendix C, arranged according to the four sub- report, selected chemical analyses from table 15 are areas and 19 sectors. In the discussion below, com­ shown diagrammatically in figure 48. parisons are made between the ground water in the The diagrams in figure 48 are arranged so that various sectors and present Colorado River water those in each row represent Colorado River water according to the hypothetical processes described which has been subjected to uniform chemical proc­ earlier. esses and those in each column have been evaporated to the same extent. Consequently, comparing the GILA VALLEY SUBAREA diagrams by rows or columns emphasizes different The Gila Valley subarea consists of all South Gila environmental effects. Generally speaking the dia­ Valley and the east leg of the L-shaped North Gila grams are not greatly different in shape up to a Valley (fig. 49). Because of the proximity of the twofold concentration increase, regardless of the relatively saline Gila River and Wellton-Mohawk chemical processes assumed. Thereafter, the various conveyance channel, this subarea is the part of the combinations of chemical processes produce more Yuma area most likely to have the salinity of the ffi I i W> o

IX 1.5X 2X 3X 4X 1 5>-l ^ 6" 730 1090 1460 2190 2920 Colorado River EXPLANATION Concentration by evaporation water AX_ Concentration by evaporation HC0 3 1.5X 4X -S04 10, 13V Cl Sum of dissolved solids, 1080 2190 2920 in milligrams per liter H Evaporated and softened 3X 4X 5X CQ O 2060 2640 3230 Cl Evaporated and precipitated M CQ 1.5X 2X 4X 5X 8X 10X O ^ 22 21 t-1 1050 1260 1590 1910 2210 3040 3570 3O Evaporated, precipitated, 25 percent sulfate reduction H

1.5X 2X 3X 5X 8X 10X C! 30 31, O

1040 1190 1460 1710 1940 2620 3040 Evaporated, precipitated, 33 1/3 percent sulfate reduction a o 1.5X 2X 3X 10X 39, 40

1020 1140 1360 1570 1770 2350 2900 H Evaporated, precipitated, 40 percent sulfate reduction V CQ

1.5X 2X 3X 5X 8X 10X

52 53 54^ 1130 1350 1550 1750 2320 2690 1010 CQ Same as above, plus hardening equal to net increase in sulfate H

1.5X 2X 3X 4X H 65 66 67, 1000 1110 1330 1520 1710 2250 2600 Same as above, except hardening until Cl Na in milliequivalents per liter

FIGURE 48. Diagrams representative of chemical character of water represented by selected chemical analyses in table 15. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H131

114°45 U4°15'

32°45

UNITED_STATES MEXICO

GILA VALLEY SUBAREA YUMA VALLEY SUBAREA 1. Gila Siphon sector 11. California sector 2. East sector 12. East sector Mountains and hills 3. East-central sector 13. Central sector 4. West-central sector 14. Flood way sector 5. West sector Area of shallow bedrock

UPPER VALLEY SUBAREA YUMA MESA SUBAREA 6. Laguna Valley sector 15. Fortum sector Alluvial escarpment 7. North Gila sector 16. Arizona Western sector 8. Bard sector 17. Citrus sector 9. The Island sector 18. City sector 10. Winterhaven sector 19. South sector

32°15'

FIGURE 49. Subareas and sectors described in section on quality of water and listed in appendix C. ground water increased by induced infiltration. The 1965 most of the subarea was irrigated with ground natural drain of the subarea is the Gila River to its water pumped from wells perforated in the coarse- mouth and west of there the Colorado River. Until gravel zone. The pumping undoubtedly caused some H132 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA infiltration of Gila River water and, since comple­ Formerly the North Gila Valley part of the sector tion of the unlined part of the Wellton-Mohawk con­ was irrigated by diversion from the Gila Gravity veyance channel across the eastern part of the sub- Main Canal, but since 1965 it has mostly been irri­ area, some infiltration from the conveyance channel. gated by pumping from recently drilled irrigation However, the hazard from induced infiltration was wells. The South Gila Valley part of the sector has partly offset by the leakage from the unlined Gila also mostly been irrigated from wells, although there gravity canal near the east end of the subarea, and has been some diversion from the Gila Gravity Main by the fact that most of the South Gila Valley was Canal. converted in 1965 to irrigation with Colorado River Quality-of-water information for the sector is water. mostly limited to analyses of samples from the Although recent analytical data indicate that the coarse-gravel zone. Chemical analyses of water mineral content of the ground water in the coarse- samples obtained from a well at a gravel-washing gravel zone in the Gila Valley subarea is greater, on plant at the east end of the sector, east of the Gila the average, than in any of the other subareas, in­ River, and from seven irrigation wells, of which two formation on the preirrigation chemical quality of are east and five are west of the river, when ar­ water is lacking so that it is not possible to estimate ranged from east to west, do not suggest any com­ how much of the present salinity of the water has position pattern that can be related to well location resulted from long-continued irrigation without alone. All the pumped water has been somewhat drainage. more mineralized than recommended for domestic Emplacement of irrigation canals has greatly use but has been less mineralized than water com­ changed the ground-water quality in some parts of monly used in the main part of South Gila Valley the Gila Valley subarea and has produced only small for many years to irrigate salt-tolerant crops. Sev­ effects elsewhere. Also, irrigation developments in eral of the wells were sampled more than once, and the South Gila Valley and adjacent parts of the it appears from successive analyses that there has Yuma Mesa produced effects which have extended to been an erratic but generally upward change in con­ only part of the subarea. Consequently, the subarea centration of the pumped water, particularly in is divided for detailed discussions into five sectors, chloride concentration. However, none of the sam­ each of which differs in some respects from neigh­ pled water has reached concentration levels recently boring sectors. prevalent in the lower Gila River or the Wellton- Mohawk Conveyance Channel. GILA SIPHON SECTOR In the future, water pumped from wells probably The east leg of the North Gila Valley and a small will contain increments derived from the Gila Gravi­ area east of the south-flowing reach of the Gila ty Main Canal, Gila River, and Wellton-Mohawk River immediately downstream from the Gila Gravi­ Conveyance Channel, and from recirculation of ap­ ty Main Canal Siphon are combined in the Gila plied irrigation water. The proportions derived from Siphon sector of the Gila Valley subarea. The un­ these sources will vary with place and time, so that lined Gila Gravity Main Canal, which carries Colo­ prediction of future water quality is not possible. rado River water, is at the north boundary of the However, the average concentration of dissolved sector and turns southward across the sector near solids and chloride probably will increase at sites its eastern boundary. The Gila River, which gener­ near the Gila River. ally contains water three to four times as concen­ trated as the canal water and with relatively more EAST SECTOR chloride, is the natural drain and flows southward The east sector of the Gila Valley subarea lies east across the sector from the Gila Siphon, then bends of County Avenue 10E and south of the Gila Siphon west at the south edge of the sector. The Wellton- sector, in R. 21 W. of the Federal land net in Ari­ Mohawk Conveyance Channel, which was placed in zona. The sector is too far from the irrigated area use in 1961 and which is unlined across the sector, on Yuma Mesa for the water quality to be affected flows south from the siphon and turns west south of by the water-table mound under the mesa. Water the bend in the Gila River. The salinity of the water levels and water quality have been mainly affected in the conveyance channel is controlled almost entire­ by the transition from limited development on the ly by selective pumping of drainage wells in the east side of the sector to complete irrigation on the Wellton-Mohawk area to the east but is generally west. The Gila Gravity Main Canal, which traverses greater than that in the Gila River although of the sector diagonally from northeast to southwest, is somewhat similar composition. a possible source of infiltrating water. Before the GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H133

recent change to irrigation with surface supplies in Information about the wedge zone is limited, but the western part of the sector, pumpage of ground near-uniformity of water-quality characteristics in water was sufficient to prevent a shallow water table, one sample from a test well in the northern part of and the recent expansion of irrigation east of the the sector, and samples from three deep supply canal may keep the water table far enough below the wells at the south edge of the sector suggest the land surface to prevent salinization of soils and presence of water of relatively low salinity in the ground water. There are no drainage wells in the wedge zone under a considerable part, and perhaps area, although one is just outside of it on the all, of the sector.

southwest. WEST-CENTRAL SECTOR All chemical analyses from the sector represent water from the coarse-gravel zone. During the past The part of South Gila Valley bounded by County few years the mineral content of the water has been Avenues 4E and 7E, the Gila and Colorado Rivers, higher than in most other parts of the Gila Valley and the Yuma Mesa escarpment is called the west- subarea (pi. 11). In general, the water has been of central sector of the Gila Valley subarea. The sector the mixed chloride sulfate type in which the ratio of is immediately north of the citrus sector of the chloride to sulfate is greatest in the most concen­ Yuma Mesa subarea, and, as a result, both water trated samples. levels and water quality have been considerably EAST-CENTRAL SECTOR affected by irrigation on the mesa. The part of the South Gila Valley bounded by All the original nine drainage wells drilled for the County Avenues 7E and 10E, the Gila River, and the U.S. Bureau of Reclamation to control water levels escarpment at the north edge of Yuma Mesa consti­ in South Gila Valley are in the southern part of the tutes the east-central sector of the Gila Valley sub- sector. Periodic analyses of water samples collected area. Factors controlling quality of water in the from these wells have indicated a pattern of slowly sector are mostly like those in the east sector. How­ declining salinity with long-continued pumping. ever, infiltration of canal water probably has con­ Analyses of samples obtained from irrigation wells siderably less influence on the quality of the ground suggest that usual concentrations north of the drain­ water because the Gila Gravity Main Canal bounds age wells may be less than those in the vicinity of the sector for only about 1 mile along its southeast the drainage wells. However, some of the irrigation corner. The intensely irrigated part of Yuma Mesa wells appear to have produced water of slowly in­ begins about 1 mile southwest of the west edge of creasing salinity. Dissolved-solids concentrations the sector. However, this irrigated area is sufficient­ throughout most of the sector have ranged from ly far away so that the deep seepage from the irriga­ 1,800 to 3,600 mg/1, with fewer wells yielding con­ tion probably has not affected the water quality of centrations above 3,600 mg/1 than in the east-central the east-central sector as much as it has affected the sector. Samples obtained from a domestic well, a sector immediately west. public-supply well, and a test well (appendix C, The east-central sector, like most of the remainder analyses 56a, 66, 87a, b, c) indicate that the water of South Gila Valley, was irrigated for many years in the wedge zone is less mineralized than the water by pumping from wells perforated in the coarse- in the coarse-gravel zone. gravel zone but has been converted to primary de­ WEST SECTOR pendence on Colorado River water. Therefore, re­ The part of South Gil-a Valley between County cent ground-water-quality conditions are probably Avenue 4E and the city of Yuma, in R. 23 W. of the transient and may not closely resemble conditions Federal land net for Arizona constitutes the west which will exist after a few years. sector of the Gila Valley subarea. Several factors Many analyses of water pumped from both irriga­ that influence the patterns of ground-water move­ tion wells and new drainage wells in the sector indi­ ment probably affect the water quality in the sector. cate a general southward increase in the mineral The sector is south of the Colorado River and west content of the water in the coarse-gravel zone (pi. of the mouth of the Gila River, so the local infiltra­ 11). Sodium and chloride are invariably the domi­ tion from the river channel probablv is less saline nant constituents, but their relative amounts in­ than in the sectors farther east. Pumping of ground crease as total salinity increases. Water from some water for irrigation in The Island across the Colo­ of the wells has had fluctuating concentrations ap­ rado River to the north may reduce water movement parently caused by different duration of pumping south and southwest. The deposits flanking the periods and by simultaneous pumping from other buried slopes of "Yuma Hills" on the west side of wells. the sector are less permeable than those to the north H134 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

and east (fig. 25). The east half of the sector is Most of the remainder of "Laguria Valley" is low north of the citrus sector of Yuma Mesa, but the lying and swampy so that chemical processes just west half is north of the urban area of Yuma. below the water table may be like those in Mittry Chemical analyses of water samples obtained from Lake. Analyses of samples obtained from four hand- irrigation and drainage wells in the sector show the auger holes suggest that two patterns of chemical general southward increase in salinity that also oc­ change occur in the shallow deposits on both sides of curs farther east (pi. 11). However, the analyses the Colorado River. Two of the analyses suggest also indicate an increase in salinity toward the west concentration by evaporation, slight sulfate reduc­ and southwest, which suggests that recirculation of tion, and considerable softening. The other two indi­ pumped water has been greater in the southwest cated greater concentration by evaporation, moder­ corner of the sector than elsewhere in South Gila ate sulfate reduction, and hardening instead of Valley. softening. Nevertheless all samples contained less UPPER VALLEY SUBAREA than 1,600 mg/1 dissolved solids. The upper valley subarea is the part of the Yuma A well at the Imperial Irrigation District's Im­ area where water quality in both the upper, fine­ perial Camp, probably screened in the coarse-gravel grained zone and the coarse-gravel zone is most zone, yields water very similar in composition and nearly related to the average quality of the Colorado concentration to Colorado River water. Water ob­ River. The subarea comprises "Laguna Valley," tained from the coarse-gravel zone at test well LCRP "Bard Valley," and the western part of North Gila 14 just north of Laguna Dam is comparable to re­ Valley. The Colorado River flows through the east­ cent Colorado River water (appendix C, analysis ern part of the subarea and forms most of its south­ 206a). Thus, water of the Colorado River type may ern boundary. The Ail-American and Gila Gravity be present in the coarse-gravel zone in much of the Main Canals are emplaced mostly on cuts along the valley. lower parts of the slopes at the sides of the valleys Analyses of samples obtained from the mud scow and are about 20-40 feet higher than the Colorado during drilling of LCRP 14 did not show the pres­ River. Consequently, ground-water movement is ence of water of better quality below the coarse- mainly away from the two canals toward the river. gravel zone like that found in "Bard Valley" to the Most of the subarea is irrigated with Colorado southwest. Water pumped from the nonmarine sedi­ River water except for The Island sector, where irri­ mentary rocks perforated after the well was com­ gation is by pumping from wells screened in the pleted at depths of 470-490 feet was the most saline coarse-gravel zone. Thus, most of the recharge in of any water sampled in the entire upper valley area, the subarea is Colorado River water infiltrating with 3,420 mg/1 dissolved solids, 1,450 mg/1 chloride, from the two principal canals or their diversions. and 660 mg/1 sulfate (appendix C, analysis 206b). In order to describe local conditions, the upper Water of this character could not have been formed valley subarea is subdivided into five sectors. The from recent Colorado River water without being "Laguna Valley" and the North Gila Valley are concentrated by evaporation "about 10 or 12 times treated as individual sectors, whereas "Bard Valley" and being subjected to substantial sulfate reduction. is subdivided into three sectors termed the Bard sec­ It is difficult to explain the quality of the water at tor, The Island sector, and the Winterhaven sector. this site except by assuming that the water has been "LAGUNA VALLEY" SECTOR in the sediments for a long time. The "Laguna Valley" sector, which is bisected by NORTH GILA SECTOR the Colorado River, includes the ovate part of the The North Gila sector, which is east of the Colo­ Colorado River flood plain between the All-American rado River across from the more comprehensively Canal and the Gila Gravity Main Canal above La­ sampled Bard and The Island sectors and immedi­ guna Dam and below Imperial Dam. Before the ately downstream from the "Laguna Valley" sector, construction of Hoover Dam most of the sector includes the part of North Gila Valley irrigated with probably was flooded every year. Mittry Lake, a Colorado River water. The sector contains no irri­ permanent water body between the river and the gation wells or other large-capacity wells in use. Gila Gravity Main Canal, is continually fed by Consequently, appraisal of water-quality variation ground-water seepage. Analyses of several samples is based on analyses of samples of water obtained of outflow from Mittry Lake indicate that evapo- from small domestic and stock wells, auger-test transpiration has concentrated the lake water to two wells, and a U.S. Bureau of Reclamation test well or three times as much as the river and that mod­ which may not have been pumped long enough for erate sulfate reduction occurs in the lake. stabilization of water quality, and on the assumption GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H135 that test wells LCRP 14 and 23, which are in ad­ fate reduction (appendix C, analysis 231a). A well jacent sectors, indicate conditions in this sector. at the San Pasqual Valley School was perforated The data indicate that ground water containing from 120 to 204 feet and yielded water closely re­ between 900 and 1,800 mg/1 dissolved solids can be sembling 1950 Colorado River water which had been obtained in most of the sector, although water con­ concentrated about four times, had undergone mod­ taining as much as 2,500 mg/1 dissolved solids and erate sulfate reduction, and had been considerably relatively high in chloride may be present locally in hardened (appendix C, analysis 241). the upper, fine-grained zone. Water of better quality than that represented by the analyses may be gen­ THE ISLAND SECTOR erally present in the wedge zone, and the best water The Island sector includes the part of "Bard Val­ is probably near the Colorado River. Most of the ley" south and southeast of the Bard sector that is sampled water appears to be Colorado River water not supplied with Colorado River water by a canal only moderately altered by concentration and system. The sector, somewhat larger than the aban­ softening. doned Colorado River meander cutoff known as The Island, contains a considerable acreage irrigated BARD SECTOR The Bard sector is the part of "Bard Valley" from wells and scattered acreages which are either downstream from Laguna Dam, north of The Island, covered with small sand dunes or overgrown with phreatophytes and which are not irrigated. Infor­ and east of the Yuma Main Canal. Chemical analy­ mation about shallow water is not available for the ses of samples of water obtained from auger test sector, but such water is probably variable in com­ wells drilled along washes outside the sector, a short position and more highly mineralized than the water distance north of the All-American Canal, are in­ in the coarse-gravel zone because of concentration cluded in the tabulation (appendix C) because they by evapotranspiration and because there is no pro­ indicate the presence of water similar to that ob­ vision for drainage in the sector. tained from auger test wells on the valley side of Chemical analyses of water samples obtained from the canal. Most of the Bard sector is irrigated with 13 irrigation wells, probably all perforated entirely Colorado River water, although strips of unculti­ vated land overgrown with phreatophytes are scat­ or mainly in the coarse-gravel zone, indicate that tered along the All-American Canal and laterals. concentrations of dissolved solids in the pumped Water quality along the east margin of the sector water ranges from about 900 to 1,900 mg/1. Some of the analyses indicate only moderately altered is probably similar to that indicated, by test wells Colorado River water, slightly concentrated by LCRP 14 and 23 which are close by but in other sec­ tors. Water samples obtained from scattered farm evaporation, whereas others suggest more than 50 percent sulfate reduction and several times wells and auger test wells mostly tapping the top of the coarse-gravel zone indicate only moderate varia­ concentration. bility of water-quality patterns. The composition Test well LCRP 23 at the northeast corner of The ranges from water like Colorado River water to Island sector probably indicates the general varia­ water from the river moderately evaporated and tions in water quality with depth in parts of the Bard and North Gila sectors as well as in The Island with somewhat reduced sulfate. Nine samples ob­ tained from very shallow house wells used by Indi­ sector. Water bailed from this well at 133 feet dur­ ans at uncertainly designated sites in the western ing drilling was somewhat like evaporated Colorado part of the sector indicate that the shallow water is River water (appendix C, analysis 243a). Samples generally more mineralized than Colorado River obtained when pumping from perforations extend­ water; this is likely to be true for shallow water ing from a depth of 120 to 548 feet represent a mix­ throughout most of the sector. ture of water from the wedge zone and the coarse- A well drilled into the coarse-gravel zone a short gravel zone. This water contained less than 600 distance east of the Yuma Main Canal near Indian mg/1 dissolved solids and was like highly reduced Hill yielded water similar to recent Colorado River, Colorado River water (appendix C, analysis 243c). which suggests that such water might be available Water from the interval 634 to 694 feet, which came in favorable areas close to many of the canals. U.S. from the Bouse Formation (marine), was higher in Bureau of Reclamation test well CH-8, which pene­ concentration than the river water and contained trated a buried volcanic hill (basalt or basaltic an- much more chloride and somewhat less sulfate than desite), yielded water containing 1,380 mg/1 dis­ the river water (appendix C, analysis 243b). solved solids from 355 feet which was softened and WINTERHAVEN SECTOR also appeared to have undergone considerable sul­ The Winterhaven sector, most of which is in the H136 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Yuma Indian Reservation, includes the part of of the alluvium. The logs also indicated fairly uni­ "Bard Valley" west of the Yuma Main Canal. Most form electrical conductivity for the water through­ of the sector is accessible to a network of irrigation out the alluvium. Thus, it is inferred that the water canals but not all the valley land has been cultivated; yielded by the coarse-gravel and wedge zones alone a considerable acreage of scattered low-lying tracts would be slightly fresher than that actually pumped overgrown with phreatophytes has accumulated sur­ from the well and might contain less than 700 mg/1 face salts as a result of evapotranspiration. dissolved solids. A shallow well used to furnish Few wells have been drilled in the sector. Water- water for drilling the test well yielded water con­ quality information is mainly limited to analyses of taining 2,460 mg/1 dissolved solids (appendix C, water samples obtained from auger test wells. Sam­ analysis 269a). This analysis indicates that the ples from most of these small-diameter wells indi­ upper, fine-grained zone probably contains slightly cate the presence of water about like recent Colo­ to moderately saline water. rado River water or like river water concentrated The only irrigation well in the Winterhaven sec­ two or three times but with its sulfate slightly to tor, well 16S/22E-29Dba, less than a mile northwest moderately reduced. of test well LCRP 26, obtains water of fair quality, A water-quality problem exists at the village of though not as fresh as that in the test well (appendix Winterhaven, the only important trading point in C, analyses 267a, b). The irrigation well is per­ the California part of the Yuma area. The chemical forated from 118 to 143 feet, entirely in the coarse- character of the water obtained from several wells gravel zone. drilled to supply the community is reported to have YUMA VALLEY SUBAREA changed slowly from a water something like the The Yuma Valley subarea, largest of the subareas, recent river to water almost unacceptable for public consists of all the Colorado River flood plain in Ari­ supply. Hence, operators of the company supplying zona south and west of the city of Yuma. The entire water have had to drill new wells and abandon old Yuma Valley except for a narrow strip adjacent to ones every few years. The latest well was drilled in the river on the north and west is protected by a September 1961 and by the spring of 1967 the water flood-control levee and is irrigated from the Yuma quality had deteriorated so that the well was con­ Main Canal system. The canal water enters the sidered questionable as a continuing source for pub­ valley through an inverted siphon beneath the Colo­ lic supply. rado River at Yuma but is originally diverted from An auger test well southwest of Winterhaven be­ the river at Imperial Dam and therefore has the tween the Colorado River and a flood-protection chemical characteristics of the Colorado River water levee produced water containing 3,450 mg/1 dis­ at the dam rather than the somewhat greater con­ solved solids with 1,160 mg/1 chloride when sampled centrations that occur below the mouth of the Gila at 117 feet (appendix C, analysis 266). However, as River. very poor water originating upriver in the Wellton- Irrigation in Yuma Valley began before 1900, and Mohawk district constituted much of the river flow most of the valley has been irrigated with river for many months prior to the time of sampling, the water for at least 50 years. Consequently, rather sample might represent local infiltration of miner­ complete leaching of soluble salts presant in the up­ alized water from the river. per soil zones prior to initial irrigation probably has A deep U.S. Geological Survey test well, LCRP occurred. Nevertheless, some comparatively small 26, drilled by the mud-rotary method, cased, and areas are underlain by a high water table where gravel packed, yielded water containing only 712 white saline surface crusts appear from time to time mg/1 dissolved solids (appendix C, analysis 269b). as a result of evaporation from the capillary fringe. The well is perforated from 125 to 1,127 feet An extensive network of canals and laterals be­ (throughout the coarse-gravel zone and the wedge gins at Yuma and interfingers with an equally ex­ zone) and also from 1,368 to 1,769 feet (in the non- tensive drain system which converges into a single marine sedimentary rocks), so that the water sam­ main drain near the southerly international bound­ ple represents a composite from three aquifers. Use ary. The drain water, although moderately variable of a flow meter in the well while making pumping in composition and concentration because it includes tests indicated that relatively little water was variable parts of irrigation wastes, is always con­ yielded by the nonmarine sedimentary rocks, and siderably more mineralized than the applied Colo­ electric and water-resistivity logs and thief samples rado River water. Nevertheless, it has been pumped showed that the water in these rocks was not quite across the southerly international boundary and as fresh as that in the wedge and coarse-gravel zones used for irrigation in Mexico for many years. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H137

The Yuma Valley subarea is not as easily divisible wells in the Yuma area (appendix C, analyses 303a, into sectors on the basis of topography, geology, or b, 304). analytical data as the other three subareas. Numer­ EAST SECTOR ous chemical analyses are available which represent sampling from drainage wells near the Yuma Mesa Recent water quality in the coarse-gravel zone on escarpment on the east side of the valley and also the east side of Yuma Valley probably is rather well from irrigation and other wells in the floodway strip defined by chemical analyses of water samples col­ lected from a line of drainage wells constructed near on the west side of the valley, but there are compara­ the eastern edge of the valley and west of the East tively few analyses that represent sampling from the Main Canal the eastern distributary of Colorado far larger area between the drainage wells and the River water in Yuma Valley. The drainage wells floodway strip. Consequently, the subarea is divided were constructed so that continuous pumping would into three relatively narrow sectors along the north, relieve the high water table caused by the ground- east, and west margins, and a fourth sector that in­ water mound beneath Yuma Mesa to the east. cludes the greatest part of the valley (fig. 49). The first drainage wells, placed in operation in CALIFORNIA SECTOR 1947, did not extend into the coarse-gravel zone, so At the north end of Yuma Valley, west of Yuma, that most of the water pumped from them actually the Colorado River flows slightly north of west for came from the upper, fine-grained zone, although about 5 miles, then turns abruptly toward the south- undoubtedly replaced by upward movement from southwest. A small part of the valley near the river the coarse-gravel zone. The capacity of the shallow was once included in California and is still sub­ wells proved inadequate to control water levels and divided according to the California system of the they were replaced, beginning in 1954, by large- Federal land net. For convenience in identifying capacity wells screened in the coarse-gravel zone. wells this small area is designated the California Although the shallow drainage wells obtained water sector of the Yuma Valley subarea. Part of the sec­ from the upper, fine-grained zone, the old analyses of tor is not farmed, part is or has been irrigated by samples obtained from them probably do not repre­ pumping directly from the Colorado River, and part sent the quality of water in the upper zone near the has been irrigated by pumping from the Central well sites today. Consequently, the analyses of sam­ Main and Cooper Canals of the Yuma Project. ples from the old wells are not included in appen­ There is one irrigation well in the sector. dix C. Analyses of water samples obtained from several Pumping from the high-capacity drainage wells domestic wells in the sector indicate the presence of screened in the coarse-gravel zone has generally been an unusual body of shallow ground water containing nearly continuous once a well has been placed in only a few hundred to about 1,000 mg/1 dissolved operation. Consequently, differences between chemi­ solids. This water is moderately low in chloride and cal analyses of water samples taken at intervals unusually low in sulfate. Although the water may from these wells can be interpreted as showing be residual flood water, more likely it is Colorado actual changes in water quality in the coarse-gravel River water that has undergone great sulfate reduc­ zone resulting from the continued pumping. Never­ tion. Water from two domestic wells and one obser­ theless, some care must be taken in drawing con­ vation well was considerably higher in dissolved clusions about salinity changes in the ground water solids. This fact indicates that part of the local as the chemical analyses came from several sources ground water represents considerably evaporated and are not always strictly comparable owing to and moderately reduced Colorado River water. differences in analytical methods used by individual Two samples of water obtained 2 years apart from laboratories and because some analyses suggest pos­ the irrigation well are so much like recent Colorado sible chemical precipitation prior to analysis. None River water that they suggest a considerable of the presently pumped wells yields water like the part of the water pumped from this well is recently present Colorado River water. Yet each well tends infiltrated Colorado River water, even though the to have a definite chemical pattern which is some­ well is perforated in the coarse-gravel zone (ap­ what different from that for adjacent wells, prob­ pendix C, analyses 308a, b). Two deep wells per­ ably because vertical and horizontal movement of forated in the wedge zone which have supplied water water to the wells varies from well to well, and be>- for a steam-electric plant for about 10 years have cause part of the water pumped from some of the yielded water containing much less dissolved solids wells may have come from considerable depths in than any other regularly pumped large-capacity the wedge zone.

507-243 O - 74 - 10 H138 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA The dissolved-solids content of water pumped from ently many of the canal reaches serve as line sources the drainage wells has ranged from about 1,100 to of recharge so that the chemical character of the 2,300 mg/1 and either has generally been rather water obtained from shallow sources near them is constant for an individual well or has gradually de­ very similar to that of recent Colorado River water. creased after several years of pumping; however, In contrast, wells of similar depths but closer to water from the northernmost drainage well has drains rather commonly yield water with chemical trended upward in concentration rather than down­ characteristics indicating moderate concentration by ward. The most northerly wells, which are west of evaporation and some sulfate reduction. the built-up part of the city of Yuma and farther During 1962, the U.S. Bureau of Reclamation had from the irrigated area of the mesa than those two 500-foot test wells drilled in the valley. Analyses farther south, yield water that is like moderately of water samples taken from the mud scow or with a evaporated and greatly reduced Colorado River thief sampler during drilling indicated irregular water. The drainage wells in the central part of the differences in water composition with depth. The group and west of the heavily irrigated part of the wells were perforated in the coarse-gravel zone but mesa yield water that contains more sulfate and less not pumped and sampled until about 2 years later. chloride. Wells at the south end of the group yield The pumped samples agreed only in a general way water having the lowest dissolved-solids content and with the samples obtained earlier. (See appendix containing less chloride and much less sulfate than C, analyses 360a-h, 376a-f). farther north. The different changes in composition In 1965 the city of Somerton had a deep test well of the water with time apparently result from dif­ drilled in order to prospect for water suitable for ferential movement to the wells of an increment of city use. Several samples (appendix C, analyses Colorado River water applied as irrigation water on 375a-g) were obtained from the mud scow at depths Yuma Mesa. ranging from 470 to 1,143 feet but they did not indi­ cate the presence of the hoped-for good water, and CENTRAL SECTOR the well was not completed at that time. It was Water-quality variation in the central part of completed later, however, and is now (1968) used Yuma Valley is not very well defined, because there for public supply. are only a few wells for which depth information, logs, and sampling all are available. Wells used to FLOODWAY SECTOR supply Somerton are the only ones in central Yuma At the time the Yuma Project was developed by Valley that have pumped substantial amounts of the U.S. Bureau of Reclamation a rather narrow water. Information is also available on a few wells strip along the Colorado River was separated from of moderate capacity constructed to supply labor the rest of Yuma Valley by a flood-protection levee camps, cotton gins, and feed yards. Most of the so that it did not receive canal water. Overgrown analytical information is on samples collected from with bottom-land vegetation, the strip was mostly auger test wells and small-capacity domestic wells of unused for many years. By 1940, however, some of which many of the latter are of unknown depth. The it had been cleared and was irrigated 'by pumping auger test wells were sampled through well points directly from the river. Later the irrigated area at their base. Some of the domestic wells also obtain was greatly expanded to cover most of the strip, and water through well points or open bottoms. Thus irrigation by pumping from wells replaced the the auger-well and domestic-well samples mostly pumping from the river. represent point rather than zone sampling and water Several analyses of samples from two wells near of different quality might be obtained at their loca­ the West Main Canal in the north-central part of the tions if wells of larger capacity perforated for sector have shown that these wells have always lengthy intervals were constructed. Therefore, the yielded water containing 1,200-1,400 mg/1 dissolved central part of Yuma Valley must be appraised on a solids which is similar to evaporated Colorado River more tentative basis than the rest of the Yuma area, water that has undergone slight sulfate reduction although the appraisal may not be far removed from (appendix C, analyses 344a-e, 395a, b). All the irri­ describing average water-quality conditions. gation wells farther south have yielded water that Chemical analyses of water samples collected from contains less dissolved solids, that appears to be less auger test wells and domestic wells, chiefly from the concentrated by evaporation, and to have undergone northern one-third of the valley, indicate consider­ more sulfate reduction. Four analyses of samples able erratic variation in the chemical quality of taken from a cluster of auger test wells installed to water in the upper and coarse-gravel zones. Appar­ determine differences in head (appendix C, analyses GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H139

402-405) indicate that the water in the upper, fine­ Yuma Mesa subarea, is named for Fortuna Wash, grained zone is most like evaporated Colorado River an ephemeral stream which originates in the Gila water near the water table and that its dissolved- Mountains several miles south of Telegraph Pass and solids content decreases with depth, mainly because extends northwestward, but nearly parallel to the of increased sulfate reduction. mountains, to South Gila Valley. Except for the city Several samples collected with packers from test sector in and adjacent to Yuma, the FoHuna sector well LCRP 9 (appendix C, analyses 399a-f) indicate is the only extensive part of the Yuma Mesa sub- that the quality of water obtained between depths of area where water of poor quality is widely present. 310 and 1,108 feet (in the wedge zone) does not The sector, a dissected upland 2-3 miles wide, lies vary much with depth and that the wedge zone chiefly within "Gila Mesa." Crossed by U.S. High­ probably contains better water for an extended way Interstate 8, the sector has particularly good depth than that in the river. access from Yuma so that it has been attractive to Samples obtained from test well LCRP 17, several picnickers and has been the site of several proposed miles farther south (appendix C, analyses 410a-h) desert homesite subdivisions. Land developers and consistently indicated a little more chloride and a purchasers of individual homesites have drilled more little less sulfate than in well LCRP 9. than a dozen wells in the sector. All the analyses from irrigation wells represented Analyses of samples of water obtained from seven by repeated samples showed small but definite in­ of the deeper wells during drilling and testing sug­ creases in dissolved solids content after several years gest the widespread presence of slightly to moder­ pumping, but the rate of increase was not sufficient ately saline sodium chloride type water which usual­ to suggest that the water would become unsatisfac­ ly would not be considered suitable for domestic use tory for the general farming carried on in the area because of its mineral and fluoride content. Analyses for many years. of samples obtained from three wells in the sector YUMA MESA SUBAREA but west of Fortuna Wash, which penetrated only The Yuma Mesa subarea includes small parts of short distances below the water table, indicated the "Upper Mesa" and "Gila Mesa" as well as the entire presence of water containing less than 300 mg/1 dis­ Yuma Mesa. All the subarea lies above the river solved solids with only a little fluoride. valleys (flood plains) and consequently has not been The fresh water near Fortuna Wash, derived from subject to geologically recent (Holocene) flooding by the occasional flood flows of the wash, occurs in a the rivers. The subarea includes a large central acre­ lens or thin lenses, in part perched, overlying the age irrigated by Colorado River water brought in by more saline water in the main water body. The lined canal and scattered tracts where irrigation by known thickness of the fresh-water body does not pumping from wells has begun recently or is being exceed 40 feet; the extent is less well known but planned. It also includes large sections where irriga­ probably does not exceed a few thousand acres. tion may be possible but where irrigation has not yet Development of this water of superior quality would been planned. have to be limited to domestic wells of small capacity, The alluvium beneath the Yuma Mesa subarea is carefully spaced and pumped so as not to draw in the hydraulically continuous with the alluvium under the more saline water from below. The origin of the adjacent river valleys so that a continuous water somewhat saline water of the main water body is table extends from the South Gila Valley southward uncertain; possibly it represents contamination by and southwestward under the Yuma Mesa subarea upward leakage along faults of brackish water from to the southerly international boundary and Yuma marine and nonmarine sedimentary rocks of Ter­ Valley. Early chemical records suggest that most of tiary age. The abnormally warm temperatures of the subarea may have had ground water of uniform the water support such an inference (fig. 47). chemical quality before irrigation began in the South Gila Valley and on Yuma Mesa, and that some of the ARIZONA WESTERN SECTOR old water was replaced by water more like recent Extending south from the escarpment along the Colorado River water. Irrigation on the mesa un­ south edge of South Gila Valley between the For­ doubtedly has altered the chemical quality of much tuna sector and the citrus sector is a tract of mostly of the ground water in the irrigated area so that the undeveloped land which is designated the Arizona present patterns of ground-water-quality variation Western sector of the Yuma Mesa subarea. Two are best described by sectors. wells at Arizona Western College (from which the FORTUNA SECTOR sector derives its name) are the only heavily pumped The Fortuna sector, in the northeast corner of the wells in the sector. Other wells are commercial wells H140 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA of small capacity along U.S. Highway 80 (Interstate cate the general presence of water that can be char­ 8) and scattered exploratory wells drilled mainly to acterized as Colorado River water moderately evapo­ prove up land acquisition from the State of Arizona rated and partly softened. The modified Colorado and generally not used after drilling. River water has sulfate, rather than chloride, as the Water samples obtained from 11 wells in the sec­ principal anion constituent. However, because most tor show similarly constituted sodium chloride water of the sampled domestic wells in the Citrus sector with dissolved solids ranging from 800 to 1,400 mg/1. are no deeper than about 200 feet, some of the water The two wells at Arizona Western College are of below that depth (upper part of the coarse-gravel different depth, and the water they produce is used zone) may still be of the sodium chloride type. for different purposes. The shallower well, per­ Analyses of samples obtained from a few wells in forated in the coarse-gravel zone and used mainly the northernmost part of the sector indicate water for irrigation (appendix C, analyses 517a, b), has much like that produced from the coarse-gravel zone produced water of higher concentration than that of in South Gila Valley. The analytical evidence cor­ the deeper well. The deeper well, perforated in the roborates the water-level data which indicate that wedge zone and used for public supply, produces water moved southward from under South Gila Val­ water like that pumped from the U.S. Bureau of ley to under the mesa prior to the development of Reclamation wells now supplying part of the water intensive irrigation on the mesa. After irrigation in nearby South Gila Valley (appendix C, analyses on the mesa, and particularly since drainage wells 518a-c). were drilled in South Gila Valley, the direction of Mud-rotary-drilled test well LCRP 25, about 5 movement of water in the northern part of the Citrus miles southwest of Arizona Western College, is sector has been reversed and some reduction of gravel packed and perforated from 862 to 2,002 feet salinity may have occurred.

(entirely in the wedge zone) and, when pumped CITY SECTOR during a test, yielded water similar to and only a little more concentrated than the water in the deeper Most of the city of Yuma is on or immediately college well (appendix C, analysis 521). south of a peninsulalike extension of Yuma Mesa at Although the number of wells in the Arizona West­ its northwest corner. Only a few wells now pump ern sector represented by water analyses is small, water in this sector. A municipal water department the near uniformity of water-quality patterns and (formerly a private company) supplies Colorado the general similarity to the patterns of water quali­ River water to residents of the city and a considei ty shown by the more numerous wells in the south able quantity of this water is used to irrigate yards, sector of the Yuma Mesa subarea suggest that the trees, and shrubs, so that it must provide some local general composition pattern of the deep supply well recharge. However, because of the rather high cost at Arizona Western College probably is representa­ of the water, many of the larger grassy areas around tive of water that might be produced from any new some of the motels and public buildings and in parks wells drilled in the sector. and school yards are irrigated by pumping from wells. This pumped water, although considered sat­ CITRUS SECTOR isfactory for irrigation of bermuda grass, has not The principal irrigated part of Yuma Mesa is been considered satisfactory for use on salt-sensitive designated the Citrus sector because most of it has trees and shrubs. been planted to citrus orchards. Analytical evi­ The parts of Yuma Mesa south of Yuma, and dence indicates that the chemical characteristics of Yuma Valley to the west, are irrigated with Colorado the ground water in the Citrus sector have been or River water. The part of South Gila Valley east of are in process of being altered, owing to the infiltra­ the city was long irrigated with ground water and tion of imported Colorado River water. Several has only recently been converted to irrigation with older analyses, mostly from wells no longer in exist­ Colorado River water. The "Yuma Hills" on the ence, indicate that formerly most of the ground east side of Yuma form a partial barrier to ground- water in the sector had the same chemical pattern as water movement from South Gila Valley. However, that occurring today in the Arizona Western sector. the chemical character of the water pumped from Concentration of dissolved solids generally ranged most of the wells in Yuma is more like that beneath from 800 to 1,000 mg/1, with sodium and chloride the the South Gila Valley than that beneath Yuma Val­ principal constituents. ley or the adjacent part of Yuma Mesa to the south. Recent analyses of many samples collected from Most of the wells in Yuma yield water containing domestic wells scattered throughout the sector indi­ between 1,800 and 3,600 mg/1 dissolved solids which GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H141 is like Colorado River water that has been concen­ the northern part of the south sector, adjacent to the trated several times by evaporation and has under­ citrus sector, have generally shown changing pat­ gone substantial sulfate reduction and hardening. terns of water quality with pumping. Commonly the Other wells near the west edge of the mesa yield first samples contain about 800 mg/1 dissolved solids, water which appears to have a considerable incre­ mostly sodium and chloride; after pumping the rela­ ment of infiltrated Colorado River water. tive amount of sulfate tends to increase and the dis­ In 1962 a well was drilled to a depth of 830 feet at solved solids also increase to 1,200-1,400 mg/1. This the Stardust Hotel near the center of the sector in change is probably caused by admixture of water an effort to obtain water suitable for cultivation of infiltrated from the citrus sector. flowers and shrubs and other uses at the hotel. Dur­ Farther south all the wells show the predominance ing the drilling, water-quality variation with depth of chloride over sulfate in a pattern that is so char­ was determined by frequent measurements of spe­ acteristic as to be recognizable as the original "Yuma cific conductance of the water brought up with well Mesa pattern." The average mineral content ap­ cuttings in the mud scow. Both the quality of the pears to decrease in the southern part of the sector. water and the quantity obtained were disappointing REFERENCES and the hotel left the well unused. In 1963 an agree­ Alien, C. R., 1957, San Andreas fault zone in San Gorgonio ment was made for the U.S. Geological Survey to Pass, southern California: Geol. Soc. 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Survey open-file report, 117 p., 2 pis. 43 figs., 2 recharged from the citrus sector and that this re­ tables, 2 appendixes. charge would continue and replace water removed Bryan, Kirk, 1923, Erosion and sedimentation in the Papago for irrigation. Consequently, well development and country, Arizona, with a sketch of the geology: U.S. Geol. Survey Bull. 730-B, p. 19-90. some irrigation farming in the south sector was Cooley, M. E., and Davidson, E. S., 1963, Synoptic Cenozoic begun by private developers about 1961 and has in­ geologic history of the Colorado Plateaus and Basin and creased nearly every year since. Range provinces of Arizona [abs.]: Geol. Soc. America, The analyses of water samples obtained from wells Rocky Mtn. Section, 16th Ann. Mtg., p. 21. in the south sector indicate that the quality of the Creasey, S. C., and Kistler, R. W., 1962, Age of some copper- bearing porphyries and other igneous rocks in south­ native ground water was as good as the recent Colo­ eastern Arizona, in Short papers in geology, hydrology, rado River water, although it had chloride rather and topography: U.S. Geol. Survey Prof. Paper 450-D, than sulfate as the chief anion constituent. Wells in p. D1-D5. H142 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

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Lovejoy, E. M. P., 1963a, Re^evaluation of geomorphic cri­ Norris, R. M., and Norris, S. K., 1961, Algodones Dunes of teria of "Classical basin range normal block faulting" southeastern California: Geol. Soc. America Bull., v. [abs.] : Geol. Soc. America, Program 16th Ann. Mtg., 72, p. 605-620. Rocky Mountain Section, p. 34. Olmsted, F. H., 1972, Geology of the Laguna Dam 7y2 -minute , Age of the Colorado River in the Colorado quadrangle, Arizona and California: U.S. Geol. Survey plateau [abs.] : Geol. Soc. America, Program 16th Ann. Geol. Quad. Map GQ-1014, scale 1:24,000. Mtg., Rocky Mountain Section, p. 33. Paredes, Engr. E. Arrellano, 1963, Preliminary geohydro- MacDougal, D. T., and others, 1914, The Salton Sea, a study logical report on the eastern area of the Mexicali Valley, of the geography, the geology, the floristics, and the Baja California: Mexicali, B. C.., Mexico, 7 p. ecology of a desert basin: Carnegie Inst. Washington Richard, Kenyon, and Courtright, J. H., 1960, Some Cre­ Pub. no. 193, 182 p. taceous-Tertiary relationships in southeastern Arizona Mackin, J. H., 1960, Structural significance of Tertiary vol­ and New Mexico: Arizona Geol. Soc. Digest, v. Ill, p. canic rocks in southwestern Utah: Am. Jour. Sci., v. 1-7. 258, p. 81-131. Robinson, B. P., 1962, Ion-exchange minerals and disposal McCoy, F. W., Jr., Nokleberg, W. J., and Norris, R. M., 1967, of radioactive wastes A survey of literature: U.S. Speculations on the origin of the Algodones dunes, Cali­ Geol. Survey Water-Supply Paper 1616, 132 p. fornia: Geol. Soc. America Bull., v. 78, no. 8, p. 1039- Robison, J. H., 1965, Environment of the Imperial trough, 1044. California, during the Quaternary: a paleogeographic McKee, E. D., 1939, Some types of bedding in the Colorado problem [abs.]: Geol. Soc. America, Program 61st Ann. River delta: Jour. Geology, v. 47, p. 64-81. Mtg., Cordilleran Section, p. 47. McKee, E. D., Hamblin, W. K., and Damon, P. E., 1968, Sellers, W. D., ed., 1960, Arizona climate: Tucson, Ariz., K-Ar age of lava dam in Grand Canyon: Geol. Soc. Arizona Univ. Press, 60 p., 201 tables. America Bull., v. 79, p. 133-136. Sharp, R. P., 1957, Geomorphology of Cima Dome, Mojave McKee, E. D., Wilson, R. R., Breed, W. J., and Breed, C. S. Desert, California: Geol. Soc. America Bull., v. 68, p. eds., 1967, Evolution of the Colorado River in Ari­ 273-290. zona A hypothesis developed at the Symposium on Smith, P. B., 1968, Pliocene (?) Foraminifera of the lower Cenozoic Geology of the in Arizona, Colorado River area, California and Arizona [abs.]: August 1964: Mus. Northern Arizona Bull. 44, 67 p. Geol. Soc. America, Program 64th Ann. Mtg. Cordilleran Merriam, R. H., 1965, Source of Palm Spring sediments, Section, p. 111-112. Imperial Valley, California [abs.] : Am. Assoc. Petroleum Snodgrass, H. R., 1965, Subsurface geophysical investiga­ Geologists Bull., v. 49, p. 1764-1765. tions using the General Atomic seismic reflection sys­ Merriam, Richard, and Bandy, 0. L., 1965, Source of Upper tem: General Atomic Division of General Dynamics rept. Cenozoic sediments in Colorado delta region: Jour. Sed. GA-6782, 39 p. Petrology, v. 35, no. 4, p. 911-916. 1966, Subsurface geophysical surveys using seismic Metzger, D. G., 1965, A Miocene(?) aquifer in the Parker- reflection system: General Atomic Division of General Blythe-Cibola area, Arizona and California, in Geo­ Dynamics rept. GA-7349, 42 p. logical Survey research 1965: U.S. Geol. Survey Prof. Stanley, G. M., 1962, Prehistoric lakes in Salton Sea basin Paper 525-C, p. C203-C205. [abs.]: Geol. Soc. America, Program 1962 Ann. Mtgs., 1968, The Bouse Formation (Pliocene) of the Parker- p. 149A-150A. Blythe-Cibola area, Arizona and California, in Geo­ Sweet, C. L., 1952, Report on drainage, Valley Division logical Survey research 1968: U.S. Geol. Survey Prof. Yuma Project, Arizona: U.S. Bur. Reclamation, Boulder Paper 600-D, p. D126-D136. City, Nev., 73 p. Sykes, G. G., 1914, Geographical features of the Cahuilla Metzger, D. G., Loeltz, 0. J., and Irelan, Burdge, 1973, Geo- Basin, in MacDougal, D. T., and others, the Salton Sea: hydrology of the Parker-Blythe-Cibola area, Arizona Carnegie Inst. Washington Pub. 193, p. 13-20. and California: U.S. Geol. Survey Prof. Paper 486-G. 1937, The Colorado Delta: Carnegie Inst. Washing­ Miller, W. J., 1944, Geology of the Palm Springs-Blythe strip, ton and Am. Geog. Soc. N. Y. Pub. no. 460, 193 p. Riverside County, California: California Jour. Mines Tarbet, L. A., and Holman, W. H., 1944, Stratigraphy and and Geology, v. 40, p. 11-72. micropaleontology of the west side of Imperial Valley, Morton, P. K., 1962, Reconnaissance geologic map of parts California [abs.]: Am. Assoc. Petroleum Geologists Bull., of the Picacho Peak, Laguna, Ogilby, Grays Well NE, v. 28, p. 1781. and Yuma quadrangles, California: California Div. Theis, C. V., 1935, The relation between the lowering of the Mines and Geology reconn. mapping for State Geologic piezometric surface and the rate and duration of dis­ Map (El Centro sheet), 1960-62. charge of a well using ground-water storage: Am. Muffler, L. J. P., and Doe, B. R., 1968, Composition and Geophys. Union Trans., 16th Ann. Mtg., pt. 2, p. mean age of detritus of the Colorado River delta in 519-524. the Salton Trough, southeastern California: Jour. Sed. Theis, C. V., Brown, R. H., and Meyer, R. R., 1963, Estimat­ Petrology, v. 38, p. 384-399. ing the transmissibility of aquifers from the specific Nockolds, S. R., and Alien, R., 1954, The geochemistry of capacity of wells, in Bentall, Ray, ed., Methods of deter­ some igneous rock series, pt. 2: Geochim. et Cosmochim. mining permeability, transmissibility, and drawdown: Acta, v. 5, p. 245-285. U.S. Geol. Survey Water-Supply Paper 1536-1, p. Nolan, T. B., 1943, The Basin and Range Province in Utah, 331-341. Nevada, and California: U.S. Geol. Survey Prof. Paper Thornbury, W. D., 1965, Regional geomorphology of the 197-D, 55 p. United States: New York, John Wiley & Sons, 609 p. H144 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Tipton and Kalmbach, Inc., and Jacob, C. E., 1956, Ground Wells, J. V. B., and others, 1954, Compilation of records of water and drainage of Yuma Mesa and Yuma Valley: surface waters of the United States through September Consultants' rept. to Secretary Interior, v. I, rept., 1950; pt. 9, Colorado River basin: U.S. Geol. Survey 78 p., v. II, app., 57 p. Water-Supply Paper 1313, 749 p. U.S. Bureau of Reclamation, 1953, Memorandum supple­ Wilcox, L. V., and Scofield, C. S., 1952, History of the ment to report on water supply of the lower Colorado ground-water conditions of the Valley Division of the River basin project planning report, November 1952: Yuma (Arizona) Project prior to 1936: U.S. Salinity U.S. Bur. Reclamation, 48 p. Lab., Riverside, Calif. 1963, Lower Colorado River water salvage-phreato- Wilson, E. D., 1933, Geology and mineral deposits of south­ phyte control, Arizona-California-Nevada: Reconn. rept., ern Yuma County, Arizona: Arizona Bur. Mines Bull. June 1963, 57 p. Veeh, H. H., 1966, Th230/U238 and U^/U238 ages of Pleisto­ 134, 236 p. cene high sea level stand: Jour. Geophys. Research, v. 1960, Geologic map of Yuma County, Arizona: Ari­ 71, no. 14, p. 3379-3386. zona Bureau of Mines, Univ. Arizona, map, scale Wadell, H., 1932, Volume, shape and roundness of rock 1:375,000. particles: Jour. Geology, v. 40, p. 443-451. Woodard, G. D., 1961, Stratigraphic succession of the west Wasserburg, G. J., and Lanphere, M. A., 1965, Age determi­ , and Imperial Counties, nations in the Precambrian of Arizona and Nevada: southern California [abs.]: Geol. Soc. America, Program Geol. Soc. America Bull., v. 76, p. 735-758. 1961 Ann. Mtg., Cordilleran Section, p. 73-74. APPENDIXES A-E H146 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

APPENDIX A. RECORDS OF WELLS Appendix A represents records of 936 wells in the Yuma area inventoried by the U.S. Geological Survey during the period 1961-66. These wells provide much of the basis for the interpretation of the ground-water hydrology and the subsurface geology in the main part of this report. Logs of, and chemical analyses of water samples from, some of these wells are given in appendixes B and C, respectively. Appendix A comprises five tables ^(16 through 20), in which the wells are grouped according to type or major use. Within each table, the wells are listed sequentially according to their location (well number) in the Federal land classifica­ tion. A description of the well-numbering system is given in the introduction of the report (p. H17). Locations of the wells in tables 16-20 are shown on plates 13-17, respectively. Not all wells in the Yuma area were inventoried in the present investigation; domestic wells, shallow observation wells, and destroyed wells were generally omitted except where special information was available for a well. The well inventory was terminated in the s.pring of 1966, but some well data were obtained as late as 1968. TABLE 16. Water-test wells and oil-test wells

Well number: Location of well according to the Federal land classification. See text for description of well-numbering system. Coordinates: Location of well according to grid system used by U.S. Bureau of Reclamation in Yuma area. See page H17 for explanation of grid system. Owner or user: Government agency or company that drilled the well or had it drilled. Other number: Number assigned to well by owner or user. Year completed: Known or reported year of completion of well. Altitude of land surface: Average altitude of land surface at well above mean sea-level datum. Altitudes given to nearest foot are approximate and were obtained from topographic maps; altitudes given to decimal fractions of a foot were obtained by spirit leveling to a reference point at the well and are much more accurate. Log information, water-level data, and tem­ perature data are referred to land-surface datum. Total depth: Greatest depth, in feet below land-surface datum, to which well was known or reported to have been drilled. Well may have been completed to a shallower depth or filled in subsequently. Completed depth: Depth, in feet, below land-surface datum, to which well was cased or subsequently plugged. Method of construction: Letter symbols designate C, drilled with cable-tool or percussion equipment; R, drilled with rotary-mud equipment; G, gravel packed. Casing diameter: Nominal inside diameter, in inches, of casing or pipe used in well. Where more than one figure is given, figures refer to diameter of casing in each successive segment from land surface downward. o Depth of perforated interval: Depth, in feet below land-surface datum, to top of highest perforations or well screen and base of lowest perforations or well screen.. Where more than one M major aquifer or water-yielding zone is perforated or screened, figures refer to top and bottom of perforated or screened intervals in each aquifer, in downward sequence. O Discharge: Measured or reported discharge of well in gallons per minute. W Drawdown: Measured or reported drawdown, in feet, accompanying discharge in previous column. *i Water level: Date measured by the Geological Survey or reported by owner or other agency Depth to water in feet below land-surface datum. Water temperature: Date measured by the Geological Survey. Temperature, in degrees Celsius, of most recent sample of water pumped from well believed to represent water from o the_ depth of the perforated interval in the coarse-gravel zone. In some wells, not equipped with pumps, temperature measured with a thermistor or a maximum thermometer at a depth w believed to represent the middle of the coarse-gravel zone or an equivalent depth below land surface. o Other data available: Additional information about the well available in files of the Geological Survey. Some of this information is given in other tables of the present report. The type F O

quality-of-water data; W, periodic or continuous water-level records.

Water level Water temperature W M Altitudeoflandsurface Methodofconstruction 1 Depthfeetbelowin Other Owner Other Yearcompleted Completeddepth diameterCasing Well Coordinates or number a) "8 data s user surfaceland ., 3t |1. 3 w 3o S3 3 C 3 & tS o M H P.S pQp P P o (C- 7-22)14bcd _ 6 5/8 N-7 3/16 E U.S. Geological LCRP 14 _ 1963 155.1 505 ^00 C 12 118-162. 600 8.43 11- 1-66 14.08 2-27-68 19.9 150 G, L, R, Survey. 470-490 T, HA, P, PC, iW i PT, Q N (C- 8-21)17abb2 _ 1 N-10 9/16 E U.S. Bureau Gila 1957 159 79 T, O of Reclama­ Siphon 9. tion, 17abd2 0 15/16 N-10 5/8 E do Gila 1957 160 72 T, Siphon 10. 17bab2 _ 0 15/16 N-10 1/4 E do Gila 1957 158 102 T, Siphon 4. G 17bac2 _ 0 15/16 N 10 3/8 E do Gila 1957 158 98 T, Siphon 6. O 17badl2_ __ do Gila 1957 158 105 105 16 90-105 1,390 11 _ T, . PT, Q > Siphon 7. F 17bad22_ 0 15/16 N-10 7/16 E do Gila 1957 159 102 T, I I Siphon 8. *J 17bbal2_ 1 N-10 3/16 E do Gila 1957 150 96 T, o Siphon 1. w 17bba22_ 1 N-10 3/16 E do Gila 1957 151 96 T, Siphon 2. (C- 8-22)15bdd _ 01/2 N-6 1/2 E do CH 6 1963 140.5 501 485 C 12 90 185 12 15 66 4.74 11- 2 67 22.2 120 G , L, R, T, PC, 15dab2 _ 0 7/16 N-6 13/16E Gila Valley Kamrath 1 _ 1958 145 2,140 K Oil and Gas Co. __ do ______Kamrath 2 _ 1958 147 400 372 R -\ Q -I AS/ 19ccc __ 1 S-3 E U.S. Bureau of CH-702 __ 1963 129.6 500 490 C 12 115-150, 1,060 35 12-11-66 10.29 11- 2-67 21.2 120 G. R, T, Reclamation. 370-463 PC, PT, Q 23dad _ 0 0 1 A Q O ~C* __ do ______CH 4 _____ 1962 152.4 500 500 C 8 120 G. L, R, 334-354 T, MA, W Q See footnotes at end of table. TABLE 16. Water-test wells and oil-test wells Continued

00 Water level Water temperature

Altitudeoflandsurface Methodofconstruction Depthperforatedof 1 Owner Other Yearcompleted Completeddepth Casingdiameter & Other Well Coordinates or number g g data «£j a, available user Totaldepth interval 03 "§ J3 ^ t 2 01 03 O Q Q Q n n ll H 35caal - 2 1/2 S-7 1/2 E __ do _____ 3LCRP 29, 1965 150.8 1,997 600 C.R 12 99-170, 1,625 15.3 9-26-66 17.08 2-26-68 23.4 135 C, E, G, td CH-704. 435-570 L, T, P, PC, w PT, Q w 36aaa _ 2 S-9 E _ do _ CH-705 __ 1963 152.7 250 250 C 12 88-169 11-30-66 18.37 2-26-68 22.8 120 G, L, T td (C- 8-23)27ada _ 1 3/8 S-l E do CH-701 __ 1963 133.4 250 250 C 12 84-160 1,300 19 11-30-66 17.79 11-12-67 24.4 150 G, L, R, CQ T, PT, O Q Cl Sldaa _ 2 1/2 g 2 W - do _ YVI 2a(P) 1965 113.6 182 152 R 1% 150-152 4- 8-67 7.79 10-26-67 23.1 140.4 G, L, T W 32bab - 2 S-l 3/4 W - do YVI-HP) 1965 123.8 220 "Tib" R - L o 32bdc _ 2 1/2 S-l 3/4 W -do _ YVI-2b(P) 1966 120.4 201 R iy2 148-150 G, L td 32caal _ 2 5/8 S-l 5/8 W Sinclair Kryger 1 1925 120 1,400 1,400 C 16 D, G, T CQ Oil Co. 33cdd - 3 S-0 5/8 W Stardust *LCRP 13 _ 1963 197 1,090 830 C 12-8 182-200 11-15-62 73.24 1963 27.8 182-200 D, G, L, Hotel. T, HA, Q (C- 9-22)28cbb _ 7 1/2 S-5 E U.S. Geological LCRP 25 1964 204.6 2,318 2!,002 R, G 12-8 862-2,002 595 10.8 12- 3-66 53.95 11- 7-67 24.8 158.6 E, G, L, f Survey. R, T, o P, PT, Q, W (C- 9-23)5aab __ 3 S-l 1/8 W U.S. Bureau of YM-l(P), 1966 190.4 391 230 R 228-230 12- 6-66 73.87 12- 6-66 30.6 209.4 G, L, T W Reclamation. CH-18YM. 5abc __ 3 1 I A O i 1/9 "WT do __ YVI-4(P) 1965 120.6 193 140 R 138-140 _ 12- 8-66 6.65 11- 2-67 29.5 139.6 G, L, T O 5ddc2 _ 4 S-l 1/4 W do CH-19YM _ 1966 154.4 202 170 R 1% 168-170 12- 6-66 37.73 11-29-67 29.0 168.4 G, L, T o 6abb 3 S-2 1 /2 W do YVI-2(P) 1965 120.7 203 140 R iy2 138-140 12- 8-66 9.28 11-11-67 22.2 120.8 G, L, T F 7baa 4 S-2 5/8 W do YVI-5(P) - 1965 116.1 202 145 R 11/2 143-145 12-22-66 5.72 10-26-67 23.1 143 G, L, T o Sbdcl - 4 7/16 S-l 5/8 W - do , YVI-7(P) 1965 118.3 260 132 R 1% 130-132 5 30 L 8dca _ 4 13/16 S-l 1/4 W - do YM-2(P) - 1966 155.1 232 180 R 1% 178-180 3- 3-67 38.78 11- 5-67 25.1 178.6 G, L, T 17dcd - 6 S-l 1 /4 W 1966 153.6 398 396.6 R 2 394.6-396.6 1- 9-67 41.22 2-25-67 26.4 178.6 G, L, T u 19bcd __ 6 7/16 S-2 13/16 W Co'orado Newcomer 1954 110 3,277 400 R 11 12- 2-63 8.86 3-19-65 27.0 150 G, L, T, o Basin As- and Fas- P socfates. quinelli". 25dbal _ 71/2 S-2 3/4 E U.S. Bureau of CH-7A __ 1964 204 710 650 R 4 ______2-26-64 37.50 ______E, G, L Reclamation. 25bda2 - 71/2 S-2 3/4 E do CH-7B _ 1964 204 250 260 R 8 160-250 700 12.5 12- 3-66 42.57 12- 3-66 24.2 119 PT, Q, td T 29aab _ 7 S-l 1 /4 W 1920 118 730 6 4 ? 2-25-67 w. 29cad - 7 11/16 S-l 1/2 W U.S Bureau of YM-5 ( P ) _ 1967 185.3 416 257.6 R 2 255.6-257.6 71.71 2-25-67 26.4 213.5 G, L, T > Reclamation. F 30daa _ 7 5/8 S-2 W - do YM-5a(P)_ 1967 183.6 392 247.5 R 2 245.5-247.5 2-25-67 79.33 11- 5-67 27.3 250 G, L, T H Slada - 8 1 /4 S-2 W - do CH- 16YM 1966 183.4 492 230 R iy2 228-230 12- 3-66 71.88 11- 4-67 28.0 229.7 G. L, T O 32bad _ 8 1/8 S-l 1/2 W do CH 21 YM _ 1966 188 285 2691/2 R iy2 ib t 72 ^by 72 12- 7-66 71.72 11- 5-67 27.7 257.8 G, L, T 33cdd _ 8 7/8 S-0 1/2 W -do _ CH-20YM 1966 196 64 491/2 R iy2 471/2-491/2 8-30-66 29.16 3- 7-67 23.3 49 G. L, T 35ccc _- 9 S-l E do CH-13YM 1965 202.2 504 250 R iy2 248-250 12- 3-66 34.85 11- 4-67 26.7 238 G, L, T w. (C- 9-24)8baa 4 S-7 1 /2 W U.S. Geological LCRP 28 __ 1965 118.7 2,466 292 R 12 10-11-66 17.63 2-20-68 22.2 130 C, E. G. H Survey. L, T, 5> 13cdd - 6 S-3 1/2 W 1962 105 500 484 C 8 139-170 520 21.5 5- 5-67 5.00 12-10-67 25.4 157 G, L, T, Reclamation, MA, PT. Q, 5> W W (C- 9-25)24dcdl _ do _ CH 29VD 1966 106.4 222 209.7 R 2 207.7-209.7 12-16-66 12.87 11-28-67 21.2 137.7 G, L, T td 7 S-9 3/8 W 12-16-66 24dcd2 - 7 S-9 3/8 W do CH-29VD 1966 106.4 210 149.3 R 1% 147.3-149.3 12.92 3- 3-67 22.8 147.3 L.T 24dcd3 _ 1966 106.4 210 30.4 R 28.4-30.4 12.98 3- 3-67 22.8 30 L, T 7 S-9 3/8 W do __ CH 29VD 10-20-66 35cbd - 8 11/16 S-10 7/8 W U.S. Geological LCRP 9 __ 1962 104 1,201 1,124 R 10-6 * 310-1,108 18.60 2-17-68 22.2 150 C, D, E, L, T. Survey. PTp, Q, W (C-10-23)6bbb _- 9 S-2 15/16 W U.S. Bureau of YM-7(P) _ 1966 172.2 285 270 R 268-270 12- 3-66 69.72 3-23-68 27.3 210 G, L, T Reclamation 31aaa - 14 1/8 S 2 1/8 W M. P. Stewart Federal 1 _ 1954 181 3,660 R L Co. Slbbbl - 1961 172.8 1,000 286 C 16 220-280 1,500 85 12- 3-66 80.55 3-23-68 29.2 230 G, L,, R, 14 S-3 W U.S. Geological LCRP 1 __ T, HA, Survey. PC, PT, C1*, Q 36ddd _ 15 S-3 E U.S. Bureau of CH-22YM _ 1966 285 211 211 R 2 209 211 12-14-66 188.42 12- 9-67 33.9 211.2 G, L, T Reclamation, (C-10-24)lbddl _ 91/2 S-3 1/2 W do CH--1 1962 110 500 500 C 8 144-170 12-12-66 10.87 5- 5-67 28.0 177.6 G, L, R T, MA, 0 Iccc __ 10 S-4 W do CH - 10VD _ 1964 101 126 R . L lcddl _ 10 S-3 5/8 W do YVI 23 (P) 1966 103.4 197 160 R 1% 11- -65 4.70 G, L Idad __ 9 3/4 S-3 1/16 W _ do YM-8(P) 1966 160 432 431.5 R . 429.5-431.5 ______1- 9-67 55.10 11- 6-67 27.6 217.5 G, L, T Idea 9 3/4 S-3 5/16 W do YM-8a ( P ) 1967 160.7 447 267.6 R 2 265.6-267.6 11- 6-67 27.4 238.3 G, L, T W 5ddd __ 10 S-7 W _ do CH 2 1962 100 500 500 C 8 m oi c 12-11-66 9.30 11- 3r67 24.2 188 G, L, R, T, HA, MA, Q 12acd _ 10 1/2 S-3 5/16 W _ do CH-14YM 1965 140.3 257 182 R 1% 180-182 12- -65 41.0 3-23-68 26.1 ISO G, L, T 12bdc _ 10 1/2 S-3 11/16 W _ do YVI 24(P) 1965 101.9 182 172 R 1% 170-172 11- -65 4.5 L 12cccl _ 11 S-4 W dr» WT 9Q { f> \ R 1% 10-21-66 26.9 9 5 L 12cddl _ 11 S-3 5/8 W do __ YVI-25(P) 1965 101 182 150 R 1% 148 150 11- -65 2.40 ' L 12daa _ 10 1/2 S-3 W do ______CH -15YM _ 1965 163 240 212 R iy2 210-212 12-12-66 61.60 11- 6-67 25.2 212 G, L, T 13add _ 11 1/2 S-3 1/16 W do _____ YM --IO(P)- 1967 171.6 347 347 R 2 345-347 2-25-67 75.55 2-25-67 26.1 208.6 G. L, T ISbccl _ 11 7/16 S-4 W do YVI 21(P) 1965 101 203 170 R 1% 168-170 10- -65 7.1 L 14aaa2 11 S-4 W do CH-12VD 1965 101 153 60 R iv* 58-60 10- -65 5.0 10-21-66 28.3 L 14ddd _ 12 S-4 W do YM-ll(P) 1966 167.7 242 170 R 1% 12- 3-66 73.47 3-23-68 26.4 170 G, L, T 15dcc _ 12 S-5 1/2 W do ______CH-11VD _ 1964 98 186 166 R i% 12-11-66 5.94 4-16-67 23.9 165.5 L, T, Q 23ddd _ 13 S-4 W __ do ______CH-17YM _ 1966 166.9 462 200 R 1% 198 200 12- 3-66 74.35 3-23-68 26.3 200 G, L, T 24cbb _ 12 9/16 S-3 15/16 W Colorado Federal 1 _ 1954 170 6,007 6,005 R 12-8 D, E, L, Basin As­ P sociates. 35bbb _ 14 1/8 S-4 7/8 W J. M. Hickey Federal 1 _ 1£1 SSfl R . L and Son. (C-10-25)26abal_ 13 S-10 1/4 W 1966 93 492 492 R 1^4-1 3- 7-67 11.92 11-28-67 23.2 162.4 G, L, T Reclamation, AREA,GEOHYDROLOGYOFYUMATHEARIZONAANDCALIFORNIAH149 26aba2 _ 13 S-10 1/4 W do CH 30VD _ 1966 93 492 440 R 1% 438-440 3 7 67 11.91 11-28-67 22.7 108 G, L, T 26aba3 _ 13 S-10 1/4 W __ do ______CH-30VD _ 1966 93 492 180.7 R 1% 178.7-180.7 3- 7-67 12.21 11-28-67 22.8 48.7 G, L, T 26aba4 _ 13 S-10 1/4 W do CH 30 VD 1966 93 492 21 R 1% 19-21 3- 7-67 12.16 11 28 67 24.6 19 G, L, T 35bbd _ 14 1/8 S-10 13/16 W U.S. Geological LCRP 17 1964 94 2,946 1,998 R, G 14-8 520-1,998 388 4.9 2 2 67 14.38 2-17-68 21.9 150 C, E, L, Survey. HA, PTp, Q, W, T (C-ll-21)4ddc __ 16 S-ll 7/8 E U.S. Bureau of CH-9YM 1964 403.3 373 350 R 8-6 1-11-66 296.45 1-11-66 33.3 298,7 L, T, W Reclamation (C-ll-22)13acb _ 17 5/16 S-8 9/16 E __ do ______CH-26YM _ 1966 310.6 238 238 R 2 11- 3-66 201.0 11- 3-66 30.0 208.5 G, L. T, W 23dab __ 18 9/16 S-7 7/8 E U.S. Geological LCRP 33 1967 381.6 328 328 C. R 6 9 326 328 2-21-67 303.21 2-20-67 30.6 310 G, T, W Survey. 24bab __ 18 S-8 3/8 E U.S. Bureau of CH-27YM 1966 322.3 270 270 R 2 268 270 11- 3-66 213.82 11- 3-66 30.0 231.0 G, L, T. Reclamation. W (C-ll-23)34bbc _ 20 3/16 S-0 1/16 E U.S. Geological LCRP 30 - 1965 163.0 623 600 R, G 12-10 160-600 1,340 10.0 12-14-66 85.45 12- 9-67 31.6 208.5 C, E, G, Survey. L, T, PT, Q, W (C-ll-24)23bcb _ 18 3/8 S-4 7/8 W __ do _____ LCRP 10 _ 1963 160.8 1,038 1,033 C 16-12 165-1,002 2,550 18.5 12-13-66 79.82 3-27-68 27.7 248.0 D, G, L, R. T. HA, PC, PTp. Q, W (C-ll-25)llab2 _ 16 1/16 S-10 3/8 W Yuma Valley Musgrove 1- 1940 90 4,868 1,650 R 10 D, E, L Oil and Gas Co. (C-12-21)14dab _ 23 1/2 S-13 13/16 E U.S. Bureau of CH-25YM _ 1966 422.2 369 369 R 2 11-22-66 345.55 12- 7-67 31.5 367.7 L, T, W Reclamation. 17cbc _.. 23 11/16 S-10 E __ do _____ CH 23YM _ 1966 356 320 320 R 2 12-14-66 285.21 12- 7-67 35.4 290 G, L, T, W 25add .__ 25 1/2 S-1B E __ do ______CH-24YM _ 1966 455.4 410 410 R 2 10-25-66 383.60 12- 7-67 32.5 407.9 G, L, T, W (C-12-22)9bab __ 22 S-5 5/16 E U.S. Geological LCRP 24 __ 1965 233.5 415 415 C 12 318-346 600 65.0 12-14-66 158.82 12- 9-67 35.6 328.5 D, G. L, Survey. T, PT, O. W (C-13-20)2abdl _ 27 1/8 S-19 5/8 E U.S. Bureau of CH-28YM _ 1966 577.5 1,427 1,200 R 1% 1,198 1,200 11-22-66 501.25 12- 7-67 37.6 899. 8 A, Cc, G, Reclamation t,, T, E 2abd2 _ 97 1 /Q Q 1Q F\ /Q "C1 __ do _____ CH-28YM _ 1966 577.5 1,427 600 R 2 598-600 A, Cc. G, L, T 16S/22E-21Dbb __ 2 N-3 W do _ CH-14RD 1965 128 507 120 R 1% 118-120 12-16-66 7.40 11-10-67 25.1 119.5 C, E. G, L, T 23Caa ___ 2 N-0 5/8 W do _ CH-8 1964 128.5 360 344 C 12 96-104 12 16 66 6.96 10-29-67 22.5 178.0 G. L, R, T, HA, Q 29Gca2 __ 0 5/8 N-3 3/8 W U.S. Geological LCRP 26 . . 1965 125.4 1,777 1,769 R, G 12-8 125-1,127 1,100 8.7 4-13-65 14.21 3-26-65 23.3 130.0 A, Cc, Survey. 1,368-1,769 Dip, E, G, L, R, T, PTp. Q, W See footnotes at end of table. TABLE 16. Water-test wells and oil-test wells Continued (W l Or 01 Water level Water temperature O o g V 01 1 IS I O T3 ^ CD V 2O 3 Owner Other £ ,Q Other S S 5 Well Coordinates or number JJ) 73 U S S Ug data

IS surfaclandAltitudeof constructionofMethod o i. U Owner depthCompleted Casingdiameter -S ° Other data Well Coordinates or numberOther completedYear t5 K available user £ f *l S T3 S s s a 3 -S f O3 & S 0 E-

Altitudelandsurfaceof Methodconstructionof -3o Owner Completeddepth Casingdiameter "S ,0 Other data Well Coordinates or numberOther completedYear 88 available user 5 0)» 13 3 ft O ri 0) ri O H Q Q Q HI H (C-9-23)8bbb _. __ 4 S-2 W Yuma County 33 1956 120.9 135 135 J 1% 9.38 25.3 134.0 G, L, T. W Water Users' Association, ._ _ 4 1/2 S-l 5/8 W do 85 1957 122.9 146 146 J 1% 10-18-66 9.22 11- 5-67 29.0 142.0 L, T, W H 5 S-2 W do 25 1956 116.0 131 131 J 1% 10-18-66 7.25 11-11-67 24.2 130.0 G, L, T, W £0 8dcc _ .. __ 5 S-l 1/2 W -do 26 1956 115.7 1241/2 1241/2 J 1% 10-18 66 9.20 11 11-67 26.1 126.5 G, L, T, W O 8ddc _. 5 S-l 1/8 W U.S. Bureau of 1947 157.7 64 59 R 21/2 D, G, W Reclamation. Sdddl . 5 S-l W _do ____ _ 1947 193.4 106 106 R 21/2 72.31 24.7 76.0 D, G, W O 8ddd2 . _ 5 S-l W Yuma County 40 1956 193.5 211% 2111/2 J 2 5-14-67 73.93 11- 5-67 26.8 212.4 G, L, T, W Water Users' Association. Ilbbb2 . 4 S-l E U.S. Bureau of 1947 204.5 831/2 831/2 R 2% 9-30-66 61.48 9-30-66 27.5 68.3 D Reclamation, 12baal .. _ _ 4 S-2 1/2 E do _ 1956 211.5 83 83 R 2 9-28-66 63.12 9 28 66 23.3 64.1 D, G, W IT" 4 S-2 1 /2 E D do 1956 211.5 60 R 2 O 13aaa . 5 S-3 E _ -do 1947 209.1 100 99 R 12- 8-66 54.60 12- 8-66 23.6 73.0 D, T, W 13bddl . 51/2 S-2 1/2 E _ do 1956 210.5 40 R 9- 8-66 25.61 D, W 3 13bdd2 . 51/2 S-2 1/2 E _ do 1956 210.5 93 93 R 2 D. W M 13bdd3 . 51/2 S-2 1/2 E -do­ R 13bdd4 . __ 51/2 S-2 1/2 E do R 13bdd5 51/2 S-2 1/2 E do O R 9-28-66 9-28-66 13cbbl _ 5 1/2 S-2 E do 1955 208.4 42 42 R 1% 35.56 22.8 36.5 D, G, W oIT" 13cbb2 51/2 S 2 E do 1956 208.4 103 103 R 1% 12- 8-66 48.86 23.3 97.5 D, G, T, W 13ddd . 6 S-3 E do 1947 204.4 103 103 R 21/2 12- 8-66 44.55 12- 8-66 24.2 79.4 D, G, T. W O 14bdd . 5 1/2 S-l 1/2 E do 1947 205 105 100 R 21/2 D, W 14cccl _ 6 S-l E U.S. Geological 1961 203.0 56 56 A 1V4 9-28-66 45.56 9-28-66 23.9 49.5 D Survey. d 14ccc2 _ 6 S-l E - do 1961 203.0 106 106 A 9-28-66 46.00 9 28 66 23.9 58.5 D o 14ccc3 _ 6 S-l E do 1961 203.0 170 170 A 9-28-66 45.85 12- 5-66 23.6 61.4 D, T 14cdd -.- _ 6 S-l 1/2 E U.S. Bureau of 1947 150 100 R 2'/2 D, W Reclamation, 15bbb 5 S-0 2 12- 8-66 12- 8-66 27.8 97.4 D, T, W do 1947 184.7 103 103 R 47.33 H 16bcc 51/2 S-l W - do 183.9 106 105 R 12-15-66 62.64 12-15-66 25.3 92.5 D, G, T, W 16ccc 6 S-l W do 1946 177.0 106 105 R 12 15 66 54.85 12-15-66 25.0 86.0 D, G, T, W I7abc2 2 ___ 5 1/4 S-l 1/2 W Yuma County 37 1956 115.0 125 125 J 1% L Vui Water Users' > Association, IT" 17abd . 5 1/4 S-l 1/4 W do 31 1956 120.5 132% 1321/2 12- 1-66 8.38 12-14-67 27.0 132.2 G, L, T, W J 12-14-67 H 17acc2 5 1/2 S-l 1/2 W do 36 1956 115.8 135 135 J 10- 5-66 5.80 28.1 131.5 G, L, T, W O 17bdb _ 5 1/4 S-l 3/4 W -do 32 1956 117.1 125 125 J 12 1 66 10.94 12-14-67 24.8 124.8 G, L, T, W 17ccc _ __ 6 S-2 W do 2 1956 113.4 120 120 J 12- 1-66 10.12 12-14-67 24.0 120.0 L, T, W 2 17cdd _ 6 S-l 1/2 W do 1 1956 115.0 117 117 J 12- 1-66 9.29 12- 1-66 26.7 11.0 L, W W 51/2 S-l 1/8 W 1947 149 64 62 R 21/2 D, G, W H Reclamation, > 17ddc _ _ _ 6 S-l 1/4 W do 152.9 64 R 21/2 2-25-67 38.72 2-25-67 25.8 44 D, G, W 19aaal _ 6 S-2 W U.S. Geological 1961 112.7 34 A 2-28-61 9.53 D, Q > Survey W 19aaa2 6 S-2 W do 1961 112.7 63 63 A 2-28-61 11.44 D, Q H 19aaa3 _ 6 S-2 W do 1961 112.7 81 81 A 2-28-61 10.25 D. Q 19aaa4 ___ 6 S-2 W -do 1961 112.7 136 136 A 2-28-61 9.78 D, Q 19ccc _ 7 S-3 W do 1965 109 172 149 A i4 11-29-66 8.73 11- 2-67 26.8 149.0 D, T, Q, W 20dbb _ 6 1/2 S-l 7/16 W Yuma County 30 1956 116.4 140 140 J 1% 10-11-66 6.49 4-13-67 25.0 139.9 L, T, W Water Users' Association. 21bddl 6 1/2 S-0 1/2 W U.S. Bureau of 1 QQ 9 217.9 R 9- 8-66 54.95 12- 3-66 24.2 209.4 T. W Reclamation. 21bdd2 6 1/2 S-0 1/2 W _ -do 193.2 165.8 R 9- 8-66 42.25 9-28-66 22.8 43.4 W 21bdd3 6 1/2 S-0 1/2 W do 193.2 147.5 R 9- 8-66 41.97 22.2 46.7 W 21bdd4 6 1/2 S-0 1/2 W do 193.2 R 9- 8-66 40.09 9-28-66 22.2 42.4 W 21bdd5 6 1/2 S-0 1/2 W do 193.1 101 101 R 2V2 9 f 66 39.98 9-28-66 21.7 40.4 D, W 22cccl rr Q A do 1953 193.2 70 R 2% 9-28-66 30.66 9 28 66 22.2 33.4 D, W 22ccc2 7 S-0 do 1947 193.2 119 117 R 4-13-67 35.24 4-13-67 23.1 100.4 D, G, T, W 23ccc 7 S 1 E do 1951 199.4 72 103~~ R D, W 25aaa .. _ 7 S-3 E . do 1947 205.4 103 R 2 3-16-67 45.47 3-16-67 24.4 93.7 D, G, T, W GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H153

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507-243 O - 74 - 11 TABLE 17. U.S. Geological Survey auger test holes and test wells, Yuma County Water Users' Association deep observation wells, and selected U.S. Bureau OX of Reclamation observation wells Continued

Water level Water temperature

landsurfaceAltitudeof constructionMethodof |"3 % Owner depthCompleted Casingdiameter -H J2 Other data Well Coordinates or numberOther completedYear 3 K available user 0, «JS 3 3 S3 a 3 -*j01 a S o Kj 01 a O «ji » H EH P P P P-S (C- 9-24)10ced ______5 S 5 1/2 W Yuma County 87 1957 109.5 125 125 J 1% 10-11-66 5.30 10^27-67 22.6 114.0 G, L, T, W Water Users' H Association, 2- 3-68 t/2 llccc _ _ 5 S-5 W do 95 1958 110.9 126 126 J 1% 10-11-66 6.69 22.6 125.8 3 G, L, T, W O 5 S-4 1/2 W do 86 1957 110.9 130 130 J IVa 10-11-66 7.02 10-27-67 23.2 1-8.2 G, L, T, W 15bbb __ 5 S-6 W do 92 1958 107.4 130 130 J 11/2 12- 1-66 3.8 10-11-66 28.6 9.8 L 16bbb ___ 5 S-7 W _ _do 93 1958 110.7 137 137 J 1% 10-11-66 7.12 10-26-67 22.1 133.5 G, L, T, W 10-20-66 11-12-67 o 19ccc _ __ 7 S-9 W U.S. Geological 1965 110.4 192 189 A 1% 5.60 21.3 148.0 D, G, T, Q __ Survey. CQ 20ddd2 7 S-7 W Yuma County 47 1956 106.6 138 138 J 1% 10-19-66 7.76 10-27-66 22.7 139.5 G, L, T, W Water Users' Association. 22bbb _ __ 6 S- 6W U.S. Geological 1965 107 167 107 A li/4 10-19-66 5.79 10-27-67 22.6 106.0 D, G, T, Q Survey. f 24aaa _ _ _ 6 S-3 W Yuma County 14 1957 110.5 1261/2 126% J l% 10-10-66 6.76 4-12-67 25.0 128.2 G, L, T, W o Water Users' Association. 7 S-3 W _ do 19 1956 111.3 133 133 J 11/2 12- 3-67 7.7 L, W 110.9 1391/2 1391/2 J 11/2 10-19-66 11.76 10-27-67 25.4 141.3 G, L, T, W 7 S-4 W do 18 1956 10-19-66 11-11-67 26cbb _ _ _ 7 l/S-5 W U.S. Geological 1965 105 172 147 A 1% 6.70 22.7 147.0 D, T, Q O Survev. O 26ccc _ 8 S-5 W Yuma County 17 1956 103.9 147 147 J 1% 10-19-66 5.18 11-11-67 22.6 147.0 G, L, T, W tr1 Water Users' O Association. 10-28-67 1956 110.0 142 142 J 1% 10-19-66 11.11 23.9 142.0 G, L, T, W 26ddd _ _ _ 8 S-4 W _ do 16 L 7 S-5 W _ do 45 1956 106.1 142 142 J 11/2 100.0 129 129 J 11/2 10-19-66 2.30 10-27-67 22.6 128.5 G, L, T, W 0 27bbb _ 7 S-5 7/8 W do 46 1956 (i) D 8 S-7 W U.S Geological 1965 107 202 A o Survey, to 111 172 131 A 11,4 10-19-66 14.61 11-28-67 21.4 121.0 D, T, Q 8 S-8 W do 1965 10-19-66 10-27-67 30aaa _ 7 S-8 W Yuma County 48 1956 115.5 142 142 J 1% 15.8S 22.2 143.2 G, L, T, W Water Users' H Association, W 136 136 J 1% 10-19-66 9.24 4-24-67 27.2 138.0 G, L, T, W 36aab 8 S-3 1/8 W do 15 1956 110.1 4-25-67 105.4 140 140 J 1% 10-19-66 8.70 28.1 139.3 G, L, T. W CQ 36acc _ __ 8 1/2 S-3 3/8 W do 67 1957 10- 4-66 10- 4-66 D, W 36add _ 8 1/2 S-3 W U.S. Bureau of 1947 175.7 100 100 R 2% 72.21 27.2 79.5 > f Reclamation. 2- 8-67 2- 8-67 29.1 L, W (C- 9-25)25aaa 7 S-9 W Yuma County 49 1956 110.4 150 150 J 1% 15.54 24.4 H Water Users' O Association. 1966 219.3 122 104 A 11/2 9-21-66 78.60 9-21-66 30.6 104.8 D, T, W (C-10-22)18cde ____ 12 S-3 5/16 B U.S. Geological CQ Survey. 4-28-65 D, G, W (C-10-23)3aaal ______9 S-l E U.S. Bureau of 1947 202.6 103 103 R 2% 25.0 100-103 Reclamation, 9-29-66 9 S-0 1947 194.8 101 101 R 2% 9-29-66 28.84 23.3 32.5 D, W Sbbbl do 11/2 9-22-66 37.4 D, W Tbbbl ______10 S-3 W _ _do 1955 160.4 48 48 R 35.85 23.3 100 2~03~~ R 2% 9-22-66 41.68 9-22-66 22.2 43.8 D, W 7bbb2 _ _ 10 S-3 W do 1947 160.4 12- 9-66 3-23-68 203 G, L, T, W 7bbb3 _ 10 S-3 W Yuma County 53 1956 160.6 203 J 2 56.87 26.6 Water Users' Association. 9- 9-66 W Sbbbl 10 S-2 W U.S. Bureau of R 33.30 Reclamation, 21/2 3-17-67 8bbb2 _ _ 1947 183.6 101 101 R 9-28-66 40.93 22.8 93.6 D, G, W 10 S-2 W do 9-15-64 48.14 23.3 87.0 D 9«ao1 10 S-0 U.S. Geological 1961 196 86 86 A 1% Survey 9-15-64 D 10 S-0 1961 196 126 126 A 1% 46.21 196 169 169 A 1% 9-15-64 48.13 11- 6-67 25.1 170.5 D, T 10 S-0 do 1961 9-29-66 12-12-66 21.9 89.5 D, G, T, W 9bbb 10 S-l W U.S. Bureau of 1947 188.8 101 101 R 2% 54.77 Reclamation. li,4 9-15-64 D Ilccb2 _ 10 3/4 S-l E U.S. Geological 1962 195 182 147 A 57.80 Survey. D __ do _ ___ 1966 204 91 A 9- 1-66 >90 13bcb 2 _____ 11 1/4 S-2 E 9-14-66 89.98 12-17-67 28.8 112.2 D, T, W 13cbb 11 1/2 S-2 E do . 19G6 204.2 111 110% A 1V2 221.0 122 120% A 1% 9-11-66 110.00 12-17-67 29.8 121.3 D, T, W 12 S-2 1/2 E do __ 1906 9-22-66 25.0 83.6 D, W 14bbb - - - 11 S- 1 E U.S. Bureau of 1947 194.9 103 102 R 2% 66.64 Reclamat'on. 16aaa _____ 11 S-0 -do _ __ 1947 191.2 115 113 2% 9-28-66 63.47 12-12-66 23.3 100.0 D. G, T, W 17aaa _____ 11 S-l W _ do 1947 188.9 105 2% 9-28-66 64.48 3-17-67 22.2 92.6 D, G, W 17bbbl ____ 11 S-2 W _ do 1956 182.2 83 83 D 17bbb2 ____ 11 S-2 W do 1947 182.2 101 101 2% 9-28-66 67.17 3-17-67 22.5 81.7 D, G,W 17cccl ____ 12 S-2 W -do 1947 188.0 2% 9-29-66 85.20 9-29-66 28.3 89.0 D, W 17ccc2 ____ 12 S-2 W do G 17ccc3 ____ 12 S-2 W U.S. Geological 1961 188.0 t 1 ) Survey. 17ddd _____ 12 S-l W U.S. Bureau of 1947 185.7 104 2% 9-20-66 76.97 9-20-66 27.2 89.5 D, G, W Reclamation. IScccl ____ 12 S-3 W Yuma County 83 1957 178.3 83% 83% 1% L, W Water Users' Association. 18ccc2 ____ 12 S-3 W U.S. Bureau of 1947 178.3 120 120 2% 9-29-66 80.82 9-29-66 27.2 82 D, G, W Reclamation. 18cp"!< __ 12 S-3 W Yuma County 82 1957 178.3 227% 227% 4 9-29-66 81.47 11- 6-67 28.2 219.5 G, L, R, T, W Water Users' Association 20bbb2 12 1/16 S-2 W U.S. Geological 1961 189 163 157 1% 7-11-61 86.45 Survey. 31bbb2 __ __ 14 S-3 W do 1961 172.8 157 157 V 9-16-64 80.44 Q 31bbb3 ____ 14 S-3 W U.S. Bureau of 1961 172.8 225 225 2 6-21-62 80.79 W Reclamation, 31bbb4 __ 14 S-3 W -do 1947 172.8 120 2% 9-20-66 79.77 9-20-66 27.8 83.6 D, G, W 31bbb5 ___ 14 S-3 W U.S. Geological 1962 172.8 202 189 6-21-62 81.03 D o Survey, 31bbb6 14 S-3 W do 1962 172.8 212 136 1% 6-21-62 80.71 D s 31bbb7 ___I 14 S-3 W do 1962 172.8 222 200 1% 9-15-64 79.00 D Slbbbg 14 S-3 W do 1962 6-21-62 S1.43 D 31bbb9 14 S-3 W __do 1962 1% 6-21-62 81.03 SlbbblO ___ 14 S-3 W - do 1962 172.8 1V4 6-21-62 81.13 o 33bbb _____ 14 S-l W U.S. Bureau of 1947 184.5 80 80 2% 9-20-66 >80 D, G, W *i Reclamation. (C-10-24)lbaba ____ 9 S-3 5/8 W Yuma County 65 1957 107.4 143% 143% 1% 12 2 66 4.0 L H Water Users' Association, Ibdd2 ____ 9 1/2 S-3 9/16 W do _ 80 1957 107.4 149 149 1% 10-21-66 8.46 11-29-66 26.1 12.0 G, L, W Icdd3 ____ 10 S-3 9/16 W do 58 1956 107.6 146 146 1% G, L, W 2aaa __ __ 9 S-4 W __ do ______66 1957 107.4 138 138 1% 10-19-66 10.76 10-28-67 24.0 139.2 G, L, T, W 2add _____ 9 1/2 S-4 W do 97 144 1% 12- 2-C6 6.8 L 2bbb _____ 9 S-5 W do ftl 105.7 149 149 1% 10-19-66 9.23 10-28-67 24.2 139.0 L, T, W 3caa _____ 91/2 S-5 1/2 W _ do 13 1956 99.6 149% 149% 1% 10-21-66 4.72 11-12-67 24.2 150.0 L, T, W 3ddd _____ 10 S-5 W U.S. Geological 1965 107 192 93 1% 10-21-66 8.91 10-28-67 23.8 96.0 D, G, T, Q Survey. 6bcc _____ 9 1/2 S-9 W _ do 1966 101 164 1% 10-20-66 12.65 10-28-67 21.5 166.2 D, G, T M 7ccc _____ 11 S-9 W do 98 1 Q9 180% 1% 6-24-65 23.3 178.5-180.5 D, Q 7ddd _____ 11 S-8 W Yuma County 11 1956 97 147 147 1% 10-21-66 7.07 11-12-67 24.6 145.3 G, L, T, W Water Users' Association, llaaa _____ 10 S-4 W -do­ 57 1956 104.2 144 1% 10-21-66 8.31 4-26-67 23.9 89.8 G, L, T, W lldaa _____ 10 1/2 S-4 W do 54 1956 101.8 140 1% 10-21-66 20.78 4-26-67 25.3 143.2 G, L, T, W lldab _____ 10 1/2 S-4 1/4 W do __ 55 1956 103.1 142 142 1% 10-21-66 10.11 4-26-67 24.4 143.1 L, T, W 12bccl ____ 10 1/2 S-3 3/4 W __ do ______56 1956 101.0 140 140 1% 10-21-66 5.45 10-21-66 26.7 19.8 G, L, W 12dddl ____ 11 S-3 W U.S. Bureau of 1947 162.9 103 103 2% 9-22-66 62.58 9-22-66 25.6 68.6 D, G, W Reclamation. 12ddd2 _. __ 11 S-3 W Yuma County 52 1956 163.8 207 205% 2 12-12-66 62.23 11- 4-67 25.0 205.5 G, L, T, W Water Users' Association, 13abb ____ 11 S-3 3/8 W do __ 12 1956 101.3 144 1% 10-21-66 3.01 3-23-68 26.4 144.5 G, L, T, W O 13bad _____ 11 1/4 S-3 1/2 W d:> ______74 1957 100.4 149 149 1% 10-22-66 3.46 10-22-66 26.7 8.3 G, L, W O 13bbc2 ____ 11 1/4 S-4 W - do 75 1957 99.5 149 149 1% 10-22-66 4.29 10-22-66 25.8 5.0 G, L, W !> 13bbd2 ___ 11 1/4 S-3 3/4 W - do 89 99.1 10.0 6- 2-66 3.3 L f 13dhb _____ 11 1/2 S-3 7/16 W __ do ______71 1957 1C6.7 150 150 1% 10-22-66 9.63 12-12-66 26.9 148.0 G, L, T, W 14aaa] ____ 11 S-4 W do 7 1956 101.5 147% 147% 1% 10-21-66 7.41 ' 4-26-67 23.9 148.1 G, L, T, W 14bbb _____ 11 S-5 W do _ 8 1956 99.5 145 145 1% 10-21-66 6.33 10-28-67 23.7 139.1 G, L, T, W 14daal ____ 11 9/16 S-4 W _ do 70 1957 106.2 100 92 1% 10-22-66 11.34 10-22-66 26.4 14.6 L, W 14daa2 _ __ 11 9/16 S-4 W -do­ 76 1957 106.2 149 149 1% 10-22-66 11.56 11- 6-67 24.4 148.6 G, L, T, W 15bbb __ _ _ 11 S-6 W do 9 1956 98.3 143 143 1% 10-21-66 6.02 11- 4-67 23.1 141.2 G, L, T, W ]5daa _____ 11 1/2 S-5 W do 77 1957 96.7 149 149 1% 10-22-66 3.94 10-28-67 23.4 149.5 G, L, T, W 16baal ___. 11 S-6 1/2 W do 64 1956 101.0 142 142 10-21-66 8.28 11- 4-67 23.2 139.4 G, L, T, W 17aaa* ____ 11 S-7 W do _ __ 10 1956 98.8 147 147 1% L 17dcc _____ 12 S-7 1/2 W U.S. Geological 1965 94 192 158 10-22-66 6.68 10-28-67 23.9 155.0 D, T Survev. 20aaa _____ 12 S-7 W Yuma County 91 1957 93.6 140 140 1% 10-22-66 3.89 10-28-67 23.7 136.7 G, L, T, W Water Users' Association, 21dddl ____ 13 S-6 W do __ 78 1957 97.5 149 149 1% 10-22-66 8.42 3-31-67 24.4 93.4 L, T, W 21ddd2 ____ 13 S-6 W __ do ______79 1957 97.5 95.5 93 1% 10-22-66 8.27 10-22-66 28.1 10.4 G, L, W 22acc ____ 121/2S-51/2W U.S. Geological 1966 104 187 144 10-22-66 25.15 10-22-66 23.3 27.0 D, G Survey, 22dbc _____ 12 5/8 S-5 3/8 W do 1966 121 187 166.5 1% 10-22-66 2.73 10-28-67 23.8 148.5 D, G, T

See footnotes at end of table. TABLE 17. 1/.5. Geological Survey auger test holes and test wells, Yuma County Water Users' Association deep observation wells, and selected U.S. Bureau H-w1 of Reclamation observation wells Continued Ul O Water level Water temperature

surfacelandAltitudeof constructionMethodof h Depthinfeetbelow Owner depthCompleted Casingdiameter Other data Well Coordinates or numberOther completedYear available user £ ! landsurface 3Pi $ S

fie' G'EH" of of® c'^GQ' GC'C' G> of P^EH CT EH EH aG>EHO G>f£ EH EH EH EH EH EH" EH C HfCfCc'C'HC'dl^ EH 4^ EH" G'EH 4o QQQQQGQQQQQ" aQQQQQQQQQQQQ'Q QtHhfifiQQQi^" i4oi4Q QQ

oeg OOlO OOO 10 O OO 1OOOS3 ooo eg 10 to 100030 oo c-oo * eg oo 10 O300OrHO31OtOCg to t- to to to o oo * oo cot--*t- oooo eg to 10 to-"* eg coegioegTHcgegTH corn iHcg o -*ocgco -*o3cgeg TH eg 1 1 rH 1-1 II II * * CO 1O

*~(rH rH N

0300 t-t-eg CO OOOO 00 lOCOCOrH.rHOOO TH ** oo as oo o t- 03 eg cgiot-t- t-os eg as to rH «* rH 03C-C- t> eg' t> 10° 10 03 eg eg' 10 cg'coNcoeg'cgrHcoeg IH'OTHTH * *-* eg eg eg eg eg eg eg eg eg eg eg eg eg eg eg eg eg eg eg egNegc<) eg eg V c-c- to to t- t- t- to co c-c-co»c-t-t~co to to to to COCDCDcOtOCDtOtO tototototocotototo totococo coco co eg eg 03 coosegooOtOiH1 1 1 1 1 1 1 1 o as o ** 10 o to as o o as o o ego 1 1 1 1 oeg 1OIO rH rH 4

00 00 C-1O O as eg oo 00 I to c- oo co oo * co -* OS rH t- OS OS tO O CD COCO OS O "*' 03 t- * rH OS CO' OS 00 OS O3 rHrHO3 eg to to' »-< * * cooi rHeg CO * rH10TP 1 * iH rHrH iH iH rH rH eg rH

toco ^tOTf^tO to to to c- to CO to t- t- l> CD t-toto to c- cococoto coco coco to to to to COCDCDCOCOCDCOCD 1 1 1 ,u t- t- to o to ^tJ-eg ' ctcitOTH to rH co eg oo ooo** eg eg egrH eg IH eg eg egegeg M°l 1? o eg O-HO^TfO * nrHrU^Ul ^irHrHIII O1 1O1 OOOrH1 1 1 1 iH' r-4i

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1

OO3 00 r-tCgt-00 OlOOSCOrHCOlOlOlO O TH CDOSt- CO Oio corHe

lOtO tOCDtOCOtDtDtDtOtDCDtD as as as as os as as as as as as as as as as as as as as as as as as as as os as as as as as as as as as as as as as es as as as

i i i i i i i i i i g 2fcS i 1 ' i i i i i i i i 2 222 " i 1 1 IIIIIIII 1"1 THrHrH ' 3 ] 1 1 I II" II" 1 1 i i i >,£ j is !.s ! 1 1 i i i ^ <» 5 i - i ^o i 1 1 i i c to o i be i^ i 1 1 1 g 3 ' § i ^ ! 8 & ! 1 1 f>, 1 1 o^oooooooooooco > ccocccoccccoccc occcttooracaaioo!; J ^CC "O . p'O'O'O'O 'O'O'O'O'O'O'O'C 11 ^t 1^ 11 ^ 1 1 1 W W 1 1 S r^ ^ W W 1 1 it) ! 1 1 ! iiS t>

WW E3 fe r* !> feS oo to H TH tO^fe fe to fei^^^ H ^rH 00 tO feg OOOO CO\ H \ rt OOrHrH^ ^5^^ 00 ^ N.N.\^^\.fe: fe ^i 9°7 rHrH 0? rHW tOrH "= COCO 0 H THrH^r^r^ CO 10 w °° 'S; 0 '!''"' ' "^ OOV^IH ocg'fegos rH o o eg IH r-t « f Tt "f T^^ 5? 1"1 1 OtO Z^ tO-Z^ 10 H H V ^Vto 1"1 ^ j5j5*5 r~'S r ^ S r ^S""1 ^^^! W M oo°°^ '"^ S

j \ Cg * * TH ^^ 00 | rH I | 00 eg ^i ^ ieg iegoooO|eg|eg eg eg -«t * oo rH * IH rHt-ioy r oo ,H Was \\\co^^4.\^^"^- rH OT rH £ r^l ^ ^H CO >> *Z r^l ^ r? ^H~ rH r-t S rH rH 1O IO r-l r_( ^rHC?^ ^ \G> 1O rH ^ TtTtTtcocococoegegegrHrHcgrH rHOrHOOOOOO OOO-* 1O * I S 1 1 1 1 1 1 1 1 1 1 1 1 01 1 1 1 1 1 1 1 1 1 1 1 1 IH 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 B 1 1 1 1 1 1 c3 1 01 d ., pj ?J 1 1 QJ l| ^ill|llil|g * "(2WWQ§[JO&<§PQH?!iiOr^PQQ QQOt^ Q<2 ^| aJ S! o ~ H & H H H ft O'S TABLE 18. Drainage and supply wells

Well number: Location of well according to the Federal land classification. See page H17 for description of well-numbering system.. cn Coordinates: Location of well according to grid system used by U.S. Bureau of Reclamation in Yuma area. See page H17 for explanati6nexplanatil of grid system. 00 Owner or user: Government agency or irrigation district that drilled the well or had it drilled. Other number: Number assigned to well by government agency or irrigation district. Year completed: Known or reported year of completion of well. Altitude of land surface. Average altitude of land surface at well ajbpve mean sea-level datum.Altitudes given to nearest foot ar approximate and were obtained from topographic maps. Alti­ tudes given to decimal fractions of a foot were obtained by spirit leveling to a reference point at the well and are much more accurate. Log information, water-level data, and tempera­ ture data are referred to land-surface datum. Total depth: Greatest depth, in feet below land-surface datum, to which well was known or reported to have been drilled. Well may have been completed to a shallower depth or filled in subsequently. Completed depth: Depth, in feet below land-surface datum, to which well was cased or subsequently plugged. Method of construction: Letter symbols designate C, drilled with cable-tool or percussion equipment, D, drilled, method unknown: RG, drilled with rotary-mud equipment and gravel packed; RRG, drilled with reverse-circulation rotary equipment and gravel packed. Casing diameter. Nominal inside diameter, in inches, of casing used in well. Where more than one figure is given, figures refer to diameter of casing in each successive segment from land surface downward. i Depth of perforated interval: Depth, in feet below land-surface datum, to top of highest perforations or well screen and base of lowest perforations or well screen. Where more than one H major aquifer or water-yeilding zone is perforated or screenei, figures refer to top and bottom of perforated or screenen intevals in each aquifer in downward sequence. W Type of pump and horsepower: Source of power and pump type are designated by letter symbols E, electric; T, turbine. Number indicates horsepower. » Discharge: Measured or reported discharge of well in gallons per minute. Drawdown: Measured or reported drawndown, in feet, accompanying discharge in previous column. » Water level: Date measured by Geological Survey or reported by owner or other agency. Depth to water in feet below land-surface datum. W Water temperature: Date measured by the Geological Survey. Temperature, in degrees Celsius, of most recent sample of water pumped from well believed to represent water from the depth W of the perforated interval in the coarse-gravel zone. In some wells, not equipped with pumps, temperature was measured with a thermistor or a maximum thermometer at a depth be­ o lieved to represent the middle of the coarse-gravel zone or an equivalent depth be!ow land surface. a Other data available: Additional information about tbe well available in files of Geological Survey. Some of this information is given in other tables of the present report. The type of in­ » formation is indicated by the letter symbols D, driller's log; E, electric log (spontaneous potential and resistivity); L, lithologic log made by a geologist from drill cuttings and other o information; T, temperature log; PT, pumping test or tests; C14, radiocarbon date of formation sample; Q, chemical quality-of-water data; W, periodic or continuous water-level records. W t/J Water level Water temperature O *1 1 f a a TB S % * O Owner 0 t> Other s 01a gg. 3 Well Coordinates or Other T5 C data W user number T5 ft Pfc i§ available I ° 1 » .-2 ^B '-3 be P§1 .S*S JU ^H o S p 1 |g -S "3 *- *! M M o "3 tt 01 V 3 II 1 no! £ g 5 1 A o C f o 5 o Q Q Q o Q3 o (C- 8-22)25ddd __ 2 S-9 E U. S. Bureau of CH-721 1964 152.8 163 161 RRG 20-14 100-160 T, E, 60 12- 2-65 20 10-29-66 23.4 100-160 D, L, Q Reclamation, £ 26bbb 1 S-7 E do CH-714 1964 151.0 146 135 RRG 20-14 84-134 T, E, 60 3-16-64 15.0 11- 9-66 20.6 88-135 D, L, T, Q o 26ddd __ 2 S-8 E do _____ .. CH-720 1964 150.8 170 161 RRG 20-14 90-160 T, E, 60 12- 2-65 19 10-29-66 22.5 90-160 D, Li T, Q o 27bbb __ 1 S-6 E do ______CH-713 1964 150.4 150 147 RRG 20-14 86-147 T, E, 60 12- 3-65 22.7 10-28-66 21.1 86-147 D, L, T, Q » 27ccc - 2 S-6 E - do CH-718 1964 147.5 182 177 RRG 20-14 106-176 T, E, 60 12- 3-65 19.0 10-28-66 21.1 106-176 D, L, T, Q I I 27ddd ___ 2 S-7 E __ do __ . __ CH-719 1964 148.6 169'/£ 166 RRG 20-14 95-165 T, E, 60 12- 3-65 18.3 10-29-66 22.2 95-165 D, L, T, Q < 28ccc __ 2 S-5 E do ____ .._ CH-717 1964 145.0 171 168 RRG 20-14 117-167 T, E, 60 3-11-64 18.0 10-28-66 21.7 117-167 D, L, T, Q W 30dbc 1 11/16 S-3 1/2 E _do ______CH-716 1964 138.5 171 165 RRG 20-16 106-164 T, E, 60 12- 3-65 15.7 10-29-66 21.7 106-164 D, L, T. Q 31bcc __ 2 1/2 S-3 E - do SGDW 1 1961 138.9 216 200 RG 20-16 130-200 T, E, 40 3/702 22.85 6-21-61 3.6 6- 6-67 24.3 130-200 D, Q Sldbbl 21/2 S-3 1/2 E - do ... SGDW 2 1961 140.3 216 205 RG 20-16 130-205 T, E,60 3,772 12.97 8-17-61 3.3 3-31-67 23.5 130-205 D. E, Q CQ 32cbb _ 21/2 S-4 E do SGDW 9 1961 141.0 200 189 RG 20-16 124-189 T, E, 60 3,800+ 13.89 5-26-61 13.7 10-29-66 22.8 124-189 D, E, Q > 32ccc __ 3 S-4 E __ do ______SGDW 3 1961 140.3 216 204 RG 20-16 129 204 T,E,60 3,800 19.21 3- 9-67 23.2 129-204 D, E, Q f 32cdd __ 3 S-4 1/2 E -do SGDW 4 1961 140.3 216 200 RG 20-16 90-200 T, E, 60 3,800 8.39 8-17-61 8.9 11-30-66 23.4 90-200 D, E, Q H 33add 21/2 S-6 E __ do ______SGDW 8 1962 147.5 241 225 C 20 136-186 T, E, 60 5-18-62 16.3 12- 2-66 22.6 136-186 D, T. PT, o Q 2 2 1/2 S-5 1/2 E - do SGDW 7 1961 146.2 207 RG 20-14 3,800 8.49 7.7 7-10-61 23.3 D, T, Q 21/2 S-5 1/2 E - do SGDW 7R 1965 146.6 185 180 12- 3-65 21.5 11- 9-66 22.9 119-180 D CQ 33cbb - 2 1/2 S-5 E do SGDW 6 1961 144.5 204 190 RG 20-16 115-190 T, E, 60 8-17-61 9.2 6- 6-67 22.6 115-190 D, Q W 33ccc __ 3 S-5 E do SGDW 5 1961 142.2 204 190 RG 20-16 90-190 T, E, 60 3,800 7.99 8-17-61 3.1 11-30-66 23.3 90-190 D, E. Q > 34add __ 2 3/8 S-7 E do CH-750 1964 150.0 610 610 RG 20-14 500-600 T, E, 75 12- 6-65 20.6 3-31-67 22.5 500-600 D, L. PT, Q 35caa2 __ 21/2 S-7 1/2 E __ do ______CH-751 1964 151.3 611 586 RG 20-14 484-585 T, E, 75 12- 6-65 16.6 3-31-67 23.3 484-585 D, L. PT, Q 36cad __ 2 11/16 S-8 3/8 E __ do ______CH-752 1964 149.6 647 622 RG 20-14 520-621 T, E, 75 12- 6-65 17.9 10-24-66 24.4 22 D. L, PT, (C- 8-23)26cab 1 1/2 S-1 1/4 E _ do CH-709 1965 135.7 176 174 RRG 24 14 124-174 T, E, 40 4-23-65 17.1 3-31-67 23.1 124-174 D, L. T, Q 26ddb __ - do CH-710 1965 136.2 203 196 RRG 24-14 4-23-65 15,8 3-31-67 23.4 126-196 D, L 27acb 11/4 S-O 1/2 E - do _ ___ CH-708 1965 128 225 160 RRG 24-14 130-160 T, E 4-23-65 11.3 3-31-67 24.7 132-162 D, L, T, 0 32dbcl 2 _ 2 11/16 S-1 1/2 W Yuma County USER 8 1947 120.3 1291/2 D 3- 3-67 23.9 93 D. T Water Users' Association, 32dbc2 __ 2 11/16 S-1 1/2 W do 1 1956 120.3 198 198 C 24 130-170 T, E, 60 3- 3-67 *41.8 5-13-67 27.4 130-170 D. Q 35aac _ _ 21/4 S-1 3/4 E U.S. Bureau of CH-711 1965 136.0 201 195 RRG 24-14 125-155 T, E, 60 4-23-65 10.0 3-31-67 25.0 125-195 D, L, T, Reclamation. 165-195 Q (C- 9-23)5cdal 3 3 3/4 S-1 9/16 W - do -_ 119.0 bcda.2 ___ 3 3/4 S-l 9/16 W __1964 119.0 220 220 C 24 121-143 1964 12 2- -65 2&7 121-143 D. Q Water Users' Association. 5cdb __ 3 3/4 S-l 5/8 W _ 1955 118.0 194 184 C 24 120-184 T, E, 150 _ - 11- 5-67 27.7 120-184 D, Q 6cdc 2 __ 4 S-l 11/16 W do _ _ __ 1947 120 118 118 C 18 ___ 3-24-61 5.4 W 8bdc2 __ 4 7/16 S-l 5/8 W U.S. Bureau of YVI-7 1966 118.3 157 177 RRG 24-14 118-149 T, E, ______5-11-66 4.8 2- 3-68 28.4 118-149 L. PT Reclamation. 17abcl __ 5 1/4 S-l 1/2 W Yuma County 3 1955 115.4 200 200 C 24 130-170 T, E, 150 _ _ _ _ 2- 3-68 27.3 130-170 D, PT, Q Water Users' Association, 20bab __ 6 S-l 3/4 W do 4 1956 112.5 204 194 C 24 132-192 T, E, 150 ___ _ _ 4-13-67 27.2 132-192 D, Q 20bdc __ 6 1/2 S-l 3/4 W U.S. Bureau of YVI-13 1966 112 237 229 RRG 24-14 95-167 ___ 4-30-66 7.1 10-27-67 27.9 95-167 L, Q Reclamation. 20ccc 2 _ 7 S-2 W __ do ______2 1947 110.2 121 121 C 18 __ 10- 5-62 3.6 D. Q 20cdd _ 7 S-l 1/2 W Yuma County 5 1957 110.3 262 242 C 24 130-203 T, E, 150 ______4-24-67 26.7 130-240 D, PT, Q Water Users' 213-240 Association. 29bbc __ 7 1/4 S-2 W U.S. Bureau of YVI-17 1964 110.0 230 230 C 24 148-212 T, E, 150 ___ 2-25-64 4.7 5- 7-67 27.5 148-212 D, L, Q Reclamation. 1 HQ Q 1 HQ SOcbal 2 _ 7 5/8 S-2 3/4 W 109 £J D 30cba2» _ 75/8 S-2 3/4 W Yuma County 6 1954 108.9 215 205 C 20 140-160 T, E, 150 ___ __ 5-25-62 27.2 140-203 D, PT, Q Water Users' 173-203 Association, 30cba 3 __ 7 5/8 S-2 3/4 W do 6R 1965 108.9 203 200 C 24 138-158 T. E, 150 11-29-66 26.9 138-193 D, L 175-193 (G- 9-24)36caa __ 85/8 S-3 9/16 W __ do ______7 1957 105.7 240 225 C 24 145-175 T, E, 150 ______4-13-61 4 35.1 11-29-66 26.5 145-220 D, Q 188-220

or TABLE 19. Irrigation wells

Well number: Location of well according to the Federal land classification. See page HIT for description of well-numbering system. Coordinates: Location of well according to grid system used by U.S. Bureau of Reclamation in Yuma area. See page HIT for explanation of grid system. Owner or user: Owner or user at the time well canvass was made. Other number: Number assigned to well by owner or user. Year completed: Known or reported year of completion of well. Altitude of land surface: Average of land surface at well above mean sea-level datum. Altitudes given to nearest foot are approximate and were obtained from topographic maps; altitudes given to decimal fractions of a foot were obtained by spirit leveling to a reference point at the well and are much more accurate. Log information, water-level data, and tem­ perature data are referred to land-surface datum. Total depth: Greatest depth, in feet below land-surface datum, to which well was known or reported to have been drilled. Well may have been completed to a shallower depth or filled in subsequently. Completed depth: Depth, in feet below land-surface datum, to which well was cased or subsequently plugged. Method of construction: Letter symbols designate C, drilled with cable-tool or percussion equipment; R, drilled with rotary-mud equipment; RG, drilled with rotary-mud equipment and gravel packed; RRG, drilled with reverse-circulation rotary equipment and gravel packed. Casing diameter. Nominal inside diameter, in inches, of casing used in well. Where more than one figure is given, figures refer to diameter of casing in each successive segment from land surface downward. Depth of perforated interval: Depth, in feet below land-surface datum, to top of highest perforations or well screen and base of lowest perforations or well screen. Type of pump and horsepower: Pump type and source of power are designated by letter symbols C, centrifugal; D, diesel; E, electric; G, gasoline; Ga, gas; S, submersible; T, turbine. Number indicates horsepower. Discharge: Measured or reported discharge of well in gallons per minute. 60 Drawdown: Measured or reported drawdown, in feet, accompanying discharge in previous column. Water level: Date measured by Geological Survey or reported by owner or other agency. Depth to water in feet below land-surface datum. 60 Water temperature: Date measured by Geological Survey. Temperature, in degrees Celsius, of most recent sample of water pumped from well believed to represent water from the depth H of the perforated interval in the coarse-gravel zone. In some wells not equipped with pumps, temperature was measured with a thermistor at a depth believed to represent the middle 02 O of the coarse-gravel zone or an equivalent depth below land surface. d 60 o quality-of-water data; W, periodic or continuous water-level records. H VI Water level Water temperature

& tr1 constructionMethodof o Altitudeoflandsurfac perforatedDepthof 13 O tn rO andofTypepump tU fJ Other Owner Completeddepth diameterCasing a tu completedYear « K data Well Coordinates or Othernumber **% user £"S, ,s"a available tU horsepower Discharge Drawdown S T3 3 interval S Ci 01 O 3 S n *-> *i t-1 O a V ^ Q O <3 ? pi o (C- T-22)14acb 6 11/16 N-T 1/2 E __ 1955 15,7.2 191 16 110-1T6 T Ga T5 10- 4-62 8.4 11- 1-66 26.T 12 D, PD (C- 8-21)lTdbb E. P. Roy 1 /»Q T, E, 50 Q o ITdbc 0 3/8 N-IO 9/16 E do _ 1965 163 122 120 C 20 72 112 T, E, 50 4-23-65 16.5 10-31-66 21. T T2-112 D, Q o 18add 01/2 N-10 E S. Sturges _ 5 1966 159 143 143 C 20 100-136 T, E, 100 IT T- 1-66 23.9 100-136 D, Q 0 1 /9 "W Q Q /C "K1 do T, E, T5 11- 5-64 6.3 11-15-65 23.3 TO-146 D, Q 1 Qfll 1 f\8 192 192 T, E, 50 10-31-66 18.8 6- 6-6T 21. T 115-165 D, PT, Q 30abb Hulse 3 1 Q/19 1 P\7 i f;s i P\S 20 105 155 T, E, 50 11- 9-66 22.1 105-155 D, Q 1 Q/CQ Q Q//1 TJ1 do 2 1946 160 169 169 10-29-66 22.2 104-165 D, Q 1 Q /A Q Q 1 /C TJ1 1956 155.2 1 CkC 16 150-180 T, E, 50 1-19-61 1T.4 D SOcccl 1 7/8 S-9 E do 1925 155 165 165 C 16 95 155 T, E, 50 1-19-61 16.8 D, Q 30cdc __ 1 7/8 S-9 3/8 E F. J. Hartman- __ 193T 15T 195 195 C 20 120-140 T, E, 40 2,050 11 3-2T-46 23.9 120-140 PT, Q QA/lpn Hulse 6- 6-6 T 22.9 Q 2 Q Q 1 1 /I C T7» 1953 160 149 149 T T7> JA 2,4T5 D, Q 2 G Q 1 1 A. "IT do Q 3 Q 1 A 1 /I C "C1 500 RG 12 250-500 2- 2-61 124.8 3-12-63 25.6 125-460 D, T O (C- 8-22)6bbd 2 3/4 N 3 1/4 E W F Dial 134 T, D, T8 4- 6-6 T 22.1 25 2 1/4 N-3 1/8 E 1 QP\

ES Altitudeoflandsurface constructionMethodof o perforatedofDepth U andofTypepump Vl ,0 Owner depthCompleted diameterCasing S t! Other Well Coordinates or Othernumber completedYear si data user 5 <*! available & horsepower .at: T5 interval . 3 1 1 * J3 3o 11 ill EI Q O Q Q Q ? Il (C- 8-23)32dda __ 2 11/16 S-l 1/16 W Greenwood __ 1966 202 161 161 C 8 121-145 S, E D, Q Village. IS 33bba __ Alice Byrne __ 1948 203 241 241 C 10 105-130 D School. 33bdb __ 2 5/16 S-0 11/16 W St. Francis __ 1961 203 318 318 C 12 ______1961 D, L, Q Sd Church. IS 2 3/4 S-0 15/16 W Woodard Jr. __ 1967 204 295 295 C 12 195-295 _ _ _ _ 5-23-67 85 _ Q CQ High School. O 35aca 21/4 S-l 3/4 E Barbara Ann 155 155 C 16 130-155 T, E, 30 D, Q Cattle Co. 35adb __ 2 1/4 S-l 7/8 E Gunther and 7 1949 137 180 180 C 16 140-171 T, E, 40 6 13-63 25.0 140-171 D, Q O Shirley IS 35caa _. _ 2 1/2 S-l 1/2 E S & W __ 1947 141 191 191 C 20 150-186 T, E, 50 3,290 ___ 2- 1-61 8.6 12-21-60 26.1 150-186 D CQ 36aaa _ 2 1/8 S 3 E W. R. Whitman 140 ~C 18 - T, E, 40 Q (C- 8-24)28aaa 3 __ 1 S-6 1/16 W Wohlford __ 1934 115 ~155 ~155 16 125-150 10-18-66 17.2 11- 2-67 22.2 138 D, T, W Ranch. 33bab __ Crowe and __ 1966 113 208 208 C 1 £ 1 97 1 ^9 T, D, 50 D t-1 Jessum. (C- 9-21)3cddl 3 __ 3 15/16 S-12 3/16 E V. H. Ueckert- _ 1964 327 800 800 RG 12 300-800 3-10-64 100 4-20-64 28.9 260 D, T, Q o 3cdd2 a _ 3 15/16 S-12 3/16 E do _ __ 1963 327 400 296 RG 12 257-296 Q 3 4bcc 3 __ 3 7/16 S-ll E H. Scheckert _ -_ 1962 286 500 500 RG 20 300-500 12- 2-66 150.0 12- 2-66 26.7 278 T IS 5bcc s __ 31/2 S-10 E J. Labadie _ 267.3 C 16 _ 12- 2-66 132.8 12- 2-66 25.6 259.1 T, W Sd 6bbc 3 ._ 3 3/16 S-9 1/16 E B. Palon ._ _ __ 1962 247 404 404 RG 8 284-404 12- 2-66 113.9 11- 9-67 24.3 259.0 D, T, Q 7aad 3 _ 41/8 S-10 E T. S __ 1924 279.0 401 401 C 16 165-315 12- 2-66 143.6 3-12-63 25.3 300 D, T, W o Vanderford. o 8ddd s __ 4 15/16 S-10 15/16 E V. H. Ueckert _ __ 1962 312 730 730 RG 16 12 E 9baa 3 _ 4 1/8 S-ll 3/8 E J. F. Power __ 2 1959 319 496 496 C D, PT, Q s-/ 13ccb 3 57/8 S-14 E B. Pa!on _ __ 1965 423 603 603 C 12 560-596 _ _ 9-27-66 287.5 9-27-66 34.5 333.5 D, Q 14bac 3 _ 5 1/4 S-13 5/16 E do 1,085 1,053 C 12-8 914-1,040 33.9 271.0 D, P, Q p 16add « _ 51/2 S-12 E H. Scheckert __ 1963 354 405 370 RG 10 294-370 12- 2-66 221.7 12- 2-66 30.0 299 D, T, Q O 17cdc3 __ 6 S-10 5/16 E V. H. Ueckert- _ 1962 340 350 350 RG 10 290-350 9-27-66 199.6 4-20-64 28.3 360 T O 18ddd 3 _ 5 15/16 S-9 7/8 E 1962 330 350 350 RG 10 290-350 _ _ 9-27-66 194.4 4-20-64 27.2 310 T, Q 20aad 3 61/4 S-10 15/16 E _ do __ __ 1962 367 385 385 RG 10 325-385 12- 6-66 234.4 12- 6-66 28.9 297 T w 21bab 3 61/8 S-ll 1/4 E -do _ 1962 373 350 350 RG 10 290-350 29.2 239 I I 22aaa 3 _ 6 1/8 S-12 15/16 E F. H. Tammany 1955 385 340 340 "c 8 325-340 D, Q 23abd 3 6 3/16 S-13 11/16 E __ 1965 402 602 602 12 538-582 9-27-66 268.1 9-27-66 32.5 273.8 D, Q IS (C- 9-22)2ada 3 __ 3 5/16 S-8 E C. Anderson _ __ 1966 213 602 600 RRG 99 Ifl 9P»ft Aftfi 1- 9-67 81.0 D 2baa 3 _ 3 Q r? 1 /o T71 do 1966 214 600 569 RRG 22-16 233-569 D ? 3cdb i __ 3 7/8 S-6 1/4 E __ 1923 213 250 250 C 16 160-250 11-17-23 91.8 D, Q 4dbcl 3 _ 3 11/16 S-5 1/2 E Sen. Murdy __ 160 160 12 12- 2-66 71.0 12- 2-66 24.4 193.5 T, W 4dbc2 3 3 11/16 S-5 1/2 E 210.1 240 240 ~C 12 G, W 5 baa 3 1/8 S-4 1/2 E J. Bretz, Jr. _ __ 1948 144 135 135 20 108-123 T, E, 40 2-13-63 23.3 108-123 D, Q 9bba 3 ___ 4 S-5 1/4 E Ketcherside __ __ 1921 208.0 250 250 C 16 150-250 _ 12- 3-66 67.7 11- 7-67 23.6 237.2 T, Q, W llbbbs 4 1/8 S-7 E H. R. Houck _ __ 1962 213 600 300 RG 16 161-300 12- 2-66 75.8 11- 9-67 23.6 218.0 D, T 12aaal 3 _ 4 S-8 15/16 E J F. Power _ 1 1959 249 408 408 C 12 333-400 T, D 2- 3 61 116.1 D CQ 5 3/4 S-4 3/4 E P. Hairgrove _ 1 Q9f_ 9CIQ Q 263 263 C T, E 25.0 165-218 D, G, Q, W IS 23aaa 3 _ 6 CJ Q "El V. H. Ueckert- __ 1964 262 300 300 RG 10 240-300 25.6 265 T 23cbb 3 _ 6 1/2 S-7 E do _._ 1965 242 12- 5-66 96.1 12- 5-66 25.3 24abd 8 _ 6 1/4 S-8 5/8 E do 1964 300 OK a i 70 24bba 3 _ 6 S-8 3/16 E do 1964 280 274 274 RG 10 195-274 9-27-66 143.8 4-16-64 26.3 210-260 D, T Sd 29bbc 3 _ 71/4 S-4 1/16 E L. T. Rouse __ __ 1925 204 250 250 C 16 174-249 3 16 67 48.9 11 9 67 24.9 218.5 D, T, W ts (C- 9-23)4abd 31/4 S-0 5/16 W American __ 1966 195 207 207 C D, Q Legion. 4cbd ___ 3 11/16 S-0 7/8 W Palmcroft __ 1965 184 252 252 C 16 180-230 T, E, 30 5-12-67 28.1 180-230 D. Q School. 5abd 3 __ 3 3/16 S-l 5/16 W Blalack and __ 1934 120 186 186 c 12 160-184 12- 8-66 3.7 12- 8-66 25.6 79.4 D, T Salas. 8aac 4 3/16 S-l 1/8 W V. E. Blalack _ __ 1963 190 230 230 c 12 204-214 T.E D, Q 9caa 3 __ 45/8 S-0 9/16 W M. Miller 236 236 c 16 190-236 T, E, 3 3- 3-61 69.5 D 36aab 8 S-2 13/16 E H. L. Morris _ __ 1965 200 198 198 RG 8 160-196 Q 36bdd 3 __ 8 1 /9 Q Q 1 /O TT 255 255 C 16 170-252 _ 11- 4-67 37.8 11- 4-67 25.1 170 D, G, T, Q (C- 9-24)19badl 1 _ 6 3/16 S-8 5/8 W P. E. Sterling _ __ 1934 107 180 180 C 16 140-178 D 19bad2 __ 6 3/16 S-8 5/8 W __do 195 195 C 16 145-180 T, E, 60 2- 2-67 21.7 145-180 D, Q Wbdal 1 _ 6 n to CJ O F to TTr do - 1934 107 185 185 C __ 150-178 D 19bda2 _ 6 3/8 S-8 5/8 W __do 200 200 C 16 150-175 T, E, 60 2- 2-67 22.1 150-175 D, Q 19bdb 6 5/16 S-8 5/8 W do 1966 107 194 190 C 20 16 94 190 T, E, 60 2- 2-67 21.8 94-190 D (G- 9-24)36aad 3 __ 81/4 S-3 W C. Anderson _ __ 1966 179.1 600 600 RG 22-16 250-600 3- 3-67 79.8 3- 3-67 28.3 247.5 T 36ada 3 _ 8 1/4 S-3 W - do _ _ _ _ 1966 179 615 608 RRG 22-16 256-608 5,200 58.5 12-14-66 28.3 256-608 D, G, Q (O- 9-25)25aab __ 7 1/8 S-9 3/16 W J. D. Cannon _ 1967 114 180 170 C 20-16 110-170 6 14-67 20.6 110-170 35aba _ 8 S-10 B/8 W W. W. Brand _ __ 1959 109 310 319 C 24-14 100-310 T, D, 150 8.0 36aaa __ 8 S-9 W McDaniel & _ 1952 110 193 193 C 24 130-180 T, E, 125 3,620 44 21.7 130-180 D. PT. Q Sons, Inc. (C-10-22)7add 3 __ 10 7/16 S-4 E M. T. Smith _ _ 1926 228.2 250 250 C 16 Open 1-11-66 80.5 11- 7-67 27.7 247.5 D. G, T. bottom W 10 3/4 S-1 E F. E. Booth __ _ 1961 196 603 603 C, RRG 20 130-388 T, Ga, 150 1-18-62 fi7 fl Q 99 RR 2B.6 130-388 D, Q lldca __ 10 3/4 S-1 3/4 E _do 1965 200 RRG 20 ______T, Ga, 150 ~~4~-2~3-65 28.9 ______lldcd __ 11 S-1 11/16 E - do 1965 200 509 509 RRG 20 98-495 T, Ga, 150 3,1)00 106~" 54 9-22-66 29.7 98-495 D, Q 12abal 3 _ 10 S-2 B/8 E J. F. Nutt _ 6 1963 199 704 704 C 20 176-686 2 91 ftQ 32.8 178-686 D. PT, Q 12aba2 _ 10 S-2 B/8 E do _ 1966 199 550 550 RRG 20 T, Ga 3 1 67 on e 12abb _ _ 10 S-2 1/2 E do 1953 200 220 220 C 16 202-210 T, Ga 4-27-62 49.8 0, Q 12bda __ 10 1/4 S-2 1/2 E - do 4 1962 200 694 694 C 20 150-680 T, Ga 3,940 26 1- 7-63 29.2 150-680 D, Q 12bdd __ 10 1/2 S-2 1/2 E do _ 5 1962 198 704 704 C 20 132-690 T, Ga 4,500 45 2-21-63 42.7 9-28-66 29.2 132-690 D. T, Q 12dbc __ 10 5/8 S-2 5/8 E do _ 1959 201 282 282 C 16-14 165-280 T, Ga 11- 6-63 44.8 D.Q 13abd __ 11 1/4 S-3 3/4 E -do 1966 205 500 500 RRG 20-16 200-500 T, Ga 12- -65 B6.0 13dccl 3 _ 12 S-2 B/8 E V. H. Ueckert __ 1963 220.6 254 254 RG 12 185-254 12- 3-66 108.8 12- 3-66 30.6 203.8 D. T 14aaa 3 _ 11 S-2 E J. F. Nutt 10 1965 200 550 550 RRG 20-16 77-546 12- 3-66 52.6 3-27-68 32.3 77-546 D 14bbd __ 11 1/4 S-1 1/4 E F. E. Booth _ -_ 1965 198 556 556 RRG 20-16 140-548 T, Ga 1-21-66 74 D IBaaa 3 _ 11 S-1 E J. F. Nutt __ 1 1961 194 300 300 C 20 112-285 1,500 50 9- 1-66 66.4 D, Q, W IBaab 3 _ do 2 1961 194 890 890 C 20 T 11-15-61 72.1 D, PT. Q G 20aad 3 _ 12 1/8 S-1 1/8 W Harrison and 1 1966 185 512 501 RG 16 330-490 6- 2-66 88 D, Q W Espy. O 20abd 3 _ 12 1/8 S-1 3/8 W do 3 1966 184 455 455 RG 16 305-455 6-28-66 88 _ D, Q f 20aca 3 _ 12 3/8 S 1 3/8 W - do 4 1966 188 505 504 RG 16 334-494 7- -66 88 20add 3 _ 12 3/8 S-1 1/8 W do 2 1966 190 512 501 RG 16 331-491 8-19-64 20baa 3 _ 12 1/16 S-1 1/2 W V. H. Ueckert _ 1964 185 334 334 RG 14 234-319 80.4 _ D Kj 20bcb 3 _ 12 5/16 S-1 IB/16 W - do 1964 185 254 254 RG 8-20-64 84.2 D 20ccd 3 _ 13 S-1 3/4 W - do 1963 179 350 350 RG 10 260-350 8- -63 29.4 220 D, T O 20cdd 3 __ 12 15/16 S-1 B/8 W - do 1964 181 174 174 RG 14 118-174 8-20-64 81.6 D, Q *1 21abb ___ 12 S-0 1/2 W J. F. Barkley _ 1963 191 354 264 RG 12 200-264 T, D 8- 5-63 80.1 12- 6-66 28.8 200-264 D, T, Q 21cba 3 _ 12 B/8 S-0 13/16 W V. H. Ueckert _ __ 1964 192 294 294 RG 14 214-294 8-19-64 86.9 D H 21cca 3 _ 12 13/16 S-0 7/8 W 1964 191 294 294 RG 14 234-294 12- 9-66 86.1 12- 9-66 27.8 131 D, T W 21daa 3 _ 12 1/2 S-0 Graham and 1966 191 500 ___ RG 16 Murphree. 22aaa 3 _ 12 1/8 S-0 7/8 E V. H. Ueckert 4 1964 194 294 294 RG 14 214-294 8-20-64 81.7 D 22abb 3 __ 12 S-0 1/2 E M. Thorne __ 1963 194 294 230 RG 12 9-19-66 80.0 12- 3-66 28.3 199 D, T 22acc 3 _ 12 3/8 S-0 9/16 E V. H. Ueckert 2 1964 193 294 294 RG 14 214-294 8-20-64 83.3 D 22adc 3 __ 12 3/8 S-0 3/4 E do ______3 1964 194 334 322 RG 14 242-322 8-20-64 83.7 _ D 22bab 3 __ 12 S-0 1/4 E 194 20 9-20-66 81.4 9-20-66 27.2 89.5 22bad 3 __ 12 1/4 S-0 3/8 E 193 ~478 20 9-20-66 80.8 12- 9-66 27.5 98.0 T 22bbb 3 __ 12 S-0 Harrison and 1 1966 192 ~478 RG 16 308-468 D and Espy, 22bbc 3 __ 12 1/4 S-0 do 2 19C6 192 477 477 RG D 22cbd 3 __ 12 3/4 S-0 1/4 E Graham and 1966 191 500 500 RG 16 Murphree. 23abb 3 __ 12 S-1 9/16 E Hub City Devel­ _ 1966 196.4 464 464 C 20-12 304-454 9-19-66 27.8 227.0 D, T, Q opment Co. » 23cbd 3 __ 12 3/4 S-1 1/4 E 500 500 RG 16 320-500 2,500 75 12- 6-66 84.9 12- 6-66 28.6 248.0 T, Q i i Graham and N Murphree. 28cad 3 __ 13 11/16 S-0 9/16 W 191 9-20-66 91.5 12- 9-66 30.6 158.0 T O 28ccd 3 __ 13 15/16 S-0 7/8 W 1964 185 334 330 RG 12-10 230-293 12- 9-66 86.8 3-27-68 34.2 230 D, T a: V. H. Ueckert _ 3-27-68 28cdd 3 __ 14 S-0 1/2 W -do ______2 1964 200 306 240 RG 14 160-240 31.0 190 D. T > 29acc« _ 13 7/16 S-1 7/16 W - do 184 RG 14 29add 3 __ 13 1/2 S-1 1/16 W RG 14 ______> - do ______3-31-67 29cab 3 _ 13 9/16 S-1 3/4 W C. L. Espy ___ __ 1966 180 411 410 RG 20 134-410 84.0 3-31-67 29.7 207 T * 29drtc» __ 1315/16 S-1 13/16 "W V. H. Ueckert _ __ 1964 187 294 294 RG 12 244-294 12- 9-66 88.7 12- 9-66 30.3 248 D, T, Q d (C-ll-23)36cbd 3 __ 20 11/16 S-2 1/4 E V. H. Ueckert _ __ 1965 170 700 TJ /"I 20 16 - (C-ll-24)2abd 3 __ 15 1/4 S-4 1/4 W J. F. Nutt ___ 8 1964 170 300 300 RRG 20-16 130-300 12-30-64 25.0 130-300 D, PT, Q 2baa 3 -_ IB S-4 1/2 W __ do ______7 1964 166 159 102 RRG 20-16 78-102 T, D, 200 12-13-66 25.9 145 D, T, Q 2bbd 3 __ IB 1/4 S-4 3/4 W do ______9 1965 164 400 376 RRG 20-16 140-376 3,700 19 1-22-65 76.6 5- 3-65 25.6 140-376 D, PT, Q 9ddd __ 16 IB/16 S-6 1/8 W Parker and 17 1966 154 516 516 RG 20 200-506 5,160 33 2-22-67 69.7 12-13-66 26.4 228.5 D, T. SpC others, lOcdd __ 16 IB/16 S-5 1/2 W do 11 1966 156 510 510 RG 20 214-503 5,070 33.5 12-13-66 73.3 3-27-68 26.8 230 D. T lOddd __ 16 15/16 S-5 W do 10 1966 158 503 BOS RG 20 196-493 5,300 31.0 29.5 230 D, T llbdd ___ 16 1/2 S-4 1/2 W _ -do 5 1966 164 505 B05 RG 20 215-495 5,275 34.3 12-13-66 80.3 12-13-66 26.7 229.0 D. T llcdd __ 16 15/16 S-4 1/2 W do 3 1966 162 505 505 RG 20 209-495 4,715 31.5 26.7 204-495 D llddd __ 17 S- 4 W do _ 1 1966 166 266 266 C 20 148-212 1,250 26 3- -66 90 D, Q 23bdb 3 _ 18 5/16 S-4 3/4 W R. E. Grounds- __ 1965 162 434 434 C T, D, 75 6-29-65 84 D, Q (C-ll-25)2bba __ 15 1/16 S-10 7/8 W W. A. Brown _ __ 1952 92 223 223 C 20 174-210 T, D, 90 5- 2-62 4 12-13-66 23.2 174-210 D, Q 3dac 15 11/16 S-ll 1/4 W E. Husrhes _ 1956 92 282 282 C 20 188-282 T, D, 150 10-18-62 16.9 2- 2-67 21.1 188-202 D, PT, Q See footnotes at end of table. CO TABLE 19. Irrigation wells Continued

Water temperature O5

ethodconstructioiof o Ititudelandofsurfac perforatedofepth 3 J3 andofpumpype t-i ,0 Owner Pi Other numberther V diameterasing $ QJ Well Coordinates completedear T3 03 3 v or a «H 0 data user a T3 03 available

Owner or .o Other user and Pi -g data Well Coordinates other

J3 .g -i-> i. 03 Q, M "3 "03 1 S *"* s S 03 o 1 1 jij u Q.S P 1H^ Q Q Q Q Q Q-2 (C- 5-21)19dbc __ 17 1/4 N-9 9/16 E Shepard 1961 200 240 240 PS 9- 7-62 14.0 ______-__ D, Q Water Company 2. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H165

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£ Altitudesurfacelandof Methodconstructionof Depthperforatedof Bc °_ Owner or <8 fc, -0 Other user and data Yearcompleted Completeddepth Casingdiameter a * 1« available Well Coordinates other 5 number k 8 1 .1 1 interval ss s f * _s 01 3o H 5 II 1 I I 1 I ? II 1 S 9ft D, E, 1/2 ______(C- 9-24) Saab __ 3 1/16 S-5 7/16 W J. B. . __ 118 20 30 2 Dom i Q Williams lObbb __ 4 S-6 W Watkins . __ 111 60 60 St C, E, 3 ______Q Cattle Co. 2 19 21 C, E, 1/2 _ __ - ______12daa __ 4 9/16-3 1/8 W S. Dick _ 1962 116 21 21 Dr Dom Q 12dac __ 4 11/16 S-3 1/8 W 116 145 145 C 4 ______Dom J, E, 5 _ - _ _ _ __ Q 14dab __ 5 9/16 S-4 1/4 W Yuma 1949 115 133 133 C 8 125-133 Dom, St T, E, 5 _ _ __ 4-14-61 16.5 ______D, Q Valley Cattle Co. ggWATERRESOURCESLOWEROFCOLORADORIVER-SALTONSEAAREA 14dba __ 51/2 S-4 5/16 W do _ . __ 115 120 120 4 Dom, St J, E, 5 ______Q 105 Dr Dom Q 15dbd __ 5 5/8 S-5 1/4 W K. Drysdale- J E 3/4 17add __ 5 7/16 S-7 W E. Shawn _ 1951 107 124 124 D 2 Open end Dom Q 20cdd __ 7 S-7 1/2 W G. M. 1 1 Q 160 160 D 3 Dom, St T, E, 3 ______Q Sugden. ___ 107 170 D Q Dom C, E, 1/2 _ _ - - - _ - - Q tfOdddl __ 6 7/8 S-7 1/16 W 170 J, E, 3 - 22aba __ 6 S-5 5/16 W McLaren 1945 111 125 125 C 8 Open Dom D, Q Produce bottom Co. 28cbb __ 7 1 /9 C! n "117 Woods Co _ 108 Dom Q 32ddb __ 8 7/8 S-7 1/4 W Yuma 1952 105 203 203 C 12 170-195 PS T, E, 20 - - D, Q County Labor Camp. 34dcbl i _ 8 13/16 S-5 1/2 W City of 1920 106.2 215 215 C 19 PS C, E, 20 2,000 1-12-61 12.1 _____ D, Q, W Somerton. 34dcb2 __ 8 13/16 S-5 1/2 W _ do ._ 106.2 C 16 PS 34dcb3 _ 8 13/16 S-5 1/2 W __ do _____ 1965 106.2 1,163 1,163 C 12 PS D, G, Q (C-10-22)22bab __ 12 1/16 S-6 5/16 E U.S. Marine 1958 266.7 319 319 C 12 PS S, G 1-11-66 132.5 1-11-66 28~9 139 Q Corps. 1960 203 8 170-184 Dom T, E, 7V2 5-24-61 44.1 5-24-61 26.1 170-184 Q TC-10-23)3aaa2 __ 9 1/16 S-0 15/16 E Allec Bros.- 186 186 C J E 1 11 8- 5-68 34.0 - _ 9 S-0 11/16 E R. A. 1960 199 190 190 R 4 Open Dom Q Patrick. bottom 8 185 195 Dom 3- 3-67 40.2 11- 6-67 27.3 188 D, G, T 4ada 1 9 1/4 S-0 1/16 W S. K. Lamb- 1953 197.8 211 211 C /» 9 11/16 S-l 9/16 W W. Si'va 186 D Dom 5dcc ___ 10 S-l 1/2 W Unit B 1928 186 225 ~225 C 16 190-200 Dom J, E, 1% _ _ D School. E 500 12 7-12-61 86.0 20bbbl * _ 12 1/16 S-2 W U.S. Navy- 1961 189 315 315 C 12 212 232 Ind D, G, Q (C-10-24)2aab ___ 9 S-4 1 /4 W W. Jacoby ___ 105 147 D Ind C, E, 5 _ _ - - _____ Q & Sons, Inc. 9 3/8 S-6 1/16 W Western 1962 102 189 % 189y2 C 16 155-187 Dom, T, E, 5 8-24-62 8.0 D, Q Cotton Co. Ind 4bbb ___ 9 S-7 W Williams ___ 105 25 25 Dr 2 23-25 Dom Q Store. 9bba ___ 10 1/16 S-6 7/8 W H. Rolling- 140 Dom, St C, E, 1 Q lOcdd __ 11 S--5 9/16 W .100 140 ~140 cf 8 Dom, St f1 P 1 Q 16baa2 11 S-5 9/16 W Western 1965 100 423 423 C 12 152-180 Dom, D, Q Cotton Co. Ind 28ddb __ 13 3/4 S-6 1/8 W L. P. 1962 97 217 217 C Dom, St J, E, 5 _ _ 4-22-64 26.7 Q Barkley. (C-10-25)13cca __ 11 3/4 S-9 7/8 W E. Malone _ 157 157 -- 2 Dom C, E, 1/2 _ 9- 4-62 7 __ _ Q 26dba __ 13 1/2 S-10 1/4 W A. H. Clark 1945 95 167 167 2 Dom J, E, 1/2 _ _ 9-4-62 6 Q (C-ll-25)12bca 16 3/8 S-9 3/4 W Flying A 1061 130 198 198 cf Dom J, E, 1% _ - 1-25-62 22.8 183-195 D, Q Service. 12bdb __ ib o/a b y o/s w San Luis 1964 130 213 213 C PS D, Q Water Co. 16 5/8 S-9 11/16 W U.S. Gov­ 1931 130 105 105 c 5 Dom J, E, 1 1-25-62 26.7 _ - Q ernment. 15S/23E-33Fac __ 5 5/8 N 3 7/16 E R. S. 1933 138 130 130 D 6 Open Dom J TJl 1 - Q Dillman. bottom 35Eac __ T. Cardoza- 1961 140 130 130 D 4 Dom J,E, 1 _ 12-11-61 14.2 _ - Q 16S21/E-35Qbcl i _ 0 3/4 S-6 1/2 W Southern 1953 123 107 107 C S ort nn PS. RR . D Pacific Co. D, Q 35Qbc2 0 3/4 S-6 1/2 W U.S. 1960 123 155 155 C 4 115-135 Dom, PS! S E, 2 - - - 10-10-62 23.3 115-135 Customs. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H169

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APPENDIX B. SELECTED LOGS OF WATER WELLS Appendix B presents logs of 61 water wells and water test Selected logs of water wells Continued wells in the Yuma area. These logs, which are selected from Thick­ Material ness Depth more than 700 logs in the files of the Geological Survey, are (feet) (feet) probably representative and give good areal coverage. Logs of mo^t of the private wells are by the drillers; those of the Well (C-7-22)14bcd Continued Coarse-gravel zone Continued: test wells are by Geological Survey or Bureau of Reclama­ Gravel, chiefly well rounded to subrounded; tion geologists, based on sample studies and borehole geo­ contains cobbles as much as 5 in. includ­ physical logs. The materials logged are assigned by F. H. ing abundant siliceous rocks; some coarse Olmsted to the various water-bearing units described in sand and cemented streaks 15 163 the text. Wedge zone: Sand and gravel; thin streaks of conglom­ The well number given for each well is that given in erate. Gravel finer and contains more Appendix A, tables 16-20. The name following the well num­ rocks of local derivation than that above. 17 180 bers is the Government agency that drilled the well or had Sand, fine to medium, silty, brown; scat­ it drilled, or the owner or user at the time the well canvass tered granules and small pebbles includ­ ing pebbles of clay and sandstone concre­ was made. The type or use of the well and its approximate tions ______29 209 location are also listed, as are the name of the driller and Bouse Formation: the type of drilling equipment used. The depths of perforated Clay, silty and sandy, tough, gray; contains intervals are given where available; these are indicative of concretions of clayey siltstone and sand­ stone _ - 5 214 the productive horizons within the respective areas. Altitudes Sand, silty, soft, micaceous; contains some listed are of the land surface at the well from which depths carbonized wood ______3 217 were logged (mean-sea-level datum). Altitudes given to the Clay, silty and sandy, tough, gray; contains nearest foot are approximate and were estimated from topo­ concretions of clayey siltstone and sand­ stone ______11 228 graphic maps; those given to decimal fractions of a foot Clay, silty, gray; fossiliferous ______15 243 were obtained by spirit leveling to a reference point at the Clay, silt, and fine sand; thin bedded well and are much more accurate. Other information about greenish- to bluish-gray fossiliferous __ 228 471 the wells is listed in Appendix A, tables 16-20. Nonmarine sedimentary rocks (Tertiary) : Conglomerate composed of angular to sub- rounded granules, pebbles, cobbles, and Selected logs of water ivells scattered boulders of plutonic, metamor- phic, and few silicic volcanic rocks in a Thick­ sandy and silty matrix. Fairly hard drill- Material ness Depth ____ing ______34 505 (feet) (feet) Well (C-8-21)lbbc Well (C-7-22)14bcd [U.S. Bureau of Reclamation test well 1 in Dome Valley. Drilled with [U.S. Geological Survey test well LCKP 14 at Laguna Dam. Drilled cable-tool equipment by Hamilton and Hood. Log by Bureau of Re­ with cable-tool equipment by Hamilton and Hood. Log by F. H. Olmsted, clamation. Altitude 171 ft] F. L. Doyle, and F. J. Frank. Casing perforated from 118 to 128, 152- 162, and 410-490 ft. Altitude 155.1 ft] Upper, fine-grained zone: No record ______10 10 Upper, fine-grained zone: Sand (80 percent), fine to medium, slightly Sand and silt containing plant fragments; micaceous, light-grayish-tan; silt (20 thin strata of clay and pebbly clay. Upper percent), slightly clayey; with small clay 14 ft represents fill accumulated since balls ______21 31 construction of Laguna Dam ______16 16 Sand (85 percent), fine to medium; silt (10 Sand, fine to medium ______4 20 percent), light-grayish-tan; clay (5 per­ Sand and silt containing plant fragments; cent), plastic, dark-brown ______6 37 some clay ______8 28 Clay (60 percent), dense, plastic, dark- Sand, scattered pebbles, and some clay and brown; sand (30 percent), fine to me­ silt ______9 37 dium, light-grayish-tan; gravel (10 per­ Sand, medium, and subangular gravel ___ 3 40 cent), fine to coarse, angular to sub- Sand and silt containing plant fragments; angular; composed mostly of gneiss and some gravel and clay ______13 53 granite ______13 50 Sand, fine to medium; interbedded pebbly Sand (70 percent), slightly silty, fine to silt and clay ______16 69 medium, light-grayish-tan; gravel (15 Sand, fine to medium, some gravel; thin percent), fine to coarse (2 in.), rounded; beds of silt and clay ______31 100 with a few angular pieces (mostly Sand and gravel, scattered cobbles. Gravel quartz); clay (15 percent), dense, plastic, includes well-rounded siliceous rocks ___ 3 103 dark-brown ______18 68 Sand, fine to medium, some gravel; thin Coarse-gravel zone: beds of silt and clay ______11 114 Sand (60 percent), fine to medium, slightly Coarse-gravel zone: silty, light-gray; fine to coarse gravel Gravel, well-rounded to subrounded; con­ (30 percent), with cobbles as much as 4 tains cobbles as much as 5 in.; some inches, smooth, rounded quartzite pre­ coarse sand and cemented streaks ___- 14 128 dominant; dense dark-brown clay (5 per­ Sand, medium to coarse; gravel contains cent) ; silt (5 percent) ______11 79 rounded pebbles and cobbles as much as Gravel (75 percent), fine to coarse, pre­ 3 in.; some silt ______7 135 dominantly rounded; a few cobbles as Sand, fine to coarse; scattered pebbles __ 4 139 much as 3 in.; sand (25 percent), fine to Gravel, coarse, rounded ______2 141 coarse, clean, light-grayish-tan; some clay Sand, medium; scattered pebbles ______7 148 in upper part ______13 92 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H171

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-8-21) Ibbc Continued Well (C-8-22)15bdd Coarse-gravel zone Continued: [U.S. Bureau of Reclamation test well CH-6 in North Gila Valley. Drilled with cable-tool equipment by Hamilton and Hood. Log by £. L. Gravel 70-90 percent), fine to coarse, pre­ Smith, Bureau of Reclamation: modified slightly by F. H. Olmsted. dominantly smooth and rounded; sand Casing perforated from 90 to 150 and 160 to 185 ft. Altitude 140.5 ft] (10-30 percent), clean, fine to coarse, light-grayish-tan __ 48 140 Upper, fine-grained zone: Wedge zone: Sand (about 75 percent), fine to medium, Gravel (85-90 percent), fine to coarse (2 brown; subrounded grains of quartz; silt in.); predominantly angular and sub- (about 25 percent); contains a few small angular; composed of granite and gneiss; clay balls ______32 32 sand (10-15 percent), fine to coarse, Sand (about 75 percent), fine to medium; light-grayish-tan ______20 160 subrounded grains of gray quartz; occa­ Sand (60-75 percent), medium to coarse, sional fine gravel; silt (about 25 per­ angular to subangular, predominantly cent) ; chocolate-brown plastic clay about granitic and quartzitic; gravel (15-25 6 in. thick at 44 ft ______26 58 percent), subangular; composed predomi­ Sand (about 70 percent), fine; subrounded nantly of gneiss and granite; some grains of gray quartz; occasional fine quartzite; clay (10 to 15 percent), fine, gravel; silt (about 30 percent); contains light-dun-colored ______9 169 thin layers of chocolate-brown plastic Wedge zone(?): clay ______18 76 Granite gneiss (large boulder; possibly bed- Sand (about 65 percent), fine, gray; silt rock) ______2 171 (about 20 percent); contains a little chocolate-brown plastic clay; gravel Well (C-«-21)19dad (about 10 15 percent), subrounded to [F. J. Hart man. Irrigation well in South Gila Valley. Drilled with cable- tool equipment by Frank H Leideneker (Arizona Machine & Welding well-rounded pebbles of quartzite _ 9 85 Works). Casing perforated from 115 to 165 ft Altitude 158 ft] Coarse-gravel zone: Gravel (about 85 percent), fine to coarse, Upper, fine-grained zone: well-rounded; predominantly quartzite Silt ______2 2 with some volcanic rocks, a few clasts, Sand ______12 14 cobbles as much as 4 in.; sand (about 10 Silt and sand ___ 3 17 percent), fine, gray; silt and clay (about Sand, some pebbles 1 18 5 percent) ______9 94 Sand, silt, and clay strata 38 56 Gravel (about 75 percent), fine to coarse; Clay with sand streaks 18 74 well-rounded, clasts predominantly Clay, sand, and some pebbles 9 83 quartzite; many cobbles as large as 6 in.; Coarse-gravel zone: sand (about 25 percent), fine, gray; con­ Gravel with sand _____ 14 97 tains little silt and clay ______36 130 Gravel, large, with sand _ 11 108 Gravel (about 70 percent), predominantly Gravel, good __ _ _ 8 116 fine and well-rounded; a few cobbles as Gravel with sand __ _ 6 122 much as 4 by 8 in.; sand (about 30 per­ Sand with some gravel streaks _ 3 125 cent), fine to coarse, gray; contains little Gravel with sand _ 1 126 silt and clay _ __ _ 5 135 Gravel, good, with large rock _ 10 136 Gravel (about 60 percent), poorly graded, Sand ______1 137 well-rounded; some cobbles as much as 4 Gravel, good 19 156 in.; sand (about 40 percent), fine to Boulder, very large 0 156 coarse, poorly graded; contains little silt Wedge zone: and clay ______15 150 Sand, packed; with clay layers __ 35 191 Wedge zone: Gravel with sand (increased salt in water) 1 192 Sand (about 60 percent), granitic, coarse, gray; gravel (about 40 percent), fine, Well (C-8-22)7ccd angular to subangular, granitic; contains [Johnson and Drysdale. Irrigation we1! in The Island area. Drilled by Henderson & Sons. Casing perforated from 110 to 160 ft; open bottom. a few pebbles of quartzite _ 8 158 Altitude 139 ft] _____ Gravel (about 70 percent), predominantly fine, angular to rounded; composed of Upper, fine-grained zone: volcanic rocks; sand (about 30 percent), Silt and sand, dry ______10 10 granitic, fine to coarse, angular to Clay, heavy ______8 18 rounded,, gray 11 169 Water sand, water at 18 ft; rose to 15 ft _ 86 104 Sand (about 70 percent), granitic, fine to Sand, gravel 6 110 coarse, gray; gravel (about 30 percent), Coarse-gravel zone: granitic, fine, angular to subangular; a Gravel, coarse; cobble stones and pea few well-rounded pebbles of quartzite _ 16 185 gravel ______50 160 Sand (about 60 percent), fine to coarse, Wedge zone: brown; gravel (about 30 percent), vol­ Coarse water sand and small gravel 84 244 canic, fine, subrounded to rounded; clay Sand and gravel ______8 252 (about 10 percent), moderately plastic Well (C-8-22)14cdd light-brownish-green ______25 210 [S. Sturges. Irrigation well in North Gila Valley. Drilled with cable- Sand, fine to coarse, brown and gray, angu­ tool equipment by Hamilton and Hood. Casing perforated from 80 to lar to rounded; scattered fine gravel; 129 ft. Altitude 150 ft] some yellowish-brown nonplastic clay from 233 to 244 ft ______60 270 Upper, fine-grained zone: Sand (about 60 percent), fine to coarse, Silty sand ______. 75 75 subangular to subrounded, grayish- Coarse-gravel zone: brown; gravel (about 40 percent), vol­ Gravel to 8 in. diameter ______. 57 132 canic, poorly graded, fine to coarse, sub- Gravel, cemented _ . 1 133 rounded to rounded _- _ 10 280 H172 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-8-22)15bdd Continued Well (C-8-22)19ccc Continued Wedge zone Continued: Coarse^gravel zone: Sand, fine to medium, grayish-brown; scat­ Gravel, fine to coarse; consists of subangu­ tered fine gravel -___-______45 325 lar to rounded clasts of volcanic rocks Sand (60-70 percent), fine to coarse, sub- and quartzite as much as 5 in.; some fine angular to rounded, gray; gravel (30-40 grayish-brown sand and a little gray clay percent), volcanic, fine to 1-in. angular at 93 ft ______14 102 to subrounded ______14 339 Sand, fine to medium, gray __ 4 106 Clay, silty, moderately plastic, light- Gravel, fine to coarse; predominantly well grayish-brown ______2 341 rounded clasts of quartzite (70 percent); Clay, gray, densej plastic; a small amount sand, fine, gray (30 percent) 16 122 of chocolate-brown clay; few lime concre­ Sand, fine to medium, gray (90 percent); tions and gravel near 350 ft ______34 375 interbedded fine gravel (10 percent) 4 126 Sand (about 80 percent), fine to medium, Gravel, fine to coarse, predominantly well gray; gravel (about 10 percent), fine; rounded; some cobbles as much as 7 in.; composed of clasts of volcanic rocks and interbedded sandy zones 27 153 quartzite; silt (about 10 percent); a Wedge zone: small amount of clay ______18 393 Sand, fine to coarse, gray; consists chiefly Clay, dense, plastic, chocolate-brown; with of subangular to subrounded grains of a few green streaks ______12 405 quartz; scattered granules and pebbles of Clay, sandy, silty, limy, grayish-brown, volcanic rocks and quartzite; some lime­ moderately plastic ______7 412 stone fragments (concretions) _ __ 134 287 Sand (about 75 percent), fine to coarse, Gravel, volcanic, fine, subangular (about gray; silt (about 15 percent), a small 80 percent); fine to coarse gray sand; amount of clay; gravel (about 10 per­ some concretions and a little tan to cent) , fine; occasional cobbles as much as grayish-green non-plastic clay (20 per­ 4 in. ______6 418 cent) ______5 292 Sand (about 65 percent), fine to coarse, Sand, fine to medium, gray; scattered fine gray; gravel (about 25 percent), vol­ gravel and a little grayish-green non- canic, fine to coarse; silt and clay (about plastic clay ______45 337 10 percent) ______4 422 Limestone concretions __ _ _ 2 339 Bouse Formation: Sand, fine, gray (75-90 percent); fine vol­ Clay, silty, plastic, chocolate-brown and canic gravel; with a few rounded clasts brown; gravelly and sandy moderately of quartzite _ 11 350 plastic clay; lime concretions from 439 to Sand, gravel, and tan to grayish-green 441 ft. Fossiliferous ______19 441 sandy clay ______7 357 Clay. Thin interbeds of medium-brown plas­ Sand, fine, gray; with a little brown sand tic clay, dark-grayish-brown silty and and scattered fine gravel -_ 13 370 sandy micaceous clay, and grayish-brown Gravel, predominantly volcanic, fine to moderately plastic clay; all slightly ex­ coarse, subangular (25-50 percent); fine pansive on drying. Fossiliferous ____ 49 490 to coarse sand (50-75 percent); a little clay at about 390 ft ______20 390 Sand (80-90 percent), fine to coarse, Sand, flue to medium, gray; scattered fine greenish-gray; gravel (10-20 percent), gravel ______5 395 fine to 2-in., subangular; some pieces of Sand, fine to coarse, gray (about 60 per­ limestone and sandstone ______4 494 cent) ; fine volcanic and quartzitic gravel Silt and clay, greenish-gray; little very fine (40 percent); a few limestone concre­ sand ______3 497 tions and some wood between 405 and Nonmarine sedimentary rocks (Tertiary) : 410 ft ______15 410 Gravel, very coarse; consists of cobbles and Sand, fine to coarse, gray (75 percent) ; possibly boulders; only broken pieces gravel (25 percent) ______20 430 recovered -______4 501 Sand (60 percent); fine to 1-in. subangular to rounded volcanic and quartzite gravel Well (C-8-22)19ccc (40 percent) ______5 435 [U.S. Bureau of Reclamation test well CH-702 in South Gi'a Valley. Sand, predominantly coarse (80 percent); Drilled with cable-tool equipment by Hamilton and Hood. Log by E. grayish-brown to grayish-green clay (10 L. Smith of Bureau of Reclamation; modified partly on basis of gamma log, by F. H. Olmsted. Casing perforated from 115 to 150, 370 percent); fine to 2 in. volcanic and to 390, 395 to 435, and 455 to 463 ft. Altitude 129.6 ft] quartzite gravel (10 percent) -_____ 12 447 Sand, fine to coarse, light-gray (95 per­ Upper, fine-grained zone: cent) ; fine volcanic and quartzite gravel Sand, uniform, fine, gray; brown above 10 (5 percent) ______6 453 ft ______25 25 Gravel, fine to 3 in., volcanic; quartzite (50 Sand, gray; some gray clay and scattered percent); fine to coarse gray (50 per­ fine angular volcanic gravel ______18 43 cent) sand ______2 455 Clay, sandy, grayish-brown to chocolate- Gravel, fine to 2 in., subangular, volcanic brown; interbedded in thin layers with (80 percent); fine to coarse gray sand, fine gray sand ______13 56 and a few limestone concretions (20 per­ Sand, fine, gray (about 75 percent); silt, a cent) ______5 460 small amount of clay, few pieces of sand­ Sand, fine to coarse, gray (55 percent); fine stone (about 25 percent) ______14 70 to coarse volcanic and quartzite gravel Sand, uniform, fine, gray; little fine angu­ (30 percent); lime-cemented conglom­ lar volcanic gravel and rounded quartzite erate (15 percent) ______3 463 gravel ______13 83 Clay, sandy, hard, nonplastic; light-gray Sand and gravel ______5 88 lime inclusions (80 percent); coarse sand GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H173

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-8-22)19ccc Continued Well (C-8-22)23dad Continued Wedge zone Continued: Wedge zone Continued: and fine gravel imbedded in the clay (20 Sand, fine to coarse; contains scattered peb­ percent) ______3 466 bles as much as 2 in.; thin bed of clay at Sand, fine to coarse, gray (80 percent); fine 250 ft ______76 270 to 1% in. volcanic and quartzite gravel Gravel consisting mainly of pebbles as much (20 percent) ______3 469 as 2 in., partly cemented with CaC03 (50 Gravel, fine, volcanic, and quartzite (60 per­ percent); well-graded sand (50 percent). 5 275 cent) ; sand and a little green sandy clay Sand, fine; and scattered pebbles __ _ __ 10 285 (40 percent) ______'____ 5 474 Gravel consisting mainly of pebbles as much Sand, fine to coarse, gray, and a few lime­ as 2 in., partly cemented with CaC03 (50 stone concretions (90 percent); fine vol­ percent); well-graded sand (50 percent). 11 296 canic gravel (10 percent) ______6 480 Sand (70 percent) and gravel (30 percent). Gravel, subangular to subrounded, volcanic Much of gravel subangular and cemented 14 310 (50 percent); fine to coarse gray sand (50 Sand, fine ______12 322 percent) ______4 484 Gravel, largely cemented (50 percent); and Sand, fine to medium; a few pieces of lime- sand ______-__- 39 361 cemented sandstone ______6 490 Clay, red, soft ______2 363 Gravel, subangular to subrounded, volcanic Sand, fine; and scattered angular and sub- (50 percent); fine to coarse gray sand angular pebbles _____---______125 488 (50 percent) ______5 495 Gravel, sandy; cemented with CaCOs (con­ Sand, fine to medium; a few pieces of lime- glomerate) ______12 500 cemented sandstone ______5 500 Well (C-8-22)32cdd Well (C-8-22)22cda2 [U.S. Bureau of Reclamation drainage well SGDW 4 in South Gila Val­ [B. Church. Irrigation well in South Gila Valley. Drilled with cable-tool ley. Drilled with mud-rotary equipment by Layne Texas Co, Cased and equipment by Frank H. Leidendeker. Casing perforated from 100 to gravel packed to a depth of 200 ft; screened from 90 to 200 ft. Altitude 152 ft. Altitude 149 ft] 140.3 ft] ______Upper, fine-grained zone: Upper, fine-grained zone: Soil ______5 5 Clay ______15 15 Clay______21 26 Sand, silted ______10 25 Streaks of sand and clay 34 60 Sand, clay strata ______15 40 Clay and gravel ______10 70 Clay, sticky ______5 45 Clay and sand ____ 15 85 Sand ______17 62 Coarse-gravel zone: Clay, sandy ______4 66 Gravel, coarse ___- _ ___ - 20 105 Clay, sticky ______2 68 Gravel, fine ______12 117 Sand, silted ______7 75 Gravel, coarse; and streaks of clay _____ 11 128 Sand ______16 91 Gravel, fine; and streaks of sand __ 17 145 Coarse-gravel zone: Gravel, coarse; and streaks of clay ______22 167 Gravel, water-bearing (good) ______61 152 Gravel and hard streaks ______18 185 Wedge zone: Gravel, coarse ______13 198 Sand, some gravel ______5 157 Wedge zone: Sand, packed ______14 171 Sand and gravel ______6 204 Well (C-8-22)23dad Clay, sandy ______12 216 [U.S. Bureau of Reclamation test well CH-4 in South Gila Valley. Well (C-8-22)35caal Drilled with cable-tool equipment by San Diego We1! Drillers. Log by Bureau of Reclamation; modified by F. H Olmsted, using gamma log. [U.S. Bureau of Reclamation test well CH-704; deepened by U.S. Geologi­ Casing perforated from 100 to 130 and 334 to 354 ft. Altitude 152.4 ft] cal Survey from 600 to 1,997 ft as test well LCRP 29; in South Gila Valley. Drilled to 600 ft with cab'.e-tool equipment by Hamilton and Hood; deepened (pilot hole only) from 600 to 1,997 ft with mud-rotary Upper, fine-grained zone: equipment by Desert Water Drilling Co. Log to 600 ft by Bureau of Sand, fine; and alternate layers of brown Rec'amation; modified by F. H. Olmsted using gamma log; from 600 to 1,997 ft, log by F. H. Olmsted Casing perforated from 99 to 170, and gray clayey silt and silty clay. Some 435 to 445, 480 to 490, 507 to 540, and 550 to 570 ft. Altitude 150.8 ft] sand contains mica and a considerable proportion of highly colored grains ___ 60 60 Upper, fine-grained zone: Sand, clayey, fine; and silt; contains thin Sand, silty, light-brown; some clay and layers of gray silty clay and brown organic matter _ 3 3 clayey silt ______20 80 Clay, reddish-brown; sand and silt 45 48 Coarse-gravel zone: Sand, fine, light-brown (50 percent); brown Gravel containing cobbles as much as 7 plastic clay (50 percent); occasional sub- in. (65-70 percent) ; fine to coarse sand angular volcanic pebbles __ _ 41 89 consisting of abundant colored grains Coarse-gravel zone: (30-35 percent). ______30 110 Gravel, fine to coarse; consists of rounded Sand (60-70 percent); gravel contains cob­ clasts of quartzite and a few subangular bles as much as 8 in. (30-40 percent) _ 10 120 clasts of volcanic rocks and scattered Gravel containing cobbles as much as 7 in. cobbles as much as 6 in. (65-80 percent); (65-70 percent) ; fine to coarse sand con­ fine to coarse sand; a little clay (20-35 sisting of abundant colored grains (30- percent) ______85 174 35 percent) ______22 142 Wedge zone: Sand, fine; and silt; contains 6-in. layers of Sand, fine to coarse, light-grayish-brown light-green to gray clay ______9 151 (80 percent); fine to coarse volcanic and Gravel and sand ______6 157 quartzite gravel (15 percent); yellow Wedge zone: moderately plastic clay (5 percent) ___ 13 187 Sand, fine to coarse; and scattered pebbles _ 35 192 Sand, fine to medium, light-brown; scat­ Clay, hard, dry ______2 194 tered fine pebbles ______108 295 H174 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued;d Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-8-22)35caal Continued Well (C-8-22)35caal Continued Wedge zone Continued: Bouse Formation Continued: Sand, fine to coarse, poorly graded, light- Clay, bluish-gray and pinkish-brown, fos- brown (75 percent); predominantly fine siliferous ______17 1,110 volcanic and quartzite gravel ((25 per­ Silt and fine sand, well-sorted, gray 8 1,118 cent) ______--_-__ __ 10 305 Clay and silty clay, bluish-gray and pinkish- Sand, fine to medium, light-brown; and brown, fossiliferous ___ 131 1,249 occasional pebbles ______10 315 Silt and clayey silt, gray 8 1,257 Sand, fine to coarse, poorly graded, light- Clay and silty clay, bluish-gray and pinkish- brown (70-75 percent); predominantly brown, fossiliferous _ _ ___ 40 1,297 fine volcanic and quartzite gravel (20-25 Silt and clayey silt, gray, fossiliferous 33 1,330 percent); hard medium-brown clay balls Clay and silty clay, bluish-gray and pinkish- (0-10 percent) ______20 335 brown, fossiliferous _ 15 1,345 Sand, fine to medium, light-brown; and Silt and clayey silt, gray fossiliferous __ 27 1,372 scattered pebbles ______45 380 Clay and silty clay, bluish-gray and pinkish- Gravel, predominantly fine, volcanic; and brown, fossiliferous ______24 1,396 some quartzite (60 percent); fine sand Older marine sedimentary rocks: (40 percent) ______3 383 Sand, fine, gray, somewhat indurated; some Sand, fine to coarse, light-brown; and scat­ medium sand and silt; fossiliferous _ 39 1,435 tered small pebbles ______43 426 Clay, gray; and fine gray sand, inter­ Sand, fine to coarse; some gravel and green bedded ; somewhat indurated and fos­ to brown plastic clay ______4 430 siliferous 38 1,473 Sand, fine to coarse (70 percent); fine vol­ Silt, gray; somewhat indurated and fos- canic and quartzite gravel (30 percent); siliferous ______33 1,506 chocolate-brown plastic clay at 445 ft ___ 15 445 Clay, gray; and some pinkish-brown clay; Sand, fine to medium, light-brown; and somewhat indurated and fossiliferous _ 23 1,529 scattered pebbles and pieces of sandstone 18 463 Sand, fine, gray, somewhat indurated; some Sand, fine to coarse, light-brown (70-95 medium sand and silt; fossiliferous ____ 46 1,575 percent); fine to l 1/^ in., volcanic and Clay, gray; and some pinkish-brown clay; quartzite gravel (5-30 percent) ; a few somewhat indurated and fossiliferous __ 16 1,591 green bentonitic clay balls ______27 490 Sand, fine to medium, somewhat indurated; Sand and scattered fine pebbles ______17 507 interbedded gray clay and silt __ _ _ 24 1,615 Gravel (70 percent) and sand (30 percent- 8 515 Clay, gray, fossiliferous, somewhat indu­ Sand, fine to coarse, light-grayish-brown rated ______17 1,632 (60-70 percent) ; fine to 2 1/& in. gravel; Sand, fine to medium, somewhat indurated; quartzite gravel (30-40 percent) _____ 25 540 interbedded gray clay and silt _ _ __ 19 1,651 Sand and about 10-15 percent fine quartzite Clay, gray; and some pinkish-brown clay; and volcanic gravel ______5 545 fossiliferous and somewhat indurated _ 17 1,668 Clay, slightly silty, medium-brown _____ 3 548 Sand, fine to medium, gray, somewhat indu­ Gravel, chiefly subrounded volcanic and rated ______12 1,680 quartzite; contains a few cobbles as much Clay, gray, indurated, somewhat fossilifer- as 4 in. (70-85 percent); fine to coarse 1,686 sand (15-30 percent) ______22 570 Sand, fine to medium, gray, somewhat indu­ Sand, fine to coarse, light-grayish-brown; rated ______15 1,701 and occasional fine pebbles ______11 581 Clay, gray, indurated, somewhat fossilifer­ Sand and about 30-35 percent fine volcanic ous 5 1,706 gravel ______9 590 Sand, fine to medium, gray, somewhat indu­ Sand, predominantly fine, grayish-brown; rated ______16 1,722 and scattered fine pebbles ______10 600 Clay, gray, indurated, somewhat fossilifer­ Sand and gravel, interbedded ______105 705 ous _ _ _ _ 9 1,731 Clay, soft, brown ______. 9 714 Sand, fine to medium; some silt; somewhat Gravel and sand ______14 728 indurated ______26 1,757 Silt, clayey, brown ______3 731 Clay, gray, indurated, somewhat fossilifer­ Sand and gravel, interbedded ______22 753 ous ______11 1,768 Silt, clayey, brown ______6 759 Silt, fine sand, and clay, interbedded, some­ Sand, some gravel ______35 794 what fossiliferous ______61 1,829 Transition zone(?): Sand, fine to medium; some silt; somewhat Clay, soft, grayish-brown; some gray clay _ 15 809 indurated ______32 1,851 Sand -__-______7 816 Silt, fine sand, and clay, interbedded, some­ Clay, soft, grayish-brown; some gray clay _ 15 831 what fossiliferous ______86 1,937 Sand, some gravel ______54 885 Clay, gray, bentonitic (altered volcanic Transition zone: ash) ______5 1,942 Clay, brown and gray, fossiliferous; inter­ Sand, fine to medium, gray, somewhat indu­ bedded sand ______59 944 rated ______34 1,976 Gravel, somewhat cemented, and sand ___ 25 969 Clay, sandy and silty, pale-greenish-gray __ 21 1,997 Sand and gravel; thin beds of f ossilif erous Well (C-8-23)27ada gray silty clay __ ___..______76 1,045 [U.S. Bureau of Reclamation test well CH-701 in South Gila Valley. Bouse Formation: Dril'ed with cable-tool equipment by Hamilton and Hood. Log by Bureau Clay, bluish-gray and pinkish-brown, fos- of Reclamation; modified by F. H. Olmsted using gamma log. Casing siliferous ______20 1,065 perforated from 84 to 88 ft and 125 to 160 ft. Altitude 133.4 ft] Silt and fine sand, well-sorted, gray _____ 6 1,071 Upper, fine-grained zone: Clay, bluish-gray and pinkish-brown, fos- Sand, predominantly fine, some medium and siliferous ______17 1,088 coarse; small amount of silt and brown Silt and fine sand, well-sorted, gray _____ 5 1,093 clay balls ______40 40 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H175

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (O8-23)27ada Continued Well (C-8-23)33cdd Continued Upper, fine-grained zone Continued: Wedge zone Continued: Clay, tough, brown, moderately plastic; Sand, very little gravel ______53 273 some interbedded sand ____ _ 27 67 Clay, gray, hard 5 278 Sand, clean, quartz ______5 72 Sand, small gravel ______38 316 Clay, tough, brown; some silt ______10 82 Sand, Vz inch gravel and "rock" ______14 330 Coarse-gravel zone(?) : Sand, little gravel ______30 360 Gravel, predominantly to subangular to sub- Sand, with clay balls and streaks from 372 rounded pebbles of volcanic rocks and to 392 ft ______35 395 quartzite; about 20 percent fine to coarse Clay ______15 410 sand ______7 89 Sand, with clay streaks ______15 425 Sand, silt, clay, and about 10 percent fine Clay ______5 430 gravel ______15 104 Sand ______35 465 Sand, fine, brown, and silt; scattered small Clay ______-______9 474 pebbles ______18 122 Sand ______26 500 Coarse-gravel zone: Clay and sand __ 15 515 Gravel, coarse; well-rounded pebbles and Sand ______5 520 cobbles as much as 10 in.; 14-15 percent Clay ______5 525 coarse gray sand -_ - 38 160 Sand, packed ______42 567 Wedge zone: Clay, hard ______8 575 Sand, gray; and scattered small pebbles _ 10 170 Sand ______10 585 Clay, sandy, tough, grayish-green 2 172 Sand and gravel ______15 600 Sand, fine, gray; and about 25 percent silt, 17 189 Sandstone ______5 605 Clay, sandy and limy, grayish-green; con­ Clay and gravel ______20 625 tains scattered small pebbles ______16 205 Sand ______10 635 Clay balls as much as 5 in., with sand and Clay ______58 693 fine gravel coating ______10 215 Sandstone ______57 750 Sand, silt, and gravel; occasional cobbles Clay, hard ______7 757 and a green clay ball at 220 ft _____ 12 227 Sand and sandstone ______11 768 Sand, fine, gray; and 40 percent silt, some Sand and gravel ______12 780 clay ______21 248 Clay ______45 825 Sand, fine; and loosely cemented fine sand­ Casing reduced to 8 in. at 825 ft ______stone, and 30 percent green sandy clay _ 2 250 Clay, gray sandy streaks of brown fine sand 30 855 Sand, fine on sandstone ______2 857 Well (C-8-23)29daa Sand, gray and clay ______39 896 [O. C. Johnson School. Irrigation well on Yuma Mesa, in Yuma. Drilled Clay or shale ______3 899 with cable-tool equipment by Frank H. Leidendeker Casing perforated from 160 to 262, 265 to 270, 283 to 286, and 291 to 295 ft. Altitude Sand and silt ______6 905 182 ft] Clay and streaks of sand ______5 910 Sand, clay, and silt (thin layer), cemented Older alluvium, undivided: sand and gravel at 917 ft ______10 920 Sand and silt strata ______98 98 Sand, with cemented streaks, and streaks of Sand, some pebbles __ _ 50 148 clay ______30 950 Sand, packed ______7 155 Clay, brown ______3 953 Clay, soft, sticky ______7 162 Clay, gray, and sand ______12 965 Sand, packed; and thin sandstone layers _ 32 194 Clay and sandstone ______5 970 Sandstone; some clay and sand layers __ 27 221 Sand, loose ______3 973 Quicksand ______10 231 Clay and sandstone ______12 985 Sand with sandstone and clay layers ____ 9 240 Sandstone ______3 988 Sand and gravel ______20 260 Clay, silt, sand, and sandstone _____ 37 1,025 Sand ______5 265 Sandy clay ______43 1,068 Gravel and sandstone ______3 268 Sand, loose ______3 1,071 Sand ______14 282 Clay, sandy, and sandstone ______14 1,085 Sandstone and clay ______3 285 Granite ______5 1,090 Sand, fine ______5 290 Sandstone and sand ______6 296 Well (C-8-23)36ccd [Federal Compress Co. Industrial well on Yuma Mesa, just east of Yuma. Sand, fine ______7 303 Drilled with cable-tool equipment by Freeleve Dril'ing Co. Casing per­ Well (C-8-23)33cdd forated from 185 to 196 and 238 to 244 ft, open bottom. Altitude 216 [Stardust Hotel test well; deepened from 830 to 1,090 ft as U.S. Geologi­ ft]______^^^^ cal Survey test well LCRP 13. On Yuma Mesa, in Yuma. Drilled and Upper, fine-grained zone: deepened with cable-tool eauipment by Hamilton and Hood. Log below 830 ft by G. R. Vaughan. Casing perforated from 182 to 200 ft. Altitude Sand ______38 38 197 ft] Clay ______4 42 Sand ______37 79 Upper, fine-grained zone: Clay ______11 90 Sand ______70 70 Sand ______50 140 Clay ______5 75 Clay, sandy; water test ______6 146 Sand ______30 105 Sand, loose ______36 182 Clay and sand ______30 135 Coarse-gravel zone: Clay______35 170 Gravel, coarse; little sand ______16 198 Coarse-gravel zone: Sand ______17 215 Gravel and about 40-50 percent sand ___ 30 200 Clay ______2 217 Clay______6 206 Sand ______5 222 Gravel ______10 216 Sand and gravel, mostly sand ______15 237 Wedpe zone: Gravel, coarse; looks like washed gravel __ 8 245 Clay ______4 220 Gravel and sand, loose (50-50) ______13 258 H176 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-8-23)36ccd Continued Well (09-22)17dca [P. Hairgrove. Unused irrigation well on Yuma Mesa Drilled with cable- Wedge zone: tool equipment by A. G. Tschour. Driller's log from 0 to 190 ft Sandy with some gravel, little firmer ___ 37 295 modified by F. H. Olmsted on basis of gamma log. Casing perforated Conglomerate ______3 298 from 165 to 190, 194 to 198, and 215 to 218 feet. Altitude 208.9 ftj Sand, loose, some gravel ______4 302 Upper, fine-grained zone: Well (C-9-21)14bac Silt, sandy _ 11 11 [B. Palon Unused irrigation well on "Fortuna Mesa" piedmont area west of northern Gila Mountains. Drilled with cable-tool equipment by Sand 8 19 Hamilton and Hood. Casing perforated from 914 o 1,040 ft. Altitude 395 Silt and sand 16 35 _ft]______Sand ______13 48 Older alluvium, undivided: Clay ______10 58 Clay and rock ______22 22 Sand ______20 78 Sandy clay and gravel ______11 33 Sand and gravel 5 83 Sand ______55 88 Sand 9 92 Red clay ______2 90 Clay, silt, and fine sand _ __ 34 126 Sand ______131 221 Sand 28 154 Sand and gravel, x/4 in. maximum _____ 19 240 Sand and silt ___ 12 166 Sand ______146 386 Coarse-gravel zone: Sand and gravel ______4 390 Sand and gravel 7 173 Sandstone and gravel, 3 in. maximum ___ 8 398 Gravel ______17 190 Sand ______16 414 Sand ____ 3 193 Clay ______7 421 Clay ______1 194 Sand ______27 448 Sand and gravel 4 198 Clay ______2 450 Sand ______17 215 Sand ______1 451 Gravel _ _ 3 218 Clay ______8 459 Wedge zone(?) : Sand and boulders, 4% in. maximum ____ 4 463 Clay ______3 221 Granite gravel and boulders, 5 in. maximum 12 475 Sand ______4 225 Clay ______4 479 Clay, green 1 226 Sand and sandstone ______75 554 Sand, water ______37 263 Clay ______4 558 Sand and sandstone ______98 656 Well (C-9-22)28cbb [U.S. Geological Survey test well LCRP 25 on Yuma Mesa. Drilled with Granite gravel and boulders, 4 in. maximum 6 662 mud-rotary equipment by Evans Brothers. Log by F. H. Olmsted. Sand and sandstone ______18 680 Completed to 2,002 ft and gravel-packed; casing perforated from 862 Sand and gravel, l 1/^ in. maximum ____ 3 683 to 2,002 ft. Altitude 204.6 ft]______Sandstone ______9 692 Upper, fine-grained zone: Decomposed granite and sandstone _____ 8 700 Sand, fine to medium, light-brown; some silt 25 25 Bouse Formation: Gravel and brown medium to coarse sand _ 20 45 Clay ______40 740 Sand, medium to coarse, light-brown; gravel Sand and sandstone ______10 750 and some brown clay and silt 24 69 Clay ______5 755 Clay, silty, brown; gravel and some sand _ 13 82 Sand and sandstone ______15 770 Sand, silty, brown; some gravel and brown Clay and shale ______15 785 clay ______27 109 Sand ______2 787 Sand, brown; brown clay and some gravel Clay and shale ______127 914 and silt ______33 142 Sand ______90 1,004 Sand, fine to coarse, brown ______18 160 Sand and decomposed granite ______65 1,069 Coarse-gravel zone: Clay ______13 1,082 Gravel, cemented ______5 165 Crystalline rocks: Clay, silty, brown ______10 175 Decomposed granite ______1 1,083 Sand, fine to coarse; some silt in upper part 13 188 Granite ______2 1,085 Gravel, cemented ______9 197 Well (C-9-22)9bba Sand, fine to coarse, brown; some gravel _ 10 207 [ Ketcherside. Unused irrigation well on Yuma Mesa. Drilled with cable- tool equipment by F. E. Leidendeker. Driller's log modified by F. H. Clay, silty, brown ______3 210 Olmsted on basis of gamma log. Casing perferated from 150 to 182 Sand, gravel, and some brown silty clay ___ 35 245 and 230 to 250 ft. Altitude 208.0 ft]______Coarse-gravel zone(?) Upper, fine-grained zone: Clay, silty, brownish-gray ___ _ _ 4 249 Sand ______8 8 Sand, coarse, gray ______5 254 Sand and cemented gravel ______8 16 Clay, silty, brownish-gray ______7 261 Sand ______19 35 Gravel and coarse sand, gray; much Clay and sand ______9 44 rounded quartzite and chert ______43 304 Clay ______26 70 Wedge zone: Sand and gravel ______14 84 Sand, silt, and clay, gray to brownish-gray 13 317 Sand, fine to coarse; gravel and thin beds Clay and sand ______6 90 of brownish-gray silty clay and silt ___ 110 427 Sand ______46 136 Silt, brownish-gray ______4 431 Clay and sand ______10 146 Sand, fine to coarse; gravel and thin beds Sand ______7 153 of brownish-gray silty clay and silt __ 95 526 Coarse-gravel zone(?) : Silt, brownish-gray ______4 530 Sand and gravel ______11 164 Sand, fine to coarse; gravel and thin beds Sand ______6 170 of brownish-gray silty clay and silt ___ 43 573 Sand and gravel ______16 186 Silt, brownish-gray ______5 578 Coarpe-gravel zone: Sand, fine to coarse; some gravel and thin Gravel, some interbedded sand ______23 209 beds of brownish-gray silt and silty clay 83 661 Sand ______11 220 Clay, silty, brownish-gray ______4 665 Gravel, sandy ______30 250 Sand, fine to coarse; some gravel and thin GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H177

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-9-22)28cbb Continued Well (C-9-22)28cbb Continued Wedge zone Continued: Wedge zone Continued: beds of brownish-gray silt and silty clay 68 733 Sand, fine to coarse; and gravel 33 1,535 Silt, brownish-gray ______3 736 Clay, silty _ _ 4 1,539 Sand, fine to coarse; some gravel and thin Sand, fine to medium; some gravel __ 37 1,576 beds of brownish-gray silt and silty clay 20 756 Clay, silty 1,580 Silt, brownish-gray ______4 760 Sand, fine to medium; a small amount of Sand, some gravel, and brownish-gray silt _ 11 771 gravel ______10 1,590 Silt, brownish-gray ______3 774 Clay, soft, sticky, light-brownish-gray __ 26 1,616 Sand, some gravel, and brownish-gray silt _ 8 782 Gravel (mostly plutonic, volcanic, and meta- Silt, brownish-gray ______3 785 morphic rock detritus, some chert and Sand and gravel; 'a small amount of quartzite); some sand ______15 1,631 brownish-gray silt ______32 817 Sand; some gravel and grayish-brown silt _ 17 1,648 Silt, brownish-gray ______3 820 Silt, sandy, soft, grayish-brown _ 3 1,651 Sand and fine gravel; some fine white sand­ Sand, fine to medium; a small amount of stone ______17 837 gravel ______24 1,675 Clay, silty, brownish-gray ______4 841 Silt, sandy, soft, grayish-brown - __- 3 1,678 Sand, coarse; and gravel (chiefly metamor- Sand; beds of cemented sand and gravel __ 54 1,732 phic and volcanic); some fine to medium Clay, hard, light-grayish-brown ______9 1,741 sand and silt ______50 891 Sand, fine to medium ______13 1,754 Silt, brownish-gray ______3 894 Sand, somewhat cemented, and gravel _ _ 13 1,767 Gravel and sand; some fine white sandstone 26 920 Clay, soft, light-brownish-gray ______5 1,772 Silt, sandy, brownish-gray ______3 923 Sand, fine to coarse; a small amount of Sand, fine to coarse, gray ______7 930 gravel ______28 1,800 Sand, fine to coarse; and gravel (meta- Clay, silty and sandy, soft, pale-yellowish- morphic, volcanic, chert, quartzitic, and brown (10YR 6/2); much moderate- some granitic) ______11 941 brown (5YR 4/4) clay ______23 1,823 Sand, fine to coarse, gray ______3 944 Sand and gravel, somewhat indurated ___ 35 1,858 Sand and gravel ______11 955 Silt, sandy, grayish-brown ______5 1,863 Sand, fine to coarse, gray ______10 965 Sand, fine to coarse; some gravel ___ 70 1,933 Gravel and sand ______10 975 Clay, brown ______10 1,943 Clay, silty, grayish-brown ______3 978 Sand, fine to coarse; some gravel _ 21 1,964 Gravel and sand ______8 986 Clay, brown ______10 1,974 Sand, fine to coarse; and gravel _____ 34 1,020 Sand, fine to coarse; some gravel __ _ 10 1,984 Silt, brownish-gray ______3 1,023 Clay, brown 13 1,997 Sand, fine to coarse; and gravel ______13 1,036 Sand, medium to coarse; some beds of Silt, brownish-gray ______4 1,040 gravel ______104 2,101 Sand, fine to coarse; and gravel ______3 1,043 Transition zone: Sand, fine to medium, gray ______11 1,054 Clay, hard; or pale-bluish-gray and pale Gravel and sand ______4 1,058 brown claystone; pelecypods ______2,110 Sand, fine to medium, gray ______8 1,066 Sand, fine to medium, gray ______2,117 Clay, gray or brownish-gray ______5 1,071 Clay, hard; or pale-bluish-gray and pale Sand, fine to medium; some gravel ______19 1,090 brown claystone; pelecypods ______2,122 Gravel and sand ______37 1,127 Sand, fine to medium; and interbedded clay 2,131 Sand, fine to medium; some gravel ______32 1,159 Clay and clavstone, medium-bluish-gray and Silt, sandy ______5 1,164 brown; pelecypods _ 13 2,144 Sand, fine to medium; some gravel _____ 24 1,188 Sand and silt; some gravel ______10 2,154 Clay, gray ______4 1,192 Clay and claystone, medium bluish-gray Sand, fine to medium; some cemented sand and brown; pelecypods ______31 2,185 and gravel ______62 1,254 Sand, fine to coarse; somewhat indurated, Silt, gray ______4 1,258 gray 31 2,216 Sand, fine to coarse; and gravel ______19 1,277 Clay ______3 2,219 Silt, clayey ______4 1,281 Sand, fine to coarse, somewhat indurated, Sand, fine to coarse; some gravel ______7 1,288 gray 34 2,253 Clay, hard, light-brownish-gray ______11 1,299 Clay and claystone, bluish-gray, olive-gray, Sand, fine to coarse; some gravel _____ 23 1,322 and brown; pelecypods; some interbedded Silt, sandy ______3 1,325 sand and silt ______18 2,271 Sand, fine to coarse; some gravel -_ ___ 25 1,350 Sand, fine to medium; some silt and clay in Gravel and sand ______7 1,357 thin beds ______15 2,286 Sand, fine to medium; some cemented sand Clay and claystone, olive-gray, bluish-gray, and gravel ______21 1,378 and brown; pelecypods; some interbedded Clay, silty ______6 1,384 gray sand and silt __ 8 2,294 Sand, fine to medium; a small amount of Sand, fine to medium; some silt ______13 2,307 cemented sand and gravel ______36 1,420 Clay, hard; or tough sticky olive-gray clay- Silt, sandy ______4 1,424 stone; some pelecypods ______11 2,318 Sand, fine to medium; a small amount of cemented sand and gravel ______17 1,441 Well (C-9-23)7baa Silt, sandy ______3 1,444 [U.S. Bureau of Reclamation test well YVI-5(P) in Yuma Valley. Drilled with mud-rotarv enuipment hv Bureau of Reclamation. Log Sand, fine to medium; a small amount of bv E. Burnett and E. L, Smith, modified in part by F H. Olmsted. cemented sand and gravel ______10 1,454 Well point insta'led at a depth of 143-145 ft. Altitude 116.1 ft] Clay, light-brownish-gray ______7 1,461 Sand, fine to medium, gray ______6 1,467 Upper, fine-grained zone: Gravel and coarse sand ______13 1,480 Silt, clayey, medium- to dark-brown ______4 4 Sand, fine to coarse; some gravel ______17 1,497 Sand, fine, light-brown, poorly graded ____ 2 6 Silt, sandy ______5 1,502 Clay, fat, reddish-brown ______2 8 H178 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-9-23)7baa Continued Well (C-9-23)20bdc Continued Upper, fine-grained zone Continued: Upper, fine-grained zone Continued: Sand, fine, poorly graded ______10 18 Sand, poorly graded, light- to medium- Clay, silty, reddish-brown ______6 24 brown; a few thin interbeds of fat clay Sand, fine to medium, gray ______7 31 and weakly cemented sand; scattered Clay, silty ______4 35 small pebbles ______38 45 Sand, fine to medium, gray; thin cemented Sand and clay, interbedded. Fine gray sand layers _ _ 15 50 with scattered pebbles; silty light-brown Sand; thin beds of clay and silt ______'__ 12 62 clay ______4 49 Sand, fine to medium, gray; thin cemented Clay, silty, light-brown ______4 53 layers ______10 72 Sand, predominantly fine, light-grayish- Clay, silty and sandy, bluish-gray - _ _ __ 3 75 brown ______- ___ _ 24 77 Sand, fine to coarse, poorly graded; a few Clay, silty, light-brown ______1 78 small pebbles ______13 88 Sand, predominantly fine, light-grayish- Clay, fat, reddish-brown to brown; a few brown ______27 105 silt layers ______20 108 Clay, silty, grayish-brown ______1 106 Sand ______4 112 Sand, predominantly fine, a little medium Clay and sand, interbedded ______14 126 and coarse; contains a few thin cemented Coarse-gravel zone: layers ______8 114 Gravel, poorly graded, containing abundant Coarse-gravel zone: rounded pebbles of quartzite, chert, and Gravel, fine to 3 in., predominantly rounded volcanic rocks. Thin interbeds of fine sand 4 130 (65 percent); sand, fine to coarse, gray Gravel, well-graded, otherwise similar to (35 percent) ______7 121 that above. "Pea" gravel more abundant Gravel, fine to 6 in., rounded (80 percent) ; below 157 ft. Layer of fine sand from 160 coarse to fine sand (20 percent) _ _ _ 30 151 to 161 ft ______35 165 Gravel, fine to 5 in. (65 percent) ; fine to Wedge zone(?) : coarse, gray sand (35 percent) ; thin Sand, fine, poorly graded; occasional peb­ layers of reddish- to grayish-brown clay bles or cobbles above 176 ft, thin layer of between 170 and 172 ft ______38 189 green clay at 176 ft ______37 202 Coarse-gravel zone(?) : Sand, fine to medium, some coarse, gray; Well (C-9-23)9bbb few thin interbeds of gravel (less than [Arizona Public Service Co. Industrial well on Yuma Mesa. Drilled with 30 percent) ______195 cable-tool equipment by A. G. Tschour. Casing perforated from 641 Gravel, predominantly subrounded, fine to to 670 ft. Altitude 193 ft] 16 in.; about 20 percent fine to coarse Upper, fine-grained zone: sand ______28 223 Sand, mesa _ _ - ____ _ - -______14 14 Gravel, subrounded to rounded, fine to 5 Sand and clay streaks, some water at 74 ft 143 157 in.; about 30 percent fine to coarse sand; Clay, soft ______29 186 trace of greenish limy clay ______229 Coarse-gravel zone: Sand, gray, poorly graded; scattered peb­ Gravel, good; water ______19 205 bles ______8 237 Wedge zone: Sand, quick; and fine broken sandstone Well

Selected logs of water wells Continued Selected logs of water wells Continued

Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well-(C-9-23)25dbal Continued Well (C-9-23)35ccc [U.S. Bureau of Reclamation test well CH-13YM on Yuma Mesa. Drilled with mud-rotary equipment by Bureau of Reclamation. Log by W. Wedge zone Continued: Moffttt of Bureau of Reclamation, modified above a depth of 250 ft radiation significantly higher than from by F. H. Olmsted on basis of gamma log. Well point installed at 248 sands above the coarse-gravel zone ___ 94 340 250 ft. Altitude 202.2 ft] Sand, fine, silty and clayey, grading into Upper, fine-grained zone: fine gravel; high gamma radiation ___ 30 370 Sand, fine to coarse, pebbly ______20 20 Sand, clayey, dark-gray; scattered pebbles Sand, fine to medium, a few scattered peb­ and cobbles ______-______40 410 bles 42 Sand, fine to coarse, dark-gray; about 25 Sand and rounded-quartzite gravel __ _ 6 48 percent bluish-gray sandy and silty clay_ 40 450 Sand, scattered pebbles, a few thin beds of Sand, compacted, fine to medium; about 5 pebbly clay __ _ _ _ 9 57 percent fine gravel and 5 percent gray to Sand, clean ______3 60 reddish-brown clay ______120 570 Sand, scattered pebbles, a few thin beds of Sand, fine to medium, some coarse, dark- compact silty sand and pebbly clay _____ 14 74 gray; about 50 percent gray to reddish- Sand, fine ______5 79 brown clay and 10 percent fine gravel 10 580 Gravel, sand, and red clay ______1 80 Sand, compacted, fine to medium, small Sand, fine, brown ______6 86 amount of coarse sand; about 5 percent Clay, red, and thin beds of fine sand _____ 24 110 gravel and 5 percent grayish-blue clay Sand, fine, brown ______16 126 (pebbles?) ______120 700 Clay, hard, red, and silty sand ______2 128 Sand, fine to medium; and gray clay and Sand, fine, brown ______7 135 silt, thin-bedded ______10 710 Clay, reddish-tan; some coarse sand ______2 137 Sand, fine, brown; some thin beds of red Well (C-9-23)32bad clay ______11 148 [U.S. Bureau of Reclamation test well CH-21YM on Yuma Mesa about 7 miles south of Yuma. Drilled w'th mud-rotary equipment by Bureau Clay, soft, reddish-tan ______-_ 1 149 of Reclamation. Log by E. Burnett of Bureau of Reclamation, modified Sand and scattered pebbles ______9 158 by F. H. Olmsted on basis of gamma log. Well point installed at 267 Va Clay, soft, reddish-tan ______1 159 to 269V2 ft. Altitude 188.0 ft] Sand and scattered pebbles ______13 172 Coarse-gravel zone: Upper, fine-grained zone: Sand and fine gravel; few thin beds of red Sand, fine, with little medium and coarse; clay ______10 182 scattered small pebbles; few thin seams of Sand and scattered pebbles ______6 188 hard reddish-brown clay ______46 46 Gravel, fine to 4 in., well-rounded clasts of Clay and silt, calcareous, medium-brown _ 4 50 quartzite and subrounded to subangular Sand, fine; few thin beds of medium-brown clasts of granitic and volcanic rocks; clay ______66 some coarse sand ______12 200 Clay and silt, medium-brown ______68 Sand and scattered pebbles ______2 202 Sand, fine ______-______71 Clay, hard, dark-gray to brown; silt inter- Clay, calcareous, medium-brown to reddish- beds below about 206 ft ______16 218 brown ______79 Sand, fine, brown ______18 236 Silt and clay ______82 Gravel, fine to 6 in., and coarse sand; small Sand, fine ______88 amount of dark-gray clay. Well-rounded Sand and brown clay ______92 clasts of quartzite and subrounded to sub- Clay, calcareous, brown ______96 angular clasts of granitic and volcanic Sand and layers of brown clay ______10 106 rocks ______28 264 Sand, fine ______8 114 Wedge zone: Sand, fine, and brown clay ______6 120 Sand, fine to medium, grayish-brown ____ 32 296 Clay, medium-brown to reddish-brown _____ 5 125 Sand, silty, and clay in thin interbeds ____ 1 297 Sand, fine, and layers of brown clay _____ 8 133 Sand, grayish-brown, and scattered small Sand, fine; some weakly cemented sand, pebbles ______8 305 scattered small pebbles ______34 167 Clay, dark-gray, and about 20 percent fine Clay, calcareous, brownish-gray to dark- sand ______3 308 gray; some fine sand and silt ______15 182 Sand, fine, grayish-brown ______3 311 Sand, fine ______23 205 Clay, dark-gray, and about 20 percent fine Coarse-gravel zone: sand ______1 312 Gravel, fine to 3 in., subrounded to rounded; Sand, fine, grayish-brown; a few pieces of thin beds of sand. Pebbles and cobbles cemented sand and a few thin lenses of include granitic and volcanic rocks, gray clay ______17 329 quartzite, and chert ______17 222 Clay, sandy, white to light-gray ______2 331 Sand and scattered pebbles ______3 225 Sand, fine ______3 334 Gravel, fine to 3 in., subrounded to rounded 18 243 Clay, sandy, white to light-gray ______1 335 Sand, fine brownish-gray ______11 254 Sand, fine, gray ______5 340 Gravel, fine to 3 in., subrounded to rounded 5 259 Silt, sandy, gray to black ______1 341 Sand, fine brownish-gray ______5 264 Sand, fine, gray; scattered small pebbles __ 48 389 Gravel, fine to 3 in., subrounded to rounded_ 3 267 Sand, fine to coarse, and 20-30 percent fine Crystalline rocks: well-rounded quartzite to subangular Granite. NX diamond core from 280 to 285 granitic and volcanic gravel ______6 395 ft contained friable to coherent grayish- Sand, fine; scattered small pebbles ______13 408 white granite, coarse-grained, containing Silt, sandy, light-gray ______2 410 about 60 percent feldspar, 20 percent Sand, fine, grayish-brown; occasional small quartz, and 20 percent dark minerals pebbles ______10 420 (chiefly biotite). Dry-weight density 2.7 Sand, silty, light-gray ______2 422 g per cm3 ______17 285 Sand, fine, grayish-brown ______35 457 H180 WATEE RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-9-23)35ccc Continued Well (C-9-24)8baa Continued Wedge zone Continued: Wedge zone Continued: Sand, fine to coarse, silty, and small peb­ Sand, fine to medium; some silt ____ 20 810 bles ______5 462 Sand, scattered pebbles ______50 860 Sand, fine ______5 467 Sand, fine to medium, gray; some silt __ 48 908 Sand, dense, silty, dark-gray; little bluish- Sand, medium to coarse, gray ______10 918 gray clay ______4 471 Silt, light-brown ______5 923 Sand, some interbedded fine gravel, grayish- Sand, fine to coarse, poorly sorted; granules brown ______33 504 and small pebbles mostly of black chert Well (C-9-24)8baa and silicic volcanic rocks ______52 975 [U.S. Geological Survey test well LCRP 28 in Yuma Valley on east bank Silt, light-brown ______4 979 of Colorado River. Drilled with mud-rotary equipment by Desert Water Sand, some gravel, fine to coarse, poorly Drilling Co. Log by F. H. Olmsted, F. J. Frank, G. R. Vaughan, and sorted; granules and small pebbles mostly J. H. Robison. Cased to 292 ft. Altitude 118.7 ft] of black chert and silicic volcanic rocks _ 21 1,000 Upper, fine-grained zone: Sand, fine to medium, and silt; a few thin Sand, fine, and silt; thin pebbly streaks _ 28 28 cemented streaks or flat sandstone con­ Sand, fine to medium ______57 85 cretions ______72 1,072 Clay, silty, brown 8 93 Sand, fine to coarse, pebbly ______6 1,078 Sand, fine to medium ______16 109 Sand and silt, fine to medium; a few thin Sand, some pebbles ______6 115 cemented streaks or flat sandstone con­ Sand, fine to medium ______9 124 cretions ______90 1,168 Coarse-gravel zone: Clay, brown to brownish-gray ______7 1,175 Gravel, coarse, predominantly subrounded Sand and silt, fine to medium; a few thin to rounded; some coarse sand ______62 186 cemented streaks or flat sandstone con­ Wedge zone: cretions ______202 1,377 Sand, silt, and clay; thin streaks of gravel- 28 214 Clay, light-brownish gray ______5 1,382 Sand, fine to coarse; thin beds of clay and Sand, fine to coarse, and fine gravel; scat­ silt ______76 290 tered pebbles and small cobbles ______80 1,462 Sand, fine, and silt ______36 326 Silt, light-brown, and light-brownish-gray Silt, pale-brown ______4 330 clay ______9 1,471 Sand, fine to medium ______26 356 Sand and fine gravel ______9 1,480 Silt, light-brown ______6 362 Gravel, cemented ______-_____- 5 1,485 Sand, fine to coarse, somewhat pebbly ____ 33 395 Sand, medium to coarse; scattered pebbles Silt, light-brown ______6 401 and thin beds of gravel ______187 1,672 Sand, sparse small pebbles ______7 408 Clay, gray and brown ______5 1,677 Silt, light-brown ______2 410 Sand, coarse, and gravel; thin cemented Sand, fine to coarse ______11 421 zones or flat concretions ______22 1,699 Clay, silty, brown ______4 425 Silt and grayish-white clay; possibly a few Sand, fine to coarse ______23 448 pebbles 4 1,703 Silt, light-brown ______3 451 Sand, some gravel and clay balls ______37 1,740 Sand, fine to medium, some coarse and Silt and clay, brown and gray 1,742 pebbly; a few thin streaks or pebbles of Sand, some gravel; thin cemented zones or gray and brown clay ______79 530 concretions ______14 1,756 Silt, light-brown ______4 534 Clay, silty, gray 4 1,760 Sand, fine to medium, brownish-gray; a Sand, some gravel; thin cemented zones or little silt and scattered small pebbles ___ 15 549 concretions ______34 1,794 Silt, light-brown ______3 552 Sand, coarse, and fine gravel, somewhat Sand, fine to medium; some coarse pebbly cemented ______5 1,799 sand. Pebbles mostly plutonic, volcanic, Sand, some gravel; thin cemented zones or and metamorphic rocks; a few are well- concretions ______16 1,815 rounded chert and quartzite. Many frag­ Clay, grayish-brown ______5 1,820 ments of plants and carbonized wood _ 80 632 Sand, some gravel; thin cemented zones or Silt, light-brown ______5 637 concretions __ _ 40 1,860 Sand, some fine to medium gravel; some Sand, fine to coarse; trace of gravel, silt, coarse pebbly sand. Pebbles most plutonic, and clay _ _ _ __ 67 1,927 volcanic, and metamorphic rocks; a few Transition zone: are well-rounded chert and quartzite. Clay, gray, fossiliferous ______11 1,938 Many fragments of plants and carbon­ Sand and silt, gray _ __ 17 1,955 ized wood ______14 651 Clay, gray, fossiliferous __ ___ 21 1,976 Silt, light-brown ______6 657 Sand, fine to coarse, gray; some fine gravel- 52 2,028 Sand, some fine to medium gravel; some Clay, gray, and fine sand, fossiliferous _ 17 2,045 coarse pebbly sand. Pebbles mostly plu­ Sand, fine to coarse, gray and subangular tonic, volcanic, and metamorphic rocks; a to rounded gravel composed of chert and few well-rounded chert and quartzite. quartzite in addition to plutonic, volcanic, Many fragments of plants and carbon­ and metamorphic rocks ______45 2,090 ized wood ______23 680 Clay, gray, silt and fine sand, fossiliferous- 40 2,130 Sand; a few streaks or clasts of light-gray Sand, some fine gravel ______13 2,143 clay; scattered pebbles ______30 710 Clay, silty, gray, fossiliferous __ __ 13 2,156 Sand, fine to medium, some coarse, gray; Sand, fine to medium, gray ______20 2,176 thin beds of fine gravel ______40 750 Clay and silt, gray, fossiliferous ______4 2,180 Sand, medium to coarse; scattered sand­ Sand and gravel, fine to coarse, gray, sub- stone concretions and pebbles of light- angular to rounded; composed of chert gray claystone; some carbonized wood. and quartzite in addition to plutonic, vol­ Gravel rare ______40 790 canic, and metamorphic rocks 38 2,218 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H181

Selected logs of water wells Continued Selected logs of water wells Continued

Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-9-24)8baa Continued Well (C-9-24)34dcb3 [City of Somerton. Public-supply well in Yuma Valley. Drilled with Transition zone Continued: cable-tool equipment by Hamilton and Hood. Driller's log modified by Clay, gray, fossiliferous ______5 2,223 F. H. Olmsted on basis of gamma log. Altitude 106.2 ft] Sand and gravel, fine to coarse, gray, sub- Upper, fine-grained zone: angular to rounded: composed of chert Silt and clay ______14 14 and quartzite in addition to plutonic, vol­ Sand, fine _____ - ___ 42 56 canic, and metamorphic rocks ______69 2,292 Clay ______2 58 Clay, gray, and fine sand, fossiliferous __ 10 2,302 Sand, fine _____ - _____ 22 80 Sand and gravel, somewhat cemented __ 48 2,350 Clay ______5 85 Clay, gray, and fine sand, interbedded ___ 45 2,395 Sand, fine ______51 136 Sand and gravel, somewhat cemented __ 51 2,446 Sand and gravel 12 148 Clay, gray; fossiliferous ______20 2,466 Coarse-gravel zone: Well (C-9-24)13cdd Gravel ______14 162 [U.S. Bureau of Reclamation test well CH-3 in Yuma Valley. Drilled with Sand ______10 172 cable-tool equipment by San Diego Well Drillers. Log by Bureau of Gravel ______28 200 Reclamation; modified by F. H. Olmsted, on basis of gamma log. Casing Sand ______12 212 perforated from 139 to 170 ft. Altitude 105.0 ft] Gravel ______44 256 Upper, fine-grained zone: Wedge zone: Clay and fine sand and silt, brown, contain­ Sand ______304 560 ing much organic matter ______12 12 Sand and clay ______44 604 Silt and fine sand, clayey, brown ______6 18 Sand, small amount of gravel 10 614 Sand, fine to medium; roots and bark at Sand ______169 783 25 ft ______18 36 Clay ______4 787 Clay, silt, and fine sand ______6 42 Sand, some clay 154 941 Sand, fine to medium ______12 54 Sand, clay, and gravel ______5 946 Clay, brown, plastic, and sand ______2 56 Sand ______19 965 Sand, fine to medium; scattered pebbles _ 8 64 Clay ______4 969 Clay and sand ______5 69 Sand, some clay ______33 1,002 Sand, fine to medium; few thin layers of Sand ______5 1,007 clay and silt ______57 126 Sand, clay, and gravel 4 1,011 Coarse-gravel zone: Sand ______67 1,078 Sand, fine to medium, and about 35 percent Sand, with small amount of gravel __ 5 1,083 gravel ______3 129 Clay, sandy ______18 1,101 Sand, fine to medium, silty; a few pebbles _ 11 140 Sand ______62 1,163 Gravel, fine to 8 in., much of it well-rounded (about 60-70 percent); sand, fine to Well (C-9-25)35cbd coarse (30-40 percent) ______26 166 [U.S. Geological Survey test well liCRP 9 in western Yuma Valley, on east bank of Colorado River. Drilled with mud-rotary equipment by R. Sand, fine to medium (50-85 percent); E. Anderson. Log by F. H. Olmsted, F. J. Frank, and G. R. Vaughan. gravel, fine to 5 in. (15-50 percent) ____ 29 195 Screened in 5- and 10-ft intervals from 310 to 1,108 ft. Altitude 104 ft] Wedge zone: Sand, fine to medium, containing some silt _ 25 220 Upper, fine-grained zone : Sand, fine to medium ______20 240 Sand; some thin beds of silt and clay 26 26 Sand, fine, containing some silt and clay __ 10 250 Sand; silt; some wood _ 11 37 Sand, fine; scattered angular to subangular Sand, fine gravel; some wood - 10 47 pebbles ______15 265 Sand; some silt and wood __ _ _ 44 91 Sand, fine, containing some silt and clay _ 15 280 Silt, clayey; some sand, gravel, and carbon­ Sand, fine to coarse; scattered pebbles ___ 20 300 ized wood ______- 10 101 Sand and gravel ______6 306 Coarse-gravel zone: Sand, fine __..______18 324 Sand and gravel; thin clay at 103 ft ____ 17 118 Sand, silt, and some gravel ______71 395 Gravel and sand ______13 131 Sand and 20 percent gravel up to 2 in. ___ 10 405 Gravel, coarse ____ _ 2 133 Sand, fine to medium, containing some silt Sand; some coarse gravel beds _ _ 19 152 and clay ______35 440 Gravel and sand; some clay and carbonized Sand, fine, well-sorted; some coarse sand __ 35 475 wood ______6 158 Sand, fine to coarse; layers of well-cemented Gravel, coarse; thin beds of coarse sand 21 179 sand ______25 500 Coarse-gravel zone(?) : Sand; some gravel 7 186 Well

Selected logs of water wells Continued Selected logs of water wells Continued

Thick- Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-9-25)35cbd Continued Well (C-9-25)35cbd Continued Wedge zone Continued: Wedge zone Continued: Sand; some beds of gravel ______12 403 Sand; some gravel ______4 1,153 Sand, silty ______4 407 ______5 1,158 Sand; some gravel ______13 420 Sand ______20 1,178 Silt, clayey ______5 425 Sand, silty _ ____ 3 1,181 Sand ______4 429 Sand ______- ______14 1,195 Silt, clayey ______3 432 Sand, silty ______4 1,199 Sand; some gravel «______16 448 Sand ______2 1,201 Silt, sandy ______3 451 Sand, gray, fine to coarse ______23 474 Well (C-10-23)lldcd Silt, clayey, gray ______4 478 [F. Booth. Irrigation well on Yuma Mesa. Drilled with cable-tool equip­ Sand, medium to coarse; some gravel ____ 11 489 ment by Hamilton and Hood. Casing perforated from 98 to 113, 192 to Sand ______8 497 2.22, 260 to 280, 320 to 334. and 445 to 495 ft. Altitude 200 ft] ______Sand, silty ______3 500 Upper, fine-grained zone: Sand, medium to coarse ______10 510 Sand and caliche 10 10 Sand; some beds of gravel -______31 541 Sand ______19 29 Sand, silty ______3 544 Gravel, 3 in. maximum _ 2 31 Sand __-______4 548 Sand and gravel, 1 inch maximum 32 63 Silt, sandy ______3 551 Sand and gravel, 5 in. maximum; with clay Sand ______8 559 lenses 17 80 Gravel ______2 561 Shale ______1 81 Sand ______6 567 Sand ______11 92 Gravel; some sand ______5 572 Gravel, 4 in. maximum 3 95 Sand, silty ______5 577 Sand and gravel 18 113 Sand; some gravel ______18 595 Sand ______72 185 Silt ______5 600 Coarse-gravel zone: Gravel and coarse sand ______8 608 Sand and gravel, 5 in. maximum 13 198 Sand; some gravel and silt ______31 639 Sand and gravel __ 6 204 Sand; coarse; some gravel ______13 652 Sand and gravel, 4 in. maximum 18 222 Silt __-______4 656 Sand ______34 256 Sand ______8 664 280 Silt ______6 670 Gravel, 3 in. maximum 24 Sand; some soft sandstone and fine gravel _ 10 680 Coarse-gravel zone(?): Sand ______36 316 Silt ______10 690 Sand and gravel, 3 in. maximum 18 334 Sand; some soft sandstone and very little Wedge zone: fine gravel ______33 723 340 Silt, sandy ______10 733 Sand ______6 Sand; some gravel ______50 783 Sand, cemented _ 20 360 Silt, sandy ______4 787 Shale, blue 2 362 Sand and soft sandstone ______18 805 Sand, cemented ______3 365 Silt ______4 809 Sand, cemented lenses 90 455 Sand; soft sandstone; some beds of gravel _ 59 868 Sand ______54 509 Sand, silty ______4 872 Gravel ______2 874 Well (C-10-23)20bbb [U.S. Navy. Industrial well on Yuma Mesa. Drilled with cable-tool equip­ Sand ______8 882 ment by Weber Well Drilling Co. Log by G. E. Hendrickeon. Casing Gravel; soft sandstone ______3 885 perforated from 212 to 232 ft. Altitude 189 ft] Sand ______4 889 Gravel; soft sandstone ______3 892 Upper, fine-grained zone: Sand and silt ______10 902 Sand, fine 5 5 Sand ______6 908 Clay and caliche __ _ _ 2 7 Sand, silty; brown clay ______4 912 Sand, fine to coarse 15 22 Gravel and sand ______-______5 917 Sand ______5 27 Sand, fine to medium ______10 927 Sand, fine ____-___-____ _ 3 30 Sand, silty ______4 931 Sand, coarse, with some gravel 6 36 Sand ______6 937 Sand, medium 4 40 Silt, sandy ______4 941 Do ______20 60 Sand; some beds of gravel ______39 980 Sand, coarse 10 70 Silt, sandy ______4 984 Sand, medium 10 80 Sand; some gravel ______8 992 Sand, medium, with small pebbles 10 90 Silt ______5 997 Clay, with some very fine sand 10 100 Sand; some gravel, silt, and fine white Sand, very fine _ 10 110 sandstone ______-______27 1,024 Sand, fine ______10 120 Clay ______8 1,032 Sand, very fine 10 130 Sand; some carbonized wood and gravel __ 36 1,068 Sand, very fine, with traces of silt or clay _ 10 140 Silt, sandy ______4 1,072 Sand, fine, some cemented _ 5 145 Sand; some carbonized wood and fine white Sand, fine, trace of silt or clay 5 150 sandstone ______11 1,083 Sand, fine, with about 10 percent gravel _ 2 152 Silt and white clay ______9 1,092 Coarse-gravel zone: Sand; some gravel ______22 1,114 Gravel % in. and smaller, 5-15 percent fine Sand, silty ______7 1,121 sand and clay 2 154 Sand; some gravel and soft sandstone ___ 13 1,134 Gravel, with coarse sand ______1 155 Sand, silty ______3 1,137 Sand, fine to coarse, with about 25 percent Sand; some carbonized wood ______12 1,149 gravel ____ 5 160 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H183

Selected logs of water wells 'Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-l0-23)20bbb Continued Well (C-10-23)31bbbl Continued Coarse-gravel zone Continued: Coarse-gravel zone Continued: Gravel, small with coarse sand ____-_ 10 170 and about 50 percent very fine to medium- Description missing ______5 175 grained grayish-brown sand 24 297 Sand, medium to very coarse, with clay Wedge zone: balls ______7 182 Sand, very fine to medium-grained, grayish- Pebbles, sand, and clay ______3 185 brown ______28 325 Sand, fine to coarse, about 35-40 percent Sand, medium- to coarse-grained, brownish- gravel ______5 190 gray; scattered pebbles and thin strata Sand, fine to medium; some silt or clay _-_ 5 195 of blue clay ______70 395 Sand, very fine to fine; some silt or clay _ 5 200 Gravel, a/4-3 in., and a small amount of Sand, fine, with some silt and clay _____ 10 210 medium sand ______-_ 12 407 Sand, medium to coarse, with about 40 per­ Clay, bluish-gray ______1 408 cent gravel ______2 212 Sand, medium, brownish-gray ______8 416 Gravel, with about 40 percent sand, medium Gravel, ^4-3 in., and about 40-50 percent to coarse ______8 220 medium gray sand; thin streaks of clay Gravel, with about 20 percent sand ____ 20 240 at 417 and 418 ft ______4 420 Wedge zone: Sand, fine to medium, brownish-gray, and Sand, fine to medium ______10 250 scattered small pebbles ______13 433 Sand, fine to medium, with 5-10 percent Sand, brownish-gray, and about 30-50 per­ pebbles ______10 260 cent gravel; thin streaks of clay at 435 ft 7 440 Sand, fine to medium, with 0-10 percent Sand, brownish-gray, and a few small peb­ pebbles ______10 270 bles; streaks of clay at 457 and 459 ft 32 472 Sand, fine to medium, with 5-10 percent Gravel, 1/4-% in., and about 40 percent pebbles ______10 280 sand; some wood embedded in bluish-gray Sand, fine to medium, with 15-20 percent clay from 472-475 ft ______8 480 pebbles ______10 290 Sand, coarse to very coarse, grayish-brown; Gravel, with some sand, had some water, no trace of silt and *4-in. gravel __ __ 17 497 rise ______4 294 Sand, coarse to very coarse, grayish-brown, Sand, medium ______.____ 21 315 and about 35 percent angular gravel; some cemented sand and gravel __ 3 500 Well (C-10-23)28ccd Sand, medium to coarse, brownish-gray; [V. H. Ueckert. Unused irrigation well on Yuma Mesa. Drilled with scattered gravel lA-3 in.; streaks of clay mud-rotary equipment by Gragg. Gravel-packed, casing perforated from 230 to 293 ft. Altitude 185 ft] at 527, 530, 532, and 540 ft ______42 542 Sand, medium to coarse, brownish-gray; Upper, fine-grained zone: and 10-40 percent gravel ______13 555 Sand ______45 45 Sand, medium to coarse, brownish-gray- Coarse-gravel zone: and less than 10 percent gravel, x/4-3 in. 20 575 Gravel, cemented ______25 70 Sand, medium to coarse, pebbly, medium- Gravel ______64 134 brown ______15 590 Sand, fine ______.______40 174 Sand, medium to coarse, grayish-brown; Gravel ______6 180 some sandstone and gray clay balls ___ 14 604 Gravel, sandy ______45 225 Gravel, subangular to well-rounded, x/4-2 Sandstone ______25 250 in., and 30 percent medium to coarse Gravel, small ______20 270 grayish brown sand -_ _-_-___-_ 6 610 Gravel, sandy ______64 334 Sand, well-rounded, medium to coarse, medium-brown ______10 620 Well (C-10-23)31bbbl Sand, well-rounded, coarse, grayish-brown, [U.S. Geological Survey test well LCRP 1 on Yuma Mesa. Drilled with and streaks of gray shaly clay from 630 cable-tool equipment by Arizona Machine and Welding Works. Log by F. J. Frank. Casing perforated from 220 to 280 ft. Altitude 172.8 ft] to 635 ft ______21 641 Sand, poorly sorted, fine to very coarse, Upper, fine-grained zone: and 15-20 percent gravels ^-1 in. ____ 1 643 Sand, light-brown, and about 10 percent Sand, fine to coarse; scattered pebbles and gravel; thin strata of clay at 15, 25, 60, streaks of bluish-gray shaly clay and silt- 43 686 and 65 ft ______82 82 Sand, medium to very coarse, and 15 per­ Gravel, x/4-2 in.; streak of clay and sand _ 2 84 cent well-rounded % % in. gravel, Sand, light-brown, somewhat pebbly; streaks of greenish-blue clay ______3 689 streaks of clay, cemented gravel, and Sand, poorly sorted, fine to very coarse, cemented sand from 115 to 123 ft ____ 53 137 gray ______12 701 Coarse-gravel zone: Sand, medium to coarse, gray, and 20 per­ Gravel, pebbles, and cobbles, and about 10 cent gravel, ^-^ in.; some clay at 708 percent sand; a few strata of weakly ft ______9 710 cemented sand ______16 153 Sand, medium to very coarse, grayish- Gravel, pebbles, and cobbles, and more sand brown ______25 735 than above; strata of conglomerate and Sand, medium, grayish-brown; and gray clay from 162 to 164 ft ______17 170 platy clay ______5 740 Sand, pebbly; streaks of reddish-brown clay 8 178 Sand, medium to coarse, grayish-brown; a Gravel, pebbles, and cobbles, and about 40 few pieces of broken lava rock ______5 745 percent sand; streaks of reddish-brown Sand, very fine to medium, poorly sorted, clay from 178 to 180 ft ______12 190 grayish-brown ______35 780 Sand, pebbly, grayish-brown; pebbles */4-2 Sand, coarse to very coarse, grayish-brown; in. ______6 196 some angular pieces of volcanic origin at Gravel, ^-4 in., and 10-30 percent sand; 780 and 787 ft ______15 795 some clay streaks and cemented zones _ 77 263 Sand, medium to coarse, poorly sorted, Gravel, ^4-1 in., scattered large cobbles, grayish-brown ______12 807 H184 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-l0-23) Slbbbl Continued Well (C-l0-24) Ibddl Wedge zone Continued: [U.S. Bureau of Reclamation test well CH-1 on east edge of Yuma Val­ Sand, medium, gray; 20-25 percent ^4-1 in. ley, at foot of Yuma Mesa escarpment. Drilled with cable-tool equip­ ment by San Diego Well Drillers. Log by Bureau of Reclamation, gravel and a few gray clay balls _____ 809 modified by F. H. Olmsted on basis of gamma log. Casing perforated Sand, medium to coarse, well-rounded, from 144 to 170 ft. Altitude 110 ft] gray; silt and clay at 816 ft; and a few subangular volcanics at 820 ft ______9 818 Upper, fine-grained zone: Sand, very coarse, gray; 15 percent, %-4 Sand, very fine to medium; a few thin in., angular gravel ______820 streaks of silty clay __ 25 25 Sand, very coarse, gray; some fine sand and Sand and brown silty clay with black gray silt ______15 835 streaks ______3 28 Sand, well-rounded, medium; some gray silt Sand, fine to medium __ _ __ 6 34 and a few gray clay balls at 805-850 ft _ 25 860 Sand and brown silty clay _ 2 36 Sand, fine to medium, gray; contains more Sand, fine to medium; a few thin Oi-2 in.) silt than preceding beds; poorly sorted, beds of silt, clay, and clayey sand 51 87 fairly well rounded ______20 880 Clay, sandy and silty 89 Sand, medium to coarse, gray; silt and gray Sand, fine to coarse; few thin beds of silty clay balls with a few large angular pieces clay and about 2-3 percent pebbles __ 23 112 of rock ______2 882 Sand, clayey ______4 116 Sand, medium to coarse, gray; more fine Sand, fine to coarse, and about 10 percent particles than in bed above; few gray gravel up to 3 in. _ 25 141 clay balls from 885 to 890 ft ______8 890 Coarse-gravel zone: Sand, fine to medium, gray, subangular to Gravel containing well-rounded cobbles up fairly well rounded; very few coarse to 8 in.; about 25-30 percent sand 40 181 grains ______25 915 Coarse-gravel zone(?) : Sand, fine, moderate-yellowish-brown, angu­ Sand, fine to coarse; beds of gravel (25 per­ lar to rounded; contains a few rounded cent) ______24 205 pebbles ^-l in. and some angular pebbles Gravel containing 30-40 percent sand and of volcanic rocks. Carbonized wood at a higher percentage of mafic rocks than 939 ft ______25 940 gravel from 141 to 181 ft ______5 210 Sand, fine to medium, dark-yellowish-brown, Sand, fine to coarse, and gravel up to 2 in._ 17 227 subangular to rounded; about 5 percent Wedge zone: granule gravel, rounded ______5 945 Sand, fine to coarse, and about 5 percent Sand, fine to medium, moderate-yellowish- scattered granules up to % in. __ 23 250 brown, and greenish-gray clay balls ___ 5 950 Sand, fine to coarse, containing pieces of Sand, fine to medium, light-brown, subangu­ silty clay __ 15 265 lar, fairly well sorted ______10 960 Sand, fine to coarse, containing angular Sand, fine, fairly well sorted, subangular, granules and pebbles up to 2 in. composed pale-yellowish-brown; a few yellowish- of volcanic rocks ______15 280 brown clay balls ______5 965 Sand, very fine to medium, containing Sand, fine, fairly well sorted, subangular, layers of cemented gravel 3-6 in. thick _ 20 300 pale-yellowish-brown; a few yellowish- Sand, fine to medium; some silt and clay, brown clay balls; contains a few rounded scattered granules and pebbles __ __ 13 313 pebbles %-! in. ______10 975 Sand, fine to medium _ _ 19 332 Sand, fine to medium, subangular, pale- Sand, fine to coarse; some silt and clay and yellowish-brown, fairly well sorted; some 3-4 percent gravel _ 43 375 CaCOs cementation and a few angular Clay, very hard ______1 376 pebbles of volcanic rocks ______10 895 Sand, fine to coarse, containing layers of Sand, fine to medium, subangular, pale- clay 3-4 in. thick and 2-3 percent gravel- 19 395 yellowish-brpwn, fairly well sorted; about Sand, fine to coarse; some silt and 5-8 per­ 20 percent light-gray platy clay _____ 5 990 cent gravel ______10 405 Sand, fine to medium, subangular, pale- Sand, fine to coarse; some silt, clay, and yellowish-brown, fairly well sorted; about cemented sand __ 10 415 20 percent light-gray platy clay; a few Sand, fine to coarse; silt and clay; contains subangular pebbles of volcanic rocks ___ 10 1,000 more clay than bed above ______- 10 425 Well (C-l0-23) 36ddd Sand, fine to coarse; 2-3 percent gravel; [U.S. Bureau of Reclamation test well CH-22YM on "Upper Mesa." some cemented sand and a few pieces of Drilled with mud-rotary equipment by Bureau of Reclamation. Log by light-gray sandy clay ___ _ 25 450 E. Burnett of Bureau of Reclamation. We'l point installed at end of 2-in. pipe at a depth of 209-211 ft. Altitude 285 ft]______Sand, fine to coarse; some silt and clay ___ 35 485 Older alluvium, undivided: Sand, fine to coarse; 2-3 percent gravel and Sand, fine, light-brown, poorly graded; scat­ some poorly cemented sand ______15 500 tered gravel ______7 7 Well (C-l0-24) 5ddd [U.S. Bureau of Reclamation test well CH-2 in Yuma Valley. Drilled Gravel, fine to coarse, well-graded, ^-l 1/. with cable-tool equipment by San Diego Well Drillers. Log by Bureau in., a few 3 in. Well-rounded to sub- of Reclamation; modified by F. H. Olmsted on basis of gamma log. rounded clasts of volcanic rocks granite Casing perforated from 170 to 215 ft. Altitude 100 ft]______and quartzite (amber and purple) ___ 47 54 Upper, fine-grained zone: Gravel and sand, interbedded ______3 57 Silt, sandy, and clay, brown ______13 13 Sand, fine, poorly graded; scattered gravel. 11 68 Sand, fine to medium; scattered pebbles in Sand, fine, and thin layers of fat light- lower part ______73 86 grayish-brown calcareous clay ______6 74 Silt, brown, containing a few granules and Sand, fine, poorly graded ______29 103 small pebbles ______4 90 Sand, fine, poorly graded; a few thin layers Clay, silty, brown; some gray clay ___ 6 96 of coarse sand and fine gravel. Well- Silt, brown ______12 108 rounded to subrounded clasts of volcanic Sand, fine to coarse; a few thin layers of rocks, granite, and quartzite ______107 210 silty clay; scattered pebbles below 120 ft_ 59 167 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H185

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-l 0-2 4 )5ddd Continued Well (C-l0-24) 23ddd Continued Coarse-gravel zone: Upper, fine-grained zone Continued: Gravel; some fine to coarse sand ______13 180 Clay, calcareous, reddish-brown ______2 21 Sand, fine to medium; pieces of wood at Sand, fine; scattered medium and coarse 180 ft ______18 198 sand ______23 44 Gravel, rounded cobbles up to 6 in.; some Clay, calcareous, reddish-brown _____ 14 58 sand ______22 220 Sand, fine to coarse ______4 62 Clay, silty ______1 221 Sand and fine gravel ______7 69 Gravel containing cobbles up to 8 in.; some Sand, fine to coarse ______4 73 sand ______31 252 Sand and fine gravel ______4 77 Wedge zone: Sand, fine to coarse ______3 80 Sand, fine to coarse; some pebbles up to Clay, calcareous, reddish-brown ______9 89 1% in. ______23 275 Sand, fine to medium; some silt, and scat­ Sand, fine to coarse; few thin beds of ce­ tered fine to 2-in. pebbles of volcanic mented gravel ______29 305 rocks ______19 108 Sand, fine to coarse, and 10-15 percent ce­ Sand and fine volcanic gravel ______7 115 mented gravel with angular pebbles up Sand, fine to coarse _ _ _ _ 7 122 to 2 in. ______13 318 Gravel ______1 123 Sand, fine to coarse; little gravel in thin Sand, fine to coarse ______5 128 cemented layers ______40 358 Gravel ______3 131 Sand, fine to coarse, and 20 percent gravel Sand, fine, medium-brown; scattered peb­ up to 3 in. ______5 363 bles ______~______35 166 Sand, fine to coarse; some gravel in thin Coarse-gravel zone: ____cemented layers -_-______-____ 137 500 Gravel, subangular to well-rounded, up to Well (C-10-24)13bccl 3 in., predominantly quartzite, quartz, [U.S. Bureau of Reclamation test well YVI-27(P) in Yuma Valley. and granitic rocks, some volcanic rocks Drilled with mud-rotary equipment by Bureau of Reclamation. Log by F. Mamaril and E. L. Smith of Bureau of Reclamation. Well point and sandstone ______17 183 instaLed at a depth of 168-170 ft on end of iy2 in. pipe. Altitude Sand and gravel _ _ 5 188 101.0 ft] Gravel, subangular to well-rounded, up to 3 in., predominantly quartzite, quartz, Upper, fine-grained zone: and granitic rocks, some volcanic rocks Clay ______15 15 and sandstone _--- _-_ _ 4 192 Sandy clay, sand lenses ______15 30 (Gamma log indicates lower gamma in­ Clay ______4 34 tensity from 192 to 278 ft, then generally Sand, with clay lenses ______36 70 high intensity below 278 ft.) Sand, pebbly, % in. maximum ______27 97 Gravel (geologist's log) ______51 243 Clay, with sand lenses 2 or 3 in. thick __ 23 120 Wedge zone: Sand, few gravel and clay lenses ______29 149 Sand and gravel, interbedded ______8 251 Gravel, sand lens 156 to 157 feet ______9 158 Sand, fine, some medium and coarse; small Gravel, cobbles, and sand ______22 180 amount of gravel, and traces of gray, Sand, occasional gravel ______23 203 limy clay and hard-brown clay ______95 347 Well (C-10-24)16baa2 Gravel, fine to 1 in.; thin layers of sand [Western Cotton Co. Industrial well in Yuma Valley. Drilled with cable- from 359 to 362 ft ______18 365 tool equipment by Arizona Machine and Welding Works. Casing per­ Sand, fine, gray; traces of white limy ma­ forated from 112 to 180 ft. Altitude 100 ft] terial and gray clay. Scattered fine gravel Upper, fine-grained zone : from 412 to 419 ft ______54 419 Sand ______46 46 Gravel, fine to IVa in.; pebbles predomi­ Clay and wood, sandy ______- 12 58 nantly granitic rocks and quartz, with Sand ______17 75 few volcanic rocks ______19 438 Clay ______35 110 Sand, fine, poorly graded; thin beds of fine Sand ______8 118 gravel at 441 and 450 ft ______17 455 Clay ______20 138 Sand and gravel, interbedded 7 462 Coarse-gravel zone: Well (C-l0-24) 30baa Rock and sand ______60 198 [U.S. Geological Survey auger test well in southern Yuma Valley. Clay ______8 206 Drilled with truck-mounted power auger by Geological Survey. Log by G. R. Vaugban; modified by F. H. Olmsted on basis of gamma log. Well Rock and sand ______19 225 point installed on end of iy2 -in. pipe at a depth of 183 to 185 ft. Gravel and sand ______25 250 Altitude 93 ft]______Wedge zone: Sand ______25 275 Upper, fine-grained zone: Clay ______12 287 Clay and silt, brown 10 10 Sand ______- -__ __- _- ____ _ 13 300 Sand, fine, brownish-gray 38 48 Rock and gravel ______5 305 Sand and silt, gray 12 60 Sand ______118 423 Sand, gray 5 65 Sand and silt, gray 19 84 Well (C-l0-24)23ddd Sand, gray ______16 100 [U.S. Bureau of Reclamation test we1! CH 17 YM on Yuma Mesa. Clay and sand ______6 106 Drilled with mud-rotary equipment by Bureau of Reclamation. Log by E Burnett of Bureau of Reclamation; modified from a depth of Sand ______14 120 0 to 182 ft by F. H. Olmsted on basis of gamma log. Below 192 ft, Gravel ______4 124 interpretation of gamma log does not correspond to geologist's log, Sand, some pebbly zones 26 150 as indicated be'ow. Well point installed on end of 1%-in. pipe at depth of 428 to 430 ft; later removed and reset at 198 to 200 ft. Altitude Sand and gravel 8 158 166.9 ft] Coarse-gravel zone: Gravel, coarse ______20 178 Upper, fine-grained zone: Sand ______5 183 Sand, fine, light-brown; scattered pebbles of Gravel, coarse 4 187 volcanic rocks and quartzite 19 19

507-243 O - 74 - 13 H186 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick- Material ness Depth Material ness Depth (feet) (feet) ______(feet) (feet) Well (C-10-25)lbba Well (C-l 0-25) 35bbd Continued [P. R. Sibley. Irrigation we'l in Yuma Valley. Drilled with cable-tool equipment by Frank H. Leidendeker. Casing perforated from 160 to Wedge zone Continued: 180, 195 to 205, and 250 to 285 ft. Altitude 106 ft] Sand, some gravel; a few thin beds of silt and cemented gravel _ 171 1,030 Upper, fine-grained zone: Silt ______8 1,038 Soil ______2 2 Sand, some silt and fine gravel __ _ __ 394 1,432 Clay ______2 4 Clay ______2 1,434 Sand ______3 7 Sand, compact, silty and pebbly; thin clay Clay, soft, sticky ______10 17 beds at depths of 1,520, 1,688, 1,692, 1,750, Clay and sand strata ______22 39 1,778, 1,920, and 1,934 ft ______556 1,990 Clay, tough, sticky ______24 63 Clay ______10 2,000 Sand, clay, some sharp gravel _ _ 23 86 Sand, compact; and cemented gravel __ 30 2,030 Quicksand ______10 96 Sand, silty; a few thin beds of cemented Quicksand and clay strata ______9 105 gravel ______27 2,057 Sand with approximately 10 percent gravel. 10 115 Clay, silty ______3 2,060 Clay, hard ______11 126 Sand and thin beds of grayish-white com­ Clay, soft, sandy ______22 148 pact silt ______30 2,090 Coarse-gravel zone: Sand, silty, and thin beds of cemented Gravel in silted sand ______5 153 gravels ______57 2,147 Gravel, sandy ______3 156 Silt, clayey ______3 2,150 Gravel, good water ______19 175 Sand, silt, and thin beds of clay and ce­ Quicksand ______12 187 mented gravel ______50 2,200 Gravel and sand strata ______18 205 Sand, compact; and cemented gravel __ 12 2,212 Sand with scattered pebbles ______8 213 Clay ______8 2,220 Sand ______4 217 Silt and sand ______13 2,233 Sand with pebbles ______17 234 Clay ______5 2,238 Sand, packed, gravel, and clay ______3 237 Sand, compact, silty; thin beds of clay _ 62 2,300 Sand and pebbles ______3 240 Sand, silty ______42 2,342 Gravel, sandy ______4 244 Clay, silty ______6 2,348 Gravel, good water ______35 279 Sand, compact; thin beds of cemented sand Wedge zone: and gravel ______67 2,415 Sand, packed ______16 295 Clay, silty ______2 2,417 Sand, thin beds of silt and silty clay ____ 97 2,514 Well (C-10-25)23add Transition zone(?): [U.S. Geological Survey auger test well in Yuma Valley. Drilled with truck-mountad power auger by Geologica1 Survey. Log by G. R. Clay ______6 2,520 Vaughan. Well point installed on end of I 1/*-in. pipe at a depth of Sand, some cementation; some silt _____ 154 2,674 185.7 to 187.7 ft. Altitude 97 ft] Clay ______2 2,676 Sand, silty; and thin cemented beds ____ 52 2,728 Upper, fine-grained zone: Clay ______2 2,730 Clay and silt ______27 27 Sand, silty; and thin cemented streaks __ 74 2,804 Sand and silt, clay streak at 81 ft ____ 99 126 Clay ______2 2,806 Clay ______3 129 Sand, silty; and a few thin lenses of ce­ Sand and silt ______26 155 mented gravel ______12 2,818 Gravel, small; with sand and silt ______9 164 Clay ______4 2,822 Coarse-gravel zone: Sand, silt, and thin beds of clayey silt __ 30 2,852 Gravel, heavy, with sand ______28 192 Sand and some silt and cementation ____ 40 2,892 Clay ______8 2,900 Well (C-10-25)35bbd Sand, silt, and thin lenses of silty clay 46 2,946 [U.S. Geological Survey test well LCRP 17 on east bank of Colorado River in southwestern Yuma Va.ley. Drilled with mud-rotary equip­ Well (C-ll-21)4ddc ment by Roscoe Moss Co. Log by F. H. Olmsted, F. J. Frank, J. H. Robison, and G. R. Vaughan Gravel packed and cased to 1,988 ft; [U.S. Bureau of Reclamation test well CH-9 YM on "Fortuna Plain" (). Drilled with mud-rotary equipment by Bureau of casing perforated from 520 to 1.998 ft, with a blank section from 1,398 Reclamation. Log by J. Granchi of- Bureau of Rec'amation. Cased to to 1,438 ft. Altitude 94 ft] 350 ft; perforated from 293.5 to 328.5 ft. Altitude 403.3 ft] Upper, fine-grained zone: Older alluvium, undivided: Sand and silt, some clay, gastropods, and Sand, fine, grayish-tan; lower 2 ft lime carbonized wood ______T _ 71 71 cemented ______3 3 Sand and gravel, some silt and clay 103 174 Sand, fine to medium, silty and clayey, tan; Coarse-gravel zone: scattered angular to rounded pebbles Gravel, coarse, probably somewhat ce­ composed predominantly of volcanic and mented ______32 206 granitic rocks, a few metamorphic rocks_ 7 10 Sand, some gravel ______25 231 Sand, medium to coarse, some fine, tan to Gravel, coarse, probably cemented, at least grayish-brown. Thin beds of tan and in part ______45 276 reddish-brown clay _ 27 37 Wedge zone: Sand, cemented, fine to coarse, grayish-tan; Sand and gravel ______30 306 of granitic and volcanic composition __ 12 49 Gravel, coarse, probably cemented in part _ 44 350 Clay, hard, chocolate-brown; a few angular Sand, some coarse gravel beds ______58 408 to subrounded clasts of granitic and vol­ Gravel, coarse, probably cemented in part _ 64 472 canic rocks ______5 54 Sand, some gravel ______122 594 Sand, cemented, fine to coarse, grayish- Gravel, fine to medium, cemented in part __ 50 644 brown; fine gravel ______4 58 Sand, some gravel; a few thin beds of silt Gravel, fine to medium; abundant meta­ and cemented gravel ______203 847 morphic and basaltic rocks; some medium Silt, clayey, in two thin beds, with sand to coarse gray and brown sand ______11 69 between them ______12 859 Clay, reddish-brown ______4 73 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H187

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-H-23) 34bbc Continued Well (C-l 1-24)23bcb Continued Wedg

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-ll-24)23bcb Continued Well (C-12-21)17cbc Continued Wedge zone Continued: Older alluvium, undivided Continued: Gravel, cemented (conglomerate) ______4 807 and small pebbles of well-rounded quartz­ Sand and some fine to medium gravel ____ 13 820 ite and volcanic and granitic rocks __ 4 4 Sand, fine to medium, gray, clean ______4 824 Gravel, similar in size and composition to Sand and gravel ______9 833 that above; thin layers or lenses of red­ Sandy, silty, fine; a few clay balls in lower dish-brown clay ______7 11 part ______22 855 Sand, fine to coarse, and rounded pebbles Gravel, coarse; interbedded medium to and granules of quartzite and volcanic coarse sand ______18 873 and granitic rocks ______10 21 Sand, silty, fine; scattered pebbles and Gravel, fine, rounded ______12 33 pieces of clayey sandstone ______21 894 Sand, fine to coarse; layers or lenses of Sand, fine to medium, gray ______9 903 gravel ______11 44 Sand, clayey sandstone, and fine gravel; Sand, fine; layers or lenses of fine gravel small amount of wood ______20 923 at intervals of 3-10 ft; traces of reddish- Sand, fine, silt, and sandy clay; scattered to grayish-brown clay ______28 72 granules and pieces of carbonized wood _ 57 980 Sand, fine; scattered gravel ______39 111 Sand, fine to coarse, and gravel, inter- Gravel, fine; similar in composition to that bedded. Some zones cemented ______26 1,006 above, with black chert pebbles also __ 5 116 Sand, fine, and thin beds of brown and gray Sand, fine; scattered gravel ______17 133 clay ______7 1,013 Sand and fine gravel, interbedded _____ 25 158 Clay, brown, pebbly, and sand ______14 1,027 Sand, fine; scattered gravel. More indurated Sand, some fine gravel, and thin streaks of or compacted below 235 ft ______162 320 clay ______11 1,038 Well (C-12-22)9bab Well (C-12-21)14dab [U.S. Geological Survey test well LCRP 24 on "Upper Mesa" at southerly [U.S. Bureau of Reclamation test well CH-25YM near west edge of internationa' boundary. Drilled with cable-tool equipment by R. E. "Fortuna Plain," about 2 miles north of southerly international bound­ Anderson. Log by F. J. Frank, Rex Anderson, and F. H. Olmsted. ary. Drilled with mud-rotary eauipment by Bureau of Reclamation. Casing perforated from 318 to 324, 330 to 336, and 340 to 346 ft. Log by E. Burnett and E. Smith of Bureau of Reclamation. Well Altitude 233.5 ft] point installed at a depth of 367-369 ft. Altitude 422.2 ft] Younger alluvium (alluvial-fan deposits) : Older alluvium, undivided: Sand, fine, light-brown; intermixed white Soil, brown, sandy; some pebbles ______2 2 angular coarse granitic sand ______6 6 Sand, pinkish-brown, tough, silty; gravelly Clay, sandy, calcareous, reddish-brown _ 10 16 lenses; white caliche throughout, gravels Sand, fine, light-brown; intermixed white mostly rounded to subrounded and in­ angular, coarse granitic sand ______2 18 clude quartzite, chert, and granitic, meta- Clay, sandy, calcareous, reddish-brown ___ 9 27 morphic, and volcanic rocks ______20 22 Sand, fine, light-brown; intermixed white Sand, light-brown, poorly sorted; with less angular coarse granitic sand ______11 38 than 5 percent well-rounded gravel _____ 4 26 Clay, sandy, reddish-brown; streaks of Sand, light-brown, medium to coarse, poorly coarse granitic sand ______3 41 sorted ______5 31 Sand, fine, light-brown; intermixed white Sand, brown; with 40 percent rounded to angular coarse granitic sand; few thin subrounded gravel composed of mostly seams of clay or silt ______18 59 chert and quartzite ______4 35 Clay, sandy, reddish-brown; streaks of Sand, brown, medium to coarse; poorly coarse granitic sand ______3 62 sorted with a few scattered quartzite and Sand, fine, silty, medium-brown ______10 72 chert pebbles ______15 50 Clay, silty, medium-brown; little fine sand_ 4 76 Sand, brown, medium to coarse, poorly Sand, fine, poorly graded ______3 79 sorted; some cementation and thin lenses Clay, soft, calcareous, reddish-brown _____ 10 89 of sandstone ______30 80 Sand, silty, fine; little medium to coarse Sand, brown, medium to coarse ______13 93 sand ______4 93 Sand, brown, medium to coarse; some small Older alluvium: pebbles and granules ______1 94 Sand, fine; scattered granules of angular to Gravel, with small amount of medium- well-rounded granite, chert, quartzite, and brown sand; gravel mostly well-rounded quartz; few thin layers or lenses of quartzite and chert V±-% in. ______6 100 medium-brown to light-grayish-brown Gravel, with small amount of medium to highly plastic fines ______8 101 coarse brown sand. Gravel includes well- Sand, fine, poorly graded ______6 107 rounded quartzite and chert as much as Sand, fine to coarse, and some fine gravel 3 in. with some subrounded gravel of local similar in composition to that from 93 to origin ______25 125 101 ft ______3 110 Sand, brown, medium to coarse; with a few Gravel, fine to coarse, predominantly sub- 1/4- 1/2 in. subrounded, subangular gravel. 46 171 rounded to well-rounded, similar in com­ Sand, brown, fine; silty with a few scattered position to gravels above ______11 121 subangular ^-in. gravel; some cementa­ Sand, fine, poorly graded; scattered gran­ tion ______62 233 Clay, silty, reddish-brown to buff; coarse ules and pebbles ______248 369 sand and a few subangular to angular Well (C-12-21)17cbc metamorphic and volcanic pebbles _____ 2 235 [U.S. Bureau of Reclamation test well CH-23YM on "Upper Mesa" at Silt and fine buff sand; some clay; cemented southerly international boundary. Drilled with mud-rotary equipment in part ______27 262 by Bureau of Reclamation. Log by E. Bnvnett of Bureau of Ree'ama- tion. Well point installed at a depth of 318-320 ft. Altitude 356 ft] Sand, medium, brown; with cementation and thin sandstone lenses; some pinkish- Older alluvium, undivided: brown clay balls ______13 275 Sand, fine, light-brown; scattered granules Sand, medium, brown; some cementation H190 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued

Thick­ Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-12-22)9bab Continued Well (C-13-20) 2abdl Continued Older alluvium, undivided Continued: Older and younger alluvium, undifferentiated Continued: and thin lenses of sandstone; some clay Sand, fine; little silt and clay ______175 635 balls and a few subangular pebbles of Clay, light-brown, silty ______5 640 local origin ______20 295 Sand, fine; little silt or clay ______35 675 Sand, fine to medium, brown, somewhat ce­ Clay, light-brown ______5 680 mented ______7 302 Sand, fine ______20 700 Sand, medium to coarse, brown; some sub- Clay ______5 705 rounded to subangular ^-^fc-in. gravel; Sand, fine ______10 715 some cementation ______8 312 Clay ______5 720 Gravel and sand. Gravel subrounded to sub- Sand, fine ______5 725 angular, %-% in., mostly granite and Clay ______5 730 volcanic rocks with a few well-rounded Sand, fine; cemented layer at 755 ft ____ 30 650 pebbles of chert and quartzite; some ce­ Sand, fine; clay layers, thin cemented zones, mentation and about 50 percent brown and scattered fine gravel 50 810 medium to coarse sand ______12 324 Sand, fine; thin beds of clay; cemented Sand, medium to coarse, brown, somewhat layer at 810 ft ______60 870 cemented ______6 330 Sand, fine; thin beds of cemented fine sand Sand and gravel; sand more than 50 per­ from 870 to 880 ft, 890 to 895 ft, and at cent; medium to coarse subangular ^-l 940 ft; little silt or clay ______100 970 in. gravel ______6 336 Clay ______5 975 Sand, medium to coarse, brown ______4 340 Sand, fine; thin cemented layers at 1,015, Sand and gravel; gravel mostly granitic 1,025, and 1,075 ft; little silt or clay __ 110 1,085 and volcanic, subangular to subrounded _ 6 346 Claystone (probably calcareous) ______5 1,090 Sand, medium, brown, with a few angular Sand, fine; thin cemented layers at 1,145- gravels ______20 366 1,150 ft; little silt or clay ______70 1,160 Clay and silt, buff ______4 370 Clay ______5 1,165 Sand, fine to medium, buff, somewhat ce­ Sand, fine ______5 1,170 mented ______4 374 Clay ______5 1,175 Sand, very fine, silty, buff, somewhat ce­ Sand, fine; little silt or clay ______40 1,215 mented ______18 392 Clay ______5 1,220 Sand, fine to medium; well cemented in part, Sand, fine; more indurated (higher acoustic thin gray clay and 5-10 percent subangu­ velocity) than materials above ______55 1,275 lar to subrounded ^-^s-in. gravel. Gravel Sand, coarse ______10 1,285 mostly granitic and volcanic, with a few Transition zone: well-rounded pebbles of chert and quartz­ Sand, fine, clayey, bluish to greenish-gray _ 20 1,305 ite ______5 397 Clay, gray ______5 1,310 Sand, fine to medium; a few thin lenses of Sand, fine, gray ______5 1,315 gray silty clay ______18 415 Clay, gray ______5 1,320 Well (C-13-20)2abdl Sand, fine, clayey, gray; thin cemented [U.S. Bureau of Reclamation test well CH-28YM on "Fortuna Plain" at layers at 1,320 ft, 1,360-1,365 ft, and southerly international boundary. Drilled with mud-rotary equipment 1,370 ft ______55 1,375 by Bureau of Reclamation. Log by E. Burnett, J. W. Julian, and E. Clay, gray ______10 1,385 Smith. Well point set on end of 1%-in. pipe at a depth of 1,198- 1,200 ft. Another well point installed in same hole as well (C-13-20) Sand, fine, clayey, gray; thin cemented 2abd2 at a depth of 598-600 ft. Altitude 577.5 ft] layers at 1,385, 1,405, and 1,410 ft ____ 42 1,427 Older and younger alluvium, undifferentiated: Well 16S/21E-36Fca Sand, fine; few thin layers of clay from 0 [Arizona Public Service Co., Industrial well in northwestern Yuma Val­ ley. Drilled with cable-tool equipment by Roscoe Moss Co. Casing to 21 ft; occasional thin layers or lenses perforated from 518 to 560, 592 to 650, 706 to 740, 752 to 766, 864 of cemented sand below 62 ft ______95 95 to 880, and 904 to 912 ft. Altitude 117 ft] Clay, calcareous, medium-brown ______5 100 Sand, fine; few thin layers of clay; occa­ Upper, fine-grained zone: sional thin layers or lenses of cemented Topsoil ______4 4 sand ______-__- ___ 5 105 Clay, silty, water at 11 ft ______7 11 Clay, calcareous, medium-brown; inter- Sand, fine, brown (quicksand action) _ _ ___ 28 39 bedded medium to coarse granitic sand _ 10 115 Clay, bluish, silty ______1 40 Sand, fine, predominantly quartz; abundant Sand, bluish, fine, clay streaks, slow- medium to coarse angular to subangular draining ______65 105 granitic sand; thin layers of cemented Silt, mixed, and clay with pebbles 112 sand ______165 280 Coarse-gravel zone : Clay, silty, medium-brown; interbeds of fine Gravel, clean, possible clay layer 6 in. thick 8 120 to coarse granitic sand ______30 310 Gravel, clean; fair gradation with rocks as Gravel, fine; consists of angular to well- much as 6 in. ______22 142 rounded clasts of chert, quartzite, quartz Gravel and coarse sand; rocks as much as 2 and granitic and volcanic rocks; fine to in. ______10 152 coarse sand ______15 325 Wedge zone : Clay, brown, silty ______10 335 Sand, lightly cemented fine sand lumps, and Sand, fine to coarse; considerable amount some small gravel ______10 162 of fine gravel ______45 380 Clay ______5 167 Clay, brown, silty ______5 385 Gravel, round and fractured, as much as 2 Sand and gravel, fine to coarse ______10 395 in.; brown dirty water ______3 170 Sand, fine; thin beds of light-brown sandy Gravel, small, round and fractured; lightly to silty clay ______50 445 cemented sand laminae, 3 in. thick; piece Clay, silty, light-brown ______5 450 hard to break ______14 184 Sand, coarse ______10 460 Sand, mixed; gravel with clay an ash; GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H191

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well 16S/21E-36Fca Continued Well 16S/21E-36Fca Continued Wedge zone Continued: Wedge zone Continued: soft, slimy, possibly colloidal clay _____ 16 200 Gravel, mixed, loose; angular as much as Sand and pea gravel; some lightly consoli­ 3 in., with sand and silt filler ______14 766 dated sand streaks ______7 207 Clay, firm; grades to softer mixed clay; fine Sand and gravel as much as 1% in. _____ 8 215 silty sand ______30 796 Sand, lightly cemented laminae, fine gravel, Sand and clay, mixed; very muddy ___ 16 812 few shale particles ______10 225 Sand, small gravel, and some clay _ 8 820 Sand; gravel as much as 1% in.; brown silt 10 235 Clay with some sand and gravel _ 8 828 Sand, soft, some gravel, bluish ______15 250 Clay with fine sand, very little gravel, quite Sand; some gravel as much as 1% in.; muddy water ______-______12 840 lightly consolidated sand laminae ______16 266 Clay and sand; increased amount of sand Sand; some gravel, few large rocks at 280 with small gravel, muddy water __ 10 850 ft ______14 280 Sand and small gravel ______4 854 Sand, fine; thin consolidated clay streaks at Sand and gravel as much as 2 in.; sand not 280 ft ______5 285 sharp and only moderately clean __ __ 16 870 Sand, fine ______9 294 Sand with some fine gravel, increased Firm clay strata with shale and gravel ___ 6 300 amount of sand ______14 884 Sand; some lightly cemented laminae ___ 10 310 Sand, medium ______16 900 Sand, fine ______20 330 Sand and gravel as much as 2 in. _ 12 912 Sand, mixed, and clay; some gravel _____ 4 334 Sand with silt and clay ______12 924 Sand, fine ______4 338 Silt, tight; with mixed clay and sand ___ 12 936 Sand, lightly cemented laminae with few Clay, silty red, some very firm ______8 944 shale particles ______12 350 Clay, silty; with granite pieces as much as Sand, medium; some clay balls at 335 ft _ 10 360 2 in. ______4 948 Sand, medium ______12 372 Granite detritus with clay and silt fill __ 4 952 Sand, medium, and loose gravel. Apparently Clay, firm, and brown silt __ 12 964 good aquifer -__-__-______10 382 Silt and sand with cemented layers _____ 8 972 Sand, medium, and gravel as much as 1% Sand and gravel as much as 3 in.; granitic, 6 978 in. ______6 388 Well 16S/22E-21Dbb Sand; gravel and clay layer about 8 in. [U.S. Bureau of Reclamation test well CH-14RD in western Bard Val­ thick at 390 ft ___'______4 392 ley. Drilled with mud-rotary equipment by Bureau of Reclamation. Log Sand, coarse, and fine gravel ______6 398 by Granchi and Moffitt of Bureau of Reclamation; modified by F. H. Olmsted on basis of gamma, electric, and caliper logs. Well point in­ Sand, gray; some angular and rounded stalled on end of l^-in. pipe at a depth of 118-120 ft. Altitude gravel with thin clay layers ______12 410 Sand, medium; with very little gravel, some 128.0 ft]______wood as lignite ______10 420 Upper, fine-grained zone: Sand, gravelly; some clay, cemented silt and Sand, fine, tan __ 7 7 ash layer 6 in. thick at 420 ft ______4 424 Sand and brown clay ______15 22 Sand, gravelly; some clay balls and silt ___ 6 430 Sand, fine, brown ______14 36 Sand; some gravel pieces of lignite at 475 ft 44 474 Clay, soft, reddish-brown 39 Clay layer preceded and followed by dirty Sand, fine to coarse, dark-gray to brown; clay and gravelly sand with cemented fine gravel composed of subangular to shales and gravel ______14 488 subrounded granite and quartzite clasts _ 11 50 Sand, fine; very little gravel ______10 498 Clay, soft, brown _ 1 51 Sand, lightly cemented; some small gravel _ 8 506 Sand, fine; scattered granules and pebbles, Sand, coarse; well-graded angular gravel as chiefly quartzite ______51 102 much as 2 in. ______4 510 Sand, fine to coarse; fine gravel 11 113 Sand, coarse, and fine gravel ______8 518 Coarse-gravel zone: Sand, coarse, and small gravel, some 2 in. _ 10 528 Gravel, fine to coarse; composed of sub- Sand and small gravel with clay streaks __ 10 538 angular to rounded granules, pebbles, and Sand; some small gravel ______22 560 cobbles of granite, volcanic rocks, and Sand, medium; very little gravel; few thin quartzite; fine to coarse brown sand _ _ 20 133 cemented sandy laminae ______24 584 Sand, fine to coarse, brown ______7 140 Sand, coarse; some small gravel ______16 600 Sand, pebbly ______2 142 Sand, small amount of gravel, some clay ___ 10 610 Sand, fine to coarse, brown ______14 156 Sandy gravel as much as 2 in., mixed round Sand, fine to coarse; some fine gravel ___ 5 161 and angular, clean ______12 622 Sand, fine to medium, brown 4 165 Gravel, sandy, clean; as much as 3 in.; few Sand and gravel ______19 184 cemented conglomerate zones ______6 628 Clay, dense, brown _ _ _ 3 187 Sand, coarse, and small gravel; good grada­ Sand and gravel ______5 192 tion ______4 632 Wedge zone(?) : Gravel, sandy, sharp and clean; as much as Sand, fine to medium, brown ______31 223 2 in.; firmly cemented sand layer 6 in. Clay, dense, brown ______7 230 thick near 638 ft ______8 640 Sand, silty, gravish-brown ______7 237 Gravel, sandy; as much as 2 in.; streaks of Sand, fine, grayish-brown _ 12 249 hard clay and cemented sand laminae ___ 4 644 Silt, dense, gray ______2 251 Firm clay grading to sand and silt ______36 680 Sand, fine, grayish-brown ______19 270 Sand, mixed, and clay ______24 704 Sand, some gravel composed chiefly of gran­ Sand and small gravel ______4 708 ite and quartzite ______13 283 Sand and small gravel as much as 2 in. ___ 32 740 Gravel ______3 286 Sand, gravel, and clay and cemented vol­ Sand, fine to coarse, gray ______8 294 canic ash ______10 750 Sand and clay, interbedded; soft bluish to Granite pieces, larger fractured, as much as grayish-green clay ______16 310 6 in. with sand ______2 752 Sand, fine, brown ______14 324 H192 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued

Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well 16S/22E-21Dbb Continued Well 16S/22E-29Gca2 Wedge zone (?) Continued: [U.S. Geological Survey test well LCRP 26 in western Bard Valley. Drilled with mud-rotary equipment by Kalco Development Co. Log Sand, fine to coarse, pebbly ______28 352 by F. H Olmsted, F. J. Frank, and A. G. Hely. Well cased and Sand, fine, brown ______8 360 gravel packed to 1,769 ft; perforated from 125 to 1,127 and 1,368 to Sand, fine to coarse, pebbly ______16 376 1,769 ft. Altitude 125.4 ft] ______Sand, fine, brown ______12 388 Upper, fine-grained zone: Sand, fine to coarse, pebbly ______8 396 Silt, brown ______7 7 Sand, fine, brown ______6 402 Sand, fine to medium, brown _ __ __ 18 25 Sand, fine to coarse, pebbly; gravel more Clay, silty, medium-brown __ 10 35 abundant below 415 feet ______17 419 Sand, fine to medium, and grayish-brown Sand, fine to medium, grayish-brown; scat­ silt ______-__ 11 46 tered granules and pebbles ______21 440 Clay, silty ______5 51 Clay, hard, and cobbles ______4 444 Sand, grayish-brown 18 69 Sand, fine to medium, some coarse, grayish- Silt, sand, and clay ______7 76 brown ______15 459 Sand, grayish-brown _ 8 84 Sand, medium to coarse, brown, and fine, Silt, sand, and clay 7 91 well-rounded gravel ______14 473 Sand, grayish-brown __ 19 110 Sand, fine to medium, brown ______6 479 Sand; scattered granules and pebbles 10 120 Gravel, fine, well-rounded, and fine to coarse Coarse-gravel zone: brown sand ______5 484 Gravel, coarse, loose; contains abundant Sand, silty, fine, and thin beds of bluish- well-rounded pebbles and cobbles of sili­ gray clay ______6 490 ceous rocks ______11 131 Sand, fine to coarse, brown, and fine gravel, Gravel, coarse to fine, and sand 22 153 interbedded ______17 507 Coarse-gravel zone(?) : Well 16S/22E-23Caa Sand, silty, brown, soft 3 156 [U.S Bureau of Reclamation test well CH-8 in Bard Valley. Drilled Gravel and sand, loose; subangular to well- with cable-tool equipment by E. McBride. Log by E. L. Smith of rounded pebbles, cobbles, and granules of Bureau of Reclamation; modified by F. H. Olmsted on basis of a wide variety of rocks including abun­ gamma log. Casing perforated from 96 to 104 ft. Altitude 128.5 ft] dant quartzite and chert 24 180 Upper, fine-grained zone: Wedge zone (gravel similar in composition to that above) Sand and gravel 30 210 Sand, fine to coarse, light-brown (above 20 Gravel and sand _ __ _ 30 240 ft), and grayish-brown (below 20 ft); Sand and gravel _ _ _ 52 292 interbedded reddish-brown to dark-brown Gravel and sand 33 325 clay and silty sandy clay ______38 38 Sand and gravel ______10 335 Sand, fine to coarse; little reddish-brown Gravel and sand 39 374 clay; little gravel from 72 to 75 ft ___ 41 79 Clay, silty 2 376 Sand, gray, and 10-40 percent gravel con­ Sand and gravel _ _ 20 396 taining abundant concretions of limy Gravel and sand 14 410 sandstone ______19 98 Sand and gravel 23 433 Sand, little gravel 11 444 Coarse-gravel zone: Gravel and sand _ 8 452 Gravel, fine to 3 in., angular to well- Sand ______8 460 rounded; about 35-40 percent coarse gray Gravel and sand _ 4 464 sand ______-______6 104 Sand __ __ - - _____ 5 469 Wedge zone: Sand and gravel _ 19 488 Sand, fine to coarse, gray; scattered pebbles, Sand ______11 499 and some beds of yellowish-green and Gravel and sand ______23 522 brown clay and silt -__ 57 161 Conglomerate (cemented gravel and sand) _ 14 536 Sand ______10 546 Sand, gray, and gravel ______26 187 Sand and gravel ______18 564 Sand; little gravel ______7 194 Sand; scattered gravel _ __ _ 24 588 Sand and gravel ______26 220 Gravel and sand ______11 599 Sand; little gravel ______22 242 Sand, some gravel 12 611 Gravel, fine to 2 in., and gray sand _____ 14 256 Gravel and sand ______8 619 Sand, fine to coarse, gray; scattered gran­ Sand, some gravel 27 646 ules and pebbles ______12 268 Gravel and sand ______25 671 Gravel and sand ______9 277 Silt, sand, and clay 6 677 Gravel and sand ______46 723 Sand, fine, and scattered "pea" gravel ____ 17 294 Sand and silt __ __ _ 20 743 Gravel and sand; some cobbles and concre­ Sand, some gravel and silt ______40 783 tions of limy sandstone up to 8 in. __ 26 320 Sand and silt _ 49 832 Sand, fine to medium, and about 40 percent Sand, some gravel ______42 874 fine to 1-in. subangular gravel ______8 328 Sand and silt _ __ __ 56 930 Bouse Formation (?) : Sand, some gravel; thin beds of clay _ ___ 16 946 Clay, silty, dark-gray ______3 331 Gravel and sand ______20 966 Sand, fine to medium, gray; moderately to Sand, some gravel ______-______---__ __ 34 1,000 Gravel and sand ______17 1,017 firmly cemented ______-____--_-______1 332 Sand, some gravel ______16 1,033 Clay, silty, dark-gray, partly calcareous; Transition zone: thin layers of cemented sand ______10 342 Clay, silty, gray ______7 1,040 Volcanic rocks (Tertiary?) : Clay and sand, interbedded ______-_ 43 1,083 Basalt, fine-grained, dark-gray, slightly Gravel and sand; some chert and quartzite glassy; weathered and vesicular ___ _ 18 360 granules and pebbles ______19 1,102 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H193

Selected logs of water wells Continued Selected logs of water wells Continued Thick­ Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well 16S/22E-29Gca2 Continued Well 16S/23E-8Ecc Continued Transition zone Continued: Wedge zone Continued: Sand, fine to medium, gray ______13 1,115 Sand ______5 184 Bouse Formation: Sand, locally cemented; streaks of gravel _ 18 202 Clay, silty, gray ______39 1,154 Gravel and sand ______-____ 7 209 Clay and fine to medium gray sand __-_ 6 1,160 Sand; some gravel and silty clay __ __ 4 213 Clay, silty, gray ______33 1,193 Sand, fine to coarse, and angular to sub- Sand, fine to medium, and gray clay __^__ 4 1,197 angular gravel up to 1% in. ______19 232 Clay, silty, gray ______124 1,321 Gravel, granules and pebbles, up to 2 in.; Sand, fine to medium, gray, and silty clay _ 7 1,328 sand ______17 249 Clay, silty, gray ______15 1,343 Sand and scattered granules and pebbles 7 256 Tuff or ash(?) ______9 1,352 Sand and gravel up to 2 in. ______35 291 Limestone, sandy ______28 1,380 Sand, fine ______9 300 Nonmarine sedimentary rocks: Gravel containing pebbles up to 3 in.; 40 Conglomerate composed of pebbles, cobbles, percent sand ______13 313 and boulders of gneiss, granite, pegma­ Sand, fine; about 5 percent pebbles _____ 21 334 tite, vein quartz, and other crystalline Sand and angular granules and pebbles; rocks; some beds of coarse, gritty sand­ about 10 percent cobbles; some zones con­ stone ______285 1,665 tain little gravel ______78 412 Boulder conglomerate or megabreccia: Gravel, up to 3 in., and sand ______40 452 Blocks and boulders of crystalline rocks Sand, fine to coarse; 5-8 percent gravel __ 28 480 in an earthy sandstone matrix ______112 1,777 Sand, gravel, and carbonized wood _____ 10 490 Sand, coarse; contains a few angular peb­ Well 16S/23E-2Dbd bles ______10 500 [D. W. Haygood. Irrigation well in Bard Valley, near west bank of Colorado River. Drilled with cab'e-tool equipment by Frank H. Leidendeker. Casing perforated from 115 to 153 ft. Altitude 140 ft] Well 16S/23E-9Naa [M. E. Spencer. Irrigation well in Bard Valley. Drilled with cable-tool Upper, fine-grained zone: equipment by Frank H. Leidendeker. Casing perforated from 124 to Clay with wood roots ______8 8 150, 154 to 164, 198 to 204, 205 to 217, and 218 to 225 ft. Altitude Sand, silted ______10 18 137 ft] ______Clay, soft ______2 20 Upper, fine-grained zone: Water sand and some sharp gravel ______25 45 Soil ______4 4 Quicksand with some gravel and clay Clay ______1 5 streaks ______62 107 Sand, silt, and clay mixed __ 2 7 Coarse-gravel zone: Sand, silted ______30 37 Gravel, good ______33 140 Clay, sand with pebble strata ______28 65 Gravel, small, coarse sand ______13 153 Sand and clay strata ______13 78 Wedge zone: Quicksand ______9 87 Gravel, very sandy ______6 159 Clay and gravel in sand ______10 97 Gravel, sandy 6 103 Well 16S/23E-8Ecc Sand _____. 11 114 [U.S. Bureau of Reclamation test well CH-5 in Bard Valley. Drilled with cable-tool equipment by San Diego Well Drilers. Log by Bureau of Coarse-gravel zone: Reclamation; modified by F. H. Olmsted on basis of gamma log. Casing Gravel ______. 36 150 perforated from 110 to 141 ft. Altitude 130 ft] Wedge zone: Upper, fine-grained zone: Sand _____- 152 Sand, silt, and clay; 1-ft layer of black Sand, coarse, and fine pea size gravel ___ 12 164 organic silt and clay at 10 ft _____ 11 11 Sand, some pebbles ______14 178 Sand, fine, light-brown, grading downward Gravel, sandy 181 into fine gray sand ______26 37 Clay ______182 Clay, brown, silty, and fine sand ______3 40 Sand and some gravel 188 Clay, pebbly ______1 41 Sand, coarse, and pea size gravel ___ _ 16 204 Clay, brown, silty, and fine sand; also Sand, some pebbles 210 layers of gray silty clay; scattered peb­ Gravel, sandy ______218 bles in lower part ______19 60 Gravel, not too large 225 Sand, fine, gray ______5 65 Sand, some pebbles __ 226 Clay, brown, silty, and fine sand; scattered Sand ______235 pebbles ______12 77 Well 16S/23E-10Rcc Sand, fine, varicolored; scattered pebbles [U.S. Geological Survey test well LCRP 23 in eastern Bard Valley, on and small cobbles up to 4 in., and a few west bank of Colorado River. Drilled with cable-tool equipment by lenses of clay ______32 109 Hamilton and Hood. Log by F. H. Olmsted and G. R. Vaughan. Casing Coarse-gravel zone: perforated from 120 to 548 and 634 to 694 ft. Altitude 143.8 ft] Gravel containing rounded pebbles and cob­ Upper, fine-grained zone: bles up to 4 in.; 30-40 percent fine to Sand, fine, silty, brown ______14 14 coarse sand; more sand in lowest several Sand, fine to medium, grayish-brown; scat­ feet ______39 148 tered granules and pebbles ______35 49 Wedge zone: Clay, silty and sandy; some sand and scat­ Sand, fine to coarse; silt, clay, and scat­ tered granules and pebbles ______13 62 tered fine gravel ______18 166 Sand, fine to medium, grayish-brown ____ 11 73 Sand, fine to coarse, and fine gravel. Below Sand, fine to coarse; some clay and silt, and 166 ft the materials are characterized by about 10-15 percent gravel ______28 101 higher gamma radiation than those Sand, fine to medium, grayish-brown ____ 11 112 above; this is probably due to a high per­ Coar?e-gravel zone: centage of both clay and gravel to coarse Gravel containing abundant well-rounded sand containing abundant silicic volcanic and subrounded pebbles and cobbles of and granitic rocks ______13 179 quartzite, chert, silicic volcanic rocks and H194 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Selected logs of water wells Continued Selected logs of water wells Continued

Thick- Thick­ Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well 16S/23E-10Rcc Continued Well 16S/23E-10Rcc Continued Bouse Formation: Coarse-gravel zone Continued: Clay, greenish-gray, and interbedded gray various types of crystalline rocks; some silt and fine sand; fossiliferous 86 634 medium to coarse sand, probably as lenses 43 155 Conglomerate composed chiefly of angular Wedge zone: to subrounded clasts of gneiss and gran­ Sand, fine to coarse, and thin beds of ce­ ite; some coarse sandstone ______22 656 mented gravel ______11 166 Clay or mudstone, bluish-gray _____ 3 659 Gravel, fine to coarse, subangular to well- Conglomerate composed chiefly of angular rounded; chert and quartzite somewhat to subrounded clasts of gneiss and gran­ less abundant than in interval from 112 ite; some coarse sandstone ___ 22 681 to 155 ft; medium to coarse sand, prob­ Limestone, pale-yellowish-gray 6 687 ably as lenses ______49 215 Nonmarine sedimentary rocks: Gravel containing abundant bluish-gray, Fanglomerate composed chiefly of angular pink, and green volcanic detritus; some and subangular blocks and slabs of gran­ vein quartz, quartzite, and chert and vari­ ite, gneiss, schist, and various other able amounts of crystalline rocks (pre- crystalline rocks similar to those now ex­ Tertiary). Fine to coarse sand present in posed in Laguna and Chocolate Moun­ variable amounts throughout. Gamma ra­ tains ______16 703 diation noticably higher than in overlying Quartz monzonite, porphyritic, coarse; materials. Sample of charcoal from a either in large boulders and blocks or as depth of 224-234 ft gave an age of bedrock (crystalline rocks of pre-Tertiary >36,000 years by the C14 method ____ 333 548 age) ______- 12 715 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H195

APPENDIX C. CHEMICAL ANALYSES OF GROUND WATER Appendix C presents 776 chemical analyses of ground-water samples from 396 wells in the Yuma area. Most of the analyses were made in laboratories of the U.S. Geological Survey in Yuma, Ariz., or in Albuquerque, N. Mex., during the period 1961-67; a few earlier analyses were obtained from the files or publications of the Geological Survey, the Bureau of Reclamation, other Federal or State agen­ cies, or from individuals. Some of these earlier analyses were recomputed from originally reported values in order to agree with the format of the Survey analyses. The 776 analyses were selected from a substantially larger number so as to pro­ vide a representative sample of the various chemical types of ground water in the Yuma area. The analyses are grouped according to the four subareas and 19 sectors described in the chemical-quality section of the report (p. H129) and are listed se­ quentially by well number (Federal land classification) within each sector. Most of the analyses are reported in terms of concentration, in milligrams per liter, of six principal ionic constituents (calcium, magnesium, sodium plus potassium, bicarbonate, sulfate, and chloride) and also silica, hardness as calcium carbonate (both calcium plus magnesium and noncarbonate), and sum of dissolved solids. Some analyses also include the concentrations of sodium and potassium separately, and of fluoride, nitrate, and boron. Additional information includes specific conductance, pH, and percent sodium. All the above characteristics adequately describe the chemical quality of the ground water as it relates to its suitability for common uses in the Yuma area. Almost all the analyses are identified according to depth (usually the depth of the perforated interval in a well) and the aquifer from which the sample was obtained. Most of the analyses represent water in the coarse-gravel zone the zone of greatest hydrologic significance in the areas of present and probably future water development. Changes in water quality with time are documented by records of drainage wells for which analyses are listed for a period of years (commonly 1961-67). Chemical analyses of ground water Analysis number: Number used for identification in text and on illustrations. <£> Well number: Location of well according to the Federal land classification. See text for description of well-numbering system. O5 Use: Letter symbols designate AC, air-conditioning; Dom, domestic; Dr. drainage; Ind, industrial; Irr, irrigation; Iru, irrigation, unused; Ob, observation; PS, public supply; St, stock; T, test; Ta, auger test. Depth of sample: Source according to well-perforation record or other infomation. Aquifer: Letter symbols designate B, Bouse Formation; C, coarse-gravel zone; N, nonmarine sedimentary rocks; O, older alluvium undivided, U, upper, fine-grained zone; W, wedge zone. [Analyzed in laboratories of the U.S. Geological Survey at Yuma, Ariz., or Albuquerque, N. Mex., unless otherwise noted. Analyses given in milligrams per liter, except as indicated. Dissolved solids calculated]

Hardness ~ as CaCOs)

O 01 g S «" W 0 3 0> 8 H Analysis Well Use Depth of sample Aquifer "5 a a a S S W (feet) g | 03 03 -3 ^ 03 O °3! s 6 01 1 g g w § E g a ai 05 w 3 3 o il p ""^ 0> 8 o g o ,Q $ S'5 g I ° *H 3 I _3 W '3 d, o cd o '3 « ! § w 1 S w & ! £ n I It !* a § o W 01 O O a w § S Na + K £ 1 § 1 £5 Q 11 P, d GILA VALLEY SUBAREA Gil a Siphon sector la Ind 30-396 O, N 5- 1-63 27 97 51 437 288 350 568 . - 1,670 450 214 2,860 7.4 68 ___ Ib 30-396 0, N 6-28-63 28 68 39 426 264 412 430 1.6 ___ 1,540 330 114 2,550 7.4 74 30-396 O, N 1-20-67 26 90 44 481 236 375 615 . _ 1,750 405 212 3,140 7.7 T 90-105 C 11-18-57 25 73 32 386 3.9 281 365 398 1.3 316 86 2,320 8.0 72 0.57 3 _ . 17dbb __ Irr <100 C (?) 7- 1-65 28 110 86 620 340 750 650 1.2 2,410 630 351 3,880 7.7 68 4 _ - . 17dbc __ Irr C 7- 1-65 24 78 52 581 416 700 425 1.6 _ _ 2,070 408 67 3,170 7.8 76 . _ 18add _ Irr 100-136 C 11-22-67 27 214 106 650 428 675 942 1.0 2,830 970 619 4,610 7.6 59 6a . _ 18bdc _ Irr 70-146 C 11- 5-64 21 119 62 374 436 438 388 1.0 _ 1,620 550 192 2,570 7.6 60 M 6b 70-146 C 7- 1-66 24 153 62 316 360 475 378 . - 1,770 635 340 2,740 7.5 52 6c C 11-22-67 26 206 89 396 396 525 615 .9 880 556 3,550 7.8 49 7a - _ (C- 8-22)13bdd2 Irr 1 ftQ 1 9fi C 4- 9 64 26 234 91 459 292 575 795 . 2,330 960 720 3,840 7.5 O 7b 1 Aft 1 9ft C 7 1 66 26 230 99 456 468 625 665 . 2,340 980 596 3,800 7.4 O 7c 109 128 C 11-20-67 26 246 106 482 488 675 705 .9 2,480 1,050 650 4,070 7.6 50 F 8a . _ 13dad Irr 85-118 C 11-15-65 25 141 61 282 376 450 308 .9 600 292 2,390 7.6 51 O 8b 85-118 C 7-- 1-66 24 170 68 300 408 500 355 1.0 _ 1,620 705 370 2,640 7.5 48 8c _ . 85-118 C 11-22-67 26 206 91 377 452 600 505 .9 9 ftQft 890 520 3,340 7.8 48 7- 1-66 o 9 14cddl Irr 80-129 C 24 132 51 290 356 425 308 .9 ___ 1,410 540 248 2,320 7.6 54 ___ o East sector lOa __ (C- 8-2l)19dad Irr 115-165 C 9-11-62 28 105 40 270 280 375 278 0.9 _ 1,240 428 198 1,990 7.4 58 115-165 C 23 274 94 419 332 525 825 1,070 798 3,840 7.3 46 w 12a . _ 29acc Ind <250 C (?) 21 416 161 1,580 516 1,150 2,500 6,090 1,700 1,280 9,690 7.4 67 12b <250 C (?) 10-25-67 22 332 163 1,490 552 1,100 2,220 1.1 _ 5,600 1,500 1,050 9,010 7.5 68 F 13 30abb Irr 105-155 C 10- 4-62 16 144 85 644 246 675 855 _ 2,540 710 508 4,360 7.8 66 ___ 14a 30acd __ Irr 104-165 C 10- 31 182 121 942 330 1,050 1,160 _ 3,650 950 680 5,790 7.6 68 ___ 14b _ . 104-165 C 6 13-63 26 182 89 609 436 600 825 2,550 820 462 4,200 7.3 £9 15a SOcccl Irr 95-155 C 10- 5-62 22 270 92 461 256 675 808 1,050 840 4,080 7.4 49 15b 95-155 C 24 250 111 623 360 512 1,140 2,840 1,080 785 4,790 7.7 56 ____ o 16 30cdc Irr 120-140 C 10- 9-62 23 344 151 1,000 432 750 1,790 4,270 1,480 1,130 7,130 7.2 60 K 17a Irr 26 200 117 903 368 1,020 1,120 o C7O 980 678 5,790 7.5 67 ___ 17b 6-13-63 27 210 101 786 478 825 992 3,180 940 548 5,220 7.4 64 w 18a Irr 95-145 C 6 1 Q ft 9 24 464 210 1,020 336 850 2,180 4,920 2,020 1,740 7,910 7.6 52 w 18b 95-145 C 27 468 168 1,120 376 1,030 2,020 5,100 1,860 1,550 7,910 7.4 57 0.47 > 19 Irr C Q £0 24 276 139 967 292 725 1,680 1,260 1,020 6,630 7.6 62 > » East-central sector M 20a (C- 8-22)22caa Irr 100-165 C 5 on rn 18 124 49 264 357 300 338 1.2 510 218 2,250 7.4 53 __ 20b C 10- 5-62 24 150 63 314 360 400 429 .8 ___ 1,560 635 340 2,580 7.4 52 ____ 20c 100-165 C 4-10-63 24 238 93 440 344 488 810 9 9ff\ 975 693 3,830 7.3 50 __ 21a Irr <136 C 5 Oft en 16 127 57 284 362 183 480 1.1 I oon 550 253 2,540 7.6 53 21b <136 C 26 128 55 323 394 317 421 .7 1,470 545 222 2,480 7.5 56 ____ 21c _ , <136 C 4-10-63 24 118 55 321 368 233 478 1,410 520 218 2,470 7.4 57 21d _ . <136 C 25 170 70 348 376 350 562 .9 710 402 2,950 7.5 52 22a 22cda2 Irr 100-152 C 5-29-62 19 125 50 299 383 288 392 .9 ___ 1,370 518 204 2,380 7.5 56 ___ 22b 100-152 C 24 126 51 308 392 308 392 1,400 526 204 2,370 7.5 56 23 Irr 100-150 C 24 116 50 305 364 233 438 1,350 496 198 2,360 7.5 57 ____ 24 T '500 w 2 9C C9 8 73 29 228 202 138 346 Q9O 302 136 1,740 7.6 62 ___ 25 Irr 97 140 C 22 146 62 264 320 342 408 620 358 2,420 7.1 48 26 Irr 100-114 C 9 on /jo 28 194 79 554 476 500 780 9 37O 808 419 3,900 7.3 60 ____ 27 25cbd Trr 7° 118 C 10 5 P2 23 185 76 454 278 375 812 775 547 3,710 7.3 28a __ . 25ddd _ Dr 100-160 C 4-20-64 416 180 1.120 388 950 2.060 _ 4.940 1,780 1.460 8,000 7.3 58 28b 2 ___ 100-160 C 7- 7-65 425 186 1,190 393 946 2,220 ______5,160 1,830 1,500 8,360 59 ___ 29a __ _ 26adb __ Irr <184 C 1-20-61 32 108 43 270 298 197 414 _ 2.9 1,210 445 201 2,060 7.6 57 0.32 29b <184 c 10- 8-62 22 148 58 345 344 288 552 1,580 610 328 2,840 7.2 55 __ 29c <184 c 1 17 63 23 99 43 271 288 208 398 1,190 425 189 2,120 7.7 58 ___ q A 26bad __ Irr 90-170 c 21 222 91 426 284 258 960 _ _ _ 2,120 930 697 3,840 7.3 50 31a _ _ 26bbb __ Dr 84-134 c 3-24-64 23 114 43 294 298 275 402 .9 .1 1,300 460 216 2,240 7.4 58 .31 31b 84-134 c 25 97 37 267 288 267 328 ___ _ _ 1,160 395 159 1,940 7.8 60 31c 2 ___ 84-134 c 7- 7-65 110 42 278 304 256 1,230 446 197 2,120 58 ___ qo 3 26cbd __ Irr 94-150 c 5- -60 224 97 553 281 350 1,110 _ __ 2,470 957 726 3,500 56 qq 26dcal __ Irr 95-125 c 10- 5-62 23 151 69 474 288 250 848 1,960 660 424 3,660 7.4 61 34 _ 26dca2 _ Dom 184-190 w 3-25-65 21 137 48 299 222 125 622 .8 1,360 540 358 2,470 7.4 55 35a _ 26ddd __ Dr 90-160 c 3-30-64 20 272 120 745 376 512 1,380 1.2 _ _ 3,240 1,170 862 5,510 7.6 58 _ __ 35b 2 ___ 90-160 c 4- 6-65 395 170 1,080 387 740 2,130 __ _ _ 4,710 1,690 1,370 7,660 58 ___ 35c 2 ___ 90-160 c 12- 2-65 ~~22 365 160 1,150 384 746 2,120 4,730 1,570 1,250 7,760 61 ____ 27aca _ _ Irr 102 134 c 4-24-63 204 80 426 400 300 795 2,030 836 508 3,600 7.1 52 27bbb __ Dr c 4-12-64 25 226 98 442 488 338 833 _ _ 2,210 965 565 3,870 7.3 50 37b __ _ c 1-22-65 26 242 104 504 528 350 942 2,430 1,030 597 4,080 7.3 52 O 37c 2 ___ 86-147 c 7- 7-65 ~~25 195 82 411 457 310 748 2,020 825 450' 3,360 ~~7.4 52 38 __ _ 27bda Irr 6-13-63 106 45 278 268 140 487 .8 1,220 448 228 2,240 57 __ O 27bdd Irr 80-161 c 23 219 92 472 248 350 982 _ 2,260 925 722 4,190 73 53 W 40a 27cad Irr 95-141 c 25 198 105 495 288 288 1,040 _ 2,300 925 689 4,210 7.2 54 40b __ _ 95-141 c 4-24-63 21 214 87 536 300 275 1,080 2,360 890 644 4,280 7.3 57 __ o 41a 27ccc __ Dr 106-176 c 4- 6-64 23 206 93 564 336 283 1,100 2,440 895 620 4,300 7.3 58 41b 2 ____ 106-176 c 7- 7-65 149 64 499 259 230 896 1,970 638 426 3,530 63 o 41c 2 ___ 106-176 c 12- 2-65 149 65 491 268 251 874 _ 1,960 636 416 3,450 63 ___ tr1 42 __ 27dad __ Irr 100-118 c 5-23-62 13 194 89 432 269 200 965 _ 2,030 850 630 3,880 "T.4 52 ___ O 43a 27ddd __ Dr 95-165 c 11 198 77 545 252 425 955 2,340 810 604 3,790 7.5 59 43b 2 ___ 95-165 c 4- 5-65 208 81 494 253 266 976 _ 2,150 852 644 3,950 57 ___ 43c 2 ___ 95-165 c 7- 7-65 233 94 532 253 299 1,160 _ 2,490 966 759 4,320 54 ___ 3 44a Irr QO ] 77 c 3-30-63 13 338 150 1,090 297 550 2,140 4,430 1,460 1,220 7,670 62 ___ 0 44b _ _ QO 1 77 c 10- 9-62 22 160 66 375 244 208 758 1,710 670 470 3,210 ?'. 3 55 ___ 44c 93-177 c 5- 8-63 20 151 69 422 220 225 825 _ _ 1,820 660 480 3,320 7.8 58 Dr 500-600 w 10- 7-64 21 66 14 222 216 72 321 1.0 825 224 47 1,490 7.7 68 H 45b _ - 500-600 w 11-12-65 19 63 18 205 216 62 308 1.0 784 232 55 1,480 7.6 66 W 46 34bacl Irr 115-184 c 27 182 84 454 244 217 965 _ 2,050 870 600 3,910 7.5 55 K 35aaa2 Irr 90-137 c 10 5 62 24 177 85 410 260 325 802 _ 1,950 790 577 3,560 7.4 53 47b 90-137 c 6-13-63 22 412 195 1,230 336 750 2,450 5,230 1,830 1,550 8,790 7.3 59 48 __ 35babl _ Irr c 5- 8 -63 21 256 122 755 200 375 1,580 3,210 1,140 976 5,710 7.5 59 T 435-570 w 12-22-63 20 66 15 220 216 70 322 .8 822 228 51 1,500 7.6 68 49b 99-170 c 21 182 88 467 236 225 995 _ 2,100 815 622 3,890 7.4 56 *£> 50a _ 35caa2 _ Dr w 5- 7-64 18 64 17 218 211 75 319 1.0 818 230 57 1,530 7.2 67 50b 484-585 w 10-13-64 20 66 16 223 214 70 331 .8 834 232 56 1,530 7.7 68 __ E^ 50c 484- -585 w 7- 1-66 17 62 18 224 218 70 328 .9 829 230 51 1,540 7.4 68 51a Irr 95-175 c 21 118 50 354 236 192 622 1,480 500 307 2,730 7.9 61 _ M 51b 95 175 c 7-23-64 24 138 57 394 228 250 700 _ 1,680 580 393 3,050 7.5 60 52 36abb __ Irr 100 155 u, c 6-13-63 25 558 267 1,480 432 1,020 3,050 6,620- 2,490 2,140 10,700 7.3 56 53a Irr 85-140 c 10- 5-62 22 189 77 503 292 575 2,250 790 550 3,790 7.4 58 53b _ 85-140 c 6-13 63 23 372 163 1,680 396 1,050 6,210 1,600 1,280 10,100 7.4 70 54a 36bba __ Irr 110 135 c 24 160 66 327 246 192 765 1,700 670 468 3,220 7.2 55 S 54b c 21 354 157 1,220 384 800 2,160 4,900 1,530 1,220 8,200 7.5 64 N 55a Dr 520 621 w 5-26-64 19 97 27 245 220 85 435 .6 .1 1,010 352 172 1,950 7.8 60 .23 O 55b 520 621 w 10- 1-64 19 98 25 254 222 85 445 .5 _ 1,040 348 166 1,920 7.5 61 55c 2 ____ 520 621 w 10-26-65 15 98 23 261 226 83 442 .6 ___ 1,040 338 154 1,870 7.8 61 .21 West-central sector £> 56a (C- 8-22)19ccc __ T 370-463 w 11-13-63 14 202 59 316 244 120 785 0.4 0.3 1,620 745 545 3,080 7.4 48 0.23 ^ 56b 115 150 c 2-17 64 15 199 81 499 482 512 700 _ .7 2,250 830 435 3,740 7.4 57 .45 U 57 _- _ 19ccd Irr 103-135 c 3-19-63 26 127 43 293 329 272 408 1.2 1,330 492 222 2,220 7.7 56 .22 o 57a 21ddd __ Irr 105 150 c 5-29-62 20 138 60 307 393 325 422 1.0 1,470 590 268 2,490 7.6 53 ____ 57b .. ___ 105 150 c 10-10-62 25 140 56 311 384 338 418 1,480 580 265 2,530 7.2 54 __ - 58a 28aaa __ Irr 105- 150 c 20 159 68 356 393 262 605 _ 1,670 675 352 2,960 7.6 53 58b 105 150 c 10-10-62 24 156 66 360 400 283 582 1,670 660 332 2,980 7.3 54 \ 58c 105 150 c 1-22-65 24 145 64 365 376 258 595 .9 1,640 625 316 2,770 7.5 56 o 59a Dr 117 167 c 3- 2-64 21 204 88 504 264 438 918 2,300 870 654 3,990 7.6 56 59b 117-167 c 4-20-65 25 202 84 650 320 350 1,160 2,630 850 588 4,580 7.7 62 59c 2 ___ 117 167 c 12- 2-65 203 89 691 317 403 2,750 872 612 4,730 ~~7.8 63 ___ t t 60 ___ -_ 28cdb __ Irr <248 5- 8-63 23 127 66 401 244 208 742 1,690 590 390 3,100 60 __ - 61 28dca __ Irr 1 OO 1 GQ c 18 185 75 414 306 233 835 1,910 770 519 3,430 7.6 54 62a . _ 29cdd __ Irr 138-185 c 1-25-61 32 260 110 625 277 443 1,270 ___ 3.8 2,880 1,100 873 4,900 7.4 55 .47 62b 138-185 c 3-26-63 27 258 101 631 285 405 2,

T 5 g co we» coco w co co co co cowco co w co cow co coco coco to to to to to tototo H> )->>-> )-> o gj noes' SB SB 0.0.0. n o ocfes &. cfo'CsS' o* SB a, O.SB O.SB Co a« g g,&.SB 0* n SB SB O. HI a' S' ° NH« M » » III 1 III 1 1 1 1 II 1 1 1 1 1 1 III 1 III III 1 1 1 1 1 1 1 III 1 III

MMM M M M MM O t) >-<>-< d i*<3 *< 3 3 o 3 i i *< 3 3 i ^ 33 ft o

H-» o co co -''-^cocococococcoototototoa>oooooooooooooooooocococcooc»coco<3iooooooooooooooo*i^cococoa^ "i o CT 05 O5O5O5O5 o cncnO'-a t-1 o o o o o o o o o o *.*» fe. * *»*'* >i^ co co co co coco o -^ CTOTCT CTCT CTOO o o o o o o o oooo ft* £ 00000000000000000000000000000000000000000000000000000000030000 1. Ms » o t-' t-' 1-1 1-1 1

M to h-«t-i 13 101-' IStOtOtOI tO 13 tO I I-" tO tOCO total tatOtOKH-1 l-> CO tO tO tO tO tO tO tO >- *-* tO t-1 tO t-i H-" s- Date of sample nNN g^ t0^5tOtOI»<»CT4xtOtOIM4wl»tO^^OUCOCOtOtOtOtOK' S Hj Calcium (Ca) ^h a, CD «5 <6 C^ 2 EMMEcO^a^^KcOgOCO^OOCOgOg^ESog^gag^ 15 Magnesium ( Mg ) s «g1 » a Sodium (Na) § SB «a « 1 + a Ss i Potassium (K) Io 1£T. 3 co"S"MSSwSKgg§S|oco|»||g"SSS§§OOoSS2MM|M|S§2gMg"S^ Bicarbonate (HCOs) &g

IsilllllKllIsiililllllllislllllissslllgllsllilaliligililifelSil Sulfate (SO4 ) i-1 i^i^ *-* ij ij,to,t~1 r1 i^.f~'.l^yij i^ i^ f iiiliiiiiiiiiiliiiiiiiiisiiiiiiiiiiiiiis^siiiiiiiiiii^iigiiiii Chloride (Cl) 1 II 1 II II II III II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 III III 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 . 1 1 Pi II II II III II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Fluoride (F) 1 -q 1 1 -31 II II II III II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 III III II 1 II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 III III 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 .. 1 1 1 1 _ 1 111 .111 i i 5°i . i i E°i i i i i i i i F°i i i i f-1 1 i w i i t-1 i Nitrate (NOs) 1 -q 1 1 CO 1 1 1 1 1 C0| to 1 1 -q 1 1 1 1 1 1 1 1 to 1 1 1 1 CO 1 1 H* 1 1 4>- 1

QO^>^QlOCOCOCOCOGOCnC^^^OCOC^Cn(^(^OQOCOO^CO>^^GOCOOCOCOCTCOCOCOCOCOCOtOOCO>^O^>^COHJHi COCOCOCO**.O5COCC<3iCOCOCn|>0 Dissolved solids (sum) OOOOOOOOOOOOOOOOOOOOOOOOOOoOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

't-'oocot-icc-q-a-q-acc co ">-""»-' to coo -q co co coo o"t-J to I-J"OCTCT OiOiOi-qoocoaioi-q-a-qco-qoo-q-qcococococooocococooi-'toji.Oi-q-aoito Calcium magnesium _s» OOOOCTOOTOOCTCTOOOOOOOOOOOOOOOOOOOOOOOOOOOOO1OOOOO1OOCTOOOOOOOOOOOOOO p & w""*-*""4 ""* i""*i""* OB coos^cOOTCnorcncno^cncocoo^^^^-^^cooocoocooocococo^^Qrcncnt^i(wt^t^cnoscn0>QiCTOiO)-<)O^O)OiO)os-qcocootoi(^t^cncoco SoKaooSooStoEooEogSocoSooto^SS^SoSggS^S^SacoSoSK^ogcog^og^ggfefeggenSSaco Noncarbonate *, w

H-^OO^rf^CO^^CO^OOCOC^COCOCCOH^tNDCOWCOO^l^DtNDOiCCOOHJKJ^QT^OT^K^OO^^OSOiW Specific conductance oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo (micromhos at 25° C)

PH

CTCTCT^agOTgOT^a^Cn^aCTOsaCTWgggTgOTCTaaaW^g^W^^.W^gW^aggWg^W Percent sodium II III 1 1 1 1 1 1 1 1 1 1 III III III III 1 1 1 1 1 1 1 1 1 1 1 1 1 1 II II II II III 1 1 1 1 III 1 III 1 1 1 . 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 1 . 1 1 1 1 1 II I I 0 1 Boron (B) 1 1 col 1 1 1 1 tOP Oil 1 1 1 Oil 1 1 1 1 1 1 1 1 £t 1 1 1 oil 1 1 1 1 4^ 1 1 1 1 1 1 1 1 1 id 1 1 1 1 1 ift. 1 1 col 1 tO 1 I I I to I ! 1 1 1 oocni-»l 1 1 1 col I I 1 1 1 J I I -q i 1 1 col 1 1 P&. I I 1 i 1 1 i 1 1 1 1 1 1 to 1 1 1 I 1 ol 1 cnl 1 col 1

vaav vas Nonvs-aaAin oavaoioo saoanosaa 86TH 85b __ __ 115-190 C 2-21-62 26 255 93 638 289 376 1,260 .8 .3 2,790 1,020 783 4,780 7.4 58 .56 85c __ _ 115-190 C 11- 8-62 25 222 94 619 286 400 1,160 _ __ 2,660 940 706 4,680 7.5 59 ____ 115-190 C 12-13-63 24 230 94 608 282 412 1,150 _ _ 2,660 960 729 4,540 7.4 58 ____ 85e ___ 115-190 C 20 206 101 588 280 412 1,100 2,570 930 700 4,530 7.4 58 QK.f 115-190 C 27 228 102 655 278 462 1,210 2,820 990 762 4,900 7.4 59 ___ 85g _ 115-190 C 23 230 99 644 284 450 1,190 _____ 2,780 980 747 4,760 7.5 59 ___ 33ccc __ , Dr 90-190 C 1 22 62 24 308 117 472 249 475 1,120 2,640 1,250 1,050 4,630 7.8 45 ____ 90-190 C 2 91 en 26 315 101 524 239 512 1,140 2,740 1,200 1,000 4,500 7.5 49 90 190 C 11- S-62 25 274 101 517 246 575 1,010 2,620 1,100 898 4,350 7.4 50 ____ 0/5 j 90-190 C 2-19-64 19 242 99 499 256 612 885 2,480 1,010 800 4,120 7.3 52 ___ 86e _- 90-190 C 25 222 79 522 266 650 795 2,430 880 612 3,870 7.5 56 86f ____ 90-190 C 1-24-66 24 198 72 493 280 600 715 2,240 790 560 3,610 7.5 58 ___ 87a 33daa __ PS 260-280 w 5-23-63 21 74 24 236 208 85 379 .9 ___ 924 284 114 1,720 7.4 64 ___ 260-280 w 11-29-63 17 62 22 230 180 80 362 .8 _ 864 244 96 1,620 7.6 67 ___ 260-280 w 10-13-67 17 74 33 253 196 100 428 .8 _ 1,000 320 160 1,880 7.6 63 88a (C- 9-22)5baa ___ Irr C 24 278 99 568 292 775 915 2,800 1,100 860 4,530 7.7 53 QQU C 4-24-63 22 274 109 581 288 725 995 1,130 894 4,750 7.2 53 O QQ- i no. 199 C 19 1 Q flQ 23 254 94 570 298 750 875 2,720 1,020 776 4,360 7.4 55 ___ H SQ 5bbc Ta m i si C 3-24-66 21 119 47 475 336 725 348 1.2 1,900 490 214 2,850 7.9 68 O West sector go 90 __ __ (C- 8-23)22ddc __ Irr (?) (?) 22 174 67 312 344 250 600 1,600 710 428 2,860 7.5 49 ___ # 91a 23cdb __ Irr 68-90 C 1-17-63 28 193 90 377 384 550 555 1,980 850 535 3,180 7.6 49 ___ o 91b fifi Q/1 C 5- 8-63 24 196 93 392 392 550 588 870 548 3,270 7.6 50 ____ f Q9a Irr 115-135 C 3- 4-63 26 193 75 295 432 388 478 790 436 2,850 7.5 45 o 92b C 5- 8-63 25 179 76 318 384 425 492 1,710 760 445 2,800 7.7 48 24dec ___ Irr (?) (?) 3- 4-63 29 204 78 406 370 350 740 830 527 3,330 7.8 52 0.28 9 (?) (?) 25 242 73 414 444 375 745 _ 2,100 905 541 3,570 7.5 50 94a 25aeb __ Irr 115-175 C 10- 5-62 26 180 71 360 365 233 695 1,750 740 440 3,200 7.2 51 ___ O 94b 115-175 C 5 8 63 23 169 75 375 336 242 722 730 454 3,140 7.6 53 ____ *l QC a 25bcc __ Irr 130-180 C 2 3 63 24 190 82 476 350 312 875 2,130 810 523 3,850 7.5 56 ____ H 95b __ _ 130-180 C 3- 4-63 25 212 61 435 346 287 810 .2 2,000 780 496 3,390 7.9 55 .32 W QK/i 130-180 C 6-13-63 23 194 84 459 398 325 825 830 504 3,660 7.3 55 96a __ Irr 115 170 C 1-27-61 32 240 76 499 403 337 950 4.5 2,340 910 580 3,960 7.4 54 .54 M 96b _ 115-170 C 3- 4-63 24 183 74 441 360 242 832 1,980 760 465 3,590 7.4 56 ___ Kj 115-170 C 4-10-63 24 185 74 442 364 267 815 765 466 3,560 7.4 56 ___ d Q7n 25dab Irr 115-175 C 10- 5-62 24 194 73 393 348 242 782 1,880 785 500 3,400 7.3 52 ___ 97b 115 175 C 4-10-63 24 191 79 399 354 233 805 1,910 800 510 3,460 7.3 52 ___ § 26acd __ Irr 116-175 C 3 q /?<> 22 258 101 610 438 350 1,180 2 740 1,060 701 4,850 7.4 56 > 99a 26bac _ _ Irr 142-180 C 10-10-62 23 300 117 557 432 475 1,130 1,230 876 4,860 7.1 50 99b C 5 8 63 22 278 123 577 360 450 1,200 1,200 905 4,850 7.4 51 > 101 __ 26cab __ Dr m l 74. C 23 588 234 1,680 416 725 3,540 2,430 2,090 11,600 7.3 60 » 102a ___ 26cda __ Irr 145-173 C 5 9Q £9 18 366 148 940 338 475 1,980 1,520 1,240 7,120 7.4 57 ____ w 102b ___ 145-173 C 6-13-63 21 358 155 964 368 512 1,980 1,530 1,230 7,190 7.4 58 ___ > 103a ___ 26ddb __ Dr 126-196 C 3 29 65 28 402 189 1,180 384 575 2,440 1,780 1,460 7,780 7.4 59 ___ 103b* __ 1 9fi 1 Qfi C 333 137 899 357 432 1,850 1,400 1,100 6,590 58 ____ > 104a ___ 26dbd __ Irr 160-200 C 17 316 137 785 344 362 1,700 3 490 1,350 1,070 6,320 7.5 56 ____ w 104b ___ 160-200 C 24 355 135 872 361 413 1,850 3,830 1,140 1,140 6,530 7.7 57 .55 i i 104c ____ 160-200 C 27 238 94 632 448 500 1,040 980 612 4,570 7.5 58 ___ N 105a ___ 27abb __ Irr 85-180 C 5 99 fll 28 275 98 448 344 273 1,040 2,340 1,090 808 4,050 7.6 47 .26 0 105b ___ 85-180 C 24 258 123 484 296 312 1,160 2,510 1,150 908 4,670 7.3 48 ___ 25 106 __ 27acb Dr 130-160 C 25 278 109 493 320 233 1,210 2,510 1,140 878 4,360 7.3 48 > 107 27ada __ T C 12 2 63 21 860 256 1,160 336 600 3,420 6,480 3,200 2,920 10,700 7.2 44 108a ____ 27ddd __ Irr 135-158 C 1-30-61 28 292 110 739 339 394 1,520 ___ 2.2 3,250 1,180 902 5,550 7.2 58 .61 > 108b ___ 135-158 C 10- 8-62 23 312 132 715 340 438 1,610 3,460 1,320 1,040 6,190 7.0 56 ___ 25 108c ___ 135-158 C ff 1 q /?q 22 342 128 832 348 500 1,690 3,690 1,380 1,090 6,360 7.4 57 ____ o 108d ____ 135-158 C 2-19-64 17 350 128 796 348 512 1,640 1,400 1,110 6,210 7.2 55 ____ 109a ___ 35aac ___ Dr 125-195 C 4-19-65 24 242 87 671 312 562 1,120 2,860 960 704 4,640 7.5 60 0 109b2 ___ 125 195 C 254 93 742 320 576 1,250 1,010 750 5,180 61 :> HOa ___ 35aca ___ Irr 130-155 C 3-26-63 22 258 109 742 332 575 1,300 3,170 1,090 818 5,500 7.7 60 ___ if i HOb ___ 130-155 C 23 262 73 741 340 625 1,250 3,140 1,080 801 5,190 7.5 60 ____ *i 111 35adb Irr 140-171 C 23 187 73 465 272 338 852 2,070 765 542 3,590 7.6 57 0 112a ___ 35caa __ Irr 150-186 C 3-26-63 25 182 54 406 246 454 627 ___ 0.3 1,870 675 474 3,060 7.5 57 .26 w 112b ___ 150-186 C 11-19-63 25 214 62 469 248 562 725 2,180 790 586 3,560 7.6 56 ___ 25 113a ___ 36aaa __ Irr (?) (?) 24 274 94 446 248 512 925 2,400 1,070 866 4,050 7.5 48 ___ i i 113b ___ (?) (?) 20 267 91 412 232 425 925 1,040 850 3,950 7.6 46 ___ > 113c ___ (?) (?) 4-10-63 21 270 92 415 252 425 925 1,050 844 4,030 7.4 46 ___ UPPER VALLEY SUBAREA "Laguna Valley" sector 201a ___ 15S/24E-17L ___ PS (?) (?) 1-24-61 20 93 28 115 174 297 108 ____ 0 748 348 206 1,160 7.4 42 0.16 201b (?) (?) 1- 4-62 20 97 29 178 325 115 _ 806 362 216 1,220 7.8 44 _ 202 17K5 T 17 U qQ 7 2 255 1 Q9 300 150 856 0 1,370 8.3 81 91 o 203 20H1 T 1 fi. U 5-14-62 CQ 1 9Q 780 601 2,230 7.6 26 0 204 30R1 T 1 Ct u 5-14-62 212 227 372 400 435 1,550 2,690 7.0 37 205 (C- 7-21)6ccd _ T 13 u 5 14-62 91 190 242 826 264 1,540 7.8 61 _ 206a ____ (C- 7-22)14bdc __ T 118-162 5-29-63 15 103 30 180 330 126 ____ .1 825 382 234 1,280 7.7 43 .14 C 132 W 206b ___ 470-490 N 5-23-63 32 297 57 860 136 660 1,450 ___ .4 3,420 975 864 5,610 7.9 66 .76 h-1 207 OQ 01 U OQ 194 362 qi 7 11 _ 1,180 582 423 CO See footnc>tes at end of tab!e. CO h-1 Chemical analyses of ground water Continued t-M to Hardness o -, as CaCOs) o g 6 D 5 O 111 B Analysis Well Use Depth of sample Aquifer "3 1 J« g i 1 "o W -S (feet) g 0) fc 6 eg eg C m -3 a O .2 -p 6w fc a 1 1 I g o ° « o g 1 1 « 3 1 g !H 1 o o 8 c "o .3 '3 (L, o eg °3 f § 1 g "S 1 g w 1 I lH >H g O B 0) O W g Na 0,^1 3 o + K S 1 O 1 5 5 3 ft > UPPER VALLEY SUBAREA Continued H W North Gila sector » 208 __ __ (C- 7-22)14ddc Dom 30 U 10- 4-62 13 98 31 155 166 362 137 0.7 880 370 234 1,400 7.3 48 ____ » 209 _ 27bba __ Dom 28-30 U 8-28-62 19 167 57 234 362 550 204 1.1 1,410 650 353 2,320 7.2 44 ___ W 210 __ - 27cad __ Dom 33-35 U 8-28-62 26 196 61 453 368 875 362 .9 2,160 740 438 3,270 7.4 57 W 91 1 27ccd _ _ Dom 130 c 8-28-62 26 218 57 264 258 325 570 .5 1,590 780 568 2,860 7.3 42 ____ o 212a _ 28acc ___ Ta 142-144 c 5- 7-65 21 158 15 210 324 412 155 .4 1,130 456 190 1,670 7.7 50 d 212b ____ 142-144 c 7- 6-65 14 150 31 181 320 401 152 .6 1,090 500 238 1,650 7.9 44 ____ » 213 _____ 28ddc Dom <100 c 8-28-62 23 148 35 170 245 450 151 .6 1,100 515 314 1,710 7.4 42 ____ o 214 _____ 34bdc Dom <130 c 8-28-62 23 42 12 249 221 325 123 .9 885 154 0 1,480 7.6 78 ___ w 215a ___ (C- 8-22 )3cb ___ Ta 112-114 c 5-10-65 30 106 48 543 368 600 505 1.2 2,020 460 158 3,190 8.0 72 ___ w 215b ___ 112-114 c 7- 6-65 25 86 50 525 384 550 475 1.4 1,900 420 105 3,170 8.2 77 ___ o 216 _ _ 4abc _ __ Dom c 8-28-62 25 150 45 172 259 412 207 .6 ~~o72 1,140 560 348 1,830 7.4 40 *1 217a ___ 15bdd __ T 90-185 c, w 1-30-64 30 114 44 216 304 400 189 .6 1,140 464 214 1,800 7.5 50 217b ____ 491 w 12-20-63 6 111 25 254 152 125 478 .8 1,080 378 254 2,050 7.8 59 ___ f 218 _ _ St 110-148 c 8-28-62 27 97 40 242 347 400 162 1.0 1,140 406 122 1,850 7.5 56 ____ o 219 ___ Dom 30 U 8-28-62 28 182 67 205 487 500 180 .8 1,410 730 330 2,200 7.2 40 3M Bard sector » 220 _____ 15S/23E-31Cbb __ Ta 106-108 0 4-16-63 22 227 79 172 130 350 562 0.6 1,480 890 784 2,580 7.3 30 ___ o 221a ____ 3lFcd __ Ta 92-94 o 4-16-63 28 170 62 335 278 575 412 .3 1,720 680 452 2,760 7.9 52 ____ 221b ___ 92-94 0 5 4 64 19 143 52 327 316 575 300 1,570 570 311 2,490 7.6 56 __ - otr1 222 ____ 32Rdd _ Ta 114-116 c 24 74 13 78 195 95 102 482 234 74 838 7.4 42 o 223 _ __ 33 Fac Dom 130 c 5- 9-64 16 164 40 201 304 512 162 .9 1,250 575 326 1,860 7.5 43 - » 224 _ __ 34Dbb _ Ta c 4-29-64 12 73 22 202 208 350 126 889 272 102 1,410 7.2 62 _ - 225 B ___ 35Eac _ Dom <130 3-17-64 50 35 158 204 195 174 .4 -- 714 270 102 7.9 56 ____ > 227a __ 16S/22E-lLab __ Ta 59-61 U 2 9 62 94 31 133 175 342 109 809 364 221 1,1220 7.9 44 ___ o 227b 59-61 U 5- 1-64 10 105 28 120 168 308 127 782 376 238 1,270 7.5 41 _ o 228 _ _ 2acd _ _ Ta 0 5- 1-64 14 66 20 181 152 183 231 771 248 124 1,360 6.9 61 » 229 12Hdd _ Ta 1 9fi 1 9Q c 4-28-64 16 73 12 110 161 120 151 562 230 98 1,000 7.3 51 H-i 230 14Mba Ta U 4-28-64 7 96 30 136 188 317 125 805 364 210 1,290 7.7 45 < 231a ___ 23Caa __ T «320 w 3-22-64 16 100 9.4 271 234 362 217 1,090 288 96 1,790 7.6 67 w 231b ___ 6 355 w 15 99 27 348 70 412 447 1,380 302 99 2,370 7.8 68 ____ 232 23Fcd Ta c 4-28-64 14 84 22 128 156 292 102 720 298 170 1,130 7.6 48 ___ ? 233 _ _ 26Bbb __ Ta 116-118 c 13 191 47 173 256 333 348 1,230 670 460 2,070 7.7 36 ___ w 234 26Gcd __ PS 140-150 c 5-31-66 16 114 38 118 200 275 173 .6 835 440 276 1,430 7.3 37 > 235 16S/23E-3Dbb __ Dom, 108-118 19 11 fil 25 150 38 161 280 450 131 1,100 532 302 1,600 7.8 40 F c H St 236 _ _ 3Ncc Ta 126-128 c 19 239 57 310 200 775 262 1,860 830 502 2,710 7.4 45 O 237a ___ 6Cba __ Ta 62-64 U 4-16-63 20 80 35 173 194 342 145 .6 893 344 185 1,420 7.8 52 ___ X 4-30-64 237b ___ 62-64 U 16 62 39 189 170 362 147 .7 ____ 901 314 174 1,420 7.3 57 ____ W 238 6Gcb Ta c 4-29- 64 21 89 24 114 178 267 102 706 320 174 1,120 7.6 44 w 239 Dom 113 c 12-12-61 24 209 54 173 356 559 174 .3 1.2 1,370 898 606 1,970 7.8 34 240 8Ecc __ T 110-141 c 12-18-63 18 194 49 256 392 600 208 .7 1.5 1,520 685 364 2,320 7.6 45 0.29 > 241 _ 19Mbc __ PS 120-200 c, w 5-18-61 11 230 56 278 6.4 376 606 332 .3 .3 1,710 805 497 2,530 8.0 43 > » The Istland sector H 242a ___ 16S/23E-9Naa __ Irr 124-225 c, w 5-24-62 28 130 36 138 292 250 195 0.5 973 474 234 1,630 7.2 39 ____ > 242b ____ 124-225 c, w 4-20-63 23 159 50 231 277 490 262 "T.3 1,350 604 377 2,050 7.7 45 ____ 242c ___ 124-225 c, w 6-15-67 21 161 60 212 332 462 252 " .7 1,330 650 378 2,150 7.5 41 ____ 243a ___ lORcc __ T «133 c 10-16-64 12 188 15 231 302 525 169 .7 1,290 532 284 1,930 7.7 48 ___ 243b ____ 1 634 -694 B 1-21-65 26 108 27 281 144 200 468 1.9 1,180 380 262 2,120 7.6 62 ___ 243c ___ 1 120-548 c, w 4- 7-65 19 75 18 104 4.2 207 126 129 .4 .1 581 260 85 964 . _ 0.12 244 _ Irr 10-23-65 23 223 74 222 404 500 348 .6 1,590 860 528 2,630 7.7 36 245 _ Irr 10-29-62 24 147 57 298 332 350 432 .7 1,470 600 328 2,570 7.4 52 246 _ 22Rbd Irr 105 130 c 6 15 67 24 170 62 347 312 238 660 1,660 680 424 3,010 7.3 53 247a ___ SlDbc __ Ir 100-144 c 20 165 63 311 394 412 422 1,590 670 347 2,570 7.6 50 _ 247b ___ 100-144 c 4-30-63 25 169 60 322 392 400 448 1,620 670 348 2,650 7.3 51 ____ (O- 8-22)6cda _ Irr 128 166 c 6-15-67 21 111 37 164 300 205 232 .6 920 430 184 1,430 7.3 45 249a ____ 7ccd __ Irr 110-160 c 4-27-64 21 151 49 379 304 283 608 .7 ____ 1,640 580 330 2,880 7.6 59 249b ____ 110-160 c 12-15-66 21 153 53 388 334 228 615 1.0 1,690 600 326 2,950 7.6 58 ____ 250a ____ 18cbd __ Irr 110-160 c 5-29-62 18 178 67 417 334 210 805 .8 1,860 720 446 3,560 7.8 56 ___ 251 _ _ _ 18ddd _ Irr 100-155 C 23 91 38 256 264 292 299 1,130 384 168 1,930 7.4 59 __ 252 _ _ (C- 8~23)lldca _ Irr 110 160 C 6-15-67 23 183 54 224 348 325 385 .6 _ _ 1,370 680 394 2,370 7.4 42 _ __ Irr 6-15-67 22 156 51 252 352 350 350 .7 _ 1,360 600 312 2.310 7.4 48 __ 254a ___ Irr 115-171 C 11 8-62 23 175 52 293 330 183 585 1,480 650 380 2,720 7.4 50 254b ___ 115-171 c 23 194 60 338 376 238 645 730 422 3,010 7.3 50 ___ 255 16S/22E-25Mbb2 _ Ta 117 119 c 4-28-64 22 117 41 196 314 375 170 1,080 460 202 1,660 7.7 48 ____ Winterhaven sector

256 __ _ 16S/22E-16Lda ___ Ta c 23 65 20 139 168 283 81 695 244 106 1,070 55 __ 257 __ _ Ta /»q cef u 7- 6-65 24 14 316 268 325 151 12 976 116 0 1,680 86 oeo 17Pdd Ta c 4-30-64 22 51 17 203 216 308 100 809 188 21 1,270 69 ___ 20Hdd _ Ta m l 1 Q c 4-30-64 21 156 44 279 360 525 238 _ _ 1,440 570 275 2,220 52 260 _ 21Rdd __ Ta 124-126 c 4-30- 64 11 201 65 396 364 750 392 2,000 770 472 2,990 53 ____ oat 22Dbb __ Ta 126-128 c 4-29-64 22 144 40 209 304 488 158 _ 1,210 525 276 1,850 46 __ 262 _ _ _ 22Gdc __ Ta c 4-29-64 22 130 32 218 328 350 210 __ - 1,130 455 186 1,770 51 Q 263a ___ 26Ecc _ PS 121-133 c 9-20-61 29 120 34 138 4.2 218 374 120 .4 0.1 927 440 262 1,390 40 0.40 M 263b ____ 121-133 c 4-28-65 22 156 51 207 296 500 202 .7 ___ 1,290 600 358 1,980 43 ____ O 263c ___ 121-133 c 5-26-66 23 150 50 220 298 525 188 .7 ___ 1,310 580 336 1,990 45 ___ 264 _____ 27Hda _ PS 135-146 c 7-19-61 29 128 36 185 5.0 262 437 142 .2 1.4 1,600 467 252 1,600 46 Ei 265 27Jda __ Ta 124-126 c 5- 4-65 23 172 56 231 356 538 218 .9 1,420 660 368 2,190 43 _ O 266 _ _ 27Mdd Ta 104-106 c 23 414 118 642 484 850 1,160 3,450 1,520 1,120 5,200 48 ___ W 267a ____ 29Dba __ Irr 118-143 c 2-10-64 17 168 49 178 282 200 403 .4 ___ 1,160 620 389 2,060 38 ____ O 267b ____ 118-143 c 2 1 Q Rf\ 23 164 44 185 272 200 398 1,150 590 367 1,980 40 ____ f 268a ___ 29Gcal _ Ta 140-142 c 4-30-64 19 76 20 120 207 130 161 630 270 100 1,080 49 ___ o 268b ___ 140-142 c 4-30-65 17 78 16 120 192 120 168 .5 ___ 616 260 102 1,040 50 ____ 268c ___ 140-142 c 7- 9-65 4 52 16 114 148 100 155 .2 ___ 515 196 74 944 56 ____ 269a ____ 29Gca2 __ T 7 38-40 u 2-17-65 19 310 87 428 368 700 730 2,460 1,130 828 3,870 45 ____ 3 269b ____ 125-1,769 C, W, N 4-13-65 19 100 24 118 4.8 200 102 244 712 349 185 1,270 42 .14 0"_ YUMA VALLEY SUBAREA H California sector W 301 ___ 16S/21E-25Gca Ta 121-123 c 7- 7 65 1 23 16 109 84 82 143 1.7 418 123 55 797 7.2 66 M 302 _ __ 25R Dom 110-120 c 2 28 64 22 102 26 113 252 210 128 .1 727 360 154 1,170 7.8 41 K! 303a ____ 36Fca __ Ind 518-912 W 6-14-61 18 58 13 80 182 82 98 .3 0.6 439 196 47 750 7.5 47 0.26 303b ___ 518-912 W 2- 1-66 15 61 15 80 186 80 107 451 212 60 810 7.5 45 ____ c! 304 _ 36Mad Ind 471-740 W 11- 1 65 IB 58 13 80 178 75 103 .4 433 196 50 761 7.6 47 S 306 16S/22E-27Pcb Dom u 23 159 45 175 464 208 205 1,050 580 200 1,740 7.4 35 > 307 28Kcc Dom 130 c 17 60 15 69 172 82 96 .4 425 212 71 719 7.6 42 308a ____ 28Paal __ Irr 120-143 c 8- 2-62 15 103 28 130 282 308 149 .8 ___ 925 372 141 1,410 7.4 51 ___ > 308b ____ 120-143 c 5-19-64 16 106 24 176 276 300 145 .7 ___ 906 362 136 1,420 7.4 51 ___ » 16S/22E-28Paa2 _ Dom <248 O, W(?) 27 50 15 68 192 57 80 .4 qno 184 26 675 7.7 M 310 28Rabl __ Dom qq qe u 8 00 cq 22 166 55 374 532 550 315 1,750 166 55 2,800 7.6 56 > 311 28Rab2 _ Dom 8 23 63 18 84 22 80 242 115 109 .4 298 100 1,030 7.7 37 28Rab3 _ Dom 117-132 c 1 25 65 18 71 25 94 214 150 106 .3 ___ 571 278 102 955 7.7 42 ___ > Irr » 313 29Jcc __ Ta 106-108 u 5- 6-65 21 190 40 294 378 562 272 .7 1,570 640 330 2,470 7.7 50 t i 315 SIBcc _ Ta 1221/2-1241/2 6 QQ fiK 22 132 39 173 276 412 148 .6 488 262 1,630 7.9 44 CS3 c O East sector >z 316a 2 ___ (C- 8-23)32dbc2 __ Dr 130-176 c 5-22-57 24 162 46 236 7.0 278 217 470 0.2 0.1 1,300 594 366 2,250 7.7 46 0.23 316b ___ 130-170 c 1- 2-62 23 203 60 280 257 258 628 _ 1,580 755 544 2,800 7.6 45 ___ > 316c ____ 130-170 c 5-25-62 22 219 53 288 258 244 655 .3 .4 1,610 765 554 2,760 7.4 45 .08 * 316d ____ 130-170 c 11-27-62 22 210 63 274 252 242 655 1,590 785 578 2,890 7.2 43 0 316e ___ 130-170 c 2- 4-63 19 210 62 271 252 233 652 _ 1,570 780 574 2,880 7.2 43 ____ 316f ____ 130-170 c 1-13-64 17 223 62 281 246 267 668 1,640 810 608 2,930 7.3 43 ____ o 316g ____ 130-170 c 2 5 65 21 228 67 302 244 283 715 1,740 845 645 3,070 7.4 44 ___ > 316h ____ 130-170 c 11- 3-67 20 242 72 331 248 325 765 _ 1,880 900 696 3,230 7.4 44 ___ fh 1 317 (C- 9-23)5cda2 _ Dr 121-143 c 2- 5-65 25 242 72 466 248 525 825 O OQ/1 900 696 3,700 7.6 53 "_ 318a ___ 5cdb __ Dr 120-184 c 1 2-62 26 196 80 460 141 512 832 2,180 820 705 3,660 7.8 55 ____ 0 318b ____ 120-184 c 5-25-62 26 241 73 462 248 488 845 ___ 2,260 900 697 3,680 7.4 53 .14 318c ____ 120-184 c 11-27-62 26 226 82 459 244 500 835 _ 2,250 900 700 3,810 7.3 53 ____ » 318d _ __ 120-184 c 2- 4-63 24 230 77 463 246 512 825 890 688 3,800 7.4 53 ___ 1z 1 318e ____ 120-184 c 1-13-64 23 234 79 440 240 488 825 9 91 rt 910 713 3,810 7.3 51 ___ > 318f ___ 120-184 c 3- 3-64 19 222 76 441 256 500 775 2,160 865 655 3,730 7.4 53 ____ 318g ___ 120-184 c 2- 5-65 26 226 74 476 240 538 815 2,280 870 673 3,760 7.4 54 ____ 319a ___ 17abcl __ Dr 130-170 c 1- 2-62 26 185 67 494 230 725 615 o 9qn 735 546 3,500 7.8 59 ___ 319b ___ 130-170 c 5-25-62 27 205 62 463 244 674 615 _ 2,170 765 565 3,380 7.5 57 .25 319c ____ 130-170 c 11-27-62 26 182 65 447 248 625 595 2,060 720 516 3,460 7.6 58 ___ 319d ___ 130-170 c 2- 4-63 24 172 62 455 242 625 585 2,040 685 486 3,430 7.4 59 ____ 319e ___ 130-170 c 22 175 59 471 244 700 550 680 480 3,280 7.4 60 ____ 319f ____ 130-170 c 2- 5-65 26 169 56 478 244 700 540 650 450 3,200 6.5 62 ___ 320a 2 _ 20bab __ Dr 132-192 c 5-22-57 26 155 50 402 5.9 247 432 584 .6 .6 1,780 592 390 2,910 8.0 59 ____ 320b _.__ 132-192 c 25 136 50 423 214 550 508 _ 1,800 545 370 2,830 7.8 63 ____ 320c ____ 132-192 c 5-25-62 26 162 59 379 258 494 525 .5 .4 1,770 645 434 2,820 7.7 56 .21 320d ____ 132-192 c 11-27-62 26 150 51 401 260 525 495 585 372 2,890 7.5 60 ____ h-i 320e _ .__ 132-192 c 2- 4-63 24 146 51 382 256 475 498 1,700 575 365 2,850 7.4 59 ___ M-i 320f ___ 132-192 c 1-13-64 20 145 48 335 258 500 472 _ 1,700 560 348 2,820 7.4 60 N> O See footnotes at end of taWe, Chemical analyses of ground water Continued tow Hardness o ~ as CaCOa) to « 3 01 S W 3 (micromhos°C)25at 8 Specificconductance "aJU w Analysis Well Use Depth of sample Aquifer I I a 1 (feet) s o> 6 Q a Percentsodium a 6 W Eli a 01 I a i M W 0 s I i 'o o Oia o ^ *° A S '§ 'ill'O QJ fx a 'S_3 PL, s03 '3_3 u C $ 1 Ido I S Na + K !S 1 S E fc S 3 Z, ft YUMA VALLEY SUBAREA Continued East sector Continued H Ed 320g _ __ (C- 9-23)17abcl __ 1 99 1 Q9 C 24 143 47 382 256 475 480 .. __ _ 1,680 550 340 2,790 7.6 60 321a ___ 20bdc __ Dr 95-167 C 23 121 41 305 248 400 365 .~_ _ __ 1,380 470 266 2,310 7.3 59 Ed 321b ___ 95-167 C n o /jrr 22 122 40 327 252 425 378 . __ __ 1,440 470 264 2,330 7.6 60 H 322a ___ 20cdd __ Dr 130-240 C, W 1- 2-62 26 125 46 396 183 525 472 . 500 350 2,630 7.8 63 05 322b ___ 130-240 C,W 5-25-62 25 155 40 366 249 464 465 0.6 0.4 1,640 550 346 2,610 7.5 59 ~0.23 O 322e ___ 130-240 C, W 25 140 43 362 252 450 452 . _ __ 1,600 525 318 2,650 7.5 60 a 322d ___ 130-240 O, W 23 143 41 353 246 450 442 .._ _ _ __ 1,580 525 324 2,650 7.4 59 Ed 322e ___ 130-240 C,W 19 136 41 353 250 462 420 .. _ _ _ 1,560 510 305 2,590 7.4 60 O 322f ____ c,w 2 5 65 24 132 41 353 256 450 418 . _ __ 1,550 500 290 2,560 7.6 61 M 323a ___ 20bbc __ Dr 148-212 c 2-17-64 21 108 35 273 220 145 478 .9 ___ 1,170 415 234 2,140 7.6 59 05 323b ___ 148-212 c 3- 6-64 22 109 33 269 216 125 472 .6 ___ 1,130 390 213 2,150 7.4 60 323c 148 212 c 4-30-64 24 114 37 299 222 200 492 .6 _ 1,280 436 254 2,270 7.4 60 323d ____ 148-212 c 2- 5-65 26 130 43 319 232 275 508 .._ _ _ 1,420 500 310 2,440 7.5 58 324a 2 __ 30cba2 _ Dr 140-203 c 11- 5-54 30 140 41 320 6.6 247 296 504 .6 ___ 1,460 520 318 2,440 8.0 57 ".20 F 324b _ _ 140-203 c 1 9 £9 24 139 49 387 208 388 578 .. _ __ 1,670 548 378 2,810 7.9 60 ".56 O 324e ___ 140-203 c 5-23-62 24 163 42 371 250 340 585 .4 .6 1,650 580 375 2,770 7.7 58 324d ___ o 23 150 48 355 252 312 575 .. _ __ 1,590 570 364 2,840 7.4 58 324e ___ 140-203 c 21 151 48 345 244 312 568 .- - _ _ 1,570 575 375 2,820 7.4 57 324f 140-203 c 1-13-64 19 150 48 352 240 338 558 .._ - - 1,580 570 373 2,790 7.2 57 Ed 324g ____ 140-203 c 2 5-65 22 151 47 375 240 350 585 .._ _ 1,650 570 373 2,770 7.4 59 o 325a ___ (C- 9-24)36caa __ Dr 145-220 c 1 3 62 25 160 59 416 178 325 752 . _ 1,830 640 494 3,220 7.8 59 ".54 o 325b ___ 145-220 c 5-25-62 25 193 56 414 258 311 760 .3 .6 1,890 710 498 3,210 7.6 56 2- 4-63 F 325c ____ 145-220 c 22 185 53 407 256 300 740 680 470 3,240 7.2 57 O 325d ___ 145-220 c 1 13 64 22 178 55 389 256 300 705 1 780 670 460 3,170 7.5 56 325e 1 A.*\ 99A c 2 5 65 24 177 56 408 252 317 725 - _ _ _ 1,830 670 464 3,140 7.6 57 326a 2 __ (C-10-24)12bcc2 __ Dr 150-178 c 3-21-57 26 143 47 290 5.9 223 174 605 .4 ___ 1,400 550 368 2,460 7.9 53 ".24 326b ___ 150-178 c 4-13-61 26 127 33 253 235 179 440 .3 .7 1,180 452 260 2,060 7.9 55 .35 O 326c ___ 150-178 c 1- 2-62 27 118 38 273 233 206 452 1,230 450 259 2,150 7.8 57 o 326d ___ c 25 115 40 240 236 150 442 1,130 420 256 2,110 7.5 54 326e ___ 150-178 c 2 4 63 24 116 39 238 234 150 438 1,120 448 256 2,110 7.5 54 326f ___ 150-178 c 1-13-64 22 122 36 246 232 190 425 1,160 452 262 2,120 7.4 54 326g ___ 150-178 c 2 5 65 26 116 39 266 230 208 442 450 262 2,110 7.6 56 M 327a ___ ISbddl __ Dr 142-185 c 27 118 36 307 231 238 478 1,320 444 254 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LQZH. VINHO^IIVO QNV VNOZIHV 'V3HV VHHA 3Hi ^0 H208 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

APPENDIX D. SELECTED PUMPING TESTS Selected pumping test data are shown in figures 50-54, markedly different from those necessary if the formula that inclusive. The data illustrates some of the problems that was used to compute the transmissivity is to yield valid arise when pumping tests are made under less than ideal results. conditions for determining representative transmissivity The recovery-of-water-level data following step 2 of the values. pumping test made the previous day could not be used to WELL 16S/23E-10Rcc, LCRP 23 TEST compute the transmissivity because the plotted data had a Figure 50 shows selected data for well 16S/23E-10Rcc, negative slope. The water level in the well attained its LCRP 23. Graphs A, B, C, and D show some of the data maximum recovery, which was the prepumping level, about obtained on January 21, 1965, during and following a step- \Vz minutes after pumping stopped. During the next 15 drawdown test. Graph E shows recovery data for strata at minutes the water level declined about 0.03 foot; about 10 much shallower depths than those tested in January. hours after, it had declined an additional 0.15 foot. Pertinent data for the January tests are as follows: The conditions responsible for these unusual water-level Method of drilling ______Cable tool. recoveries are unknown. It seeems possible that the surge Casing diameter ______12 inches. from the 680-foot column of water in the pump column Perforated interval ______634-694 feet. might be responsible for part of the unusual recovery pat­ tern, and, possibly, the elasticity of the aquifer might also Aquifer tested ______Bouse Formation conglomerate. Test conditions: be partly responsible. Te water in the zone tapped by the Pumped with turbine pump and gasoline engine. well has an artesian head about 3 feet above the water table. Graph B shows that practically all the yield was obtained Orifice installed at end of discharge pipe. Steady rate of discharge maintained by manually con­ from a 40-foot section of material between depths of 640 trolling valve in discharge pipe to maintain con­ and 680 feet, and that the rate of yield from the various stant head on orifice. strata was quite uniform. The lithologic log indicates that the March 20, 1965: material is predominantly conglomerate containing a 3-foot Step 1 of test consisted of pumping well at interbed of clay or mudstone between depths of 656 and steady rate of 423 gpm for 45 minutes. 659 feet. (See appendix B.) The rate of yield from the Step 2 consisted of pumping well at steady conglomerate as computed from the test data is about 30 rate of 847 gpm for 45 minutes. gpm per foot of thickness, and the formation head loss as March 21, 1965: shown in graph A is about 5 feet. On this basis, the average Step 3 consisted of pumping well at steady hydraulic conductivity is almost 9,000 gallons per day per rate of 1,235 gpm for 2 hours after comple­ square foot, which is comparable to the known maximum tion of step 2. hydraulic conductivity of Colorado River gravel of compar­ able thickness in the Yuma area. Some secondary porosity, DISCUSSION OF TEST DATA therefore, is indicated because elsewhere the hydraulic con­ The specific capacity data in graph A shows that head ductivity of similar conglomerate is generally much less. losses in the well are substantial at moderate rates of Secondary porosity may be indicated by the manner in pumping. The separation of observed drawdown into com­ which the well developed. Although the well pumped very ponents of drawdown due to loss of head in the formations little sand, it never yielded clear water during the 8 hours tapped by the well and drawdown due to well construction it was pumped. The water was always milky or whitish. Ex­ and friction losses was made on the basis of the extrapola­ amination of the residue of a sample of water by means of a tion of the straight-line plot shown in the lower part of 30-power binocular microscope showed the very fine residue graph A to its intersection with the ordinate of zero dis­ to be rock of probable granitic origin. When subjected to charge. The intersection at 0.004 foot of drawdown per hydrochloric acid only a mild effervescence was observed. gallon per minute of yield is equivalent to 250 gallons per Thus, some development of the aquifer probably persisted minute per foot of drawdown, which is the slope of the throughout the tests. line shown in the upper part of graph A, which separates On the basis of the hydraulic conductivity of almost 9,000 the drawdown into the two components. gallons per day per square foot and the thickness of 40 From Theis, Brown, and Meyer (1963, p. 333), it is esti­ feet, the transmissivity of the conglomerate is about mated that for the conditions of this test the transmissivity 360,000 gallons per day per foot, rather than the 5 million should be about 1,500 times the specific capacity, or almost gallons per day per foot computed from the recovery data 400,000 gpd per foot. This value is 50 percent more than shown in graph D. that obtained by using drawdown data of step 3 to compute Graph E is recovery data for a pumping test to deter­ transmissivity. Drawdown data during steps 1 and 2 were mine the transmissivity of the coarse-gravel and wedge not suitable for analysis because they showed no consistent zones, from a depth of 120 feet to 548 feet. This test was downward trend. made April 6, 1965, after the well had been perforated The transmissivity computed on the basis of recovery with a Mills knife in the above interval and plugged to a data shown in graph D is unreasonably large, perhaps 5-10 depth of about 550 feet. Considerable difficulty was experi­ times too large. The pattern of the recovery data from enced in developing the well. The well tended to sand in, about 2 minutes after pumping stopped to 40 minutes after and eventually caving occurred at the land surface. Several pumping stopped is very near the theoretical pattern, and tens of cubic yards of gravel were dropped into the caved were this the only data available, one might consider the area before the formations adjacent to the well were stabil­ value to be fairly reliable. However, the water level began ized. Some sort of gravel pack thereby resulted, at least to drop after 40 minutes, which shows conditions were in the upper part of the well. On April 6, a 5-inch diameter AS /AQ«, IN FEET PER GALLONS 3 B WATER LEVEL, IN FEET BELOW DEPTH BELOW LAND SURFACE, IN FEET PER MINUTE s' LAND SURFACE DRAWDOWN (S), IN FEET

OS CT O * *. H> M « ^ ! m :i P"

cW Q

^ P

,». &

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B. 9*

h-. cr w *to s? r> WATER LEVEL, IN FEET BELOW LAND SURFACE WATER LEVEL, IN FEET BELOW LAND SURFACE S 2 (3 E !» ^ P n> 3. 3 e-ff 3 3

p S7 fi2. 1? s- 3 P * 2 o* o

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->"»«! El 8. § H210 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA mum value, and is less than the drawdown on any of the while the well was being pumped at the rate of 250 gpm water-yielding strata except the uppermost. Granting that indicates a maximum value of 335 gpm per foot of draw­ the specific capacity for computing transmissivity would be down as the specific capacity. Recognizing that this value less than the above figure, the transmissivity computed is larger than the value that would be valid for computing from the recovery data appears reasonable. The drawdown transmissivity on the basis of specific capacity, it appears data obtained during the test were not consistent enough that the transmissivity of 400,000 gpd per foot computed for computing transmissivity. on the basis of rate of recovery of water level shown in The oscillations of water-level that were measurable for graph C is a reasonable value. at least 5 minutes after pumping stopped probably are due The specific-capacity data in graph A imply specific capac­ in large part to the imbalance between the head in the ities much less than the 330 gpm per foot that was com­ 500-foot long column of water inside the eductor pipe and puted for the airlift pumping test of March 11, 1965. Some­ the head in the hollow cylinder of water of comparable what lower specific capacities are to be expected as the length between the eductor pipe and the casing that per­ discharge rates increase, because for any part of the system sisted after pumping stopped. in which turbulent flow exists, (and this type of flow occurs in the vicinity of the perforations even at rather low rates WELL 16S/22E-29Gca2 LCRP 26 TEST of yield), the loss of head increases at a faster rate than Figure 51 shows selected pumping-test data for well the yield. This increase in rate of drawdown with yield is 16S/22E-29Gca2, LCRP 26. The graphs are of the same shown by the increasing slope of the line through steps 1, general nature as those for well LCRP 23 which were ex­ 2, and 3, as contrasted with the line of uniform slope which plained in the preceding section. separates the drawdown into components of formation head Pertinent information regarding the well and the tests is loss and wellhead loss. However, at comparable yields one as follows: ordinarily expects comparable specific capacities. Method of drilling ___Mud rotary. The reasons for the large differences in specific capacity Casing record ______12-inch diameter from land surface at comparable rates of discharge between the two tests are to depth of 121 feet; 12- to 8-inch not all known. A small part of the differences may be due reducer, 121 to 124 feet; 8-inch to errors in measurements of yields or drawdown. Also, diameter, 124 to 1,765 feet. part of the differences are due to differences in the pumping Horizontal-louver type perforations equipment. The measurement of drawdown in the annular between depths of 124 and 1,105 space between the eductor pipe and the casing as made for feet; and between 1,345 and 1,765 the airlift pumping test excludes all internal well losses, feet. Gravel packed from land sur­ whereas the measurement of drawdown in the annular space face to depth of 1,105 feet. between the pump column and the well casing as made for Aquifers tested ____-Coarse-gravel zone; wedge zone; non- the test using a turbine pump includes all internal well marine sedimentary rocks. losses. Furthermore, the distribution of drawdown along Test conditions: the perforated sections of casing is different for the two March 11, 1965: Recovery period followed 2 hours of tests. When the well was pumped by the airlift method, continuous pumping at rate of 250 gpm at end of a the maximum drawdown opposite the perforated sections 90-hour intermittent period of developing the well by of the casing occurred near the bottom of the sections at the airlift-pressuring method. The 5-inch diameter a depth of 1,740 feet, whereas when the turbine pump was eductor pipe was set 1,740 feet below land surface, and used, the maximum drawdown occurred near the top of the drawdown was measured in the annular space between perforated section at a depth of 124 feet. It is also possible the well casing and the eductor pipe. that the well sanded in below a depth of 1,100 feet between April 13, 1965: The well was pumped by means of a the times of the two tests. turbine pump and gasoline engine. An orifice was in­ The transmissivity of 550,000 gpd per foot shown in stalled on the end of the discharge pipe. A steady graph B, which was computed on the basis of recovery data, rate of discharge was maintained by manually con­ appears somewhat high, although not unreasonably so, if a trolling a valve in the discharge line to maintain a formation specific capacity of about 200 gpd per foot is constant head on the orifice. Drawdown was meas­ accepted as a valid value. The transmissivity computed ured in the annular space between the pump column on the basis of recovery data, following the test in which and the well casing. Step 1 consisted of pumping the the turbine pump was used, is only slightly higher than the well at a uniform rate of 380 gpm for 2 hours; step transmissivity computed on the basis of recovery data fol­ 2 of pumping at a uniform rate of 715 gpm for 2 lowing the test for which the airlift method was used. hours, 30 minutes; step 3 of pumping at a uniform Graph D shows that either the permeability of the strata rate of 1,100 gpm for 1 hour, 30 minutes; and step below a depth of 730 feet is very low relative to the average 4 of pumping at a uniform rate of 1,365 gpm for 2 permeability above that depth or these lower strata were hours, 40 minutes. not developed (cleared of drilling mud). The graph also DISCUSSION OF TEST DATA shows that particular strata within the zone of average The recovery data obtained on March 11, 1965 (graph higher permeability differ greatly in permeability (or possi­ C), shows surging, which also was noted in well LCRP 23. bly in degree of development), some strata apparently being This phenomenon seems to be characteristic of recovery data practically impermeable (or undeveloped) and others being following the airlift method of pumping when the recovery very permeable (or well developed). The latter evidently measurements show the changes in water level in one long occur at depths of about 390, 450, and 530 feet. A compari­ column of water that is freely connected with another of son of the relative permeabilities as indicated by the current- comparable length. The drawdown of only 0.75 of a foot meter survey shown in graph D with relative permeabilities GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H211

DISCHARGE (Q), IN GALLONS PER MINUTE 200 400 600 800 1000 1200 1400 100 Top of perforated section of casing

200 -

300 -

12 400 Step 4 0.014 A 0.012 Specific capacity data 500 Apr. 13,1965 0.010 _ Qfz < 9 0.008 600

0.006

0.004 700 400 800 1200 1600 2000 2400 2800 o #( -!)+Q»,IN GALLONS PER MINUTE

I I I TTT 800 13.8 T= 264 (1385) 0.67 = 550,000 gpd per ft 900 14.2 D Yield data B 1000 Apr. 13,1965 14.6 Recovery data Apr. 13,1965

1100 15.0 10 100 TIME, IN MINUTES, AFTER PUMPING STOPPED 1200 12.0 300 600 900 1200 1500

YIELD, IN GALLONS PER MINUTE

12.2

3 12.4 C j _ Recovery data II Mar. 11,1965 12.6

12.8 i i i i i i i 0.1 1 10 40

TIME, IN MINUTES, AFTER PUMPING STOPPED

FIGURE 51. Pumping test data for well 16S/22E-29Gca2 (LCRP 26). suggested by the lithologic logs (appendix B) shows sub­ cated by the current-meter survey substantially exceeds that stantial differences for some strata, although in general the indicated by the lithologic log, the log probably is in error. relative permeabilities indicated by the two methods agree WELL (C-9-22)28cbbl, LCRP 25 TEST quite well. In the few places where the permeability indi­ Figure 52 shows selected test data for well (C-9-22) H212 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

DISCHARGE (Q), IN GALLONS PER MINUTE

100 200 300 400 500 600 700 800

Top of perforated section of casing 900

1000

Step 3 12 Specific capacity data 1100 IL 0.03 Jan. 19,1965 "-UJ 00z £MI z 3 = 0.02 1200 0.01 o.oo 200 400 600 800 1000 1200 1400 E 1300 IN GALLONS PER MINUTE

54 s woo

Z 55cc 1500 B Recovery data Jan. 18,1965 1600

57 4 8 12 16 20 24 28 1700 TIME, IN MINUTES, AFTER PUMPING STOPPED

1800 E Yield data 54 Jan. 19,1965 1900 C 55 Recovery data Casing filled with sand below this depth Jan. 19,1965 2000 Lower limit of perforated section

56 4 8 12 16 20 24 28 TIME, IN MINUTES, AFTER PUMPING STOPPED 2100 100 200 300 400 500 600 53 YIELD, IN GALLONS PER MINUTE

54

u_ 55 o D Recovery data 56 Jan. 19,1965

57 i 10 100 TIME, IN MINUTES, AFTER PUMPING STOPPED GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H213

52

Nonpumping level 54

56 Q=206 gpm Step-drawdown and recovery data Jan. 19,1965

? 58

Q=412 gpm 60

62

64 Q= 595 gpm

66 700 800 900 1000 1100 1200 1300 1400 1430 HOUR OF DAY

FIGURE 52. Pumping test data for well (C-9-22)28cbbl (LCRP 28).

28 cbbl (LCRP 25). Pertinent information for the well and Graph C shows recovery data following the step-draw­ tests is as follows: down test shown in Graph F. Method of drilling ___Mud rotary. The period of virtually no recovery is 2 minutes to 6 Casing record ______12-inch diameter blank casing from minutes after pumping stopped. The failure of the latter land surface to depth of 320 feet; recovery data to follow the theoretical pattern, is shown by 8-inch blank casing from 320 to graph D. Theoretically, the recovery data should plot very 862 feet; 8-inch horizontal louver- nearly as a straight line sloping upward to the right. type casing from 862 to 2,002 feet. The reasons for the interruptions in recovery that were Drilled hole, 16-inch diameter, observed are not fully understood. A possible explanation gravel packed from 2,002 feet to is that there is considerable movement of water from deep land surface. strata to shallower strata when pumping is stopped. This Aquifer tested: Wedge zone. is probable because when pumping is in progress, the draw­ Test conditions: down in the deep strata is less than the drawdown in the Pumped with turbine pump and gasoline engine; pump shallower strata because of friction losses within the well. bowls 100 feet below land surface; orifice installed at When pumping is stopped the friction losses within the end of discharge pipe; steady rate of discharge main­ well virtually cease and thus water from the strata that tained by manually controlling valve in discharge had the lesser drawdown will flow to strata where the pipe to maintain constant head on orifice; deep-well drawdown was greater until the drawdown in both are current meter installed below pump. equal, after which recovery in both will proceed at a uni­ January 18, 1965: form rate. Further developed well with turbine pump after Evidence that this internal movement was occurring dur­ well had previously been developed by airlift ing the recovery period shown in graph B are the observa­ method; developed for 2 hours and then made tions of rate of flow through the deep-well current meter recovery measurements. that was suspended in the well at a depth of 1,000 feet. January 19, 1965: This depth is near the bottom of the better-than-average Using same equipment as on preceding day made water yielding zone near the upper part of the perforated a step-drawdown and recovery test. Also made a section of casing (graph E). The current meter indicated rate of flow survey during the test. an upward flow of at least 60 gpm during the early part DISCUSSION OF TEST DATA of the period of non-rising water level. This rate gradually Graph B shows recovery data following a 2-hour pump­ lessened to about 30 gpm 10 minutes after pumping stopped, ing period, the last hour of which the rate was kept fairly and ultimately became less than that needed to actuate the constant at about 700 gpm. The pattern of the recovery meter. data is unusual in that after an initial recovery period of Graph F illustrates still another anomaly. The water level 3 minutes, recovery ceased for the next 6 minutes, but then is lowest in the well immediately after an increase in the resumed at a rate that appeared to be fairly normal and pumping rate and then recovers to a high stage for the which resulted in a rise of 2 feet in 15 minutes. pumping rate within a 10- to 20-minute period.

507-243 O - 74 - 15 H214 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

The reason for this phenomenon is not fully understood thick clay beds, but that it is only fair for beds logged as but it is probably due to a change in the distribution of sand or gravel. This" lack of good correlation for sand and drawdown with time along the 1,100-foot length of perforated gravel strata may indicate either that the borehole geo­ casing following a sudden increase in pumping rate. physical logs are not dependable guides as to the permeability Graph E shows the cumulative yield from strata below a of sand and gravel strata, or more likely, that some of the given depth when the well was being pumped at the rate permeable sand and gravel strata were still sealed with of 585 gpm. The rate of yield from strata between specific drilling mud and therefore were not yielding water. depths is easily computed by dividing the difference in yield Further development work confined to particular strata between the given depths by the difference in the depths. by the use of packers and use of chemicals to break down It is seen that strata below 1,900 feet yield a relative drilling mud would determine which of the above inferences small percentage of the total discharge; that between 1,900 is more nearly correct. and 1,300 feet the yield per unit thickness of strata gen­ Graph A indicates that when well losses are excluded, the erally increases; that between 1,300 and 1,050 feet the yield specific capacity is about 100 gpd per foot. The specific is much less, with some strata apparently yielding no water; capacity is considered to be the most useful value of all and that from 1,050 to about 920 feet, the yield per unit the pumping-test data for computing the transmissivity of thickness is as high as, if not higher than anywhere in the the water-bearing material tapped by the well. entire section. WELL (C-10-25)35bbd LCRP 17 TEST A comparison of the yield data graph with the borehole Figure 53 shows selected test data for well (C-10-25) gephysical logs shows that the correlation is good1 for rather 35bbd (LCRP 17).

14.1 500 Top of perforation 14.2 section of casing

600

14.4

700

? 14.6

A 800 14.8 Recovery data Mar. 28,1964 900

1000

15.2

1100

15.4 c Yield data 15.5 1200 Apr. 21,1964 o 12 16 20 24 28 32 36 40 TIME, IN MINUTES, AFTER PUMPING STOPPED

14.2 1300

=264 (388) 0.64 14.4 1400 = 160,000 gpd per ft

14.6 1500 B 0 20 40 60 80 100 Recovery data YIELD, IN PERCENT it! 14.8 Mar. 28,1964

15.0 10 100

TIME, IN MINUTES, AFTER PUMPING STOPPED FIGURE 53. Pumping test data for well (C-10-25)35bbd (LCRP 17). GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H215

Pertinent information regarding the well and tests is tions were less thrn 1 inch; after which they began to as follows: increase and reached the full-scale deflection 16 minutes Method of drilling ___Mud rotary. after observations began. Other near-full-scale deflections Casing record ______18-inch diameter blank casing from were noted 21, 31, 33, 35, 36, 38, 41, 47, and 50 minutes land surface to depth of 300 feet; after observations began. Less than one-half inch deflections 8-inch blank casing, from 270 to generally were observed between the above times. From 520 feet; 8-inch horizontal-louver about 37 to 53 minutes the deflections tended to stay in the casing from 520 to 1,398 feet; 8-inch neighborhood of 2 inches. Observations were discontinued diameter blank casing 1,398 to after 53 minutes. The tendency of the deflections to center 1,438 feet; 8-inch diameter screen about a value of 2 inches suggests that after equilibrium from 1,438 to 2,000 feet. Drilled was attained some vertical movement of water at a uniform hole, 15-inch diameter, gravel rate probably occurred at the depth of 590 feet. packed from 300 to 2,000 feet. The apparently erratic pattern of the deflections suggests Test conditions: that water was moving through the meter at varying rates March 28, 1964: which probably resulted from imparting an oscillatory The well was pumped by the air-lift method. A movement to the 500-foot long column of water in the 4-inch diameter eductor pipe extended to a depth casing above the uppermost perforations and to a column of of 1,420 feet below land surface. A packer to water of unknown length inside the casing below the upper­ prevent upward movement of water from strata most perforations as the meter was lowered to the 590-foot below a depth of 1,398 feet was set in the sec­ depth. The rest of the oscillatory system presumably is tion of blank casing 10 feet below the eductor water that was going into or coming from some of the pipe. After an initial period of development of strata that were tapped by the well. the well, the well was pumped at the rate of Water levels corresponding to the means of the oscilla­ 388 gpm for a 4-hour period. Pumping was then tions shown in graph A are plotted in graph B. Some of stopped and the recovery measurements shown the higher than theoretical values of water levels that oc­ on graphs A and B were made. curred during the first 6 minutes of the recovery period April 21, 1964. may have been due to leakage of water from the pump A centrifugal pump was used to pump the well at suction hose to the well. The value of about 160,000 gpd the rate of about 165 gpm for a 2-hour period. per foot for the transmissivity appears to be reasonable, During the pumping period a survey of the rate although not necessarily precise. of upward movement of water within the well The yield data in graph C shows that about 80 percent was made by means of a heat flow velocity meter of the water was derived from strata between depths of furnished and operated by the Hydrologic Equip­ 520 and 620 feet and that only 10 percent was yielded by ment Laboratory of the U.S. Geological Survey, strata below a depth of 900 feet. An average hydraulic Denver, Colo. conductivity of about 1,400 gpd per square foot is indi­ DISCUSSION OF TEST DATA cated for the strata between depths of 520 and 620 feet if The oscillations of water level that are shown on graph A the value of 160,000 gpd per foot is accepted as a reason­ persisted longer than observed oscillations at any other site. able indication of the transmissivity of all the strata tapped Most of the same explanations that were postulated for by the well. oscillations noted at wells LCRP 23 and 26 are probably valid for well LCRP 17. However, the movement of water WELL (C-ll-24)23bcb LCRP 10 TEST into and out of the formations tapped by the well may be Figure 54 shows selected data for well (C-ll-24)23bcb more significant at this site than at the other test sites. (LCRP 10). Support for this probability is offered by the observations Pertinent information regarding the well and the tests made on May 5, 1964. On that date the thermal velocity from which the data in figure 54 were obtained are as meter was lowered to a depth of 590 feet. An annular follows: plate had been attached to the meter so as to limit most Method of drilling _Scow and cable tool. of any movement of water within well casing to a path Casing record ______16-inch diameter steel casing, land through the meter, thereby causing the meter to respond surface to depth of 240 feet; 12-inch to very slow movements of water within the 8-inch casing. diameter casing from 220 to 1,055 The lowering of the meter to the depth of 590 feet was feet; horizontal-louver perforations accomplished over a period of more than an hour. made in place at following depth The meter was being used in an attempt to determine if intervals in feet below land surface: there was any movement of water in the well at the depth 165-170; 190-202; 213-220; 240- of 590 feet under non-pumping conditions. Movement of 250; 280-305; 320-325; 375-395; water in either direction through the meter was indicated 405-425; 475-500; 520-545; 630- on a chart by the trace of a pen, whose deflections increased 635; 643-648; 685-705; 855-875; from zero for no flow to a limit of 4 inches as the rate of 985-1,002. flow through the meter increased. For a period of 53 minutes Test conditions: after observations began, the pen continued to move in an February 26, 1963, to March 1, 1963: apparently erratic manner, throughout the 4-inch wide Pneumatic packers were used to isolate the perfo­ range. Much of the pattern, especially during the first 7 rated intervals shown in figure 54. The packers minutes suggested alternate times of zero and maximum were placed in position by means of string of flow through the meter; from 9 until 13 minutes, the deflec­ 4-inch pipe which also functioned as the eductor H216 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AEEA

Yield Drawdown Specific Permeability (gpm) (ft) capacity (gpd per (gpm per ft ) ft) 78.8 100

264 (2500) 1 1 60 3600 V 80 1.4 79.0 0.9 200 31 | -730,000 gpd per ft 1 33 1190 J > 105 3.2 ' ~* 79.2 300 1T J I/ Blank casing

^^Perforated 79.4 400 3 section of casing Interval J -i tested 10 570 > 100 10.0 3 Zl 79.6 A 500 T J Recovery data Apr. 11,1963 1 79.8 600 \ 31

3.7 265 80.0 700 _ j> 80.0 22.0 ] 3 _ o.i i 10 100 TIME, IN MINUTES, AFTER PUMPING STOPPED

800

4.6 332 ] \ 90 19.5 ] D 900

7.5 635 1000 _ ^> 91 12.0 i _ J D ^ Data obtained with packers Feb. 26-Mar. 1, 1963 1100

FIGURE 64. Pumping test data for well (C-ll-24)23bcb (LCRP 10).

pipe for the airlift method that was used for Graph B shows that the permeability of the deposits de­ developing and pumping the well. Water levels creases rapidly with depth. The deposits between depths of were measured inside a string of %-inch pipe about 165 and 220 feet have a hydraulic conductivity of whose lower end extended 21 feet below the about 3,600 gpd per square foot, whereas, those that were 1%-inch pipe through which the air was intro­ tested between depths of 240 and 325 feet had an average duced, both pipes being inside the 4-inch eductor hydraulic conductivity of almost 1,200 gpd per square foot. pipe. At greater depths the hydraulic conductivity is considerably April 10, 11, 1963: less, ranging from 265 to 635 gpd per square foot. On the A turbine pump was used for this test. The well basis of specific capacity, it might be expected that strata was pumped for 9% hours at varying rates to above a depth of 325 feet (the coarse-gravel zone) will pro­ develop the well and then pumped steadily at vide about three-fourths of the total yield from all the 2,500 gpm for 8 hours prior to the recovery test strata that were tested. shown in graph A. Discussion of test data: APPENDIX E. MOISTURE INVESTIGATIONS Graph A shows that during the first 2 minutes of the recovery period water levels were influenced considerably by One of the major items of the water budget for the Yuma the return flow of water from the pump column. After this area appeared to be the water that went into storage beneath initial period the recovery data followed the theoretical pat­ the Yuma Mesa and Yuma Desert ("Upper Mesa" and "For- tern quite well. The reliability of the transmissivity com­ tuna Plain"). It was desirable, therefore, to ascertain as puted from the data is considered good. closely as practical how much water was represented by a GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H217

given increase in volume of saturated material. The latter This objective was never fully realized because of the could be computed on the basis of the rise of water levels caving of material, the removal of material beyond that in observation wells which had been recorded periodically needed to obtain a skintight fit between the drilled hole and by the U.S. Bureau of Reclamation. Pumping tests did not the tubing, or the migration of moisture from the position appear to be a practical means for obtaining estimates of it occupied at the time drilling began. The principal advan­ storage coefficients. There were only a few wells that possibly tage of this method of constructing access holes is that holes would have been suitable for pumping tests, and then only can be drilled to greater depths in unsaturated material than after observation wells were drilled at each site. Further, it is practical either by augering by hand or by driving the was thought that the storage coefficient computed from a casing. pumping test would be too low, because the coefficient com­ During the latter part of the study, the access holes were puted from the pumping test would be no larger than the constructed by driving a length of steel tubing (1.75 inches drainage during the pumping test, whereas, the water table outside diameter, 1.62 inches inside diameter) to depths of of the mound was rising through material whose moisture as much as 16 feet. Portable steel scaffolding was used to content was no more than the residual after long-term drain­ enable two men to place a gasoline operated mechanical age and possibly considerably less. It was concluded that a hammer atop the steel tubing and drive it to the required more reliable estimate of the storage coefficient under water- depth. After the tubing was cleared of the material that table conditions could be obtained by determining the average commonly became packed in the first few feet of the tubing moisture content of material below the water table and sub­ a rubber stopper device was installed near the lower end tracting therefrom the average moisture content of material and made water tight. All water was then bailed from the above the capillary fringe. A neutron moisture probe to­ tubing. The above method was relatively rapid and probably gether with access tubes appeared to be a practical means resulted in truer indications of moisture content than could for obtaining the moisture content both above and below be obtained by the air drilling method. Under certain con­ the water table. The sites for access holes in which moisture ditions somewhat more reliable results can be obtained by content was to be determined were selected with the view augering material from inside the tubing as it is advanced. of obtaining representative values for clay, silt, and sand, However, the improvement in reliability probably will not and various combinations of these materials. A comparable be substantial enough on the average to warrant the con­ study was made for Imperial, Palo Verde, and Parker Val­ struction of access holes by the more time-consuming hand- leys. The results of the studies for the above valleys are augering method. given in other chapters of U.S. Geological Survey Profes­ Several field tests were made to determine to what extent sional Paper 486. In general, the results in the other areas and under what conditions access holes constructed by the substantiate the results in the Yuma area. hand-augering method gave different counts per minute The probe used in the soil-moisture studies consisted of a from those constructed by the driven tubing method; also 5-millicurie fast neutron source, a slow neutron detector to what extent the counts per minute for the air-drill tube, and a transistorized amplifier circuit. The number of aluminum-tubing holes differed from those for the driven- fast neutrons that were converted to slow neutrons and steel tubing holes. The tests suggested that the counts per picked up by the detector depended primarily on the number minute in driven-steel tubing holes was about 400 less adja­ of hydrogen atoms in the material surrounding the probe. cent to saturated silt and clay than in steel tubing holes in The number of hydrogen atoms in inorganic material in which the material had been removed by hand auger as the turn, was largely a function of the free water in the ma­ tubing was advanced. In saturated sand, the counts per terial. Thus, when the probe was surrounded by inorganic minute in the driven-steel tubing holes was about 200 less material, as it was during the soil-moisture determination than in the holes in which they had been installed by the studies, the rate at which the detector picked up slow neu­ hand augering method. trons was a function of the water content of the material Differences in counts per minute in the zone of saturation surrounding the probe. When the relation between pick-up between holes of the air-drill aluminum-tubing type and those rate by the detector, commonly referred to as the counting of the driven-steel tubing type were checked at three sites. rate, and water content of material surrounding the probe At site (C-8-23)22ddc the counts per minute in the alu­ had been determined, the water content of the surrounding minum tubing exceeded those at comparable depths in a material could be computed from the observed counting nearby driven-steel tubing by 500 to 1,000, but at sites rate. (C-9-24)18cdd and (C-9-25)35dcd the differences in counts The counting rate was registered visually by the glow of per minute between the two types of access holes were five decade counters. Determining the relationship between negligible. counting rate and moisture content for the various types of Although the foregoing results suggest that counts per materials and for specific types of access tubes posed many minute in the zone of saturation in access holes of the problems. air-drill aluminum-tubing type may exceed those in holes The first access holes were drilled with an air drill that of the driven-steel tubing type, the average indicated differ­ could remove cuttings either by vacuum, air pressure, or ence of about 250 counts per minute (equivalent to some­ with slight modification, by circulating water or mud. As what less than 2 percent moisture) did not appear to be the drilling progressed the holes were cased with 2-inch large enough in view of all the other uncertainties relative outside-diameter and 1.75-inch inside-diameter aluminum to the relation between counts per minute and moisture con­ tubing. The objective was to obtain an access hole in which tent to justify separate rating curves for the two types of the moisture content of the material within a foot or so of access holes. the hole at any particular depth was a function of the After trying several different methods for obtaining a moisture content of the material at that depth before the rating curve for the neutron moisture probe it was decided hole was drilled. that the most practical method consisted of obtaining counts H218 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

per minute with the probe in place in the access tube in 60 the field and then averaging the moisture content of several samples obtained from a depth near the center of a zone 2 or more feet thick in which the counts per minute were nearly constant. 50 The relation between counts per minute and moisture content for material having a moisture content of about 10 per cent or less was relatively easy to establish because the moisture content of the sample that was sent to the 40 laboratory for determination of moisture content was likely to be the same as the moisture content at the depth from which the sample was collected. Relating counts per minute to moisture content for mois­ 30 ture contents between relatively dry values and values for the zone of saturation was impractical. In this interval, there was no way of knowing to what extent water had migrated from the sample as it was being collected. In clay soils the migration undoubtedly was much less than in sand, 20 - but the migration still was a problem. The rating curve in this intermediate interval thus had to be estimated on the basis .of the relationships for relatively dry materials and those for saturated material. The latter were determined 10 on the assumption that the counts per minute were a func­ tion of the porosity of the material, which in turn was a function of the apparent specific gravity of the material and its absolute density. Twenty-five samples of material ranging from sand to 2461 10 clay that were thought to be representative of the bulk of THOUSAND COUNTS PER MINUTE the material in which water-level fluctuations occur in the lower Colorado River valley were analyzed by the Geological FIGURE 55. Relation between counts per minute and moisture content. Survey Hydrologic Laboratory, Denver, Colo. average count per minute in the zone of saturation. As The absolute specific gravity of these samples ranged from stated previously, it was found during the calibration pro­ 2.66 for a sandy loam in Imperial Valley to 2.81 for a dark cedure work that the average count per minute in silt or brown clay loam in the Palo Verde Valley. clay was several hundred to a thousand higher than in sand. Fourteen samples classified as sand had absolute specific It was also found that the counts per minute in the zone of gravities that ranged between 2.66 and 2.70 and averaged saturation tended to be less in holes constructed by driving 2.68. Five samples classified as silt had values that ranged steel casing than for those constructed with the air drill from 2.69 to 2.75 and averaged 2.72. Six samples classified or by hand auger. as clay or clayey silt had values that ranged from 2.72 to A combination of these factors may have caused the counts 2.81 and averaged 2.76. Thus it appears that the absolute per minute in the zone of saturation for the access holes on density increased as the particle size decreased. It also Yuma Mesa to average almost a thousand counts per minute appears that the absolute density of a sample of a given less than the average maximum count per minute for access particle size is predictable within about 1 percent for sand, holes in the South Gila and Yuma Valleys. 1% percent for silt and 2 percent for clay. It was con­ Using the data shown in figures 56-58 and the rating cluded therefore that using the volume of the sample as table, average moisture content^ both below and above the computed in the field, its oven-dry weight, and the average capillary fringe were computed where the data was con­ absolute density of the material was a better basis for sidered adequate to give meaningful values. Table 21 lists determining its porosity, and hence moisture content when the pertinent data for each of the access holes and segre­ saturated, than was its volume and its loss of weight when gates them according to location. The average capacity for oven dried. storage is seen to vary quite widely between the three The values of the rating curve for the higher percentages subareas, from a minimum of about 28 percent for the of moisture versus counts per minute that were adopted for access holes on Yuma Mesa, to 37 .percent for the holes in use in the present study are based on computations using the South Gila Valley, to about 42 percent for the holes average absolute density values for different types of ma­ in the Yuma Valley. terial. Figure 55 shows the rating curve that was used for Undoubtedly the higher percentages for storage capaci­ the present study to determine the average moisture con­ ties in the flood-plain valleys are related to the larger per­ tent of all material penetrated by access tubes. centages of fine-grained material in the flood plain. Figures 56-58 show the counts per minute observed at Although the moisture studies made during this investi­ various depths at the individual sites. gation are neither precise nor as adequate as desirable they The profiles show that at some sites the capillary fringe is do provide a basis for estimating storage capacity under thin, less than a foot, whereas at other sites it may be certain given conditions. In particular, they show that in 8 feet or more thick. The thin fringes indicate relatively desert areas the moisture content of alluvium above the clean sand, whereas the thick fringes are associated with capillary fringe is only a few percent of the volume occu­ fine silt and clay. There are also differences in the maximum pied by the material. Therefore, the storage capacity during GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H219

an initial rise of water levels is principally a function of for the lower Yuma Mesa was used. Originally a value of the porosity of the material less a few percent for the 35 percent about midway between values for the Mesa moisture that already is present. A more economical means and the Valleys was selected for analog model studies for determining the porosity of alluvium in place at depths because the access holes were thought to have penetrated a beyond 10 feet than is presently available would increase a larger percentage of sand and a lesser percentage of silt the practicability of the above method for determining stor­ and clay than the average percentages of these materials age characteristics. that occur beneath the mesa. However, the analog model In computing quantities of water that have gone into studies indicated that the correlation between model response storage during the build up of the ground-water mound and observed changes in water level was better when the beneath Yuma Mesa a storage coefficient of 31 percent storage coefficient was modeled as 31 percent rather than rather than the 28 percent indicated by the access-hole data 35 percent.

TABLE 21. Moisture content and storage capacity of allu­ vium as indicated by neutron moisture probe study. All quantities in percentage by volume

Average moisture content Storage Location Below water Above capillary capacity table fringe South Gila Valley (C-8-21)21bca ____ 33.0 6.0 27.0 (C-8-22)22bbb ____ 45.0 4.0 41.0 (C-8-22)31cbb ____ 48.0 (C-8-22)33daa ____ 36.5 9.0 27.5 (C-8-23)22ddc ____ 45.5 15.0 30.5 (C-8-23)25ccc ____ 10.0 (C-8-23)27cad ____ 40.0 4.0 36.0 (C-8-23)36bcc ____ 47.5 5.5 42.0 (C-9-22)6aad ____ 50.0 5.0 45.0 16/22E-36B ______47.5 4.0 43.5 Average ____ 43.7 6.9 36.6

Yuma Valley (C-9-24)18cdd ____ 44.0 2.5 41.5 (C-9-25)25bad ____ 49.0 3.0 46.0 (C-9-25)26ddd ___ 43.0 4.0 39.0 (C-9-25)35dcd ___ 47.5 5.5 42.0 (C-9-25)36ddd ____ 53.0 (C-10-25)2dcd ____ 51.0 4.0 47.0 Average ___ 47.9 3.8 42.6

Yuma Mesa (C-9-23)27cbb ____ 34.0 (C-9-23)28aaa ___ 34.0 (C-9-23)28acd ____ 34.0 7.0 27.0 (C-9-23)28dcc ____ 38.0 .(C-9-23)32caa ___ 6.0 (C-9-23)32ddd ___ 4.0 (C-9-23)33bbb ___ 6.0 (C-9-23)33bcd ___ 36.0 8.0 28.0 (C-10-23)2aaa ____ 6.0 (C-10-23)8bbb ___ 4.0 Average ____ 35.2 5.9 27.5 H220 WATER EESOUECES OF LOWEE COLOEADO EIVEE-SALTON SEA AREA

0 (C-8-22)22bbb (C-8-21)21bca2 Driven Air drill Steel tubing Aluminum tubing

12 12 Water level

16 16 10

20

(C-8-23)22ddcl Air drill 24 Aluminum tubing

2 28 QC

32 12

(C-8-23)36bcc Air drill Aluminum tubing 16 8 10

(C-8-23)27cad Air drill 12 Aluminum tubing

Stage to which water level rose 16

Water level first penetrated 20 12

24 16

28 20 10 12 0246 8 10 THOUSAND COUNTS PER MINUTE

FIGURE 56. Counts per minute at various depths below land surface GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H221

(C-8-22)31cbb (C-8-22)33daa Driven Air drill Steel tubing Aluminum tubing

12 12

16 16 10

20

24 10

12

Water level 16 10

12

16

20 10 0 10 THOUSAND COUNTS PER MINUTE obtained by use of a neutron moisture probe at 10 sites in South Gila Valley. H222 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA o

(C-9-23)27cbb (C-9-23)28aaa Driven Steel tubing

Water level

12

16 0

(C-9-23)32caa (C-9-23)32ddd

^. 4

Water level below 9 feet

12

16 10 -i i i r

(C-10-23)2aaa

12

16 0246 8 10 THOUSAND COUNTS PER MINUTE FIGURE 57. Counts per minute at various depths below land surface GEOHYDROLOGY OF THE YUMA AREA, ARIZtiNA AND CALIFORNIA H223

(C-9-23)28dcc

Water level

(C-9-23)33bcd

10

6 8 10 THOUSAND COUNTS PER MINUTE obtained by use of a neutron moisture probe at 10 sites on Yuma Mesa. H224 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

(C-9-25)35dcd

12

16 0 2 4 6 8 10 0 2 4 6 8 10

2 4 6 8 10 8 10

i i

(C-10-25)2dcd

12

16

20

24 10 02 8 10 THOUSAND COUNTS PER MINUTE

FIGURE 58. Counts per minute at various depths below land surface obtained by use of a neutron moisture probe at six sites in Yuma Valley. INDEX

[Italic page numbers indicate major reference*] Page Page Page Canebrake Conglomerate _____ H46 Deposits, older alluvium classified by Carbonate precipitation .-_-.- 127 source _____ . __ H.47 Age and correlation of older alluvium.. 13.46 Cargo Muchacho Deposits, older alluvium of local origin 47 Age of volcanic rocks ------39 Mountains _ 12,16, 30. 39, 66. 87 Deposits, older alluvium of mixed origin 48 Agriculture, use of irrigation ______6 Castle Dome Mountains ______-- 37 Deposits, water bearing, Pliocene to Alamo Canal ------._ 84 Castle Dome Plain ______.-._ 24 Holocene age 66 Alfalfa hay, use of water ------98 Cenozoic deposits --_____ ..______12 Desert pavement . 47 Algodones Dunes ______16,28,56,61 Central sector of Yuma Valley 138 Desert varnish --- 48 Algodones fault ____ 19, 23, 60, 61, 107, 123 Chemical analyses of ground-water Distribution and thickness of older All-American Canal __ 9, 84, 91, 103, 108, 134 samples _____.. 15, 69, 124, 134 alluvium .. 46 Alluvial-fan deposits -__ _-_--_._ 56 Chemical changes in ground water Dome Valley ____... 29 Alluvial section between Pilot Knob derived from recent Dordos gaging station 92 and Cargo Muchacho Colorado River _____ 12k Drilling of test wells ___ IS Mountains _---_--.- ___ 87, 91 Chemical quality of ground Alluvium, older ------. 45, 66 water _____ 15, in, 136,140 Alluvium of Yuma area, younger __ 53, 66 Yuma area -______-__ 129 Ammonia beccarii _--_--.-_.._--___-__ 42 Chinle Formation _-__---_____-. 51 East-central sector of Gfla Valley Analog model, reliability ------113 Chocolate Mountains ______12,33,37,45 subarea --- 133 East Mesa ______. 27 verification studies ___-__---_----_- 113 Cipriano Pass ______--. 22 East sector Gila valley subarea 1S2,137 Analog-model studies ____-_-_-_-._-__ 15, 107 Citrus and other crops, use of water.._ 98 Analyses, hypothetical __.___-__--___ 129 Electric logs of wells ... 14,66,67 Andesite, older ______.__. 37 Citrus orchards ___--__--__-_-- . 6 Elphidium gunteri _____ .______42 Apache Group .______51 Citrus sector of Yuma Mesa _____ HO Eponidella palmerae ___ _ 42 Aquifer, the term _---___.---_-.______72 City sector of Yuma Mesa _.._._.._ 140 EQUUS sp _____-_-__-______._ 30 Aquifer characteristics __------_._ 15 Classification, deposits by source -___ 47 Evapotranspiration, concentration by ___, 126 Aquifers, hydrologic characteristics ____ 72 landforms ------__.-..._ IS Evapotranspiration on flood plain 70 Arizona system for numbering wells .__ 17 rocks ._.__. ... SO Exploration, geophysical IS Arizona western sector of Yuma Mesa Climate of area -..._.______.__ 6 subarea --_-_.__.----_-._ 139 Coachella Valley ______61 Arkose ______-______.__ 32 Arrowweed in Yuma Valley ___-____-_ 87 Coarse-gravel zone, mineral content __ 132 Farmstead and ditches, use of water 98 Ai-tesian storage coefficients ______82 variations in temperature -____. 121 Faults, reverse and thrust ------_ 34,61 Average annual discharge of ground water-bearing deposits __._._-__. 67 Flood plains of Colorado and Gila Rivers 6 water _____.______--__-__. 107 Coefficient of storage _ _.-__..- 78 Floodway sector of Yuma Valley -_.-__ 138 Coefficient of transmissibility ____.._ 74 Flows and vent tuff of Laguna B Colorado Basin Associates Federal 1. 33, 40, 65 Mountains -_.__ 38 Colorado flood plain ______6 Foraminifers ______40,44 Banning-Mission Creek fault ..-- 61 Colorado River, older alluvium deposits 48 Formation sample studies 13 Bard Lake ------______.__ 29 Fortuna basin --_--____-______69, 61, 65 Bard sector ______135 source of ground water .-.-----. 70 Bard subarea __--_--___-___ . ___- 99 younger alluvium deposits _____.-_ S3 Fortuna Dunes ______------23, 28, 56, 96 Bard Valley _____ 23,29,50,56,66,97,134 Colorado River basin ------6 Fortuna Plain ______. 25,66,69,97.109 Basalt or basaltic andesite of unknown Concentration by evapotranspiration __ 126 Fortuna sector of Yuma Mesa _.___ 139 age ______38 Conglomerate and breccia _____.____ S3 Fossils of area ______30,40,43 Basaltic andesite or basalt of Cholocate Conglomerate of Chocolate Mountains.. 45, 63 Fresh water, definition ---- -._. . 63 Mountains --______38 Consumptive use of water on Yuma Basin and Range structural features Mesa ------___---.-_ 98 (Tertiary) ______58 Corals 42 Bicarbonate concentrations in ground Correlation and age of the older Gamma-ray logs ---__. . ... 14, 42 water ____...______126 Geologic mapping __ IS Block faulting in the Yuma area ___-_ 58 alluvium __------... 46 Geologic structures _.-.- ___ 1*2 Bolivina interjuncta _---_---__-_-__-_- 40 Cottonwood in Yuma Valley .-_...__ 87 Borrego Formation ______46 Creosote bush (Larrea tridentata) ---- 28 Geologic studies of Yuma area 16 Boundary Hills ___-______22,60,62 Crystalline rocks (Pre-Tertiary) 30 Geology of area . 18 Bouse Formation Cucupas Mountains ------_-__ 30 Geomorphology of area . --_-_._ ... 18 (Pliocene) __ 35,37,39,40,60,65 Geophysical exploration IS Brawley Formation ______47 D Gila City ______21 Breccia and conglomerate _-_-_----___ SS Gila flood plain 6 Butler Mountains ______19,22,56 Dacite ______..______38 Gila Gravity Main Canal _ 9,132 Davis Dam _-. . 88 Gila Gravity Main Canal Siphon ____ 132 Davis Plain ______22,25,69 Gila Mesa _____. .__ 24,122,129,139 Cable-tool method of drilling ______13 Definition of fresh water ______63 Gila Mountains ______12,21, 33,67 California sector ______137 Definition of terms ...__------72 Gila River ______71 California system for numbering wells. - 17 Deposits, Colorado and Gila Rivers _ S3 older alluvium deposits ____.___ £8 Camino del Diablo -----_------,____ 22 Deposits, old Colorado and Gila Rivers 48 younger alluvium deposits _..__ 83 H225 H226 INDEX

Page Page Page Gi!a Siphon sector -._-_ Laguna Mountains _._ H12, 33, 39, 59 Picacho Peak ...... H38 Gila Valley subarea ___ 129 Laguna Valley ------28,134 Picacho Wash - - 24 Glen Canyon Dam _____ ...____ 71 Laguna Valley sector _-_-__ 134 Piedmont and stream-terrace deposits__ 47 Globigerinita uvula ____ .______40 Laguna Valley subarea --- 98 Piedmont slopes, dissected 24 Globquaderina hexagona .______40 Lake Cahuilla ------27 undissected - . . ------__ 24 Gneiss ___--_---__ .______30 Lake Mead ____ 70 Pilot Knob ______22,30,60,61, 87, 91 Granite ______30,32 Landform classification ------19 Planulina sp 40 Gravel deposits in Yuma area ______49 Laramide faults ------___--_--_ 58 Pliocene and Pleistocene older alluvium 45 Great Basin section of Basin and Laramide orogeny _ ------32,57 Pliocene transition zone .______45 Range province _____---_- 58 Lechuguilla Desert ___--_- 22,25 Plutonic rocks --- ______30 Greenstone ____-_____-__--_____._---__ 32 Ligurta Mesa ------.___ - --- 24 Potassium-argon age determinations. 37, 39,45 Ground water, areal variations in Limitrophe section of Colorado River.- 87, 91 Precipitation, local ._ 72 temperature __-_-__---. 121 Location of area ------______6 Precipitation of insoluble carbonates __ 127 rate of movement under natural Pre-Tertiary structural features 57 conditions _._-__---_------87 Proving Ground Dome ______... 23 sulfate reduction _--__. 127 M Pumping tests in area ___-._.___ _ 82 Ground-water discharge for a given Pumping wells for irrigation ______10 year ______107 McCoy Mountains Formation -- 32 Pyroclastic rocks of silicic to inter­ 37 Ground-water discharge to the Colorado McPhaul Bridge ____ 33, 36 mediate composition ______River between Imperial Dam Main Drain _-_--.__- 7 and the northerly inter­ Marine sedimentary rocks (Tertiary) -- 89, 65 national boundary --__-___ 105 Measurements of ground-water Ground-water hydrology -______12,63 temperature -___ __..___. 15 Ground-water movement ___----_---_-_ 82 Mesa basement high ______60,62 Quality of water, subdivision of Yuma area _ - ____ 129 after 1960 ______...__ 95 Mescal Limestone ______.__-__- 51 Quantitative determinations of aquifer toward limitrophe section --___--_ 103 Mesquite, use of water ______-__-__--- 88 characteristics ______--. 15 Ground-water origin and source of Yuma Valley ______87 Quartz monzonite ______32 recharge __-_---_------_ 70 Metaconglomerate __-___--____-____-_-_ 32 Quaternary alluvium, younger _ - 53 Ground-water reservoir _--__-_------61 Metamorphic rocks ______30 Quaternary windblown sand ... . 56 major subdivisions --______-_-_- 63 Mexicali Valley ______10, 19, 30, 84, 92,109 Ground-water samples ______.__ 15 Middle Mountains --_. 23,37 Ground-water temperatures ------15,113 Middle Mountains Plain _._.__-_. 23 Gulf of California ______6 Mineral composition of clay and silt in Yuma aretei ______..__ 52 Radiocarbon dating method 46,66 H Mittry Lake ______29,98,134 Rate of movement of ground water Model characteristics of analog model _ 107 under natural conditions 87 Modeled system, stresses applied _____ 109 Hanzawayai sp ______._--__-_-___ 40 Raven Butte _-_- - 22,39 Hardening of water ______128 Mollusks ______40,42 Recharge diverted to Yuma Valley Montmorillonite ______52,128 Haughtelin Lake ------___---_----._-_ 29 subarea - ______- __ 102 More!os Dam ______61, 92 Heavy-mineral analyses of alluvial sand 48 Recovery tests for wells ______15 Morelos gaging station ___ 84 Hills and mountains of area .-_-_- 19 Red beds _._ 35 Mountains and hills of area ______19 History of water-resources development 6 Reservation Division of Yuma Project__ Holocene flood plains ______28 Movement of ground water ______82 Reservation subauea 99 after 1960 ______95 Hoover Dam ______70 River deposits, old dissected ______23 Hydraulic conductivity, the term __-__ 74 direction in 1960 --_-___-___.___ 88 River terraces and mesas SB Hydrologic characteristics of aquifers __ 72 under natural conditions _._--. 87 River valleys - ______- _- 28 Hydrologic regimen _---______-__ 9 Mud-rotary method of drilling ____ 13 Rocks of Yuma area, classification 30 Muggins Mountains .._--- _. 19, 30 Hydrologic studies ____-_-_-_.____._ 16 Rosalina columbiense ______42 Hydrology, ground-water ______63 Rubidium-strontium age determination_ 32, 57 N Runoff, local .______7S

Nonmarine sedimentary rocks ____ SS Ignimbrite ___-_-_.--__-_.-_____ 38 North Gila Sector ______134 Imperal Dam ______9,42,70,98 North Gila Valley ______29,68,132 Salton Sea _._.-_ . _ 19,61 Imperial East Mesa ______26 North Gila Valley Unit of Yuma Project 9 Salton Trough ______, 6,16,18,37,57 Imperial Formation ___-__---___*---_ 40 North of Gila Valley subarea ______100 San Andreas fault system 28,57,61 Imperial Valley ____----_-__-_-_ 40 San Luis basin _ - - - -- _ __ 60,65 Indian Hill ______135 Sand, windblown 56 Inventory of existing wells and well Sand deposits in Yuma area _ _ 48 records ______14 Sand dunes 28 Investigation, objectives of present ... 11 Objectives of present investigation...- 11 Sand Hills ______28,56,61 Investigation methods .-_-_-______-___ 12 Ocotillo Conglomerate ------_-____ 47 Sandstone _ 32 Investigations of Yuma area, earlier - 16 Odocoileus sp .-_____..._.___... 30 Sangamon Interglaciation . 27 Irrigation in Mexicali Valley ______10 Ogilby Hills ______22,39 Schist . _ _ 30 Irrigation in Yuma Valley _.. 6,10, 71, 136 Older alluvium, undivided, water­ Scope of report _ _ 11 Irrigation of area ______-.______6 bearing deposits -_---_-_- 69 Sedimentary rocks, nonmarine 32,65 Irrigation well, first ______--______10 Origin of ground water and source of older marine ______39, 65 recharge 70 other nonmarine _ _ - - 37 K Orocopia Schist ______-_____ 32 Senator Mesa - 24 Senator Wash . ... 4$ Kinter Formation ______33, 34, 39, 45, 59 Senator Wash Dam ______58 Sheet-Wash and wash deposits 56 Shinarump Member 61 L Palm Spring Formation ____._. __ 46 Sinclair Oil Co. Kryger 1 test well _ 42 Phyllite ______.-_____ 32 Slate ______32 Laguna Dam ______7,12,38,50,70,98 Picacho-Bard basin ______59,65 Softening of water 1&6 Laguna Mesa ______23,56 Picacho Mesa ______24,35,49 Soil-moisture studies ______--. 109 INDEX H227

Page Page Page Sonoran Desert .______H6, 18, 57, 60 Test drilling _ -__.- -- _ HI2 Water-bearing deposits of Pliocene Source of recharge of ground water __ 70 The Island __.___. 9,17, 56, 99, 134 to Holocene age H66 South Gila Valley ____ 6,50,59,68,88,139 The Island sector ______135 Water-bearing rocks 12 South Gila Valley subarea ______100 The Island subarea _-___.__ 100 Tertiary age ______-- 64 South Gila Valley Unit of the Gila Thickness and distribution of older Water budget for Yuma area 105 Project ___-______9 alluvium ______.._ 46 Water budgets - 95 South sector of Yuma Mesa ______141 Thiem method for computing Water hardening 128 Specific capacity of the well _ ____ 78 transmissivity __.__._ - 75 Waterlogging of lands near Yuma mesa 10 Specific conductance ______129 Tinajas Altas Mountains 19,22,39,56 Water movement direction in I960. 88 Sphaerhoidinella dehiscens ______40 Trachyte ______38 Water quality in Bard Sector 135 Split Mountain Formation ______40 Transition zone (Pliocene) ___ 45,60,63,66 Water-resources development, history 6 Spontaneous potential logs -___-_--____ 14 Transmissivity ____ _ 75,88,103 Water samples from Arizona western Step-drawdown tests ______15,75 the term .______74 sector ___ - _-__ _ __ 140 Storage coefficient, the term .-_-______74, 78 Transmissivity at specific sites _ 15 Water softening 126 Storage coefficient determinations ___ 15, 102 Transmissivity values ______108 Wedge zone of water-bearing deposits.- 66 Storage-coefficient values _-_.___._ 109 Tuff, ash-fiow ______38 Well-numbering systems 17 Stratrgraphy of area ______30 water-laid ___.-_--_ _._ __ 38 Well records, inventory 14 Stream-terrace and piedmont deposits _ 47 Tuff breccia ______- . 32,38 Wellton Hills ____ _ 23 Stresses applied to the modeled system 109 Tumco Formation ______30 Wellton Mesa ___ 26 Structural features, late Tertiary and Wellton-Mohawk Conveyance Channel 132 Quaternary ______60 U West-central sector of Gila Valley pre-Tertiary ______57 subarea _ 1SS Structural patterns, regional ______57 Unharvested fields, use of water __._ 98 West sector of Gila Valley subarea 1SS Wildcat drilling for oil _ ____ 16 Structure of area ____-.___-______57 Upper, fine-grained zone, water-bearing deposits ______68, 124, 139 Willow in Yuma Valley ______87 Subdivision of Yuma area for description Upper Mesa __ 23,27,49,56,61,97,108,139 Windblown sand (Quaternary) ______56,66 of quality of water ____ 129 Upper Valley subarea ------134 Winterhaven sector ______13S Subsurface outflow to limitrophe section 103 Uranium-lead age determination ______32 Wireline logging of wells _-_-.-_____ 14 Sugarloaf volcanic knob ______21 Urban and suburban use of water _ _ __ 98 Sulfate reduction ______127 Uvigerina sp _____ 40 Surface water deliveries to Mexico _ 105

Valley Division (Yuma Valley) ____ 6 Yuma area __-___ . _ _ _.____ 103 Variations of temperature with time__ 113 Yuma Auxiliary Project _- ______9 Tapeats Sandstone --_------_--___ 50 Verification studies of analog model ___ US Yuma Hills ______22,29,48,59 Telegraph Pass ______22,139 Vertebrate fossil from Miocene _ -_ _ 30 Yuma Main Canal . ____ 9,135 Temperature of ground water ______15, 113 Vertical hydraulic conductivity 74 Yuma Main Drain _____. ______29 variations with time ______113 Vertical variations in temperature ____ 116 Yuma Mesa ______6,9,16,26,50,53,67,97 Vitrefrax Formation ____------30 vertical variations __--__-______116 Yuma Mesa Division of the Gila Project 10 Volcanic rocks, age ______39 Yuma Mesa subarea --.. ------101,139 Tertiary and Quaternary conglomerate 45 Volcanic rocks (Tertiary) ..____ 57,45 Tertiary and Quaternary structural Yuma Project ______6 Yuma trough ______60,65 features ______60 W Yuma Valley ______6, 19, 29, 50, 87, 93 Tertiary marine sedimentary rocks _ 39 Yuma Valley Oil and Gas Co. Musgrove Tertiary sedimentary rocks ______32 Wash and sheet-wash deposits 56 1 test well ______40,42 Tertiary volcanic rocks ______37 Water, fresh, definition __. 63 Yuma Valley subarea ____ .. 102,186

U.S. GOVERNMENT PRINTING OFFICE : 1974 O - 507-243