HYDROGEOLOGIC FRAMEWORK OF THE MESJLLA BASIN IN NEW MEXICO AND WESTERN TEXAS
John W. Hawley and Richard P. Lozinsky
New Mexico Bureau of Mines and Mineral Resources New Mexico Institute of Mining and Technology Socorro, New Mexico
Open-File Report 323
1992 ABSTRACT
The two major objectives of this study of the Mesilla Basin between Las Cruces, New Mexico and the International Boundary zone west of El Paso, Texas were (3.) to develop a detailed conceptual model of the basins hydrogeologic framework that is baaed on a synthesis of available geological, geophysical, and geochemical data, and (2) to present that information in a format suitable for use by the U.S. Geological Survey, Water Resources Division (USGSWRD) in developing an up-to-date numerical model of the groundwater flow system. The basins hydrogeologic framework is graphically portrayed in terms of (1) the lithologic character, geometry, and geologic history of basin-fill deposits; and (2) the bedrock units and structural features that form the basin boundaries and influence intrabasinal depositional environments. The basic “architecture” of mappable subdivisions of basin deposits that can be defined in terms of their aquifer properties is characterized in the conceptual model. The Santa Fe Group forms the bulk of basin-filling deposits and the major aquifer system of the region. It comprises a very thick sequence of alluvial, eolian, and lacustrine sediments deposited in intermontane basins of the Rio Grande rift stru%ural province during an interval of about 25 million years starting in late Oligocene time. Widespread filling of several structural subbasins, which in aggregate form the Ml-silla Basin, ended about 700,000 years ago (early Middle Pleistocene time) with the onset of Rio Grande (Mesilla) Valley incision. Post-Santa Fe deposits include (1) inset valley fill of the ancestral Rio Grande and tributary arroyos that forms terraces bordering the modem floodplain, and (2) river and arroyo alluvium that has been deposited since the last major episode of valley incision in late Pleistocene time (about 15,000 to 25,010 years ago). The three basic hydrogeologic components of the Mesilla Basin model con-p&e: 1. Structural and bedrock features that include basin-boundary mountain uplifts, bedrock units beneath the basin fill, fault zones within and at the edges of basin that influence sediment thickness and composition, and igneous-intrusive and -extrusive rocks that penetrate or are interbedded with basin deposits. 2. Hydrostratigraphic units which are mappable bodies of basin and valley fill that are grouped on the basis of or&i-i and position in a stratigraphic sequence. Genetic classes include ancestral-river, present river-valley, basin-floor playa, and Piedmont alluvial fan deposits. Rock-&at&rap1 ic classes in&de units deposited during early, middle and late stages of rift-basin filling (i.e. lower, middle and upper Santa Fe Group), and post-Santa Fe valley fills (e.g. channel and floodplain deposits of the Rio Grande, and fan alluvium of tributary arroyos) . 3. Lithofacies subdivisions are the basic building blocks of the model. II- this study, basin deposits are subdivided into ten lithofacies (I through X) that are ma?pable bodies defined on the basis of grain-size distribution, mineralogy, sedimentary structures, and degree of post-depositional alteration. They have distinctive geophrsical, geochemical, and hydrologic attributes. The hydrogeologic framework of the Mesilla Basin area is graphically presented in map and cross-section format (Plates 1, 16 and 17). Supporting stratigraphic,
i lithologic, petrographic, geophysical, and geochemical data from 61 wells are illustrated in stratigraphic columns and hydrogeologic sections (plates 2 to 15). A new computer-generated graphics system was utilized in the presentation of these data. Tables 4a and 4b summarize the subsurface information used in this study, including (1) well location and depth; (2) ground-water levels; (3) drill-stem sample intervals; (4) selected data on ground-water chemisq; and (5) data sources. Major hydrostratigraphic units and aquifer zones sampled are also identified in Tables 4a and 4b. The report has four major narrative sections (I. Introduction; II. Geologic Setting; 111. Sand-Fraction Petrography; and IV. Conceptual Model), a wmprehexive reference list, and two appendices (A. Basic petrographic data, and B. Preliminary hydrogeologic cross sections extending into adjacent parts of the Jornada del Muerto and Hueco basins). Previous work on basin hydrogeology and study methods are covered in Section I. A team approach was used in the analysis of borehole (geol~~gical, geophysical, and geochemical) data to develop the final conceptual model of hydrostratigraphic and lithofacies unit distribution. Section 11 provides a general geological overview of the MesiUa Basin region including the structure of flanking mountain uplifts and relationship to contiguous basin areas in New Mexico, Texas, and Chihuahua. Emphasis is on the past 25 million years of geologic time when major structural and topographic elements of the present landscape formed. The interval was characterized by regional extension of the earth's crust, and differential uplift, subsidence and tilting of individual crustal blocks along major fault zones to form internally complex basins and ranges. This continental "rifting" process produced the Rio Grande rift structural zone that extends from southern Colorado to western Texas and northern Chihuahua. A major contribution of this study has been the significant improvement in definition.of the physical limits of the MesiUa Basin and its component subbasins. Much of the information on bedrock distribution and geologic structure was derived from published maps and cross sections, with supplemental data from unpublished geophysical and geothermal surveys. Seismic reflection profiles specially prepared for the USGS-WRD at two sites in the lower MesiUa Valley have also been utilized in this study. Rift basin fill comprising the Santa Fe GIOUP has a maximum thickness of about 3,000 ft (915 m) in the Mesilla Basin. The lower and middle parts of the Santa Fe. form the bulk of the basin fill and were deposited in an internally drained complex of tllree subbasins that were initially separated by a central (north-trending) intrabasin upl'ft (Eastern, Northwestern, Southwestern subbasins, and Mid-basin uplift on Plate 1) Eolian sands and fine-grained playa-lake sediments are major lithofacies. These wits are locally well indurated and only produce large amounts of good quality ground water from buried dune sands (lower Santa Fe) in the eastern part of the basin beneath the MesiUa Valley. Poorly consolidated sand and pebble gravel deposits in the middle to upper part of the Santa Fe Group form the most extensive aquifers of the area. Widespread channel deposits of the ancestral Rio Grande fist appear in upper Smta Fe beds that have been dated at about 3.5 donyears (Ma) in southern New Mxiw and 2.5 Ma in western (Trans-Pews) Texas.
ii Expansion of the Rio Grande (fluvial) system into upstream and downstrem basins, and integration with Gulf of Mexico drainage in the early to middle part of the Quaternary (Ice-Age) Period about 700,000 years ago led to rapid incision of the Mesilla Valley and termination of widespread basin aggradation (ending Santa Fe Group deposition in the Mesilla Basin). Cyclic stages of valley cutting and filling are represented by a stepped-sequence of valley border surfaces that flank the modem valley floor. Fluvial sand and gravel deposited during the last cut-and-€ill cycle fom a thin, but extensive shallow aquifer zone below the Rio Grande floodplain. Recen? fluvial sediments are locally in contact with ancestral river facies in the upper Santa Fe Group, particularly in the northern Mesilla Valley. They form the major recharge and discharge zones for the basin's ground water, and are quite vulnerable to pollution in this urban-suburban and irrigation-agricultural environment. Structural deformation along subbasin boundaries and changes in topographic relief between deeper basin areas and flanking uplifts continued throughout the lite Cenozoic. During early stages of basin filling (lower Santa Fe deposition) many of the present bounding mountain blocks had not formed or had relatively low relief. Tl ickest basin-€ill deposits (up to 1500 ft [455 m] of the middle Santa Fe Group) were emplaced between 4 and 10 million years ago during most active uplift of the Organ-Franklin-Juarez range and the Robledo Mountains, and subsidence of the Eastern (La Union-Mesquite) subbasin. The major basin-bounding fault zone (MIsilla Valley) is now covered by the recent river floodplain deposits. The petrographic investigations described in Section III emphasize the fundamental properties of rock fragments and mineral grains that in aggregate fom the various lithofacies subdivisions of the five hydrostratigraphic units (Tables 1 and 2). Cuttings from the Afton (MTl),Lanark (h4l'2), La Union (Mn), and Noria (MT4) were analyzed initially with a binocular microscope in order to construct a stratignphic column for each of these key wells (Plates 12-15) and to determine intervals (approximately every 100 ft, 30 m) where subsamples of representative sands would be collected for thin-section petrographic analyses. Samples were also collected from representative sandy intervals in the two wells in the Canutillo Field (CWFLD an4 4D) and from six outcrops of the Upper and Middle Santa Fe units. Petrographic anal rsis of sand samples analyzed from the six water wells and from outcrop areas in the.Mehla Basin shows that the basin €ill was derived from more than one source terrane. The abundance of plagioclase (zoned and twinned) and andesitic lithic fragments strorgly suggest an intermediate volcanic source area for most of the detrital material. Chert, chalcedony, and abundant quartz (many well rounded with overgrowth rims) indicate reworked sedimentary units as another major source. A granitic source area is also suggested by the presence of microcline, strained quartz, and granitic rock fragmeJts. The paucity of metamorphic-rock fragments and tectonic polycrystalline quartz rules out a metamorphic terrane as a major sediment source. It appears that even in early to middle Santa Fe time (Miocene) the centra' Mesilla Basin area was receiving sediment from a very large watershed. A much larger source region was also available for sand and finer grain-size material when the mechanism of eolian transport is taken into account. By middle Pliocene time the
iii ancestral Rio Grande was delivering pebble-size material to the basin from source terranes as far away as northern New Mexico (e.g. pumice and obsidian from the Jemez and Mount Taylor areas). In most cases, visual and binocular microscopic examination of the gravel-size (>2mm) fraction is still the best way to establish local versus re.giona1 provenance of coarse-grained fluvial and alluvial deposits. The conceptual hydrogeologic model is described in detail in Section IV and illustrated on Plates 1, 16, and 17 with supporting data and interpretations on Plates 2 to 15.The basic hydrogeologic mapping unit used in conceptual model development is the hydrostratigraphic unit. It is defined in terms of (1) environment of deposition of sedimentary strata, (2) distinctive combinations of lithologic features (lithofacies) such as grain-size distribution, mineralogy and sedimentary structures, and (3) general time interval of deposition. The attributes of four major classes into which the area’s basin and valley fib have been subdivided are defined in Table 1. The Upper, Middle, and Lower hydrostratigraphic units of the Santa Fe Group roughly correspond to the (informal) upper, middle and lower rock-stratigraphic subdivisionsof Santa Fe Group descnied in Section II. The other major hydrostratigraphic unit comprises Rio Grande alluvium of late Quaternary age (<15,000 yrs) that.foms the upper part of the re.gional shallow-aquifer system. The ten lithofacies subdivisions that are the fundamental building blocks of the model are defined primarily on the basis of sediment texture (gravel sand, silt, chy, or mixtures thereof), degree of cementation, and geometq of bodies of a given textural class and their relative distribution patterns. Lithofacies I, 11, ID[, V, and VI are unconsolidated or have zones of induration (strong cementation) that are not continuous. Clean sand and gravel bodies are major constituents of facies I, 11, V, and VI; while clay or cemented sand zones form a significantpart of facies 111 and IV. Subdivision N is characterized by thick eolian sand deposits of the lower Santa Fe unit (LSF) that are partly cemented with calcite. Coarse-grained channel deposits of the modern and ancestral Rio Grande (lithofacies I and II) are the major component: of the upper Santa Fe (USF) and river-alluvium (RA) hydrostratigraphic units. They form the most important aquifers and potential enhanced-recharge zones in the-basin. Lithofacies VI and WIare partly to well indurated piedmont-slope.deposits; while facies IX and X comprise thick sequences of fine-grained basin-floor sediments that include playa-lake beds. Unconsolidated deposits make up the bulk of the middle and upper Santa Fe Group and all of the recent valley fill in the MesiUa Basin. Textural classes include sand, gravelly-sand, silt-clay, and sandy to gravelly materials with a siltclay matrix Secondary calcite and gypsum are the primaIy cementing agents in the basin fill, however, continuously indurated zones are uncommon except in basal parts of the. Santa Fe section. Coarse-grained fan alluvium and debris-flow deposits, with gravel prirrarily in the pebble- to cobble-size range ( iv beneath the Rio Grande Valley floor constitute the major shallow aquifer system Outside the valley area, however, most of the ancestral river deposits are in the vadose zone. Interbedded sand and silt-clay deposits of the Middle Santa Fe Unit (MSU, primarily lithofacies IIJJform the basin's thickest and most extensive aquifer system (the "medial" aquifer in this report; Tables 4a and b). This unit is as much as 1000 ft (305 m) thick in the eastern (La Union-Mesquite) subbasin (Plates 3-5, 10, 11, 16b-4 17a\. Well-sorted fine to coarse sand deposits of lithofacies IV make up a significant part of the lower Santa Fe Unit (LSU) and are here interpreted as being primarily of eo.!ian origin. These partly-indurated beds are as much as 600 ft (185 m) thick in the eastern (La Union-Mesquite subbasin); and they may be 900-1000 ft (275-305 m) thick in the southwestern subbasin immediately east of the east Potrillo fault zone (Plates 3-5: 7, 10, 11, 16b-e, 17a). All basin fill units (USF, MSF, LSF) become finer grained to south; and fine- to medium-grained basin-floor facies, with only minor amounts of gravel, dominate the basin fill section in the international boundary zone west of Cerro de Cristo Rey (Plates 6, 7, and 16e; facies ID, IX and X). Most of the Upper Santa Fe hydrostratigraphic unit (USF) in that area is in the vadose zone; and sand beds in the basal Upper Santa Fe unit and upper part of the Middle Santa Fe unit (MSF, lithofacies III) appear to be the only major aquifer east of the Mid-Basin uplift. Lithofacies IV in the Lower Santa Fe hydrostratigraphic unit (LSU) may also be a potential deep aquifer in the Southwestern subbask, but this zone has not yet been tested for either quantity or quality of grmnd water production. Assignment of specific hydraulic conductivity ranges to individual lith0facie.s subdivisions is beyond the scope of this investigation. However, as a first approximation, the following general ranges appear to be reasonable: 1. Conductivities of lithofacies I and I1 are relatively high (30 to 300 ft/day, 10-100 m/day); 2. Lithofacies IX and 2- and well-cemented sandstone and fanglomerate zones in facies VI1 and VIZI will defiritely have very low conductivities (usually much less than 0.3 ft/day, 0.1 m/day); 3. Conductivities in uncemented sand layers in lithofacies Ln. and N,and sand and gravel beds in facies V through VI11 should primarily be in the intermediate range (0.3 to 30 ft/day, 0.1-10 m/day). V CONTENTS Section Page ABS.. ABS...... i I. INTRODUCTION ...... 1 Background ...... 1 Previous Work on Basin Hydrogeology ...... 3 Methods and Techniques ...... 8 DataCollection and Analysis ...... 8 Drill Cuttings and Thin Section Ann2ysis ...... 8 Digitizhg Borehole Geophysical Logs ...... 9 Hydrostratigraphic Unit Correlation and Conceptual Model Development ...... 9 Well Numbering System ...... 9 Acknowledgments ...... 12 II . GEOLOGIC SETTING OF THE MESILLA BASIN ...... 13 Introduction ...... 13 Basin Structure and Bedrock Units ...... 13 Bedrock Units of Basin-Margin Upl@ ...... 16 Bedrock Unils Beneath the Basin Fill ...... 17 BasinFill Stratigraphy ...... 17 Santa Fe Group ...... 18 Post-Santa Fe Deposits ...... 20 111 . SAND-FRA(=TION PETROGRAPHY ...... 21 Introduction ...... 21 Methods and Techniques ...... 21 Preliminary Dd-Cutting Analyses ...... 21 Thin Section Sample Collection and Preparation ...... 21 Thin Section Analysis ...... 22 Sand Petrology of Selected Samples of Well Cuttings ...... 25 Comparison with Santa Fe Outcrops ...... 25 Provenance ...... 29 IV . A CONCEPTUAL HYDROGEOLOGIC MODEL OF THE MESILLA BASIN ... 30 Introduction ...... 30 Hydrostratigraphic Subdivisions of Basin and Valley Fills ...... 31 Lithofacies Subdivisions of Basin and Valley Mus ...... 31 Structural and Bedrock Elements of the Hydrogeologic Framework ...... 33 Basin-Boundary Faults and Santa Fe Group Thickness ...... 34 Structural Influences on Intrabasin Sedimentntion Patterns ...... 34 v . SUMMARY ...... 37 Introduction ...... 37 ReportFormat ...... 38 SectionI ...... 38 Section17 ...... 38 SectionIII ...... 39 Section ...... 40 Discussion ...... 43 REFERENCES ...... 44 APPENDIX A BasicPetrographicData ...... 51 APPENDIX B Hydrogeologic Cross Sections of the Mesilla Bolson Area, Doha Ana County, NM and El Paso County, TX (NMBMMR Open-file Report 190) ...... Pocket vii FIGURES Figure 1. Location of study area ...... 2 2. Well2. numbehg systems 2a. Diagramshowing system of numbering wells in NewMexico ..... 10 2b.Diagram showing system of numbering wells in Texas ...... 11 3. Index map of MesillaBasin area showing locations of major boundary and intrabasin faults, adjacent mountain uplifts, and geologic cross sections (Fig. 4) ...... 14 4. Diagrammaticgeologic cross section of the northern and central Mesillabasin...... 15 Figures 5-6. Ternary diagrams of sand-fraction petrography (thin-section point-count data, Tables 5 and 6) for well cuttings from representative Santa Fe hydrostratigraphic units at: 5. Mon (MT l), Lanark (MT 2),and Canutillo WellField (CWF 1D) ...... 26 6. La Union (MT 3), Noria (MT 4), and Canutillo WellField (CWF 4D) ...... 27 Figure 7. Ternary diagrams of sand-fractionpetrography (thin-section point-count data, Tables 5 and 6) for samples from representative Santa Fe Group outcrops ...... 28 TABLES Table 1. Key to hydrostratigraphic units in the MesillaBasin (Plates 2-17, Tables 3 and 4) ...... 4 2.Key to bedrock units and upper Cenozoicvolcanics (Plates2-17) ...... 5 3. Lithofacies subdivisions of basin- and valley-fiU hydrogeologic units, and their Occurrence in lithostratigraphic and hydrostratigaphic units in the Mesilla Basin (Plates 2-17) ...... 6 Selected Well 4. Selected Data ...... Pocket 4a. MesillaBasin, New Mexico 4b.Mesilla Valley, Texas 5. Point-count grain parameters. Modified from Dickinson (1970) ...... 23 6. Means (x) and standard deviations (s) of point counts on water well and outcrop samples...... 24 PLATES Plate 1. Index map to Mesilla Basin showing major structural features and locations of selected wells, hydrogeologic cross sections, and outcrop sample sites (Table 4, Plates 2-17, AppendixA) ...... Pocket Plates 2-11. Hydrogeologic sections, with borehole geophysical and geochemical data ...... Pocket Plate 2. Las Cruces Fairground to Fire Station 3. Afton to Mesquite 4. Aden to La Tuna 5. La Union to Vinton 6. Noria Test to Mesa Boulevard 7. Potrillo Mountains to Noria Test 8. Afton Test to Noria 9. Las Cruces to SantaTeresa 10. Las Cruces Fire Station to Vado 11. Vado to Lizard Plates 12-15.Geological Data on TestWells ...... Pocket Plate 12. Afton Test Well(25.1.6.333; MT1) 13. Lanark Test Well(27.1.4.121; Ml2) 14. La Union Test Well(27.2.13.331; MT3) 15.Noria Test Well(28.1.34.414; MT4) Plate 16.Hydrogeologic sections (E-W) of the MesillaBasin, Las Cruces to El Paso area, showing inferred distribution of major hydrostratigraphic and lithofacies units, and fault zones...... Pocket 16a. Plate 2 section area (Las CNWSFairgrounds to Fire Station) 16b. Plate 3 section area (Afton to Mesquite) 16c. Plate 4 section area (Aden to La Tuna) 16d. Plate 5 section area (La Union to Vinton) 16e. Plates 6 and 7 section areas (Mesa Boulevard to Noria Test to P ~trillo Mountains) Plate 17.Hydrogeologic sections (N-S) of the MesillaValley and west- central Mesilla Basin areas, showing inferred distribution of major hydrostratigraphic and lithofacies units, and fault zones ...... Pocket 17a. Plates 10 and 11 section area (Las Cruces Fire Station to Vado t? Lizard) 1%. Plate 9 section area (Las Cruces to Santa Teresa) 17c. Plate 8 section area (Afton Test to Noria) X I. INTRODUCTION With ever-increasing demands on the ground-water resources of the Mesilla Basin there is a continuing need for a better understanding of the hydrogeologic framework of deposits that form one of the major aquifer systems of the region. The area (Fig. 1) includes the major centers of population and potential economic growth in the southern New Mexico, Trans-Pecos Texas and north-central Mexico region (I= Cruces, El Paso, and Ciudad Juarez). From a water-supply perspective, both the private and public sectors of society (except for irrigation agriculture) rely solely on grould water. At a minimum, characterization of basin hydrogeology should include detailed descriptions of major lithologic,. stratigraphic, structural; and geochemical subdivisions, and accurate delineation of basin boundaries and major recharge areas. Suitable numerical models of the ground-water flow system must be based on a conceptual model that is a synthesis of this type of baseline information (Frenzel and Kaehler, 1990; Kernodle, 1992b). Such modeling efforts are-particularly important because of the potential for saline-water encroachment and.land subsidence due to ground-water withdrawals in some parts of the basin (Contaldo and Mueller, 1992; Kernodle, 1992a, MacMiUan et al., 1976). This report describes the results of a hydrogeologic study bythe New Mexico Bureau of Mines and Mineral Resources (NMBMMR) of the Mesilla Basin and Vdey fill between Las Cruces, New Mexico and the International Boundary west of El Paso, Texas (Fig. 1).The investigation, done in cooperation with the Water Resource Pivision of the U.S. Geological Survey (USGS-WRD) and the New Mexico State Engineer Office (NMSEO), was originally proposed (1986) because there needed to be better utilization of hydrogeologic information in the management of the area's ground-vater resources. The two major objectives of the study were (1) to provide a synthesis 04 available geological, geophysical and geochemical data that can be used to create a detailed conceptual model of the basin's hydrogeologic framework, and (2) to conq?ruct that model in a format suitable for use in developing the best possible numerical models of the ground-water flow system. Funding for the initial phase of data compilation and model development.iy 1987 was jointly provided by the NMBMMR and USGS-WRD, contract number 14.08-DOOl- G-726; and subsequent support has been furnished by the NMl3"R. Intormation in this open-file report will ultimately be integrated with geologic, geophysical, and geochemical data from adjacent parts of the Jornada del Muerto Basin north and east of Las Cruces. A final report on the area will then be published by the NMBMMR as part of its Hydrologic Report series. Background The MesiUa Basin has thick fill deposits, locally as much as 3000 ft (915 m), that are mostly unconsolidated and include the major fresh-water aquifers of the region. Of particular importance, with respect to both water-supply and ground-water recharge, are 1 32' 30' $ 3 8s 3 32' W' \ \ I. NEW MEXICO i..-.. -..-..- ..-.. L.. CHIHUAHUA t\ EL PD.90 0 5 lOmi \ ,0 JlJAREZ .. \ /- - \ / CIUDAD \ / JLIARU \ \"/'/ BOLSON DE LDS MUERTOS NEW MEXICO t EXPLANATION AREA ___BO~NDARYOFMESIW&~SIN-A~~~.ZM~ i q Frsnrsl and MW,1880 TEXAS MEXICO ~- .. ~ ~ I Figure 1. Loation of study area. widespread channel deposits of the modem and ancestral Rio Grande system tha.t are a major component of the upper fXl sequence. A large body of subsurface geologic information (e.g. borehole samples, geophysical logs, and geochemical data) has been collected, particularly since 1980 when a significant increase in development of the basin's ground-water resources was proposed by the City of El Paso. Prior to this study, however, much of this information had not been analyzed or organized within the framework of a conceptual model that accurately descnies the "architecture" of t asin deposits with respect to the distribution of geological units that have distinct difEerences in structural, lithostratigraphic, and hydrologic properties. The model developed here has three basic components: 1. Structural and bedrock features include basin-bounding mountain upWs, bedrock units beneath the basin SU, -fault zones within and at the edges of the basin that influence sediment composition and thickness, and distribution of igneous intrusive and extrusive (volcanic) rocks that penetrate, cap or are interbedded with basin and valley fius. The locations-of major structural features and bedrock units in the study area are shown on Plates 1-11, 16 and 17. Fedrock units, including volcanic rocks associated with upper Cenozoic basinand vt-illey fills, are identified in Table 2. 2. Hydrostratigraphic units include major mappable subdivisions of the ba-in and valley fill that are defined on the basis of genetic origin and age of a stratiyaphic sequence of deposits (Table 1). Genetic classes include ancestral-river, recent river-valley, basin-floor alluvial and playa-lake, and piedmont alluvial-fan environments. Time-stratigraphic classes include units deposited during early, middle and late stages of basin filling (lower, middle, and upper Santa Fe Group); and deposits of the present Rio Grande (Mesilla) Valley system. Distribution patterns of hydrostratigraphic units are shown on Plates 2-11, 16 and 17. 3. Lithofacies units are the fundamental building blocks of the model. Ten major lithofacies subdivisions of the basin-filling sequence have been identified in this study (Table 3). These units are mappable bodies that have distinctive compositions, depositional and post-depositional environments, distribution patterns, geophysical and geochemical properties, and hydrologic characteristics. Dism%ution patterns of lithofacies units are also shown on Plates 16 and 17. Previous Work on Basin Hydrogeology The present Mesilla Basin study is part of a more comprehensive investigat:on of the hydrogeologic framework of southern Rio Grande rift basins initiated by the s-nior author in 1962. Work was initially supported by the U.S. Soil Conservation Service (SCS), Soil Survey Division in cooperation with the New Mexico State University (NMSU) College of Agriculture (1962-1974) and subsequently funded by the NMBMMR (Soil Survey Investigations-Desert Project). Early research emphasis wqs on the influence of hydrogeologic factors on the genesis of desert soils, particularly on the development of secondary carbonate, clay, silica, and gypsum accumulation in basin-fill 3 Table 1. Key to informal hydrostratigraphic unitsin the Mesilla Basin (Plates 2 to 17, Tables3 and 4) Unit Description Valley-Fill Deposits -- Post SantaFe Group RA Riveralluvium; channel and floodplain deposits of inner Mesilla Valley; as much as100 ft thick. Map unit "Qvyf" of Seager et al. (1987). Lithofacies subdivision Iv* is themajor hydrogeolo'3ic component. Forms much of the "shallow aquifer" of Leggat et al. (1962), and "flood-plain alluvium" of Wilson et al. (1981). Holocene to late Pleistocene VAValley-border alluvium; tributary arroyo (and thin eolian) deposits in areas bordering the inner Mesilla valley (river floodplain), with locally extensive river-terrace deposits; as much as 140 ft thick. Map unit "Qva" of Seager et al.(1987'; Fillmore, Leasburg (Ft. Selden), Picacho, and Tortugas morphostratigraphic units of Gile et al. (1981). Includes lithofacies subdivisions Iv andV. Most of unit is inthe unsaturated (vadose) zone. Holocene to middle Pleistocene Basin-Fill Deposits -- Santa Fe Group Rio Grande rift basin fill in New Mexico and adjacent parts of Texas, Chihuahua (MEX) and Colorado. Includes alluvial, eolian, and lacustrine deposits; with interbedded volcanic rocks (basalts and silicic tuffs). In the Mesilla Basin areathe Santa Fe Group may locally exceed2,500 ft in thickness. The groupcomprisw four lithostratigraphic units- Hayner Ranch, Rincon Valley, Forc Hancock, and Camp Rice Formations (Hawley et al., 1969; Seagnr et al., 1987). It also includes the major aquifers of the area (King et al., 1971; Wilson et al., 1981;Hawley,.1984) and~issubdivided into three informal hydrostratigraphic units: USF Upper Santa Fe Unit; coarse- to medium-grained deposits of tte ancestral Rio Grande intertongue mountainward with piedmont- alluvial (fan) facies, and southward with fine-grained lake and playa sediments; volcanic rocks (mostly basalt) and sandy eolian deposits are locally present; as muchas 750 ft thick. Unit includes the Camp Rice (CR) and upper Fort Hancock(FH) Formations (Strain, 1966; Hawley, 1978; Gustavson, 1991); also includes lithofacies subdivision Ib; much of facies11, V, and VI; and parts of facies I11 and VIII. Forms lower part of the "shallow aquifer" in the northern Mesilla Valley, and the upper aquifer zone outside the Valley area where much of the unit is above the water table. Middle Pleistoceneto middle Pliocene 4a MSFMiddle Santa Fe Unit; alluvial, eolian, and playa-lake facias; interbedded sand and silt-clay basin-floorsediments intertcngue mountainward with piedmont-alluvial (fan) deposits, and southward with fine-grained lake and playa facies; basaltic volcanics and sandy eolian sediments are locally present;as much as 1500 ft thick. Unit includes basin fill that correlates with much of the Fort Hancock (FH) and Rincon Valley Formations, whose type areas are in the Hueco Bolson and western Jornada del Muerto (Rincon) Basin, respectively; also includes much of lithofacies subdivisions 111, and parts of facies 11, V, VI, VII, VI11 and IX. Forms major part of "medium aquifer"of Leggat et al. (1962). Middle Plioceneto middle Miocene LSFLower Santa Fe Unit; eolian, playa-lake, and alluvial facies; sandy to fine-grained basin-floor sediments, which include thick dune sands and gypsiferous sandy mudstone, intertongue with conglomeratic sandstones and mudstones nearthe basin margins (early-stage piedmont alluvium); as much 1000 as ft thick. Unit includes basin fill that correlates with much of the Ha:mer Ranch and the lower Rincon Valley Formations, whose type arens are in thewestern Jornada del Muerto (Rincon) Basin; also includes much of lithofacies IV andX, and parts of facies VII, VI11 and IX. Forms major partof "deep aquifer" of Leggat et al.(1932). Middle Miocene to late Oligocene * Lithofacies subdivisions of hydrogeologic units are defin,?d in Table 3 4b TABLE2 Key to bedrockunits and upper Cenozoic volcanics (Plates 2-17) These rocks areprimariiy hydrogeologic boundary units with very low hydraulic conductivities. However, limestones may locallybe highly permeable in zones with solution-enlarged joints and fractures. Fractured sandsto?e, conglomerate, welded tuffs, and lavas also form aquifers in a few areas. QbBasaltic volcanics, mostly flows, with local cindercone and conduit material, that cap or areinterbedded with the upper and middle Santa Fe Group. Quaternary and upperPliocene 2b Basalticplugs and minor flows that penetrate, cap, or are interbedded with the lower and middle SantaFe Group. Miocexe Tr Rhyoliticvolcanics, with some interbedded sandstone and conglomerate mostly ashflow tuff and lava. Oligocene Tri Rhyoliticigneous-intrusive complexes; mostly sills, plugs and associated lava domes. Oligocene Ti Silicic to intermediateintrusive rocks. .Oligocene andEocene Tv Andesiticand other intermediate.volcanic and volaniclastic rocks, including lava flows and laharic breccias and mudstones. Eocene and Oligocene Tvi Undivided Tv andintermediate intrusive rocks. Tvs Intermediatevolcaniclastic rocks, with minor lava flows and intrusive units; primarily Palm Park Formation. Eocene and Oligocene Trv Undivided Tr andTv or Tvs T1 Mudstone,sandstone, and conglomerate with local gypsum beds. Lower Tertiary, mainly Eocene TVl UndividedandTvT1 K Cretaceous rocks--undivided;.includes limestone,.sands,tone.ard mudstone. TK UndividedTi, Tv, T1, K. KP UndividedCretaceous and Permian rocks. PU UpperPaleozoic rocks (Pennsylvanian and Permian); includes limestone, shale, sandstone, and mudstone, with local gypsum beds. P Undivided Paleozoic and Precambrian rocksof the southern Franklin Mountains; includes limestone, shale, sandstone, metamorphosEd sedimentary and volcanic rocks, and granite. 5 Table 3 Lithofacies subdivisiarr of kin- and valley-fill and their occurrence in rock-stratigralhic and hydrostratigraphic rnits in the nesilla Basin. Rock-stratigraphic units Informalhydrostratigraphic units and correlative lithofacies end aquifer system (Table 1) (Table 1) Sard and gravel, river-valley and basin-floor fluvial facies; recent and ancestral Rio Grade channel and floodplain deposits underlying 1) the nxrdern river-valley floor--facies Iv, 2) river-terracesurfaces-. deposits primarily in the vadose zone, and3) relict or buried basin-floor fluvial plains--facies Ib. The latter surfacesinclude the La Mesa gemrphic surface (Gile et al. 1981). Gravel is characterized by sub-rounded to well-rourded pebbles and smallcobbles ofresistant rock types (mainly ign,eous ard metamorphic) derived in part from extra-basin source areas. 1v. sand and pebble to cobblegravel, with thin, organic-richsilty sand to Younger valley fill, river- River alluvim, upper part of - silty clay lenses; indurated zones ofcarbonate cementation rare or absent; as floodplain and ChaMel aquifer system rmch as 100 feetthick. deposits Ib. Sand and pebblegravel, with thin discontinuous beds and lensesof Major component of the Camp Major component of wrSanta Fe sandstone, silty sard, and silty clay;extensive basin-floor fluvial facies; Rice Fm (Upper Santa Fe hydrostratiqraohic unit; mostly in usuallynonindurated, but with local zones that are cemented with calcite Grq); intertongueswith vadose zone in basin areas outside the (cmn), and otherminerels (uncmn) including silicate clays, iron-manganese facies 11, Ill, V, and locally MesillaVallev: occurs in lower Dart oxides, gypsun, silica, and zeolites; 200 to 400 feetthick in centralbasin IX of shallow a&fer system in northern areas. MesillaValley; and forms part of the wraquifer system outside the valley. Sand, withdiscontinuous beds and lensesof pebbly sand, silty sad, sandstone, Major component of Camp Rice Major conponent of uwer Santa Fe silty clay, and nuistone;extensive basin-floor fluvial facies and localeolian Formation, and present in the hydrostratiqraphic unit; partly in deposits;gravel carposition as in facies I; usuallynonindurated, but local Fort Hancock Fm (Middle to vadose~~~ zme ~~ in basin ~~ areas~~ ~ outside ~~~ ~ the ~ cemented zones as in facies Ib; clean sand and pebbly-sandbodies make up an Upper Santa Fe Group) in the MesillaValley; occurs in lower part estimated 65-85 percentof unit; 300 to 750 feet thick in central basin areas. Mesilla Basin; intertongues of shallow aquifer system in northern withfacies Ib, 111, V, and MesillaValley; forms parts of the locally IX uooer and medial aquifer system throughout the basin. Interbedded sard, silty sad, silty clay, and sandstone; withminor lenses of Majorccxpment of Fort Major component ofmiddle Santa Fe pebbly sand and conslaneretic sandstone; basin-floor alluvial and playa-lake Hancock Formation, and present hydrostratigraphic unit, and minor facies;clay mineralogy of silty clay beds as in unit IX; usuallynonindurated, in the Carrp Rice Formation; constituent of unit umer Santa Fe: but withLocal cementedzones as in facies Ib and 11; secondarycarbonate and intertongueswith facies 11, sad, pebbly sand and'bilty sand beds' gypsunsegregations locally present in silty clay beds; cunnon sheet-like to V, IX, and Locally Ib. in facles I11 form a major part ofthe broadly-lenticular strata 10 to 40 feet thick: clean sard layers make up en medial aquifer system. estimated 35 to 65 percentof unit; 300 to 1,000 feetthick in centralbasin areas. sand to silty sand, with Lenses ordiscontinuous beds of sandstone, silty clay, Major canpOnent of unnamed Majorcmponent of lower Santa Fe and mudstone; eolian and alluvial facies primarily deposited on basin floors ard formation in the Lower Santa hydrostratigraphic unit; sand and contiguous piedmont slopes; nonindurated to partly indurated, with cementing Fe Group; probably correlative silty sand beds in facies IV form a agents including calcite (cmn), silicate clays, iron-manganese oxides, with parts of the Rincon large part of a deeo aquifer system. gypsm, and zeolites (uncmon); clean fine to mediun sand makes up an estimated Valley and Hayner Ranch 35 to 65 percentof unit; as much as 600 feetthick. Formations in northern Dona Ana County; intertongueswith facies VI1 srd X V. Gravelly sand-silt-clay mixtures (loamy sands to sandy clay loam) Major conponent of Camp Rice Component of both umr and middle interstratified within discontinuous beds and Lenses of sand, gravel, loamy sand and Fort Hancock Formations; Santa Fe hydrostratigradlic units; an silty clay; distal to medial piechnt-slope allwial facies (mainly intertongueswith facies 11, clean to Loamy sand and gravellenses coaleascentfan deposits), with minor cOmpOonent of eolian sediments; gravel Ill, VI, and IX in facies V form parts of the primarily in thepebble and small cobble size range, and clast composition and mer aouifer systems. reflects character of sourcebedrock terrane; usually nonindurated, but with thin discontinuouslayers that are cemented with calcite; clean sand and gravel makes up an estimated 25 to 35 percentof unit; as rmch as 600 feet thick. VI. Coarse gravelly sand-silt-clay mixtures (loamy sard and sandy loam to loam) Cmpcnent of Cerrp Rice and CompMent of both umr and middle interstratified with lensesof sand and gravel;proximal to medial pi-nt- Fort Hancock Formations; Santa Fe hvdrostratigrahic units; slope alluvial facies--fan and coalescentfan deposits; gravel primarily in the intertongues with facies V and clean sand and gravel Lenses in facies pebble to cobblerange (up to 10 inches); clast composition reflects lithologic Vlll. VI form parts of themedial and upper characterof source bedrockterranes; usually nonindurated, but with aquifer system. discontinuous layers that are cemented with calcite; clean sand and gravel Lenses make anestimated 15 to 25 percent of unit; as rmch as 300 feet thick. VII. Conglmratic sandstone, silty sandstone. and mudstone with Lenses and Majorconponent of unnamed discontinuous beds ofconglomrate, sand, gravel, and gravelly sand-silt-cley formation in lower part of mixtures(as in unit V); distal to medialpi-nt-slope alluvialfacies, with Smta FeGroup; probably minorccmpnent of eolian sediments;coarse clast sizes and canposition as in correlative with piedmont unit V; moderately-wellto poorly indurated; cementingagents includecalcite facies of the Rincon Valley aquifer system. (cwrmon) and silicate clays, iron-manganese oxides, silica and zeolites and HaynerRanch Formations; (ummn); cleanueakly-cemented sard and gravel beds make up an estimated 5 to intertongueswith facies IV, 15 percentof unit; as much as 600 feet thick. VI11 and X. VIII. Coarse conglmratic sandstoneand silty-sandstone,fanglomerate, and minor Component of basal Camp Rice Minor component of all three - lenses ofsard and gravel;proximal to medialpiedmont-slope allwial facies-- and Fort Hancock Formations, hvdrostratiarachicunits; neakly- and coalescent fan deposits; coarse clast sires and compositions as in unit VI; and mmedformations in cemented sand and gravel beds in moderately towell indurated; cementingagents as in unit VI; moderately to well Lower part ofSanta Fe GrOUp facies VI11 form small parts. of the indurated;cementing agents as in unit VII; clean,weakly-cemented sand and (as in units VI1 and IV); mr. medial and deep aquifer gravellenses make up an estimated 5 to 10 percentof unit, as nuch as 300 feet intertongueswith facies V, VI systems. thick. and VI1 I'X Silty clay interbedded uith thin silty sand, sad, sandstone, and &stone beds; Major component of the Fort Makes up fine-grained part of middle basin-floor playa-lake and allwial-flat facies;clay mineral assemblage Hanckco Formation and locally Santa Fe hydrostratigrarhic unit; sard includes calcim smectite, mixed layer illite-smectite illite, and kaolinite present in the Carrp Rice and silty sand beds in facies IX form (Anderholm, 1985); secondary depositsof calcite, gypsun, sodiun-magnesiun- Formation; intertongueswith very minor to negligible component of sulfate salts, and zeolites are locally present; weakly-cemented fine to medim facies Ill, 11, V, and locally the medial aquifer system. sand and silty sand makes up an estimated5-10 percent of unit; as nuch as 600 Ib; gradesdounuard into unit feet thick in centralbasin areas. X in centralbasin areas X. Mudstone and claystone interstratified uith thin sandstone and silty sandstone Major component of unnamed Major component of lower Santa Fe beds; basin floor playa-lake and alluvial-flat facies; clay mineral and non-clay formation in lower part ofthe hydrostratiarahic unit; ueakly- secondary mineral assemblages as in facies IX; weakly cemented fine to medim Santa Fe Group; probably cemented sand and silty sand beds in sard and silty sand makes up an estimated 0 to 5 percent of unit; as nwch as 600 correlative uith basin-floor facies X form very minor to negligible feetthick in centralbasin area. facies of the Rincon Valley coolponent of deep aquifer system. and HavnerRanch Formstions: intertbngueswith facies IV' and VI1 deposits. This work included geological loggingof commercial and domestic wate.r wells being drilled in the Mesilla and Jornada del Muerto Basins, and developing a water-well database that ultimately could be used to update existing ground-water reports by Sayre and Livingston (1945), Conover (1954), Knowles and Kennedy (1958), and Leggat et al. (1962); and complement ongoing studies by the City of El Paso (Cliett, 1969). Re.ports summarizing stratigraphic and geomorphic aspects of this research were published in 1969 (Hawley; Hawley and Kottlowski, Hawley et al.). In 1965, a formal study of geology and groundwater resources of central and western Dofia Ana County was initiated by the NMSU Earth Science Department in cooperation with the SCS and funded by the New Mexico Water Resources Research Institute and the U.S. Department of Agriculture. W. E. King was Principal Investigator and Hawley was responsible for geological-aspectsof the research. -This study was completed in 1968 and published by the NMWRRI and NMBMMR (King et al., 1971). A threefold division of basin-fill aquifers into lower;.intermediate (medium);and upper (shallow) zones, oiiginally proposed by Leggat and others (1962) and Cliett (1969) was recognized as being characteristic of lithofacies distribution.patterns that are widespread in the Santa Fe Group, at least in the southeastern Mesilla Basin. These early investigations demonstrated the need for a much more comprehensive and quantitative evaluation of the area's water resources. In 1972, the USGS-Water Resources Division established a field office in Las Cruces and initiated ground-water investigations under the direction of C. A. Wilson. The results of this major continuing effort, now headed by R. G. Myers, have been published by the NMSEO and the USGS (Wilson et al., 1981; Wilson and White, 1984; Myers and Orr, 1985; Nickerson, 1986, 1989; Frenzel and Kaehler, 1990). After the untimely death of Clyde Wilson in 1980, a new effort on integratkg all available subsurface geological and geophysical data on the Mesilla and southern Jornada Basins was initiated by Hawley, now Senior Environmental Geologist with the NMBMMR. This work was primarily funded by the Bureau of Mines and partly supported by the NMWRRI through a grant to the New Mexico Tech Geoscience. Department (Dr. Raz Khaleel, P.I.). A set of 17 hydrogeologic sections (Ix and " 1Ox vertical exaggeration) and a map (1:125,000) showing major boundaIy faults were prepared for that study and published as an appendix to a WRRI report by Peterson, Khaleel, and Hawley (1984) on "Quasi Three-Dimensional Modeling of Ground Vater Flow in the Mesilla Bolson, New Mexico." The hydrogeologic sections and base map were also published as NMBMMR Open-File Report 190, which is included in th" present report as Appendix B. The provisional 10-unit classification of lithofacies distribution in basin and valley i% and the hydrogeologic cross sections developed for the 1984 study have been used in the present investigation; but they have been modified considerably (compare Appendix B and Plates 1, 16 and 17). Continued research on basin hydrogeology also included cooperation with staff and graduate students at NMSU and the University of Texas System working in the areas of geology and geophysics, and with L. H. Gile (SCS soil scientist-retired) on Desert Project soil-geomorphology studies. Syntheses of geologic and geophysical 7 aspects of these studies are published as Geologic Maps 53 and 57 (Seager et al., 1982, 1987) of the New Mexico Bureau of Mines and Mineral Resources. Desert Project research publications include Bureau Memoir 39 (Gile et al., 198l), and Gile (1S87, 1989). Research reports and graduate theses have been completed by Figuers (1587) Gross and Iceman (1983), Mack (1985), Snyder (1985), VanderhiU (1986), and Ven (1983). Related work on siting of future radioactive-waste disposal facilities has also been done under contract with the US. Geological Survey, Basin and Range Working Group (Bedinger et al., 1989). This study included preparation of hydrogeologic sections of basins and ranges in the Mesilla-Hueco Bolson area of New Mexico and westcrn Texas. Methods and Techniques Data Collection and Analysis The initial step of the 1987 investigation was to collect and review all pertinent geologic and hydrologic information on the Mesilla Basin. This was done in order to develop a comprehensive database from which the hydrogeologic framework was constructed. Much of this information had already been collected for the earlier modeling study by New Mexico.Tech (Appendix B; Nawley, 1984; Peterson et al., 1984). Key sources of surface and borehole data were identified and located on base maps of the Mesilla Basin (scales 1:24,000 and 1:100,000) for use as control points. These data include borehole cuttings and geophysical logs, geothermal and geochemical repods, and geologic maps. Six water-test wells drilled by the USGS and the City of El P-<.so as part of this study provided supplemental information. The Afton, Lanark, La Unitm, and Noria test wells (MT 1 to 4) were drilled in the basin area west of Mesilla Valley (La Mesa surface). The other two wells (CWFlD and 4D; Nickerson, 1987, 1989) are located in the CanutiUo Well Field area on the Rio Grande floodplain west of Vinton, Texas. Subsurface data were supplemented by detailed seismic.reflection profiles made at two sites near the Canutillo Well Field (C. B. Reynolds and Associates, 1986, 1987). Drill Cuning and 7% Section AnaIysis Cuttings from the Afton, Lanark, La Union, and Noria test wells (MT 1 to 4) were initially analyzed with a binocular microscope in order to construct a geologic log for each well and to determine sample intervals for thin section work. No preliminary cutting analysis was performed on samples from the Canutillo Field (CWFlD and CWF4D) because these wells were drilled very late in the study. Color, grain size, and other major characteristics of the sediments were noted on the geologic logs. Cutt'ngs were analyzed in approximate 10 ft (3 m) intervals. Geophysical and driller logs aided in the initial examination of the cuttings. Based on the cutting analysis, samples for thin section study were collected at approximately 100 ft (30 m) intervals from representative sand beds in the Afton, Lanark, La Union, and Noria wells. Samples were also collected from sandy intervals within the CWFlD and CWF4D wells, and from Santa Fe Group outcrops in the area. Locations of sampled wells and outcrops are shown on Plate 1. Forty-six thin sectilms 8 were analyzed using criteria described by Dickinson (1970) in order to determine detrital modes and provenance. Thin-section petrographic data and interpretatiors are presented in Section 111 and Appendix A. Four hundred framework grains per thin section were point counted using a petrographic microscope. Ternary diagrams were constructed based on the point counts and data were also plotted on the geologic.- petrographic logs of the Afton, Lanark, la Union and Noria Test Wells (Plates 12-15). Digitizing Borehole Geophysical Logs Concurrently with the cutting and petrographic analysis, borehole geophyskal data from selected key wells were digitized and then plotted onto computer-generated worksheets with a basin cross-section format. The borehole data were plotted to an altihide datum-of 4,500 ft (1372 m) above MSL(vertica1 scale 1 in = 100 ft, 1cm = 12.2 m). Digitizing of geophysical .logs,and plotting of :cross-section worksheets was .done at the USGS-WRD District Office in Albuquerque. The ComputerLgenerated. graphics system utilized in this study for.integrating geophysical, geologic.and -hydrologic data (Plates 2-15) was developed by Ken Stevens; formerly with that office. Hydrostratigraphic Unit Correlation and Hydrogeologic Framework The basic approach of this investigation was the correlation of borehole-electric (resistivity), geologic-petrographic, and driller logs. Plates 12-15 summarize this information for the four test we& (W 1 to 4) drilled as part of this study in representative areas of the central and southern parts of the basin. After detailed review of geophysical and geologic-petrologic data, and supplemental geothermal and geochemical information (Tables 4 to 6), initial correlations were made between these key boreholes and other wells in the basin (Plate 1).Ken Stevens of the USGS-U'RD and Francis West of the NMSEO collaborated in this phase of the study. Prelimirary cross section plots based on analyses of these data were prepared and reviewed prior to preparation.of ten representative-hydrogeologicsections of the basin. The sections, with selected borehole geophysical and geochemical data, are illustrated in Plates 2 anll 11. Plates 1, 16 and 17, with supporting data in Tables 1 to 3, integrate the above information into a conceptual model of the basin's hydrogeologic framework. The model's base elevation is 1,000 ft (305 m) above mean sea level. Well-Numbering Systems Wells in New Mexico are identified by a-location-number system based on the township-range system of subdividing public lands. The location number consists of four segments separated by periods, corresponding to the township, range, section, and tract within a section (Fig. 2a). The townships and ranges are numbered according to their location relative to the New Mexico base line and the New Mexico principal meridian. The smallest division, represented by the third digit of the final sequent, is a 10-acre (4 ha) tract. If a well has not been located precisely .enough to be placed within a particular section or tract, a zero is used for that part of the location number. Wells in Texas are officially given a well number consisting of five parts (F'g. 2b). The first part is a two-letter prefix used to identify the county, with El Paso County 9 Figure h.Well numbering system: Diagram showing system of number& wells in New Mexico. 10 LOCATION 'OF WELL JL-49-04-501 49 1-degree quadrangle 04 71-minute quad-angle 5 24-minute quad-angle 01 Well number within 24-minute quadrangle JL Symbol for El Paso County 2 13 21-minute quadrangles Figure 2b. Well numbering systems: D&am showing system of numbering wells in Texas. 11 being represented by JL. The second part of the number has two digits indicating the 1- degree quadrangle. Each 1-degree quadrangle is divided into 64 7%-minute quadrangles. This is the third part of the well number. The first digit of the fourth part indicates the 2%-minute quadrangle, and the last two digits comprise a sequence number that identifies the well from others in the same 2%-minute quadrangle. As an example (Fig. 2b), well JL-49-04-501 is in El Paso County (JL),in 1-degree quadrangle 49, in 7%- minute quadrangle 04, in 2%-minute quadrangle 5, and was the first well invento.-ied in this 2%-minute quadrangle. Acknowledgments Numerous individuals and organizations provided assistance during the course of this study and earlier related investigations. Valuable contributions have been personally made by a large number of the authors of cited references. Many of the basic concepts on the area’s geology have been developed by F. E. Kottlowski and W. R. Seager. Other important collaborators on geological and geophysical aspects of the study include R. E. Clemons, L. H. Gile, Tom Gustavson, G. R. Keller, Shari Kelley, Greg and Pamela Mack, Paul Morgan, C. B. Reynolds, Jay Snyder, W. S. Strain, and Jim Vanderhi’l. The conceptual model of the basin’s hydrogeologic framework was developed over a period of three decades in collaboration with Tom Cliett, W. E. King, Bob Myers, Dave Peterson, Andrew Taylor, and the late Clyde Wilson. Ken Stevens, formerly with the U.S. Geological Survey-Water Resources Division, Francis West. of the New Mexico State Engineer Office, and Tom Cliett, formerly with the El Paso Water Utilities Department, were the driving forces behind the present study; and they played a key role in defining the geological, geophysical and geohydrologic eleme7ts that are basic building blocks of the conceptual model. Special acknowledgment iq due to Ken Stevens who developed the computer-generated graphics system used in tl is study. Logistical and financial assistance by the U.S. Geological Survey-Water Resources Division (Albuquerque, Las Cruces and El Paso offices), El Paso Water Utilities Department, Elephant Butte Irrigation District, International Boundary Commission, New Mexico Bureau of Mines and Mineral Resources, New Mexico State Engineer Office, and New Mexico Water Resources Research Institute is gratefury acknowledged. Bob Myers, Ed Nickerson and Don White of the USGS Las Cruces and El Paso offices have been particularly helpful, as have Peter Frenzel, Charles Haywood, and Mike Kemodle of the USGS Albuquerque office. This report is dedicated to the memory of Clyde k Wilson, who headed the USGS-WRD office in Las Cruces from 1971 until his untimely death in 1980. Clyde was an unassuming and highly motivated public servant who played a key role in putti2g ground-water hydrology and hydrogeology of the Mesilla Bolson area on a sound technical and scientific footing. His expertise and common-sense approach to watcr- resource investigations are greatly missed. 12 11: GEOLOGIC SETIWG OF THE MESILLA BASIN Introduction The Mesilla Basin (Figs. 1 and 3) is at the southern end of a north-trending series of structural basins and flanking mountain uplifts that comprise the Rio G-ande rift (Chapin and Seager, 1975; Seager and Morgan, 1979; Chapin, 1988). The rift extends through New Mexico from the San Luis Basin of south-central Colorado to the Hueco Bolson and Bolson de 10s Muertos area of western Texas and northern Chihuahua (Hawley, 1978). The rifting process began in Oligocene time, about 25 to 30 million years ago (Ma), and is continuing at present. During this long intervab extensional forces have stretched the earth's crust, causing large basin blocks to rqtate and sink relative to adjacent mountain uplifts. All rift basin fill that was deposited prior to formation of the Rio Grande Valley in the .early to middle Pleistocene (1.7 to 0.7 Ma) is included in the Santa Fe Group (Bryan, 1938; Spiegel and Baldwin, 1963; Hawley et al., 1969; Hawley, 1978; Chapin, 1988). The upper Rio Grande now flows southward through a series of valleys cut along the deeper parts of most of the riftbasins as far as El Paso. Beyond the Paso del Norte gap (El Paso "Narrows" between the Franklin .and Juarez uplifts, Fig. 1) at the so-lthern end of the Mesilla Basin, the river flows southeastward down the Hueco Bolson exis along the International Boundary . toward the Big Bend area of Trans-Pecos Texa9. Intermontane-basin and river-valley tills of the Rio Grande rift comprise the major aquifer systems of the region and are the principal subject of this report. The Mesilla Basin, covering an area of about 1,000 sq mi(2590 km?, is in the southeastern part of the Basin and Range physiographic province (Fig. 3; Hawley,. 1986). It extends southward about 60 mi (100 km) from the upper Mesilla Valley betwee.n the Robledo and Doiia Ana Mountains to a poorly defined ground-water divide near the International Boundary west of El Paso and Ciudad Juarez. Basin width varies from about 5 mi (8 km) at its northern end to about 25 mi (40 km) in its central part. Flanking mountain uplifts (Juarez-Franklin-southern Organ on the east and East Potrillo-Robledo on the west; Plate 1) are narrow and relatively low-lying (less than 8,000 ft, 2440 m, elev.) in comparison with ranges of the northern and central Rir Grande rift (Hawley, 1978). Broad plains with low topographic relief (less than 500 ft, 150 m) .characterize much of the basin area (Hawley, 1975; Gile et al., 1981). The single major erosioral feature is the broad Mesilla Valley of the Rio Grande located on the east side of the basin (Fig. 1). An extensive remnant of the,basin-floor surface that predates river-valley incision is preserved between the Mesilla Valley and the East Potrillo and Robledo uplifts. This geomorphic surface is called "La Mesa" in many earlier reports on the area (Conover, 1953; King et al., 1971; Gile et al., 1981) but is simply designated the "West Mesa" in recent water resources publications (Wilson et al., 1981; Myers and Orr, 1986). Basin Structure and Bedrock Units The internal structure of Mesilla Basin is complex (Figs. 3 and 4, Plates 1, 16, and 17). Structural interpretations in this report are based on oil and geothermal test- well, water-well, and both surface and borehole geophysical data (Plates 2-15, Table 4). 13 C 4LLL Fault-hatchures on downthrown sidqdashed I 10 20mi where inferred or buried Cross section -I 10 20km - - - - Figure 3. Index map of Mesilla Basin area showing locations of major boundary and intrabasin faults, adjacent mountain uplifts, and geologic cross sections (Fig. 4). 14 W n Figure 4. Diagrammatic geologic cross sections of the northern and central Mesilla basin. 15 The major structural elements include three large subbasins (eastern, southwestern, northwestern), with general north-south trends, a buried mid-basin uplift, and an inferred south-central basin that extends into Chihuahua west of the Cristo Rey (Sierra Juarez) uplift- The northeastern boundary of the Mesilla Basin is formed by a pa-tly- buried bedrock ridge, designated the Doiia Ana-Tortugas uplift on Plate 1. Topographically, the basin merges northward with the Jornada del Muerto Basin, northeast of Las Cruces, and southward with the Bolson de Los Muertos plains, southwest of El Paso-Ciudad Juarez (Figs. 1 and 3). AU boundaries between the major subbasins and flanking uplifts appear to be formed by zones of high-angle normal faults. Many of the exposed mountain blocks are strongly tilted, and at least some of the basin blocks have a tilted half-graben morphology and listric boundary faults that.are.typica1 of most continental rift baqins (Rosendahl, 1987; Seager, 1989; in press; Seager et al., 1984; 1987). Dips are usually very low in the central basin area, however; and the major subbasins and intrabash uplifts are here interpreted as only slightly tilted graben and horst blocks which a-e bounded by high-angle normal faults that may or may not flatten signiscantly with depth (Fig. 4, Plates 16 and 17). Basin subsidence was initiated in late Oligocene time, but maximum differential displacement between the major basin and range structural blocks probably occur-ed between 4 and 10 million years ago (late Miocene to early Pliocene). By late Mio:ene time rock debris eroded from adjacent highlands, and possiblyfrom adjacent parts of the Rio Grande rift, had filled existing subbasins (mostly half grabens) to the point where intrabasin uplifts (horsts) were buried by lower and middle Santa Fe Group deposits. The broad topographic basin formed by this infilling process continued t? aggrade as a single (upper Santa Fe) unit through the early middle Pleistocene when widespread basin filling ceased due to entrenchment of the Rio Grande Valley system. The thickest Santa Fe Group fills in the Mesilla Basin (about 3000 ft, 900 m) are located in areas adjacent to themost active segments of major boundary fault zones-the Mesilla Valley, East Potrillo, and East Robledo (Figs. 3 and 4, Plates 16 and 17). Bedrock Units of Basin-Margin UpIifts The Mesilla Basin, in contrast to many basins of the northern and central Rio Grande rift, is not bounded by continuous ranges of high mountains (Hawley, 1978; Chapin, 1988). Onlap of basin fill has buried most of the Doiia Ana-Tortugas and southern Organ-Bishop Cap uplifts on the northeastern basin margin, and the East Potrillo and Robledo uplifts to the west. Only the Franklin and Juarez uplifts at the basin’s southeastern edge form well-exposed structural highlands (Fig. 1). Tertiary igneous intrusives (granites to monzonites) and volcanics (rhyolites to andesites) are the dominant rocks exposed in the Dofia Ana and southern Organ Mountains (Seager et al., 1976; Seager, 1981). Marine sedimentq rocks, mainly carbonate types, of Paleozoic and early Cretaceous age are the dominant lithologic units exposed in the Tortugas, Bishop Cap, Franklin, Juarez, East PotriUo, and Robledo uplifts (Harbour, 1972; Kelley and Matheny, 1983; LeMone and Lovejoy, 1976; Lovejoy, 16 1979; Seager et al., 1987; Seager and Mack, in press). A variety of sedimentary ald intermediate-intrusive rocks of Cretaceous and early Tertiary age crop out in the Paso del Norte area between Franklin Mountains and Sierra de Juarez, which includes Cerro de Cristo Rey on the Chihuahua-New Mexico border (Fig. 1; Lovejoy, 1976). Middle Tertiary volcanic and intrusive rocks of intermediate to silicic composition are exposed in isolated upland areas such as the Sleeping Lady and Aden Wsin the western part of the Robledo uplift, and Mount Riley northwest of the East Potrillo Mountains (Fig. 1; Seager, in press). No additional information on the configuration of the basin's buried northeastern boundary (Doiia Ana-Tortugas-Bishop Cap trend) was collected during the presext study. Provisional interpretations in Hawley (1984; Appendix B, Plate H-H) will be revised in a future report after surface geophysical surveys and test driUing programs in that area have been completed by the U.S. Geological Survey. Bedrock Units Beneath the Basin Fill Analyses of drill cuttings and geophysical logs from a few deep test wells (oil and gas, water, and geothermal), and surface ,geophysical surveys are the only sources of information on the lithologic character and structure of bedrock units beneath the rift- basin fill. Oil and gas test holes descnied by Seager and others (1987), including wells 25.1.32.141 and 26.1.35.333 in the central part of the basin (this report), encountered a thick sequence of lower to middle Tertiary volcanics and, lower Tertiary sedimentary rocks. The latter unit of continental origin was deposited in deep, northwest-trenc'ing basins of Laramide age (Seager et al., 1986). The lower Tertiary section is only erposed in a few places along the northern and eastern basin margins (Seager et al., 198r. Cretaceous and upper Paleozoic underlie the middle to lower Cenozoic sequence at great depth in most parts of the basin; but Cenozoic units may rest directly on lover Paleozoic or Precambrian rocks in a few areas (Seager 1989; Seager et al., 1986). All deep test drilling to date indicates that lower to middle Tertiary volcanic and volcaniclastic rocks of intermediate to silicic composition are the dominant units tllat immediately underlie Santa Fe Group basin till. .Besides the previously mentioned oil tests, water test wells that have definitely penetrated these units include wells24.1.8.123, 25.1.6.333, and 27.1.4.121 in the central part of the basin, and wells 24.2.4.334, 29.3.2.243, and 49-04-109 east of the Mesilla Valley faukzone near the east edge of the basin (Plates 1, 16 and 17). Basin-Fill Stratigraphy Middle and upper Cenozoic sedimentary deposits of the Rio Grande rift can be subdivided into two major units: 1) Santa Fe Group basin fill of late Oligocene to middle Pleistocene age, and 2) post-Santa Fe, river-valley and basin deposits of m'ddle and late Quaternary age. These sediments are locally interbedded with and capped by basalt and andesite flows and pyroclastic (vent) deposits. Associated with these extrusive rocks are intrusive bodies that include feeder dikes, plugs, sills and breccia pipes. Dated basalts in the southwestern New Mexico region include scattered occurrences of middle Miocene to Pliocene age and extensive lava fields of Quaternary age. Pleistocene basalt 17 flows and associated vent units (e.g. cinder cones, lava shields, and maars) form a widespread cover on the upper Santa Fe Group in the west-central Mesilla Basin area, and they also cap large parts of the southern Robledo and East Potrillo uplifts (ITQffer, 1976; Seager et al., 1987; Seager, 1989, in press). Basaltic andesites of late Oligocene age, which are interbedded with lower Santa Fe beds and extensively exposed the. Sierra de Las Uvas area of northwestern Dofia Ana County (Fig. l),may be present in the basal part of the Mesilla Basin fill. Volcanic layers of basaltic to andesitic composition have been reported in drilling records of two water wells in the northern basin area including the Mesilla ValleJr near Las Cruces (24.1.13.411) and may be either flows of siUs interbedded with or intruded into the basin fill. A new well drilled at the Las Cruces waste-water treatment plant (about 1.5 mi, 2.4 lan, WSW of.23.1.13.411) reportedly,encountered a basalt layer at a depth of about 880 ft (270 m) in the middle to lower part of the basin-fill section (R. G. Myers, oral communication 7-14-92). Santa Fe Group The Santa Fe Group (Spiegel and Baldwin, 1963; Hawley et al., 1969; Chapin, 1988) is the major fill component of Rio Grande rift basins. In southern New Mexico and western Trans-Pews Texas the Group ranges in age from about 25 to 0.7 Ma and inchdes alluvium derived from adjacent structural uplifts and nearby rift-basin areas, and locally thick eolian and playa-lake sediments. Fill thickness in most of the central basin area (between the Mesilla Valley and East Potrillo-Robledo fault zones) ranges from 1,500 to 2,500 ft (460-760 m). In this report, the Santa Fe Group is subdivid-d into informal lower, middle and. upper lithostratigraphic units defined on the basis of general lithologic character,' depositional environments, anddiagenetic features related to age and post-depositional history. Generally-equivalent hydrostratigraphic units are discussed in Section IV. The lower Santa Fe Group is dominated fine-grained basin floor sediments that intertongue with alluvial fan deposits beneath the distal piedmont slopes that border adjacent mountain uplifts. Sandy eolian sediments locally form thick sheets and lenses that are interbedded with both basin-floor and .piedmont-slope deposits. Buried dune complexes as much as 500 ft (150 m) thick have been identified beneath the Mesilla Valley in the Anthony-Canutillo area (Cliett, ,1969; Hawley, 1984) and are probably preserved in other parts of the eastern (La Union-Mesquite) subbasin (Plate 1). Pick eolian deposits possibly also occur in the deeper parts of the southwestern subbasin east of the East Potrillo fault zone. Lower Santa Fe beds probably range in age from 25 to 10 Ma and were de3osited in a closed-basin setting prior to the final interval of deep basin subsidence and ..lift of the higher flanking range blocks (e.g. Organ, Franklin, East Potrillo, and Robledc Mountains). Formal lithostratigraphic subdivisions of the lower Santa Fe Group have not yet been proposed for the Mesilla Basin. However, the unit is generally correlative with the Hayner Ranch Formation and the lower part of the Rincon Valley Formltion mapped in the Jornada del Muerto-Rincon Valley area of northern Dofia Ana Ccunty (Seager and Hawley, 1973; Seager et al., 1971, 1982, 1987). 18 The middle Santa Fe Group was deposited between about 10 and 4 Ma when rift tectonism was most active and deposition in subbasins adjacent to the major boundary fault zones (Mesilla Valley, East Potrillo, East Robledo) was most rapid. In many areas erosion of uplifted basin borders and deposition on adjacent piedmont slopes also accelerated relative to early Santa Fe time. Rapidly aggrading central basin plain? were characterized by broad alluvial flats that terminated in extensive playa lakes; and, most mid-basin uplifts are deeply buried by Middle Santa Fe deposits. Alternating bed: of clean sand, silty sand, and silt-clay mixtures are the dominant lithofacies (Section:: LII and IV) in much of the central basin area. Eolian sediments also continued to accumulate in leeward (eastern) basin area; but the thickest buried dune sequences appear to be confined to the bwer Santa Fe Group. .Formal lithostratigraphic.subdivisiom.havenot yet been proposed; but the middle Santa Fe unitprobably correlateswitkat least~theupper partof the Rincon Valley Formation (Seager et al., 1982, 1987) and-thelower Fort Hancock Formation, which has a type area in the southeastern. Hueco Bolson (Strain, 1966; Hawley et al., 1969; Gustavson,1991). The upper Santa Fe Group contrastsmarkedly with older.Santa Fe units in terms of lithologic character. About 3 to 4 million. years ago, the floor of the Mesilla Bssin was transformed from an internally-drained feature to the broad fluvial plain of a throughgoing river. Braided distributary channels of the ancestral upper Rio Grarde spread southward across the basin-floor and ultimately terminated in large playa-lake plains in the Bolson de 10s Muertos of north-central Chihuahua and the southern Tularosa Basin-Hueco Bolson area of New Mexico and western Texas (Hawley et al., 1969, 1976; Hawley, 1975, 1981; Gile et al., 1981; Seager et al., 1984, 1987). Sandy deposits.,of this complex fluvial-deltaic system continued to accumulate on the Mesilla Basin floor through early Pleistocene time. Recent research on basin-fill magnetostratigraphy panderhill, 1986; Mack et al., 1991) and dating of volcanic ash lenses in the upper part of the Santa Fe sequence (Gile et al., 1981) demonstrate that widespread fluvial aggradation of the Mesilla.Basin floor.(and Santa Fe Group deposition) had ceased by about 0.7 Ma. By 0.6 Ma, significant incision of upstream and downstream canyon areas (Selden and El Paso) had.already occurred; and entrenchment of the Mesilla Valley by the ancestral Rio Grande had begun. The uppermost part of the Santa Fe Group in the south-central New Mexico and western Texas area, and the main upper Santa Fe component, is the Camp Rice Formation of Strain (1966). It has now been.recognized and mapped in detail from the southern Palomas and Jornada del Muerto Basins, across the Mesilla and souther? Tularosa Basins, and throughout the Hueco Bolson to its type area near Fort Hancock in Hudspeth County, Texas (Hawley et al., 1969; Seager et al., 1971, 1976, 1982, 1987; Hawley, 1975, 1978; Gile et al., 1981; Gustavson, 1991). Camp Rice deposits are very well preserved throughout most of the Mesilla Basin, with significant erosion only occurring in the Mesilla Valley and valleys of a few major arroyos. The formation’s thickness ranges from about 300 to 700 ft (90-215 m) in central basin areas. The dominant lithofacies of the Camp Rice Formation is the complex of fluvial sand and pebbly sand deposits laid down by the ancestral Rio Grande. However, 19 because of complex channel shifts (influenced by both tectonism and climatic factors) in the ancestral river system during the long interval of basin-floor aggradation, &ne- grained (slack-water) facies are locally present. The other important Camp Rice lithofacies is a piedmont-slope facies assemblage that is primarily composed of fax alluvium and associated debris-flow deposits. To the south and southeast, the basal Camp Rice of the Mesilla Basin area appears to intertongue with and overlap fine- grained alluvial and playa-lake deposits of the upper Fort Hancock Formation of Strain (1966). In their type areas near Fort Hancock in Hudspeth County, Texas, the Camp Riceport Hancock Formation contact has been dated at about 2.5 Ma (Vanderhill, 1986; Gustavson, 1991). Post Santa Fe Deposits :Post-Santa Fe Group sedimentary units of middle and late Quaternary age were deposited in two contrasting geomorphic settings: (1) valleys of the Rio Grande a7d tributary arroyo system, and (2) extensive.intermontane-basin 'areas still not integrated with the river (Hawley and Kottlowski, 1969;Hawley, 1975; Gile.et al., 1981). Valley-€ill units were deposited during repeated episodes of river incision separated .by intervals of partial backIXing that produced the present ,landforms of the Mesilla Valley. The stepped-sequence of geomorphic surfaces (mainly alluvial .terraces and fans) that border the inner-valley (floodplain) area are mainly the product of valley-entrenchment episodes during Pleistocene glacial (pluvial) stages, and subsequent intervals of vdley aggradation during interglacial (pluvial) stages. The 60 to 100 ft (18-30 m) of medium- to coarse-grained alluvium beneath the modem river floodplain ("flood-plain alluvium" of Frenzel and Kaehler,l990) is a product of (1) valley cutting by a high-energy fluvial system during the late Wisconsinan .(full) glacial substage about 15 to 25 thousand years ago pa), and (2) valley filling during the late-glacial and ongoing, Holocene inte-glacial stage that started about 10 Ka. Tributary alluvial systems have delivered more sediment to the valley floor than the river could transport out of the drainage basin during this ongoing period of fluvial aggradation. The shallow aquifer system in the Mesilla Valley is formed by (1) the saturated part of the inner-valley SU, and (2) channel sands and gravels in underlying beds of the upper Santa Fe Group that were deposited by the ancestral Rio Grande during .th e mid- to late Pliocene interval of basin filling. Older valley fills, of the tributary arroyo systems as well as the ancestral river, that are preserved in terrace remnants on the valley borders ("valley-border surfaces"), are generally above the water table and are not descriied in this report. Thin (<30 ft, 10 m) alluvial, eolian, and playa-lake sediments deposited in areas of the Mesilla Basin still not integrated with the Rio Grande a1e also not discussed. They are included with the upper Santa Fe unit in the hydrogeologk cross sections (Plates 2-11, 16-17) that are covered in Section Tv. Younger valley and b,-lsin fills, and soil-geomorphic relationships are descriied in detail by Gile et al. (1981) and Seager et al. (1987). 20 III: SAM)-FRACTION PETROGRAPHY Introduction Prior to the present study, no detailed geologic or geophysical informatior had ever been collected from deep water test wells in the central and southern basin area west of the Mesilla Valley. The four test wells drilled in 1986 for the U. S. Geological Survey and the City of El Paso at the Afton, Lanark, La Union, and Noria sites (Plate 1, 25.1.6.333, 27.1.4.121, 27.2.13.331, and 28.1.34.414) were specifically designed to provide baseline information on general basin fill lithology, sand-fraction petrography, borehole geophysics, and ground-water quality at selected drill-stem sample intenals. Because no core samples were taken, lithologic and petrographic analyses could cdy be done on sets of drill-cuttings carefully collected at ten-foot intervals from these test wells. Sand-fraction petrographic interpretations described in this section have be.en integrated with selected borehole lithologic and .geophysical.data .in .four geologic columns (Plates 12-15). These columns illustrate basic hydrogeologiccharacteristics of basin-fill deposits in the area of the four.test.holes; and they demonstrate that correlation of the major lithostratigraphic subdivisions of the Santa Fe Group (lover, middle, upper) descriied in Section II-ispossible .throughout much ,of the Mesilla Basin. The hydrostratigraphic units described in detail in Section IV, which generally correspond to these basin-fill subdivisions, are also shown on Plates 12 through 15. Supplemental analyses of sand-fraction petrography from two recent test holes in the Canutillo Well Field (CWF 1D and 4D; JL-49-04-481; Nickerson, 1989) were also done as part of this study. This is the area where Santa Fe Group basin fill was originally subdivided into "lower, medium, and upper" aquifer zones by Leggat an1 others (1962; Cliett, 1969). Methods and Techniques Preliminary Drill-Cutting Analyses Cuttings from the Afton, Lanark, La Union, and Noria test wells were analyzed initially with a binocular microscope in order to construct a stratigraphic column for each well and to determine intervals where subsamples of representative sands an4 sandstones would be collected for thin section analyses. Color, grain size, and,,otht:r major characteristics of the sediments were noted on the.stratigraphic columns. Cuttings were analyzed in approximate 10 ft (3 m) intervals. Geophysical and driller logs aided in the initial analyses of the cuttings. Thin Section Sample Collection and Preparation Based on the cutting analysis, thin section samples were collected in approJimate 100 ft intervals from the above four wells. Samples were also collected from sandy intervals penetrated by the Canutillo Well Field test holes (CWFlD and CWF4D). In addition, samples from representative Santa Fe Group outcrops were collected to use as a standard for comparison with the subsurface samples. Locations of sampled outcrops are given in Appendix A. 21 Wherever possible, medium- to coarse-grained sand was sampled. Finer-grained samples were used only when coarser samples were unavailable. Ingersoll et al. (1984) have shown that sand grain size does not affect point counting results. Sand samFles were sieved (2.0-0.125 mm) to collect only the sand fraction. To guard against po.sible contamination, the sieved sand was re-examined with a binocular microscope to r5move foreign material (i.e., wood, cement, seeds, drill bit shavings). Next, the sand samdes were impregnated with epoxy and cut into standard thin sections. The final step i7 thin section preparation was to stain half the thin section slide with sodium cobaltinitr3e to facilitate potassium feldspar identification. Thin Section AnaEys.6 Thin sections of the well cuttings and outcrop samples were analyzed using criteria described by Dickinson (1970) in order to determine detrital modes and provenance. Other workers (i.e., Mack, 1984; Lozinsky, 1987) have shown that point counting is a powerful tool for analyzing Santa Fe Group deposits. A total of 46 thin sections were examined; 37 from well cuttings and 9 from outcrops. Four hundred framework grains per thin section were counted using a Nikon binocular polarizirg microscope and a Swift digital point counter. Counts were primarily made at 100% but other magnifications were sometimes used. Nicols were usually crossed, except fcr occasional glances at plain light. Parameters counted and used to define petrofacies are listed on Table 5. Only framework grains were counted. Matrix and interstitial mace were not counted because most samples were loosely consolidatedand broken apart in the drilling process. After each point count, the thin section was further examine3 to determine grain size, sorting, roundness, and other important features. Point comt results are summarized in Table 6 and listed in Appendix A. Ternary diagrams (Figs. 5- 7) were constructed based on the thin section point counts. 22 Table 5. Point-count grain parameters. Modified from Dickinson (1970) Counted rmrameters Qm = monocrystalline quartz Qpt = tectonic polycrystalline quarts Qpn = nontectonic polycrystalline quartz (inc. chert) P = plagioclase feldspar K = potassium feldspar Lv = volcanic lithic fragments Lm = metamorphic lithic fragments Ls = sedimentary lithic fragments (silt and shale) LC = carbonate lithic fragments M = phyllosilicates Reaalaulated Darameters QP = QPt + QPn Q = Qm + Qp F=P+K LSC = LS + LC Lst = Qp + Lsc L = LV + Lm + LSC QFL%Q = lOOQ/ (Q+ F + L) QFL%F = 100F/(Q + F + L) QFL%L = lOOL/(Q + F + L) LmLvLsc%/Lm = lOOLm/L LmLVLSC%/LV = lOOLV/L LmLVLSC%/LS = lOOLS/L LvLstLm%Lm = lOOLm/Lm + Lv + Lst LVLStLm%LV = lOOLV/Lm + LV + LSt LvLstLm%Lst = 100Lst/Lm + Lv + Lst 23 Table 6. Means (x) and standard deviations (s) of point counts on water well and outcrop samples. N = number of samples. Uater Yells Qn QPt Qpn P K LV Lm Ls LC Afton (25.1.6.333) MT-1; N = 7 2.1x .35 43.8 28.0 7.0 17.6 .03 .5 .42 s 4.2 .37 .5 3.2 2.1 2.8 .34.09 .27 Ml-02158 3.8 11 26 0 .8 .25 0 .25 Lanark (27.1.4.121) MT-2; N = 5 x .4542.4 3.0 26.3 9.1 18.1 .I .25 .4 s.45 3.3 .9 4.4 .8 4.4 .14 .30 .28 M2-015 00 0 0 0 100 0 0 0 La Union (27.2.13.331) MT-3; N 7 x 47.0 .46 2.5 26.2 8.3 13.6 0 .6 .8 s.3 2.6 1.1 3.25.8 3.5 0 .2 .5 Norla (28.1.34.414) MT-4; N = 5 x .45 43.8 2.9 29.1 8.5 14.6 .05 .45 .2 6 1.9 .I .?a 3.7 1.3 4.7 .I .3 .I CWF 40 .15 x 47.8 2.4 12.2 21.9 14.1 .05 .7 .5 .9 1.9 .45 .3 .45 (JL-49-04-469) 1.9 s.12 2.2 .9 .a 2.9 .1 49.1 0.3 2.4 20.4 16.3 10.3 16.3CUF ID20.4 2.4 0.3x 49.1 0 .6 .4 (JL-49-04-481) s 2.9 0.4 1.4 0.8 1.8 2.6 0 .13 .28 N=5 ID-009 1 6.0 3.00 4.0 .o 30 550 1.0 Mcrops Qn QPt ppn P K LV Lm 15 LC Upper Santa Fe Gp 2.3 .2X 43.8 19.4 11.6 21.7 .I .8 .I N=71.8 s.3 3.5 4.2 3.2 2.3 .2 .4 .I Middle Santa Fe Gp x 17 0 32.8.75 14.6 34.0 0 .4 0 N=2 s 2.2 0 .3 .24.9 2.2 0 .2 0 24 Sand Petrography of Selected Samples of Well Cuttings Well cuttings analyzed petrographically consist of loosely consolidated, moderately to well sorted sands that can be classified as lithic arenites and litharenites after Folk (1974). Sand grains are fine- to coarse-grained and subangular to subrounded. As shown on Table 6, monocrystalline quartz (42-49%) and plagioclase (20-29%) are the dominant detrital grains in the well cuttings. Many quartz grains are clear, exhibit rapid extinction and overgrowth rings. Detrital plagioclase and plagioclase phenocrysts occurring in rock fragments range in composition from oligoclase to labradorite, but most are andesine (determined by the Michel-Levy method), The grains usually display twinning and sometimes oscillatory zoning. Most feldspar grains are fresh, but some show sericitic alteration. Volcanic-rock fragments (10-16%) ?.re the dominant lithic fragment. They-exhibit .porphyritic:and::microlitic textures and appear to be mainly andesitic. Most potassium feldspars are orthoclase and sanidine, but significant amounts of microcline are also present. Minor amounts of detrital che.rt (2- 3%), carbonate-rock fragments (<1%), sedimentary-rock fragments (<1%), and metamorphic-rock fragments (< < 1%) occur. When the point counting results are plotted.on the various ternary diagrams (Figs. 5 and 6), little variation in sand composition-isseen with depth except for a slight increase in lithic fragments (L) and a decrease in potassium feldspar (K). Most cf the point counts cluster in the same general field. The only exceptions are samples hrl-021 (Afton), M2-015 (Lanark), and CWF 1D-009 on Fig. 5 and Table 6. These samp'es contain very high percentages of lithic fragments and represent pre-Santa Fe or bwl Santa Fe Group deposits. On the QFL plots, wells CWF 1D and CWF 4D have the highest mean quartz percentages (51.8 and 50.4) whereas wells MT 1 and 2 (Afton and Lanark) have the lowest (46.3 and 45.8). Feldspars averaged between 3437% in all wells, with K-feldspar being relatively abundant only in the Canutillo Well Field (CWF, Table 6, Appendix A), particularly in well CWF 1D located east of the Rio Grande at the base of the Franklin Mountain block. Lithic fragment percentages are highest in wells MT 1 and 2 (19 and 18.7) and lowest in wells MT 4 (Noria) and CWF 4D (11.3 and 14.7). Except for the bottom sample from CWF-lD, the LvLsLm plots show no groupings, as more than 90% of all lithic fragments are volcanic in origin with 3-5% being sedimentary and Comparison with Santa Fe Group Outcrops Results of point counts on the outcrop samples are also summarized on Ta4le 6, listed in Appendix A, and plotted on Fig. 7. Except for the two Rodey samples, all outcrop samples plot within the same fields on the ternary diagrams as the well cutting samples. All outcrop samples in the Mesilla and Palomas (T or C area) Basins are. from the upper Santa Fe Group whereas the two Rodey samples are from the middle Smta Fe - Rincon Valley Formation. The Rodey samples also had source areas that differed from those of the middle Santa Fe units penetrated by test wells in the Mesilla Basin. 25 Figure 5. Ternary diagrams of sand-fraction petrography (thin- section point-count data, Tables 5 and 9 for well cuttings from representative Sank Fe hydrostratigraphic unib at: Afton (MT l),Lanark (MT 2), and Canutillo Well Field (CFW 1D). 26 Fig. 5 -26,a 0 AFTON CWF- 1 D F i Lm Lv Ls Lm Figure 6. Ternary diagrams of sand-fraction petrography (thin-section point-count data, Tables 5 and 6) for well cuttings from representative Sank Fe hydrostmtigrap’lic units at: La Union (MT 3), Noria (MT 4), and Canutillo Well field (CWF 4D). 27 Fig.6 27% 0 LA UNION NORIA A CWF- 4D P fL2-" F L Lv Ls Lm Lv Lst Figure 7. Ternary diagrams of sand-fraction petrography (thin-section pointaunt data, Tables 5 and 6) for samples from representative Santa Fe Group outcrops. 28 Fig. 7 28a UPPER SANTA FE GROW Q +TorC x BOX CANlllN *mRA A US HWY70 0 LAUNION MIDDLE SANIAFE GROUP o RODEY F L Lm Lv Lst Overall, point counts (Figs. 5-7) from this study are consistent with counts by Mack (1984) of samples from Santa Fe Group sandstone outcrops near Las Cruces. Provenance Sand samples analyzed from the six water wells and from the outcrop areac (except the two Rodey samples) were derived from more than one source terrain. The abundance of plagioclase (zoned and twinned) and andesitic lithic fragments str02gly suggest an intermediate volcanic source area for most of the detrital grains. Che-t, chalcedony, and abundant quartz (many well rounded with overgrowth rims) indirate reworked sedimentary units as another major source. A granitic source area is also suggested by the presence of microcline, strained quartz, and granitic rock fragments. The paucity of metamorphic-rock fragments and tectonic polycrystallinequartz rules out a metamorphic terrane as a major source area. In the middle Santa Fe Group Rodey samples, the abundance of plagioclase and intermediate volcanic lithic fragments and the paucity of quartz, chert and sedimentary lithic fragments strongly suggestan intermediate volcanic terrane as the only major source area. Due to lack of paleoflow indicators, it is difficult to determine the exact sw~rce area for these deposits. However, it appears that even in early to middle Santa Fe time (Miocene) the central MesiUa Basin area was receiving sediment from a very larg? watershed aIea. A much larger source region was also available for sand and finer grain-size material when the mechanism of eolian transport is taken into account. By middle Pliocene time the ancestral Rio Grande was delivering even pebble-size material to the basin from source terranes as far away as northern New Mexico (e.g. pumirx and obsidian from the Jemez and Mount Taylor? areas). In most cases, visual and birocular microscopic examination of the gravel-size (>2mm) fraction is still the best way to establish local versus regional provenance of coarse-grained fluvial and alluvial deposits. 29 IV: A CONCEPTUAL HYDROGEOLOGIC MODEL OF THE MESILLA FASIN Introduction The conceptual model of the Mesilla Basin's hydrogeologic framework and its development are descnied in this section. Emphasis is on stratigraphic and lithologic characteristics of basin and valley fills, intrabasin geologic structures, and basin- bounding bedrock features that influence the movement, storage, recharge, discharge, and quality of ground water. The area covered extends from the Mesilla Valley on the east, the Robledo and East Potrillo uplifts on the west, 1-10 (west of Las Cruces) on the north, and the International Boundary (west of El Paso) on the south (Plate 1). The base of the model is at 1000 ft (305 m) above mean sea level (Plates 16 and 17); and the water table elevation in the area ranges from about 3750 to 4000 ft (1145-1220 m). Highest basin elevations are about 4400 ft (1340 m), .and,vadose zone thickness e-wxeds 400 ft (120 m) in a few areas outside the Mesilla Valley. Much of the zone of saturation occurs in basin fill that ranges from unconsolidated sand, silt, clay and gravel to partly indurated deposits with layers of sandstone, mudstone and conglomerate. The major aquifers in the area are in the upper 1500 ft (455 m) .of the saturated section. The conceptual model is presented in a combined map and cross-section format (Plates 1, 16, 17), with supporting lithologic, stratigraphic, petrographic, geophysical and geochemical data illustrated in Plates 2-15, and listed in Tables 1 to 4. Informatilm on thin-section petrography of the sand-size fraction was discussed in the preceding section (m>, with supplemental data in Appendix A. A three-dimensional view of basin hydrogeology is provided by eight cross sections, comprising five cross-basin profiIes (approx. west to east; Plate 16) and three longitudinal sections that have a general south to southeast orientation (Plate 17). Horizontal scale is 1:100,000 (approx. 0.6 in Fer mi) and vertical exaggeration is 1OX (approx. 1.2 in per 1000 ft, 1 cm = 100 m). Supporting geological, geophysical (resistivity-log) and geochemical data on individual wells are graphically illustrated in columnar diagrams with a vertical scale of 1in = 100 ft (1 cm = 12.2 m) and unspecified horizontal scale (Plates 2 to 11). The spatial arrangerent of wells on these diagrams corresponds to the cross-section format of Plates 16 and 17. The basic geologic elements that form the,model's framework were descriied in Section II; and historical development of hydrogeologic concepts was outlined in the discussion of previous work (Section I). Earlier .descriptions of basin hydrogeologr (Conover, 1954; Leggat et al., 1962; King et al., 1969; Wilson et al., 1981; Hawley. 1984) were based on limited subsurface data. With the exception on a few deep oil-test holes (e.g. 25.1.32.141, and 26.1.35.333) and a water well at the MARC0 site (25.1.16.111), deep exploration of the Santa Fe Group was confined to areas in or close to the Pfesilla Valley. Inferences on basin-€dl thickness and aquifer characteristics were, for the most part, based on interpretations of uncalibrated surface geophysical data (Merman, 1982; Birch, 1980; Figuers, 1987; Gates et al. 1980; Wen, 1983; Wilson et al., 1981; Zoh'ly, 1969; Zohdy et al., 1976). The present investigation is the first attempt to systematically analyze borehole geophysical and petrographic characteristics of the Santa Fe Group over a large p,~rtof the Mesilla Basin. The conceptual model discussed in this section also contains rany of the hydrogeologic features observed in other Rio Grande rift basins (e.g. Gustavson, 1991; Hawley and Haase, 1992; Hearne and Dewey, 1988; Lozinsky, 1987, 1988), and it 30 is important to note that, throughout the region, current estimates of thickness a.1d areal extent of major aquifer units within the Santa Fe Group are significantly le-s than earlier interpretations. For example, compare Haase and Hawley (1992) with Bjorkland and Maxwell (1961) in the Albuquerque Basin, and King and others (1971), Wilsqn and others (1981), and Hawley (1984; Appendix B) with Plates 2 to 10, 16 and 17 in this report. Still further improvements in characterization of basin hydrogeology will only be possible when additional borehole geophysical data are available in a digital fonrat, where there is more depth-specific geochemical information, and when representative core samples have been obtained from the major aquifer units and confining bed:. The electrical resistivity logs (standard, single-point, and dual induction), drill-cutting sample suites, seismic-reflection profiles, and drill-stem geochemical data used in the present study clearly need to be supplemented with more-sophisticated subsurface and su-face information. Hydrostratigraphic Subdivisions of Basin and Valley Fills The basic hydrogeologic .unit used in conceptual-model-,developmentis the. hydrostratigraphic unit. This informal geologic-material subdivision is analogous to a rock-stratigraphic unit of formational rank: the basic ,mappable body of rocks (sedimentary, igneous, and metamorphic) or unconsolidated earth materials. The. hydrostratigraphic-unit concept used here (as well as in other parts of North America; Back et al., 1988; Barrash and Morin, 1987) requires that it be definable in terms of environment of deposition (of sedimentary strata) or emplacement (of igneous bodies), distinctive lithologic features (textures, mineralogy, sedimentary structures), and general time of deposition or emplacement (in a dated sequence of strata or igneous everts). Geohydrologic characteristics must be definable, and a hydrostratigraphic unit must be mappable in subsurface, as well as at the surface, at a useful map scale in terms of ground-water resource management (e.g. 1:24,000 to 1:250,000). The attributes of four major hydrostratigraphic units (RA, USF, MSF, LSF) and one minor (VA) unit, into which basin deposits have been subdivided, are descnied in Table 1. The major subdivisions of Santa Fe Group basin fill. (Upper, Middle and Lower units - USF, MSF, LSF) broadly correspond to the informal rock-stratigraphic subdivisions discussed in Section II. The river alluvium (RA) unit forms the upper part of shallow aquifer system in the Mesilla VaUey: The eight diagrammatic cross sections of the Mesilla Basin (Plates 16 and 17) illustrate representative distribution patterns of hydrostratigraphic units in subsurface. Because of the large (lox) vertical exaggeration and diagrammatic nature of the cross sections (Plates 16 and 17), the inclination (dip) of faults and stratified sequences cannot be accurately shown. Fill units, however, are highly deformed only in narrqw zones adjacent to major faults. True dips of even basal Santa Fe units rarely exceed 10- 20", and the Upper Santa Fe Unit (USF) is nearly level (Fig. 4; Appendix B - Havley, 1984). Lithofacies Subdivisions of Basin and Valley Fills The second major feature of the hydrogeologk model is the subdivision of basin deposits into distinct material categories (lithofacies) that are defined primarily on the 31 basis of sediment texture, degree of induration, geometry of bodies of a given textural class, and distribution pattern of zones of contrasting texture. They form the basic building blocks of the conceptual model developed for this study. The ten-unit lithofacies clasiflcation system used here (Table 3) is a modification of a scheme originally developed by Hawley (1984; Appendix B) to facilitate numerical model'ng of groundwater systems in the Mesilla Bolson area between Las Cruces and El Pasc by the New Mexico Water Resources Research Institute (Peterson et al., 1984). The lithofacies categories and their subdivisions are defined in Table 3; and a distribution pattern of these units in Mesilla Basin HI is illustrated on Plates 16 and 17. These fundamental hydrogeologic components of basin and valley fills have also been recognized in all major basins of the Rio Grande rift in New Mexico and adjacent parts of Colorado, Texas and Chihuahua. (Spiegel and Baldwin, 1963; Hawley et al., 1969; King et al., 1971; Hawley, 1978; Seager and Morgan, 1979; Gile et al., 1981; Wilson et al., 1981; Seager et al., 1982, 1987; Chapin, 1988; Hearne and Dewey, 1978; Brister, 1990; Gustavson, 1991; Lozinsky and Tedford, 1991). They have been formally defined, however, only in the Albuquerque and Mesilla Basins (Hawley and Haase, 1992; this report). Anderson's.(1989) paper on "hydrogeologic facies models" relating to "glacial and glacial fluvial sediments" is an excellent account of how lithofacies-unit concepts are being used in ground-water research in other geographical areas. Lithofacies units I,JI,Ul,V and VI are unconsolidated or have only discontinuous zones of induration. With the exception of subdivision 111, clean sand to pebbly sand bodies are major components of these units and have relatively high hydraulic conductivity. Clay, silty sand, and weakly indurated sandstone beds interstratified with fine to coarse sand layers characterize lithofacies HI and IV. The latter facies is mainly composed of thick, well-sorted sands that are partly cemented with calcite. Lithofacies W to X are partly to well-indurated units with significant amounts of fine-graine,-l material (silt-clay beds or a sand to gravel framework with clay-silt-fine sand matrix). Channel deposits of the modern and ancestral Rio Grande (facies I and JI\, which are the major components of hydrostratigraphic units RA and USF, form the most important aquifer and potential enhanced-recharge zones in the basin. Coarse- grained distributary channel deposits of large alluvial fans in the Middle and Upp-r Santa Fe units (MSF and USF; parts of facies V and VI) may also have good aquYer potential in local areas. Thick, buried dune-sand deposits in the Lower Santa Fe unit &SF, facies IV) are demonstrably a major "deep" aquifer in the CanutiUo Well Field area. Units with very limited potential for ground-water production are partly- to well- indurated piedmont deposits (facies VI1 and VIq, and thick sequences of fine-grained and locally saline basin-floor sediments that include extensive playa-lake beds in the southern part of the basin (facies JX and X). Inferred subsurface distribution patterns of lithofacies within the five hydrostratigraphic units at specific sites in the Mesilla Basin are shown on Plates 16 and 17. Documentation of these patterns varies from good (where petrographic analysis of drill cutting, bore-hole geophysical logs, and detailed drilling records are available) to strictly inferential (where few or no field data exist). This variation in basic data quality is clearly illustrated in the lithofacies interpretations given on Plates 2-11, 16 and 17. In the large areas and/or depth zones without adequate subsurface control only the most 32 general features of the major hydrostratigraphic units can be shown, and the resrltant conceptual model is based only on inference (i.e. best guesses). However, one important generalization can be made: AU basin-fill units become finer grained to the south; and fine- to medium-grained basin-floor facies are dominant in the international-boundary zone west of Cerro de Cristo Rey (Plate 16e; facies 111, IX and X. How far this fining trend in basin-fill deposits continues into the Bolson del Muertos area of northern Chihuahua is not known. Major aquifers in the border region south of Santa Ter-sa (Plates 6 and 9) will probably be confined to the upper Middle Santa Fe unit (facies II and III, Plate 16e) since the Upper Santa Fe is almost entirely in the vadose zone. The next step in characterization of lithofacies components of hydrostratigaphic units, and one that is beyond the scope of this report, will be to formally assign ranges of hydraulic conductivity values to individual lithofacies or groups of facies in cooperation with other members of the USGS-WRD, NMSEO and NMBMMR staffs. In the present conceptual model, extensive, thick-bedded deposits of fluvial sand and gravel deposits (lithofacies I and 17) are.considered to have relatively high hydraulic conductivities (e.g. in the 30 ft to 300 ft/day, 10-100 m/day range), while playa-lake clays, silts and mudstones (lithofacies IX and X)or well-cemented sandstones and . - fanglomerates (facies VII and VIIIj' have very low conductivities (commonly much less than 0.3 &/day, 10 cm/day). Lithofacies HI to VI should be expected to have average conductivities in the moderate to low range (about 30 to 0.3 ft/day, 10-0.1 m/day), See Frenzel and Kaehler, 1990; and Kernodle, 1992 for detailed information on expec.ted ranges in hydraulic conductivity values and other parameters in ground-water-flow systems. In many valley-border areas, coarse-grained river channel deposits of the IJpper Santa Fe and younger valley-fiU units (USF, VA and RA) are in duect contact (Gie et al., 1981). This relationship has a very negative context in terms of waste managment problems (Stone, 1984); but it also offers exciting possibilities for much more efficient conjunctive use of surface- and ground-water resources (e.g. artificial recharge) at a number of sites. Structural and Bedrock Elements of Hydrogeologic Framework The third major component of the-basin's.hydrogeologic framework includes the bedrock units and structural features that form important boundary zones with respect to saturated- and vadose-zone processes (Table 2). Igneous-intrusive bodies and associated extrusive (volcanic) units within the basin-fill sequence are also locally signiticant parts of the hydrogeologic framework. Structural interpretations are based on geologic studies reviewed in Section 11, and geophysical and geothermal-resour-e investigations, some of which are unpublished (Akemann, 1982; Cunniff. 1986; D: Angelo and Keller, 1988; Figuers, 1987; Gross and Iceman, 1983; Reynolds & Assoc., 1986, 1987; Snyder, 1986; Wen, 1983; Zohdy, 1969; Zohdy et al., 1976). Areal distribution of major structural elements is shown on Plate 1. Surficial geology fo- most of the area (at a 1:125,000 scale) has already been, or will soon be published (Sea7er et al., 1987; in press). Igneous and sedimentary bedrock units form the basin floor and margins, and vertical to near vertical lines on the cross sections (Plates 2-11, 16, 17) show major boundary and intrabasin faults and a volcanic feeder conduit (plug or dike). 33 One of the most significant results of the present study is that there is now much better definition of the basin-fillbedrock contact. Compare Plates 16 and 17 with interpretations by Wilson and others (1981) and Hawley (1984; Appendix B). However, additional drilling and geophysical studies, including seismic reflection surveys, will lead to significant refinements in identification of basin-boundary conditions, particularly in the northeastern and south-central basin areas. Bedrock units (Precambrian to middle Tertiary, Section II) are generally considered to be low-permeability boundary zones in ground-water-flow models (Frenzel and Kaehler, 1990; Kernodle, 1992). However, upper Paleozoic (Pennsylvanian- Permian) and Cretaceous carbonate rocks such as are present in the East PotriUc, Robledo, Franklin and Juarez uplifts may locally provide conduits for significant amounts of ground-water movement A temperature.-login carbonate rocks at the south end of the East Potrillo uplift (Snyder, 1986; Plate 7, Table 4a, 29.1W.6.410) which has isothermic profile segment indicates significant ground-waterflow (at least in that. local area). Basin-Boundary Faults and Santa Fe Group Thickness The structural segmentation of the basin into three major sub-basins (NW, SW, and E) and the mid-basin uplift is discussed in Section IT. Basin fill thickness exceeding 2000 ft (610 m) is well documented by borehole data only in the Eastern (La Unim- Mesquite) and southernmost Southwestern subbasins (Plates 1, 3-7, 16 b-e, 17, Table 4a). Significant thinning of basin fill over the Mid-basin uplift (to about 1500 ft, 455 m) is also well documented (Plates 3, 4, 7-9, 16 bc, 17 b-c). Estimates of basin-fill thickness in most parts of the Northwestern and Southwestern subbasins are based in the premise that deposits in those areas, even near the East Potrillo and Robledo faults, will not be thicker than fills in parts of the Eastern subbasin that are adjacent to the relatively large mountain masses of southern Organ and Franklin uplifts. Structural Influences on Intrabasin Sedimentation Patterns Because the Mesilla Basin is part of an active tectonic.zone (Rio Grande rift) that has been evolving for more than 25 million years (Section II), the distribution pattern of hydro-stratigraphic units and.lithofacies in space and time (Plates 1.6 and 17) must be interpreted in terms of ongoing crustal extension and basin subsidence. Active local extension of the earth's crust and differential,movement, including rotation, of basin and range blocks are the basic structural controls on basin sedimentation. As is evident from the impact on Quaternary geomorphic processes by climate change dated to Quaternary glacial-interglacial cycles, forces other than rift tectonism can also materially innuence erosion, sediment transport, and deposition (Frostick and Reid, 1989). However, on the geologic-time and space scale represented by Santa Fe Gmup deposition, structural deformation and associated igneous activity are the dominant factors that will be considered here in terms of controls on basin sedimentation. The Lower Santa Fe hydrostratigraphic unit (early to middle Miocene) and associated lithofacies (primarily IV, W, VIII, IX,and X) were deposited in a brold, shallow basin that predated major uplift of the flanking mountain blocks (uplifts) bounded by the Mesilla Valley, East Potrillo and East Robledo fault zones (Plates 1, 16, 34 17). The deepest and most actively subsiding part of this basin appears to have been in the "Southwestern" area east of the East Potrillo uplift (Plates 7 and 16e). Petrologic studies of drill cutting and core discussed in Section 111, as well as interpretations based on detailed analyses of samples and drillers logs (Plates 2-11, Tables 4a and 4b), indicate that depositional environments in the Lower Santa Fo hydrostratigraphic unit VU)contrast markedly with those in younger basin fill. During early stages of basin filling, the Mesiua Basin received a major innw of Fne- to medium-grained sediments (muds to sands) from adjacent upland source areas that were sites of late Eocene and Oligocene volcanic activity. Since high mountain areas (such as the present Organ-Franklin-Juarez chain) had not yet formed, wedges of coarse-rrained piedmont deposits were limited to the extreme basin margins. The most striking features of the Lower Santa Fe ;unit (LSF) .are thethick deposits of clean, fine to coarse sand (lithofacies IV), noted in the Eastern (La Union-Mesquite) and Southwestern subbasins, that have been interpreted as buried dune fields in the Canutjllo well-field area and elsewhere in the basin (Cliett, 1969; Wilson et al., 1981; Hawley, 1984). These partly-indurated beds are as much as 600 ft, (185 m) thick in the eastern (La Unim- Mesquite subbasin); and they may be 900-1000 ft (275-305 m) thick in the southwestern subbasin immediately east of the east Potrillo fault zone (Plates 3-5, 7, 10, 11, 16b-e, 17a). Distribution patterns of both piedmont-slope and basin-floor lithofacies (I,lI,III,V to IX) in Middle and Upper Santa Fe hydrostratigraphic units (MSF and USF) have also been greatly influenced by differential subsidence of basin fault blocks behve?n the Mesilla Valley fault zone on the east, and the East Robledo and mid-basin faults on the west (Plates 1, 16, 17). As has been previously noted (Section 1I) tectonic subsidence has been most active in areas adjacent to these fault zones particularly in the Eastern (l.a Union-Mesquite) subbasin. The Middle Santa Fe unit was deposited during late Miocene to early Pliocene time when maximum differential movement occurred between the central basin blocks and the Doka Ana-Tortugas, southern Organ, Franklin, Juarez, East Potrillo, Robledo and Mid-basin uplifts. East of the Rio Grande Valley, both the Middle and Upper Santa Fe units (MSF and USF) are dominated by coarse clastic material (fan alluvium) derived from the rapidly rising southern Organ and Franklin uplifts (Lithofacies \' to Vm>. The developing Robledo and East Potrillo Mountains contributed fan.sedi-nents to the western subbasins during the same interval. Lithofacies III is the major component of the Middle Santa Fe unit in the broad central-basin area that extends west from the Mesilla Valley. It is as much as 1000 ft (305 m) thick in the eastern (La Union-Mesquite) subbasin (Plates 3-5, 10, 11, 16b-d, 17a). This sequence of interbedded sand and silt-clay beds also forms the basin's thickest and most extensive aquifer system ("medial aquifer" in this report, Tables 4a and b). East of the Mesilla Valley fault zone, fan deposits (facies V and Vn) progrsded westward almost to present location of 1-25 during much of the Middle Santa Fe interval. Similar but smaller alluvial aprons extended basinward from the Robledo and East Potrillo uplifts. Complex intertonguing of piedmont-slope and basin-floor sediments is observed in the Middle Santa Fe unit beneath the Mesilla Valley (Plate 17a; MSF; lithofacies II,III,V,VIl, and IX). Analyses of drillers and sample logs shows 35 a mixture of alluvial-fan and basin-floor facies derived from local sources. A precursor to the through-going (ancestral) Rio Grande system may have contributed a large volume of fluvial sand and mud to actively subsiding areas, at least in the northern part of the basin, during latest stages of Middle Santa Fe deposition. Basin-floor aggradation ultimately outpaced basin subsidence and a nearly-level alluvial plair with scattered playa-lake depressions extended across most of the basin area. The Upper Santa Fe unit was deposited during a 2-3 million year interval when large volumes of sediment were washed into the basin by distributaries of the ancestral Rio Grande system that headed as far north as the San Juan and Sangre de Cristo Mountains of southern Colorado (Southern Rocky Mountain province). This fluvial system discharged at various times into playa-lake plains on the Tularosa Basin a1d Hueco Bolson (via Fillmore Pass;Fig. l), as well asthe Bolson de Los Muertos (Hawley, 1975, 1981; Hawley et al., 1976; Gile et al., 1981; Seager, 1981; Gustavslm, 1991). The final phase of widespread basin aggradation throughout the central ard southern New Mexico region (lithofacies Ib and II)occurred during eruptions of the Jemez volcanic center that produced the Bandelier Tuff and the Valles caldera 1 to 1.6 million years ago (Smith et al., 1970; Gardner et al., 1986;.Goff et al., 1989). At that time braided channels of the ancestral Rio Grande shifted across a broad fluvial plain that included most of the present Mesilla Valley and West Mesa (La Mesa) area (Fig. 1, Plate 1). Complex intertonguing of ancestral Rio Grande and piedmont slope-facies (I,II,III and V) characterize the upper Santa Fe Unit (USF)) east of the Mesilla Valley fault zone (Plates 16 and 17). At times progradation of alluvial fans from the Organ and Franklin uplifts was very active (lithofacies V), and the piedmont alluvial aprm expanded across the Mesilla Valley fault zone as far west as the present central Mesilla Valley. The patterns of Upper Santa Fe sedimentation are clearly influenced by bcth local and regional volcanic and tectonic processes, as well as by early Pleistocene and Pliocene climate cycles. Structural deformation has produced more than 2000 ft (610 m) of subsidence in the Eastern subbasin since middle Miocene time (past 10 mXion years). Hundreds of feet of basin subsidence have also occurred along the Mesilla Valley, East Potrillo and East Robledo faults in Pliocene,and Quaternary time. (past 4-5 million years) and clearly influenced the final position of the ancestral Rio Grand? and the distriiution patterns of lithofacies (I,II+IIl and V) in the Upper Santa Fe hydrostratigraphic unit (USF; Plates 16, 17). Differential movement along the major basin-bounding fault zones shown on Plate 1 continued in post-Santa Fe (Quaternary) time and has controlled the position of the inner Mesilla Valley and bordering river terraces from the Selden Canyon to Paso del Norte narrows (Fig. 1). Valley fills units (VA) are definitely offset by faults east of the Robledo Mountains (Gile et al., 19;?1). 36 v. SUMMARY Introduction This report descriies the results of a hydrogeologic study by the New Mexico Bureau of Mines and Mineral Resources (NMBMMR) in the Mesilla Basin between Las Cruces, New Mexico and the International BoundaIy west of El Paso, Texas. Ths two major study objectives were (1) to develop a detailed conceptual model of the bacin's hydrogeologic framework that is based on a synthesis of all available geological, geophysical, and geochemical data, and (2) to present that information in a format suitable for use by the U.S. Geological Survey, Water Resources Division (USGS-WRD) in developing numerical models of the ground-water flow system. These modelling efforts will, in turn, provide a much more quantitative base for management decisions on future strategies for water-resource development.,and conservation. Predictive models are particularly important because of the potential for water quality degradation and land subsidence due to excessive ground-water withdrawals that have been proposed in some parts of the Mesilla Basin. Funding for the initial phase of data compilation and model development in 1987 was jointly provided by the NMBh4MR and the U.S. Geological Survey, Water Resources Division (USGS-WRD, contract no. 14-08-D001-G-726), and subsequent support has been furnished by the NMBMMR. Work was done in cooperation with personnel of the USGS-WRD Albuquerque, Las Cruces, and El Paso offices, Nev Mexico State Engineer Office, and El Paso Water Utilities Department. In its simplest form, the conceptual model of a basin's hydrogeologic framework is a graphic portrayal of (1) the lithologic character; geometry, and geologic history of basin-fill deposits; and (2) the bedrock units and structural features that form the basin boundaries and influence intrabasinal depositional environments. When firmly based on adequate (geological and geophysical) data on subsurface conditions, the model characterizes the basic "architecture" of mappable subdivisions of basin deposits that can be defined in terms of their aquifer properties. The fill of the Mesilla Basin has two basic hydrologic components: Santa Fe Group basin fill and Rio Grande Valley fill. In terms of volume and areal extent, the Santa Fe Group forms the bulk of basin-fibg deposits. It comprises a very thick sequence of alluvial, eolian, and lacustrine sediments dep0sited.h intermontane basins of the Rio Grande rift structural province during an interval of about 25 million years starting in late Oligocene time. Widespread filling of several structural subbasins, which in aggregate form the Mesilla Basin, ended about 700,000 years ago (early Middle. Pleistocene time) with the onset of Rio Grande (Mesilla) Valley incision. Post-Santa Fe Group valley fills include (1) inset deposits of the ancestral Rio Grande and tributary-arroyo systems that form terraces bordering the modeni floodplain, and (2) river and arroyo alluvium of the inner valley area that has bee? deposited since the last major episode of Rio Grande Valley incision in late Pleistxene time (about 15,000 to 25,000 years ago). The three basic hydrogeologic components of the MesiUa Basin model comprise: 1. Structural and bedrock features. They include basin-boundary mountah uplifts, bedrock units beneath the basin fill, fault zones within and at the edges of basin that innuence sediment thickness and composition, and 37 igneous-intrusive and -extrusive rocks that penetrate or are interbedded with basin deposits. 2. Hydrostratigraphic units. These mappable bodies of basin and valley fill are grouped on the basis of origin and position in a stratigraphic sequence. Genetic classes include ancestral-river, present river-valley, basin-floor playa, and piedmont alluvial fan deposits. Time-stratigraphic classes include units deposited during early, middle and late stages of rift-basin filling (i.e. lower, middle and upper Santa Fe Group), and post-Santa Fe valley fills (e.g. channel and floodplain deposits of the Rio Graude, and fan alluvium of tributary arroyos). 3. Lithofacies subdivisions. These units are the basic building blocks of t’le model. In this study, basin deposits are subdivided into ten lithofacies (I through X) that are mappable bodies defined on the basis of grain-size distribution, mineralogy, sedimentary structures, and degree of post- depositional alteration. They have distinctive geophysical, geochemical, and hydrologic attributes. Report Format The report has four major narrative sections (I. Introduction; 11. Geologic Setting; nI. Sand-Fraction Petrography; and IV. Conceptual Model), a comprehcnsive reference list, and two appendices (A. Basic petrographic data, and B. Preliminary hydrogeologic cross sections that extend into adjacent parts of the Jomada and H.leco basins). The hydrogeologic framework of the Mesilla Basin area as defined by Frenzel and Kaehler (1990) is graphically presented in map .and cross-section format (Plates 1, 16 and 17). Supporting stratigraphic, lithologic, petrographic, geophysical, and geochemical data from 61 wells are illustrated in stratigraphic columns and hydrogeologic sections (Plates 2 to 15). Tables 4a and 4b summarize the subsurface information used in this study, including (1) well location and depth; (2) ground-vater levels; (3) drill-stem sample intervals; (4) selected data on ground-water chemistry: and (5) data sources. Major hydrostratigraphic units and aquifer zones sampled are a!so identified in Tables 4a and 4b. Section I The introductory section of this report outlines previous work on basin hydrogeology, particularly that done since 1962 when the senior author started his investigations in the Las Cruces area of Doiia Ana County. Study methods and techniques are also covered in this section. Emphasis is on the team approach uxd in the analysis of borehole (geological, geophysical, and geochemical) data to develo-, the final conceptual model of hydrostratigraphic and lithofacies unit distribution. Section II Section I1 provides a general geological overview of the Mesilla Basin regicn including the structure of flanking mountain uplifts and relationship to contiguous basin areas. The area discussed comprises parts of the Jornada del Muerto, Tularosa, Fueco, and Los Muertos basins in New Mexico, Texas, and Chihuahua Emphasis is on t’le 38 relatively recent interval of geologic time (-past 25 million years) when major structural and topographic elements of the present landscape formed (Seager an? Morgan, 1979; Gile et al., 1981; Seager et al., 1984, 1987). The interval was characterized by regional extension of the earth's CNS~and differential uplift, subsidence and tilting of individual crustal blocks along major fault zones to fonr internally complex basins and ranges. This continental "rifting" process produced the Rio Grande rift structural zone that extends from southern Colorado to western Texas and northern Chihuahua Rift basin fiUs that predate Pleistocene entrenchment of the Rio Grande Valley system comprise the Santa Fe Group. The Mesilla Basin is near the southern end of the rift zone and is relatively shallow in comparison to many other rift basins (Chapin, 1988, Lozinsky, 1987, 1388; Brister, 1990; Hawley and.Haase, 1992). :Maximum'thickness of upper Cenozoic fill is about 3,000 ft (1900 m). The lower and middle parts of the Santa Fe Group form the bulk of the basin fill. These units were deposited in an internally drained complcx of three subbasins that were initially separated by a.central (north-trending) intrabasin uplift (Eastern, Northwestern, Southwestern subbasins, and-Mid-basin uplift on P:ate 1). Even though differential movement of intrabasin and -basin-bounding faults:continued throughout late Cenozoic time, the basin-filling process outpaced structural deformation; and individual fills of early-stage subbasins ultimately coalesced to form the widespread blanket of basin fill that characterizes the upper part of the Santa Fe Group. Eolian sands and fine-grained playa-lake sediments are major lithofacies in the lower and middle Santa Fe Group. These units are locally well indurated and only produce large amounts of good-quality ground water from buried dune sands (lower Santa Fe) in the eastern part of the basin beneath the Mesilla Valley. Poorly consolidated sand and pebble gravel deposits in the middle to upper part of the Smta Fe Group form the most extensive aquifers of the area. Widespread channel depxits of the ancestral Rio Grande €irst appear in upper Santa Fe beds that have been datcd at about 3.5 million years (Ma) in southern New Mexico and 2.5 Ma in western (Trrns- Pecos) Texas. Expansion of the Rio Grande (fluvial) system into upstream and downstream basins, and integration with Gulf of Mexico drainage in the early to middle part of the Quaternary (Ice-Age) Period about 700,000 years ago led to rapid incision of the Mesilla Valley and termination of widespread basin aggradation (ending Santa Fe Group deposition in the Mesilla Basin). Cyclic stages of valley cutting and filling correlate with expansion and contraction of Alpine glaciers and pluvial lakes in ths southern Rocky Mountain, and Basin and Range region. These cycles are represented by a stepped-sequence of valley border surfaces that flank the modem valley floor. Fluvial sand and gravel deposited during the last cut-and-fill cycle form a thin, but extensive shallow aquifer zone below the Rio Grande floodplain. Recent fluvial sediments are locally in contact with ancestral river facies in the upper Santa Fe Cnoup, particularly in the northern Mesilla Valley. They form the major recharge and discharge zones for the basin's ground water, and are quite vulnerable to pollutior in this urban-suburban and irrigation-agricultural environment. 39 Structural deformation of subbasin boundaries and topographic relief between deeper basin areas and flanking uplifts continued to change over geologic time. For example, during early stages of basin filling (lower Santa Fe deposition) many of the present bounding mountain blocks had not formed or had relatively low relief. Thickest basin-fill deposits (up to 1500 ft, 455 m, of middle Santa Fe Group) were emplamd between 4 and 10 million years ago during most active uplift of the Organ-Franklin- Juarez range and the Robledo Mountains, and subsidence of the Eastern (La Union- Mesquite) subbasin. The major (Mesilla Valley) fault zone is now buried by the recent valley fill beneath the present KOGrande floodplain. Section IlI The petrographic investigations ,descn%edin Section III emphasize the fundamental properties of rock fragments and mineral grains,that in aggregate foln the various lithofacies subdivisions of the five hydrostratigraphic units (Tables 1 and 2). Tools needed to properly describe earth materials in fine .detail include the binoc-llar microscope for preliminary drill-cutting descriptions;.the petrographic.(light) micrqscope from rock and grain thin-section analyses, and.x-ray equipment and.the-scanning electron Microscope for characterization of ultra-fine-scale features (e.g. grain-surface features, cementing agents, and porosity). Only the binocular and petrographic microscopes were used in this study to analyze the sand-size fraction from selected sets of drill cuttings and outcrop samples. Anderholm (1985) describes preliminary x+ay analyses of fine-grained materials from several Rio Grande Basins (including the Albuquerque and Mesilla Basins). Cuttings from the Afton (MTl), Lanark (MT2), La Union (MT3), and Noria (MT4) were analyzed initially with a binocular microscope in order to construct a stratigraphic column for each of these key wells (Plates 12-15) and to determine intervals (approximately every 100 ft, 30 m) where subsamples of representative sands would be collected for thin-section analyses. Samples were also collected from representative sandy intervals in the two wells in the Canutillo Field (CWFlD and 4D) and from six outcrops of the Upper and Middle Santa Fe units. Sand samples analyzed from the.six water wells and from outcrop areas in the Mesilla Basin were derived from more than one source terrane. lkabundance of plagioclase (zoned and twinned) and andesitic lithic fragments strongly suggest an intermediate volcanic source area for most of the detrital grains. Chert, chalcedony, and abundant quartz (many well rounded with overgrowth rims) indicate reworked sedimentary units as another major source. A granitic source area is also suggested by the presence of microcline, strained quartz, and granitic rock fragments. The pau'5ty of metamorphic-rock fragments and tectonic polycrystalline quartz rules out a metamorphic terrane as a major source area. In the middle Santa Fe Group samples from the Rincon Valley area (Rodey site), the abundance of plagioclase and intermediate volcanic lithic fragments and the paucity of quartz, chert and sedimentary lithic fragments strongly suggest an intermediate volcanic terrane as the only major source area. Due to lack of paleoflow indicators, it is difficult to determine the exact sorrce area for these deposits. However, it appears that even in early to middle Santa Fe time 40 (Miocene) the central Mesilla Basin area was receiving sediment from a very larce watershed area. A much larger source region was also available for sand and finsr grain-size material when the mechanism of eolian transport is taken into account. By middle Pliocene time the ancestral Rio Grande was delivering even pebble-size material to the basin from source terranes as far away as northern New Mexico (e.g. pumice and obsidian from the Jemez and Mount Taylor areas). In most cases, visual and binxular microscopic examination of the gravel-size (>2mm) fraction is still the best way t7 establish local versus regional provenance of coarse-grained fluvial and alluvial deposits. Section N The conceptual hydrogeologic model is descriied in detail in Section lV and illustrated on Plates 1, 16; and.17. These plates.are.published at a horizontal scale of 1:100,000 (1 cm = 1 km; approx. 0.6 in/mi);and cross sections have vertical exaggeration of 1OX. The base elevation of the model is 1000 ft (305 m) above spa level and the water table in central basin areas ranges from about 4000 ft (1220 m) to the north and 3750 ft (1145 m) at the southeastem.end of the basin. Outside,the Messilla Valley area the vadose (unsaturated) zone is commonly 300-to 400 ft (90-120 m) thick. Supporting geological, geophysical, and geochemical ,data above an elevation of 1500 ft (455 m) are shown on stratigrapbic columns and hydrogeologic cross sections (Figs. 2- 15) at a vertical scale of 1 in = 100 ft (1 cm = 12.2 m) and variable horizontal scale. The basic hydrogeologic mapping unit used in conceptual model developm>nt is the hydrostratigraphic unit. It is dehed in terms of (1) environment of deposition of sedimentary strata, (2) distinctive combinations of lithologic features (lithofacies) such as grain-size distribution, mineralogy and sedimentary structures, and (3) general time interval of deposition. The attributes of four major (RA, USF, MSF, LSF) and o7e minor (VA) classes into which the area's basin and valley fills have been subdividtd are defined in Table 1. The Upper, Middle, and Lower hydrostratigraphic units of th- Santa Fe Group roughly correspond to the (informal) upper, middle and lower ro2k- stratigraphic subdivisions of Santa Fe Group described in Section II. The other major hydrostratigraphic unit (RA) comprises Rio Grande alluvium of late Quaternary age (< 15,000 yrs) that forms the upper part of the regional shallow-aquifer system. The ten lithofacies subdivisions that.are.the fundamental building,blocks of the model are defined primarily on the basis of sediment texture (gravel sand, silt, clay, or mixtures thereof), degree of cementation, and geometry of bodies of a given textu-a1 class and their relative distribution patterns. Lithofacies I, 11, III, V, and VI are unconsolidated or have zones of induration (strong cementation) that are not continuous. Clean sand and gravel bodies are major constituents of facies I, 11, V, and VI, while clay or cemented sand zones form a significant part of facies 111 and IV. Subdivision IV is characterized by thick eolian sand deposits of the lower Santa Fe unit (LSF) that are partly cemented with calcite. Coarse-grained channel deposits of t'le modem and ancestral Rio Grande (lithofacies I and II) are the major components of the upper Santa Fe (USF) and river-alluvium (RA) hydrostratigraphic units. They form the most important aquifers and potential enhanced-recharge zones in the basin. Lithofacies VI and VIII are partly to well indurated piedmont-slope deposits; whil: 41 facies JX and X comprise thick sequences of he-grained basin-floor sediments that include playa-lake beds. Assignment of specific hydraulic conductivity ranges to individual lithofacies subdivisions is beyond the scope of this investigation. However, as a first approximation, the following general ranges appear to be reasonable: 1. Conductivities of lithofacies I and 11 are relatively high (30 to 300 ft/da;r. 10- 100 m/day) 2. Lithofacies IX and X, and well-cemented sandstone and fanglomerate zones in facies W and VI11 will definitely have very low conductivities (usually much less than 0.3 ft/day, 0.1 m/day) 3. Conductivities in uncemented sand layers in lithofacies 111 and IV, and sand and gravel beds in facies V through WIshould primarily be in the intermediate range (0.3 to 30 &/day, 0.1-10 m/day) In addition to delineation of major hydrostratigraphic units and lithofacies subdivisions in basin and valley fills, the other major contrihtion of this study ha. been the significant improvement in definition of the physical limits of the Mesilla Bash and its component subbasins. Most of this information on bedrock.and structural geology was derived from geologic maps and cross sections, with supplemental data from geophysical and geothermal surveys, that have been recently published or are in rress (Figuers, 1987; Seager, 1989, in press; Seager and Mack, in press; Seager et al., 1987; Snyder, 1986). Unpublished seismic reflection surveys done for the USGS-WRD in the lower Mesilla Valley have also been very useful (C. B. Reynolds & Assoc., 1986, 1987). Unconsolidated deposits make up the bulk of the middle and upper Santa Fe Group and all of the recent valley fill in the Mesilla Basin. Textural classes inclule sand, gravelly-sand, silt-clay, and sandy to gravelly materials with a silt-clay matrix Secondary calcite and gypsum are the primary cementing agents in the basin fill; however, continuously indurated zones are uncommon except in basal parts of the. Santa Fe section. Very coarse-grained alluvium, with gravel primarily in the pebble- to cobble-size range ( 42 (La Union-Mesquite subbasin); and they may be 900-1000 ft (275-305 m) thick in the southwestern subbasin immediately east of the east Potrillo fault zone (Plates 3-5 7, 10, 11, 16b-e, 17a). All basin fill units (USF, MSF, LSF) become finer grained to south, and fne- to medium-grained basin-floor facies, with only minor amounts of gravel, dominate the basin fill section in the international boundary zone west of Cerro de Cristo Rey (Plates 6,7, and 16e; facies 111, IX and X). Most of the Upper Santa Fe hydrostratigraphic unit (USF) in that area is in the vadose zone; and sand beds in the basal Upper Santa Fe unit and upper part of the Middle Santa Fe unit (MSF, lithofacies III) appear to be the only major aquifer east of the Mid-Basin uplift. Lithofacies IV in the Lower Santa Fe hydrostratigrzphic unit (LSU) may also be a potential deep aquifer in the Southwestern subbasin, but this zone has not yet been tested for either quantity or quality of ground water production. Discussion The conceptual model of the Mesilla areas's hydrogeologic framework developed for this report (Plates 1, 16, 17) is simply what its name implies: 1. 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R., in press, Geologic map of the southwest quarter.of the Las Cruces and northwest part of the El Paso Yx2' sheets: New Mexico Bureau of Mines and Mineral Resources, Geologic Map 60, scale 1:125,000. Seager, W. R., and Hawley, J. W., 1973, Geology of Rincon quadrangle, New Me.xico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 102, 56 pp Seager, W. R., Hawley, J. W, and Clemons, R. E., 1971, Geology of San Diego Mountain area, Doiia Ana County, New Mexico: New Mexico Bureau of hlines and Mineral Resources, Bulletin 97,38 pp. Seager, W. R., and Mack, G. H., in press, Geology of the East PotriUo Mountaim and vicinity, Dofia Ana County, New Mexico: New Mexico Bureau of Mines a7d Mineral Resources, Bulletin 113. Seager, W. R., and Morgan, Paul, 1979, Rio Grande rift in southern New Mexico west Texas and northern Chihuahua; in Riecker, R.E. (ed.), Rio Grande rift, te1:tonics and magmatism: Washington, D.C., American Geophysical Union, pp. 87-106. Seager, W. R., Kottlowski, F. E., and Hawley, J. W., 1976, Geology of Dofia Ana Mountains, New Mexico: New Mexico Bureau of Mines and Mineral Reso-Irces, Circular 147, 36 pp. Seager, W. R., Clemons, R. E., Hawley, J. W., and Kelley, R. E., 1982, Geology of northwest part of Las Cruces l0xZosheet: New Mexico Bureau of Mines and Mineral Resources, Geologic Map 53, scale 1:125,000, 3 sheets. Seager, W. R., Shafiqullah, M., Hawley, J. W., and Marvin, R. F., 1984, New K-Ar dates from basalts and the evolution of the southern Rio Grande rift Geological Society of America Bulletin, v. 95, pp. 87-99. Seager, W. R., Mack, G. H., Raimonde, M. S., and Ryan, R. G., 1986, Laramide basement-cored uplift and basins in south-central New Mexico: New Mexilx Geological Society, Guidebook to 37th Field Conference, pp. 123-130. Seager, W. R., Hawley, J. W., Kottlowski, F. E., and Kelley, S. A, 1987, Geologic map of east half of Las Cruces and northeast El Paso 1"xT sheets, New Mexico: New Mexico Bureau of Mines and Mineral Resources, Geologic Map 57, scale 1:125,000, 3 sheets. 49 Smith, R. L., Bailey, R. A, and Ross, C. S., 1970, Geologic map of the Jemez Mountains, New Mexico: US. Geological Survey, Miscellaneous Investigations Map 1-571, scale 1:125,000. Snyder, J. T., 1986, Heat flow in the southern Mesilla Basin, with an analysis of East Potrillo geothermal system, Doiia Ana County, New Mexico: Unpublishec' MS. thesis, New Mexico State University, Las Cruces, 252 pp. Spiegel, Z., and Baldwin, B., 1963, Geology and water resources of the Santa Fe area, New Mexico: U.S. Geological Survey, Water-Supply Paper 1525, 158 pp. Stone, W. J., compiler, 1984, Selected papers on water quality and pollution in N?w Mexico: New Mexico Bureau of Mines and Mineral Resources, Hydrologic Report 7,300 pp. Strain, W. S., 1966, Blancan mammalian fauna and Pleistocene formations, Hudspeth County, Texas: Texas Memorial Museum, Bulletin 10, 55 pp. Uphoff, T. L., 1978, Subsurface stratigraphy and structure of the Mesilla and Hueco Bolsons, El Paso region, Texas and New Mexico: Unpublished M.S. thesis, University of Texas at El Paso, 66 pp. Vanderhill, J. B., 1986, Lithostratigraphy, vertebrate paleontology, and magnetostratigraphy of Plio-Pleistocene sediments in the Mesilla Basin, New Mexico: Unpublished PhD thesis, University of Texas at.Austin, 311 pp. Wen, C-L, 1983, A study of bolson-fill thickness in the southern Rio Grande rift, southern New Mexico, west Texas and northern Chihuahua: Unpublished MS. thesis, University of Texas at El Paso, 74 pp. Wilson, C. A., White, R. R., Orr, B. R., and Roybal, R. G., 1981, Water resources of the Rincon and Mesilla Valleys and adjacent areas, New Mexico: New Mexico State Engineer, Technical Report 43, 513 pp. Wilson, C. A., and White, R. R., 1984, Geohydrology of the central Mesilla Valley, Dofia Ana County, New Mexico: U.S. Geological Survey, Water-resources Investigations Report 82-555, 144 pp. Woodward, L. A., Callender, J. F., Seager, W. R., Chapin, C. E., Gries, J. C., Schaffer, W. L., and Zilinski, R. E., 1978, Tectonic map of the Rio Grande rift region in New Mexico, Chihuahua, and Texas: New Mexico Bureau of Mines and Mineral Resources, Circular 163, pocket. Zohdy, A. A. R., 1969, The use of Schlumberger and equatoria1,soundings in groundwater investigations near El Paso, Texas: Geophysics, v. 34, pp. 713-728. Zohdy, k A. R., Bisdorf, R. J., and Gates, J. S.; 1976, Schlumberger soundings ir the lower Mesilla Valley in the Rio Grande, Texas and New Mexico: U.S. Geological Survey Open-File Report 76-324, 77 pp. 50 APPWDIX A Basic Petrographic Data: Thin section analysesof grain mounts of sieved sand from representative borehole and outcrop samples of Santa Fe Group sands and sandstones, Dona Ana and Sierra Counties, New Mexico. R. P. Lozinsky Part I. Composition of the0.125 - 2 mm size fraction of sandy intervals in Santa Fe Group deposits penetrated by deep wellstest in the Mesilla Basin. Refer to Table5 for explanation ofsymbols. Test YeLL Sqle # (Depth ft) Unit P F L LSLrn LV Lrn LV LSt (PIK) Aftm, HTl (25.1.6.3331 000 ( 40’) USF 47 30 23 0 96 4 0 84 16 (2515) 002 ( 190’) USF 47 32 21 6 0 94 0 85 15 (2715) 006 ( 620’) MSF39 44 17 1 90 799 1 20 (28/11) 010 (1050‘) MSF 18 51 31 0 93 7 0 72 28 (2417) 013 (1370’) MSF 51 35 14 0 93 7 0 80 20 (28/7) 016 (1670’) LSF 43 39 18 0 100 0 0 90 10 (3316) 018 (1870’) LSF 41 39 20 0 96 4 0 84 16 (3217) 021 (2180‘) Tvs?29 12 59 0 99 1 0 98 2 (2514) Lanark ICR (27.1.4.121) 000 ( 40’) USF 44 39 17 0 100 0 0 Ea 12 (30/9) 001 ( 380’) USF33 43 24 0 98 2 0 86 14 (23110) 004 ( 450’) HSF 43 41 16 2 90 8 1 77 22 (3219) 008 ( 880’) MSF 47 30 23 1 195 4 77 22 (2218) 01 1 (1170’) LSF34 51 15 30 97 0 78 22 (24110) 015 (1550’) Tv 0 0 100 0 100 0 0 100 0 51 Test Well SqLe # (Depth ft) Unit Q F L tm LV LS Lm LV LS? (P/K) La Union Wn (27.2-13.331) 000 ( 40') USF 46 29 25 0 93 7 0 83 17 (2415) 003 ( 380') MSF 49 36 15 0 87 13 0 75 2r (29/7) 008 ( 830') MSF 53 29 18 0 95 5 0 73 27 (24/5) 011 (1170') HSF 51 38 11 0 86 14 0 70 30 (27111) 014 (1470') MSF 50 41 9 0 83 17 0 59 41 (31/10) 018 (1840') LSF 48 37 15 0 90 10 0 85 15 (2918) 020 (2020') LSF 54 36 10 0 95 5 0 74 26 (22/14) Yoria llT4 (28.1.34.414) 000 ( 40') USF 49 38 13 6 2 92 2 74 24 (28110) 001 ( 160') USF 44 32 24 0 96 4 0 85 15 (2319) 006 ( 620') MSF 47 38 15 0 98 2 0 78 22 (30/8) 009 ( 970') MSF 48 40 12 0 94 6 0 73 27 (32/8) 012 (1250')13 MSF 39 47 4 0 96 0 77 23 (3217) 52 Test Well Sample # (Depth ft) Unit Q F L LSLm LV Lm LV LS? (P/K) M 1D (JL-49-04-4811 002 ( 250')14 MSF37 49 0 93 7 0 84 16 (21/16) 003 ( 320') "SF 0 80 20 004 ( 440') MSF38 54 8 0 90 10 0 59 41 (19/19) 005 ( 550') LSF 0 74 2c 008 ( 800') LSF 53 35 12 0 96 4 0 68 32 (21114) ow ( 900') KP 10 4 86 0 34 66 0 37 63 ( 311 1 WF 4D CJL-49-04-4691 001 ( 120') MSF 68 30 002 ( 230') MSF 51 36 13 0 88 12 73 27 (24112) 003 ( 350') MSF30 49 21 0 92 8 85 15 (19/11) 004 ( 470') LSF 49 35 15 0 94 6 13 87 (23113) 007 ( 700')12 LSF34 54 0 100 0 82 re (21/13) 53 Part 11. Composition of the 0.125 - 2 mm size fraction of sandy intervals in outcrops of the SantaPe Group. Refer to Table 5 for explanation of symbols. Stratigraphic Unit a F L LS Lm LV Lm LV LSt (P/K) Wpr Santa Fe Grorp AN-la 43 3b 21 0 97 3 0 a9 11 (23/13) AN-lb 21 45 34 4 0 96 0 a3 17 m/a) AN-3 53 30 53 AN-3 17 2 0 9a 22 0 7a (20/10) tu-1 22 28 50 1 97 2 1 ea 11 (la/lo) 70- 1 22 4a 2a 0 9a 5 0 a1 19 (17/13) BC-3 45 37 la 0 96 4 0 86 14 (24/13) TC-1 40 37 23 2 95 3 2 86 12 (25/12) lliddle Santa Fe Grrq R-1 20 47 33 0 99 1 0 96 4 (31/16) R-2 16 51 33 0 w 1 0 9a 2 (3~13) 54 Part 1x1. Locations Of sampled Santa Fe Group outcrops,Dona Ana and Sierra Counties, New Mexico Upper Santa Fe (Camp Rice and Palomas Formations) Anapra Includes 3 samples from upper Santa Fe Group outcrops located west of Sunland Park(AN - la, lb and 2); 295.43.18.1131 La Union Sample from upper SantaFe Group deposits exposed just west of La Union (LU-1); 275.33.18.1411 US-70 Exposure along northside of US-70 just west of Las Cruces - ancestral river deposits(70-1); 23S.13.20.223 Box Canyon Sample from base of Ruhe’s (1962) upper Santa Fe Group section west of Picacho Mountain (BC-3); 23S.lW.2.4323 T or C Sample from Palomas Formation ancestral river deposits exposed in northern Truthor Consequences (TC-1); 13S.4W.28.211 (Sierra County) Middle Santa Fe (Rincon Valley Formation) Rodey Two samples from middle Santa Fe Group (Rincon Valley Formation) deposits exposed south of Rodey,1.5 mi southeast of Hatch(R-1,Z); 195.3W.15.344 55 EXPLANATION - PLATE 1 25.1.6.333 Key Water Test Wells, with petrographic analyses 0 (Plates 12-15, Figures 4, 5, Table 4) 25.1.16.111 Other well-control points e Upper Santa Fe Group outcrop sample sites P (Appendix A, Part 111) -Plates 3 & 16b Hydrogeologic sections (Plates 2-11, 16-17) Q-43 Locations of seismic refraction lines LU-1, VI-1 (Reynolds & Associates, 1986, 1987) CA-1 I Major normal faults; bar and ball on downthrown side EXPLANATION - PLATES 2 To 17 Informal Hpdrostratigraphic Units Unit Description Vallep-Fill Deposits-- Post Santa Fa Group RA River alluvium; channeland floodplain depositsof inner Mesilla Valley; as much as100 ft thick. Lithofacies subdivision Iv is the major hydrogeologiccomponent. Forms much of the "shallow aquifer." Holocene to late Pleistocene. VA Valley-borderalluvium; tributary arroyo (and thin eolian) deposits in areas bordering the inner Mesilla valley, with locally extensive river-terrace deposits;as much as 140 ft thick. Includes lithofacies subdivisions Iv and V. Most of unit is in the unsaturated (vadose) zone. Holocene to middle Pleistocene. Basin-Fill Deposits-- Santa Fe Qroup Rio Grande rift basin fill; includes alluvial, eolian, and lacustrine deposits; with interbedded volcanic rocks (basaltp and silicic tuffs). In the Mesilla Basin area the SantaFe GrouF comprises four lithostratigraphic units- Hayner Ranch, Rinccn Valley, Fort Hancock, and Camp Rice Formations; and locally exceeds 2,500 ft in thickness. It includesthe major aquifereof the area andis subdivided into three informal hydrostratigraphic units: USF Uuuer Santa Fe Unit; coarse- to medium-grained deposits of the ancestral Rio Grande intertongue mountainward with piedmont- alluvial (fan) facies, and southward with fine-grained lake and playa sediments; volcanic rocks (mostly basalt) and sandy eolian deposits are locally present; as much 750 as ft thick. Unit includes the Camp Rice(CR) and upper Fort Hancock (FH) Formations. It also includes lithofacies subdivision Ib; ofmuch facies 11, V, and VI; and parts of facies I11 and VIII. Forms lower part of the "shallow aquifer" in the northern Mesilla Valley, and the upper aquifer zone outside the Valley area wh2re 'much of the unit is above the water table. Middle Pleistocena to middle Pliocene. 1 MSF Middle Santa Fe Unit; alluvial, eolian, and playa-lake facies; interbedded sand and silt-clay basin-floorsediments intertongue mountainward with piedmont-alluvial (fan) deposits, and southward with fine-grained lake and playa facies; basaltic volcanics and sandy eolian sediments are locally present; as much1500 asft thick. Unit includes basin fill that correlates with muchthe of Fort Hancock (FH) and Rincon Valley Formations, in the Huecc Bolson and western Jornada del Muerto (Rincon) Basin, respectively. It also includes much of lithofacies subdivisions 111, and parts of facies 11, V, VI, VII, VI11 and IX. Forms major part of "medium aquifer" of Leggat et al.(1962). Middle Pliocene to middle Miocene. LSF Lower Santa Fe Unit; eolian, playa-lake, and alluvial facies; sandy to fine-grained basin-floor sediments, which include thick dune sands and gypsiferous sandy mudstone, intertongue with conglomeratic sandstones and mudstones near the basin margin? piedmont deposits; as much as1000 ft thick. Unit includes basin fill that correlates with much of the Hayner Ranchthe lower and Rincon Valley Formations, in the western Jornada del Muerto I (Rincon) Basin. Italso includes much of lithofacies IV X,and and parts of facies VII, VI11 andIX. Forms major partof "deep aquifer" of Leggat et al.(1962). Middle Miocene to late Oligocene. 2 EXPLANATION - PLATES 2 TO 17 Bedrock Units and Upper Cenozoic Volcanics Unit Description Qb Basaltic volcanics, mostly flows, with local cindercone and conduit material, that capor are interbedded with the upper and middle Santa Fe Group. Quaternary and upper Pliocene Tb Basaltic plugs and minor flows that penetrate, cap,or are interbedded with the lower and middle Santa Fe Group. Miocene Tr Rhyolitic volcanics, with some interbedded sandstone and conglomerate mostly ashflow tuff and lava. Oligocene Tri Rhyolitic igneous-intrusive complexes; mostly sills, plugs and associated lava domes. Oligocene Ti Silicic to intermediate intrusive rocks. Oligocene and Eocene Tv Andesitic and other intermediate volcanic and volaniclastic rocks, including lava flows and laharic breccias and mudstones. Eocene and Oligocene Tvi Undivided Rr and intermediate intrusive rocks. TVS Intermediate volcaniclastic rocks, with minor lava flows and intrusive units; primarily Palm Park Formation. Eocene and Oligocene TN Undivided Tr and Tvor Tvs T1 Mudstone, sandstone, and conglomerate with local gypsum beds. Lower Tertiary, mainly Eocene Tvl Undivided Tv andT1 K Cretaceous rocks--undivided; includes limestone, sandstone and mudstone. Tx Undivided Ti, Tv, T1,K. w Undivided Cretaceous and Permian rocks. PU Upper Paleozoic rocks (Pennsylvanian and Permian); includes limestone, shale, sandstone, and mudstone, with local gypsum beds. P Undivided Paleozoic and Precambrian rocks the of southern Franklin Mountains; includes limestone, shale, sandstone, metamorphosed sedimentary and volcanic rocks, and granite. EXPLANATION - PLATES 2 TO 17 Lithofacies Subdivisions Unit Description I. Sand and gravel, river-valley and basin-floor fluvial facies; recent and ancestral Rio Grande channel and floodplain deposits underlying1) the modern river-valley floor--facies Iv,2) river-terrace surfaces-- deposits primarily inthe vadose zone, and3) relict or buried basin- floor fluvial plains--facies Ib. The latter surfaces include theLa Mesa geomorphic surface (Gileet al. 1981). Gravel is characterized by sub-rounded to well-rounded pebbles and small cobblesof resistant rock types (mainly igneous and metamorphic) derivedin part from extra-basin source areas. Iv. Sand and pebbleto cobble gravel, with thin, organic-rich silty sand to silty clay lenses; indurated zones of carbonate cementatio? rare or absent; as much as 100 feet thick. Ib. Sand and pebble gravel, with thin discontinuous beds and lensfes of sandstone, silty sand, and silty clay; extensive basin-floor fluvial facies; usually nonindurated, but with local zones that are cementad with calcite (common), and other minerals (uncommon) including silicate clays, iron-manganese oxides, gypsum, silica, and zeolites;200 to 400 feet thick in central basin areas. 11. Sand, with discontinuous beds and lensesof pebbly sand, silty sand, sandstone, silty clay, and mudstone; extensive basin-floor fluvial facies and local eolian deposits; gravel compositionas in faciesI; usually nonindurated, but local cemented zones as in facies Ib; clean sand and pebbly-sand bodies makeup an estimated 65-85 percent of unit; 300 to 750 feet thick in central basin areas. 111. Interbedded sand, silty sand, silty clay, and sandstone; with minor lenses of pebbly sand and conglomeratic sandstone; basin-floor alluvial and playa-lake facies; clay mineralogy of silty clay beds as IX; in unit usually nonindurated, but with local cemented zones as inIb facies and 11; secondary carbonate and gypsum segregations locally present in silty clay beds; common sheet-like to broadly-lenticular strata10 to 40 feet thick; clean sand layers make up an estimated35 to 65 percent of unit; 300 to 1,000 feet thick in central basin areas. IV . Sand to silty sand, with lenses or discontinuous beds of sandstone, silty clay, and mudstone; eolian and alluvial facies primarily deposited on basin floors and contiguous piedmontslopes; nonindurated to partly indurated, with cementing agents including calcite (common), silicste clays, iron-manganese oxides, gyps?, and zeolites (uncommon); cleEn fine to medium sand makes up estmatedan 35 to 65 percent of unit; as much as600 feet thick. V. Gravelly sand-silt-clay mixtures (loamy sandsto sandy clay loams) interstratified within discontinuous beds and lensesof sand, gravcl, loamy sandan silty clay; distalto medial piedmont-slope alluvial facies (mainly coaleascent fan deposits), with minor compoonentof eolian sediments; gravel primarily inthe pebble and small cobble size range, and clast composition reflects characterof source bedrock terrane; usually nonindurated, but with thin discontinuous layers that are cemented with calcite; clean sand and gravel makes up an estimated 25 to 35 percent of unit; as much 600 as feet thick. VI. Coarse gravelly sand-silt-clay mixtures (loamy sand and sandyloas to loams) interstratified with lenses of sand and gravel; proximal tc medial piedmont-slope alluvial facies--fan and coalescentfan depcsits; gravel primarily in the pebbleto cobble range (upto 10 inches); clast composition reflects lithologic character of source bedrock terranes; usually nonindurated, but with discontinuous layers that are cemented with calcite; clean sand and gravel lenses an make estimated 15 to 25 percent of unit; as much300 as feet thick. VII. Conglomeratic sandstone, silty sandstone, and mudstone with lenses and discontinuous beds of conglomerate, sand, gravel, and gravelly sand- silt-clay mixtures (a8 in unitV); distal to medial piedmont-slope alluvial facies, with minor component of eolian sediments; coarse clast sizes and composition as in unit V; moderately-wellto poorly indurated; cementing agents include calcite (common) and silicate clays, iron- manganese oxides, silica and zeolites (uncommon); clean weakly-cemented sand and gravel beds make up an estimated5 to 15 percent of unit; as much as 600 feet thick. VIII. Coarse conglomeratic sandstone and silty-sandstone, fanglomerate, and minor lenses of sand and gravel; proximalto medial piedmont-slope alluvial facies--and coalescent fan deposits; coarse clast sizes a?d compositions as in unit VI; moderatelyto.well indurated; cementin'7 agents as in unit VI; moderatelyto well indurated; cementing agents as in unit VII; clean, weakly-cemented sand and gravel lenses make up an estimated 5 to 10 percent of unit, as much as300 feet thick. IX. Silty clay interbedded with thin silty sand, sand, sandstone, and mudstone beds; basin-floor playa-lake and alluvial-flat facies; clay mineral assemblage includes calcium smectite, mixed layer illite- smectite illite, and kaolinite (Anderholm,1985); secondary deposits of calcite, gypsum, sodium-magnesium-sulfate salts, and zeolites are locally present; weakly-cemented fineto medium sand and silty sand makes up an estimated5-10 percent of unit; as muchas 600 feet thick in central basinareas. X. Mudstone and claystone interstratified with thin sandstone and silty sandstone beds; basinfloor playa-lakeand alluvial-flat facies; clay mineral and non-claysecondary mineralassemblages as infacies IX: weakly cemented fineto medium sand and silty sand makes up an estimated 0 to 5 percent of unit; as much 600 as feet thick in central basin area. EXPLANATION - PLATES 2 To 17 Special Symbols ~ -~ ~~~ ~ ~~ Plates 2-11, 16-17 Drill-stem packer teste, water table, and faults Top of sampled interval Total dissolved solids (mg/L) P Water table (cited literature) High angle normal faults, with direction of relative 111 displacement indicated. I Plates 12-15 Lithologic Logs LITHOLOGICLOGS Plates 16-17 Seismic RefractionLines Q-43 Locations of profiles by Reynolds & Associates LU-1,VI-1 (1986, 1987) CA-1 .- I 0 r- 23.1.13.411 FIRESTATlON SWGLE +-, LOG POIN 0 Ram 0H”METERS 0 50 100 0 50 100 150 200 4500 4500 Bend in Section 4400 4,400 r- 4400 ” 1 4300 4300 Upper Santa Fe h 4200 (USF) 4200 \+- 4,192 - 4100 - 4100 4000 4000 3900 Middle Santa Fe 3900 3806 3800 I 3700 Upper Santa Fe (USF) 3700 97 3600 3600 0 34q 700 3 3500 3500 G 3400 3400 1 Q 0 3300 E 3300 ’3200 3200 8a 3100 Middle SantaFe (MSF) 3100 8 c3 3000 3000 1 4. 9 61 7 I 0 2900 51 0 2900 6 2800 2800 M 2700 2700 Q 1260 2600 640‘ 2600 I2 7 2500 2500 W“ 1448 0 8 37-I I 2400 Lower Santa (LS’F) 2$oo Fe G 2300 2300 2200 2200 2100 2100 ,06ic- 2000 I rv 2000 1900 1900 2 DH2,008, 1800 Tv s 1800 1700 no0 1600 1600 1500 1500 Plate 2. Hydrogeologic section Las Cruces Fairground to Firestation, with borehole geophysical data. 0 25.1.6.333 25.1.16.111 25.2.4.141 2523.224 AFTONTEST 8, ASARCO SAN MIGUEL MESQUrE 2000 t, NORMAL t, INDUCllON LmOLOGIC SINGLE RESIST" RESIST" LOG POINT CURVES -b CURVES RESlsmmY OHM-METERS n OHM-METERS OHM-METERS LL 0 10 20 3040 50 0 10 20 30 40 50 0 15 30 45 60 0 15 30 45 60 4500 I Ill 4500 r- - 4400 4400 4300 - 4300 4200 % - 4200 \ 4100 - 4100 USF JSF 4000 - 4000 3900 - 3900 3,850 - - d3.839- 3800 IV CT, 3700 03 CT, 7 3600 0 6 40 60 I -Jt 3500 G 392 a 3400 _I Q MSF 0 507 3300 384 W 598 '3200 '3I4 E 0 3100 74f 331 B 1170 I476 -D H 823 c3 3000 3000 _I Q Z 0 2900 2900 G 2800 2800 1 MSF m 2700 Q 1180 I- I- I585 400 12700 W 2600 1052 - 2600 W SF LL LSF 7 2500 - 2500 W" 0 3 2400 - k 2400 !i 4 2300 -/ 2300 2200 Tvs? 1700 2100 580 2100 1200 2000 2000 2096 1900 - 1900 LSF LSF 1800 - 1800 I TVS 1700 - no0 1600 -1 1600 1500 1500 Plate 5. Hydrogeologlc+ sectlon Afton to Mesquite, with borehole geophysical data. 26.2W.l!j.433 26.lW.35.131 26.lW.24.243 a, 27.1.4.l21 CD JOHNSON AFTON CONES HUNT-15 mocoGlc moLouc WGLE a, MK@ LOG LOG POW +J +J RESlSTMlY u OHM"€IERS K-OH"rnS7 U U LL 0 10 20 30 40 50 0 10 3020 40 50 0 10 20 30 40 50 0 1020304050 0 M 20 30 40 50 0 10 20 30 40 50 0 lo20304050 0 10 20 30 40 50 4500 r- I 4500 4400 - 4.400 - , 4.400 4300 4300 ' '4270 - 4200 - -4,195- 4,189 - 4200 Is, e - 4100 - 4100 - 4000 USF 4000 I - 33SII 0 - 3900 - 3900 X - 1 VF _. 3,862 - 3800 -v, - 3,823 3 - ?TVS L 3800 MSF a 3700 3700 E37 463 3600 155, 3600 0 f 3500 3500 k MSF 3400 712 1 3400 Q IC '617 0 801 902 I 3300 '1097 71 6 >E 3: .3,272 3200 - DH631- KP 3200 Middle Santa Fe c] 3100 - 3100 I134 (MSF) e 'I 288 c3 3000 -I KP 3000 Q 7 0 2900 G El 2900 2800 e LSF LSF t 2800 I zm ZOO Q I 533 '6664 1 2600 Wb 2600 LL Trv 1571 2500 7 2500 378 'MSF 1 I 0 2400 N T 1787 CI I 1238 2300 1J "I- + 2200 Trv Trv 61 2100 Lower Santa Fe =tB (LSF) LSF 2000 1900 -0) .-> 1800 cn 1 -3 L a00 tJ .-c 1600 Kp Trv Trv? 1500 Plate 4. Hydrogeologic section Aden to La Tuna, with borehole geophysical data. LL 0 10 20 30 40 50 0 10 20 30 40 50 0 50 100 150 200 0 1020304050 0 10 20 30 40 50 0 10 20 3040 50 0.10 20 3040 50 0 100 200 300 400 500 4500 1111 I I I 1 4500 4400 4400 4300 4300 4200 I 4200 4100 4100 4,023 - 4000 4000 3900 3900 J 3800 - c 3800 R MSF a 3700 a bH 320- 3700 7E2 KP 3600 195 3600 0 603 5 3500 3500 Q 3400 3400 -I Q 0 150 52 3 3300 3300 ’5200 3200 540 E 3100 304 3100 8 Middle Santa Fe MSf 3000 1 3000 -1 Q Z 1 0 2900 2900 G 2800 2800 W Bm ZOO 2700 Q Ti/ KP 2600 2600 Lf Lf z 2500 2500 W”n 2400 2400 4 2300 2300 2200 2200 no0 T no0 2000 2000 Lower Santa Fe 1900 LSF 1900 1800 1800 woo wo 1600 1600 Trv? ‘1500 I I I I 1500 Plate 5. Hydrogeologic section La Union to Vinton, with borehole geophysical datu. 28.3.32.143 JL-4-2-203 0 STATERESAtl Q-I59 t' NORMAL moLoGyc LOG ~ loG 2 R%gF a OHM-M~S 0 1030 20 40 50 0 10 20 30 40 50 0 10 20 30 40 50 4500 4500 4400 4400 4300 4300 4200 4200 4100 4100 """""""". Upper Santa Fe 4000 4000 c (USF) 3900 3900 -UllL 3800 k 3800 a 3700 3700 E27 523 3600 I 3600 0 91 I 3 Midd'le Santa Fe 2 3500 3500 k MSF' (MSF) 3400 DM700 - -I 3400 Q 0 799 '1516 t 3300 E 3300 '3200 3200 1984 E 3 a 3lOO 557 3100 0w c3 3000 I' ' MOO _I Q Z 0 2900 2900 @ * 2800 2800 m 2700 Lower Santu Fe WOO Q (LSF) 2600 , 2600 LI TVi z 2500 woo W"n g 2400 T.v i 2400 5 2300 !300 '2200 E?oo 2100 ?IO0 MOO !OOO 1' 1900 900 1800 so0 Ti, TL n00 700 i, Tl 1600 Ti, KP 600 1500 500 Plate 6. Hydrogeologic section Noria Test to Mesa Boulevard, with borehole geophysical data. 29.1w.6.410 mw.6.410 S.W.~I 29.lw5.4ll ze.lw.5.411 29.W.3.344 29.W.3.344 HUNT-1485 HUNT-t485 Hum=-lav Hum-lan HUNT-14V HUNT-I~I~ HUNT-IOI~ LITHOLOGIC TEMPWATURE UTHOu)GIC TEMPERATURE SINGLE POINT LITHOLOGIC TEMPERATURE LOG LOG LOG LOG RESISTIVITY LOG LOG DEkiaEES DEGREES OHM-METERS DEGREES CELSIUS CELSIUS CELSIUS 20 40 ea 20 40 60 a la 20 30 40 50 20 40 60 "4.230 - m KP "" Middle Santa Fe Lower Santa Fe KP -DH2..000 - KP Plate 7. Hydrogeologic section Potrillo Mountains to Noia Test, with borehole geophysical data. m 0 m20304O!xJ /i 0 10 20 30 40 50 *0° 4500 Bendin Section 4400 r" 1(400 4500 4300 - 4200 4,189 - 4200 I- 4100 4100 4000 USF 4Ooo 3900 3900 L 3800 3800 3700 3700 Fx- i 1 3600 3600 0 3 3500 MSF 3500 'Q M.iddle Santa * 3400 3400 -I ( MSF) 6 0 'I 902 3300 I IO97 5300 '3200 ! 3200 3100 E " 3100 0 1134 '1288 8, 3000 3000 LSF 29oc) .. . Lower Santla 2800 2700 I 28Ob z 2500 2500 W-n MO E 2400 2300 2300 2200 2200 no0 a00 2000 2000 1900 1900 1800 la00 no0 1700 It-I I 1600 , 1600 Ti, i- 1500 1500 Plate 8. Hydrogeologic section Afton Test to Noria, with borehole geophysical data. 00 23.1.30.422 24.1.8.123 25.1.6.333 24.1.8.123 23.1.30.422 27.1.4.Pl 27.1.10.100 28.3.32.143 28.2.25.233 CD cvQ, LAS CRUCES-36 WEST MESA Q, AFTON TEST NMSU TEST STA TERESA 9 STATERESA11 Q> + SINGLE SINGLE NORMAL NmF 8 NORMAL NORMAL NORMAL +a POINT POINT RESISWTW RESlsmmY RESlSTMlY RESlsmmY RESIST[VITY RESISWTW RESlSTNrrY2 RESISWTW CURVES 5 CURVES CURVES CURVES CURVES OHM-MEWS OHM-MmRS OHM-M€I'ERS OHM-METERS OHM-METERS OHM-METERS E n- a OHM-METERS 0 50 100 0 50 150100 72010 30 40 50 0 1020 30 4050 0 1020 30 40 50 0 1020 30 40 50 0 1020 30 40 50 0 10 2030 40 50 0 10 2030 40 50 4500 - r 1&OO "7 4400 4400 4300 4300 -4,228" 4200 "4,192 - -4.203 - -4,189 - 4200 -4,165 - -4.165 - T bJI - -" """". "4,112 - 4100 -,4,095 - 4100 - " U ppe r Sa nta Fe ,"_"" .L"""""-.7"""~ "I, (USF) "_"""""". I 4000 'LTJ Upper Santa Fe I 4000 (USF) USF 3900 3900 3800 3800 3700 ~ *-rz - 3700 Da 7 3600 .- 3600 0 .' 2 i 2 3500 3500 k Viddle Santa Fe Ix Middle Santa Fe I MSF HI 3400 3400 " (MSF) "DH700 1 (MSF) Q 0 VlSF F 3300 m 3300 c1c W -DDH950 - > 3200 3200 l OH 1,010 - E 3100 Q 3100 8 c3 3000 3000 1 Q Z 0 2900 2900 Q LSF = 2800 Lower Santa Fe 2800 (LSF) I zoo -DH1,50- Lower Santa Fe Tv i 2700 Q LSF -DH 1.565 - i66r (L S F) 2600 2600 E LSF 2 2500 2500 w" Q 2 2400 2400 6 Ti, TL - 2,3.00- Trv Trv 4 2300 - 2300 LSF T rv 2200 Tv 2200 TI, 2100 2100 I 2000 or 2000 basal 1900 LSF? 1900 t mid- 1800 1800 -" " ' I basi n -D.H2,470- Tvs 1700 lfault zone I700 Tv 1 1600 TiJKP 1600 Trv OH 21,759 1500 - I 1500 Plate ~9.Hydrogeologic section 'Las Cruces to Santa Teresa, with borehole geophysical data. cv M 23.1.13.411 23.2.30.243 0 FlRESUiTON LAS CRUCES 800 + ma SINGLE 0 POW POW - msTMTY RRlslMly OHM"€IERS OH"" U 0 20050150 100 0 25 50 75 100 0 10 20 30 40 50 0 75 1Jo 225 300 0 15 30 45 60 0 15 30 46 60 0 15 50 45 60 0 10 20 3040 50 - 4500 00 4400 4300 4300 4mo 4200 4100 4100 4000 4000 3900 -3,892 - 3900 L -3,878 IV 3,860 - g!jo RA lRiver alluvium(R4- Iv 3800 -4 River alluvium (RA) 3800 13; 3700 450C 3700 Upper Santa Fe SY.r 3600 3600 (USF) . 7 0 240 657 700 298 f 3500 3 39 MSF 3500 Q 392 404 3400 p37 3400 430 8 507 -KT- 384 3300 1460 E 3300 59 8 > 3200 314 3200 MSF ,675 fJ 494 a 3100 74! 730 3100 JlSF DH809-'1 -I Middle Santa Fe 1 m,II 1 e 639 - DH823 - 3000 c 3000 -1 M SF Q p6 I Z '51 0 0 2900 2900 G Middle Santa Fe 2800 (MSF) 2800 2700 Q I80 1260 400 120( 2600 '640 I 152( 2600 LI MSF z 2500 .SF 2500 w" n 448 937 3 2400 2400 5 LSF 4 2300 2300 2200 2200 700 no0 i80 2100 2000 T rv LSF 2Ooo 1900 L SF Lower Santa Fe 1900 1800 (LSF) 1800 woo woo 1600 1600 Trv 1500 1500 Plate IO. Hydrogeologic section Las Cruces Firestation to Vado, with borehole geophysical data. 0 F m (0 25.3.28.434 26.3.33.212 JL-49-04-113" JL-49-04-109 JL-49-04-433 JL-48-04-421 JL-49-04-723 28.3.34.331 28.3.n.111 VADO OLQUIIT FARMS (2-197 Q-63 Q, Q-202 LlPPlNCOll Q-144 LmRI3 a, NORMAL NORMAL NORMAL Q-138 NORMAL NORMAL s, + NORMAL 3 NQoc i-J NORMAL RESISrrmrI RESISTMTY RESIST" r~rRMsmmY RESISTMTY t?- rn0LOGIC CURVES CURVES CURVES CURVES CURVES u LOG CURVES cl OHM-METERS OHM-METERS OHM-METERS OHM-METERS OHM-MEIB?S E OHM-METERS 0H"METERS OHM-METW 7 leb I" 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 020 10 30 40 50 0 10 2030 40 50 0 10 20 30 40 50 4500 - 4500 4400 4400 4300 4300 4200 4200 4100 4100 4000 4000 -3,997. """_.- 3900 3900 " ___ps - 3.0 03- 3800 -3,800 - 3800 River alluvium (RA) . - 3,768- - 3,757 - ISF RA River a1 I uvi um(RA) _- Iv 3700 (T) 3700 -t 88 DJ 49 -;I4 - c31r ,3680 3600 25 184 3600 0 170 !33 507 2 312 275 ,57 !6D -J 110 3500 3500 313 800 '71 7 24 k 320 5.29 3400 a 3400 MSF 394 -1 $26 385 Middle Santa Fe M SF 586 MSF Q 697 601 4@ 0 S F) "" 47 52 3300 (M 970 3300 F $95 513 $44 3140 565 532 E3 576 428 M SF 3200 'IO 3200 ' 366 360 MiddleSanta Fe 523 67 0 679 675 506 k 3100 27d 3100 '30 707 - (MSF) 376 39 739 r15 8 1 418 354 3000 3000 320 -OH 1,004- -1 8 5t Q 747 846 3 Lower Santa Fe LS F Z 45 L 2400' 0 2900 615 405 2900 t LSF % 367 365 LSF LS F - 2,817- 2800 2800 319 334 0 50 007 H 1,050- 1057 K 1542 Y0 558 - Ti, TL no0 m 2700 357 -0H1.074 11.16 - Q "" II70 265 I- - 2600 HI, 1300 I I94 -DH1,212 I7- k 7 37 / LSF 2500 K - 2500 W" Ti c1 2400 g 2400 f 4 2300 2300 K,.? 2200 i LSF 2200 * 2100 Lower Santa Fe 2100 K Ti,KF (LSF) > 2000 2000 t WOO 1900 1800 1800 iTn 3 no0 no0 KP KP 1600 1600 E00 1500 Plate 11. Hydrogeologic section Vado to Lizard, with borehole geophysical data. GEOLOGIC UNITS LITHOLOGIC LOG RESISTIVITY CURVES OHM-METERS PERCENT PERCENT 0 25 50 10075 0 25 10075 4209 0 10 20 30 40 50 50 4200 420 0 L 4100 4100 ._-"_"" *.. ------.-""" - 4000 4000 """_""" eI- """"""F"". ""_ "" 3900 3900 3800 3800 3700 3700 a 3600 3600 cu .i"03 h- 3500 3500 0 t 3 3400 3400 nk 1 3300 3300 Q 0 F 3200 3200 >W 3100 n 8 3000 3000 c> _I 2900 2900 -7 0 +++++++++ % 2800 t 1 2800 7 W & 2700 270 0 m Q 2600 2600 W W LL 7 2500 2500 W- n 240 0 63 2400 4 2300 ~+~~~~+~++++++++ 2300 ++++++++ ++++++++ ++++++++ ++++++++ 2200 2200 + 77/27 +++++++++ +++++++++++.++++++ ++++++++ 2100 2100 T+++++++?++++++++ +++++++++ ++++++++ +++++++++ ++++++++ +++++++++ ++++++++ 2000 A++++++++++++++++ 2000 +++++++++ ++++++++ +++++++++++++++++ +++++++++ ++++++++ +++++++++ -++++++++- 1900 1900 +++++++++ ++++++++ +++++++++ ++++++++ +++++++++ +++++++++++++++++ -++++++++- 1800 +++++++++ .+ +_t+ + + + + 1700 I 1700 Plate 12. Geoloqical data on Afton test well. J ALTITUDE, IN FEET ABOVE NATIONAL GEODETIC VERTICAL DATUM OF 1929 h) h) N 10 N N GI w w w GI w w G G G 0 E w %! ul 0) c: m u3 0 9 8 w P ul 0) m u3 8 f ie 0 0 0 0 0Y 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Y 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 I Upper 'SantaFe i 22 Lower Santa Fe Middle Santa Fe Hydrostratigraphic Unit gz I Hydrostrat, Unit !, !, Camp Hydrostrat. Unit Fort Hancock Fm \ Rice Fm 0 3 0 N 0 w 0 P 0 cn 0 0 " N N N N P Lrl w Lrl 6 0 Y h) w E !2 Fi I\)u, M 0w k! w w w ul aw m (D ie d 06 0 0 0 8 0f 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 GEOLOGIC UNITS LITHOLOGICLOG WHIC FRAGMENT COMPOSEION PERCENT PERCENT 0 1020 30 4050 0 25 50 10075 0 25 50 10075 1.200 420 0 I - 1.100 4100 Cam VRF SRI EpkrE ..,..__ ..... _....:.. . :...... :...... I.. ..>:::.._.:.* ;.:: . JpperSanta FI 4000 7 1.000 lydrostrat.Uni 3900 3900 3800 3800 3700 370 0 m 3600 3600 mcu 7 k 3500 3500 0 2 2 3400 3400 % D 1 3300 3300 Q 1 0 F 3200 3200 Y -O 3100 3100 t- W n 8 3000 3000 (3 1 4 2900 I2900 Z 0 % 2800 2800 7 W & 2700 270 0 m Q + 2600 2600 W W LL 2500 2500 - W- n 240 0 63 2400 2300 2300 .-c. C 3 2200 2200 2100 2100 2000 2000 1900 1900 1800 1800 1700 1700 Plate 14. Geological data on La Union test well. GE OLOGIC UNITS LITHOLOGICGEOLOGICUNITS LOG PERCENT PERCENT 0 1020 30 40 50 0 25 50 10075 0 25 50 10075 420 0 - 420 0 I127 14 URF SR 4100 4100 4000 d""" 4000 3900 3900 3800 3800 3700 3700 3600 3600 37 LL 3500 3500 0 3 3 3400 3400 nG 1 3300 3300 4 0 F 3200 3200 >W O 3100 3100 En 8 3000 3000 c3 A < 2900 2900 Z 0 %, 2800 2800 7 W t & 2700 270 0 m Q 2600 2600 W W LL 7 2500 2500 W- n 3 2400 240 0 t 5 4 2300 2300 I 2200 2200 2100 2100 2000 2000 1900 1900 1800 1800 1700 1700 Plate Geoloqical data on Noria test well* 15. J u mk - m - M esilla Valley Mesilla md L Valley Mesilla 3 dg jl W -4: 0.7 0 4 - 4,500 -0 ;: E 9 _ .+ C. - m- 16a wo ow c aJcy 74 NO. aN La Mesa 0 2 T'v. e "2 4,209 'Jp! .: p! v) Ib,ll I" a'v. 4,000 "_"" Ib,lll - 4,000 USF ll,111 t- USF g: ZNO. "SF I 11,111 IV ' RA I <. I III USF i' 11,ib 3,500 - V,III USF k-7.- -5 - 3,500 I Ill MSF USF I- MSF """ I 3 e. - "V" - Ill - J-v A 3,000 'I VI MSF - 3,000 V,II "-A"2 " "------I Ill LSF LSL VII,IV VII,IV ""_" - 1 MSF - 1 X,IV LSF - 2,500 2,500 VII,X .. LSF MSF MSF ". LSF VII,IV ". LSF Tvs ? or LSF 2,000 - i - 2,000 ?basal LSF (X,VII)? 3 < -. - IV,VII X,IV <.- LSF Tvs 1,500 - - 1,500 aJ m c* \ ._+ N Trv L Tvs IIITvs fsFF 3 eastern (La Union-Mesquite) subbasin Plate 3 """-1;northwestern sub-basin mid-basin uplift m I 1,000 I I I I I I I I 1,000 6 5 10 mi 0 10 mi > > 4,500 Y 16c 4,500 5 -1 4,270 =4 1,111 4,000 clx,II 4,000 , '3,862 'X(Tvs?) 3,500 KP -3,500 3,000 .3,000 2,500 KP -2,500 2,000 - 2,000 - 19500 1,500 east Potrillo uplift .l,OOO 1,000 Mesilla Valley c O h 77 m N m 16d 4,500 4,023 4,000 3,500 3,000 ""- 2,500 -="" 2,000 1,500 I Plate 5 I eastern (Lo Union-Mesquite) subbasin Itu-]. , VIL 1,000 I I I I I I I I 0 1 2 3 4 5 6 7 mi I500rn 0 N - ..m ". m t Mesilla Valley x7 'v. 4,500 16e 4,500 -_P 3 3 'v. 0: 7 N I 2 c! -- % ,II I cy 4,230 L a 111,11 4,075 4,000 4,000 -111_" -x 3,500 IO00 3,500 - I Ti K -"\------IX,III IX,III L"" KP < III,IX IX,III MSF '\MSF " LSF MSF 3,000 3,000 - L"- LSF x, IV LSF I? Tvi 2,500 2,500 - Ti,TL c.. e c 0 m -+ Et 2,000 2,000 - ; r:I 0, - 500 -2. >a 0 n 1,500 1,500 - -. Franklinuplift 2 Ti,KP Cristo Rey uplift Ti,KP Plate 6 PI' ' 1,000 1,000 " I I I I I 1 I 1 I I I 25 26 mi 0 20 Horizontal Scale 1 : 100,000 Vertical exaggeration lox - I I I I I I I I I I .O 0 2 4 6 8 km Plate 16. Hydrogeologic Sections of the Mesilla Basin, Las Cruces to El Paso Area, showing inferred distribution of major hydrostratigraphic and lithofacies units, and fault zones JT W. Hawley and R. P. Lozinsky, 1992 NMBM&MR Open-file Report 323 17a .4,500 4,500 .4,000 4,000 '3,500 3,500 """- VI c-, III,V '3,000 VII,IV 2,500 -2,500 1 """""- -a " X,IV , "X" VII, 2,000 1 2 '2,000 Trv -t 3 '1,500 1,500 Ti.K, .1,000 0 17b 4,500 '4,000 - 3,500 3,000 .2,500 - 2,000 . 1,500 . 1,000 35 mi. - 5,000 I500 rn I .' 1 7c - 4,500 La Mesa 4,000 - 4,000 """""_ " 3,500 - 3,500 1000. ' "" 3,000 - 3,000 ------"""" 2,500 - 2,500 Tr 2,000 - 2,000 ----- ""_"_ ,500 horizontal scale 1,500 Ti,TL? - 1,500 Tv L 1 : 1 00,000 Tv L Tv L Tv Ti,KP? Trv mid-basin uplift mid-basin uplift Plate 8 vertical exaggeration - 1,000 1,000 1 I I I I I I I 1 -lox 0 5 10 15 20 mi. .. I I I I- I .O 0 2 4 6 8 I km Plate 17 Hydrogeologic Sections of the Mesilla Valley and west central Mesilla Basin areas, showing inferred distribution of major hydrostratigraphic'and lithofacies units,and fault zones ,JI W. Hawley and R. P. Lozinsky, 1992 .NMBM&MR Open-file Report 323