Geology and Ground-Water Features of the Eureka Area Humboldt County, California By R, E. EVENSON GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1470 Prepared in cooperation with the California Department of Water Resources UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1959 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. S EATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U. S. Geological Survey Library has cataloged this publication as follows: Evenson, Robert Edward, 1924- Geology and ground-water features of the Eureka area, Humboldt County, California. Prepared in cooperation with the California Dept. of Water Eesources. Washing­ ton, U. S. Govt. Print. Off., 1959 iv, 80 p. maps, diagrs., tables. 25 cm. (U. S. Geological Survey Water-supply paper 1470) Part of illustrative matter fold. col. in pocket. Bibliography: p. 77. 1. Water-supply California Humboldt Co. 2. Water, Under­ ground California Humboldt Co. i. Title: Eureka area, Hum­ boldt County, California. (Series) TC801.U2 no. 1470 551.490979412 GS 59-169 copy 2. GB1025.C2E9 For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. CONTENTS Page Abstract___-_____-__--_--_-_-_________-__--_--_-_-______ ___ 1 Introduction._____________________________________________________ 2 Purpose and scope of the work________ _________________________ 2 Location and extent of the area_______________-_-__-__--________ 3 Previous work_______________________________________________ 3 Well-numbering system________________________________________ 3 Acknowledgments. ________________________________________ __ 5 Geographic features..»______________________________________________ 6 Physiography and drainage._____________________________________ 6 Vegetation and culture_________________________________________ 7 Climate-________________________________ _ 7 Use of ground water__________________-_____-______________-___ 8 Geology in relation to ground water-_______-__---_____----_--__------ 11 Principles of ground-water occurrence____________________________ 11 Summary of stratigraphy.______________________________________ 12 Consolidated rocks___________________________________________ 14 Pre-Tertiary formations_______________________________ ___ 14 Pullen, Eel River, Rio Dell, and Scotia Bluffs formations of Ogle (1953), undifferentiated.__________________________ 14 Principal deposits that yield water to wells _______________________ 15 Carlotta formation of Ogle (1953) (Pliocene and Pleistocene)____ 15 Hookton formation of Ogle (1953) (Pleistocene)_______________ 17 Terrace deposits (Pleistocene)__________-____________________ 18 Alluvium (Recent)_______________________________________ 19 River-channel deposits (Recent)____________________________ 21 Dune sand (Recent)_______________________________________ 22 Structural features___________________________________________ 22 Ground-water features______________________________________________ 23 Ground-water bodies____________________________________________ 23 Recharge and movement of ground water_________________________ 26 Discharge of ground water______________________________________ 28 Natural discharge___________________-_________________-__- 28 Pumping from wells______________________________________ 28 Fluctuations of water level____________________________________ 31 Ground-water storage capacity._________________________________ 35 Subdivision of area into storage units._______________________ 35 Computation of storage capacity_______-----_-_---___---___- 38 Net change of ground water in storage.______________________ 39 Quality of the water________________________---___-__________.__ 39 Water-quality criteria______________________________________ 40 Relation between specific conductance and dissolved solids in waters of the area___________________________________ __ 41 Chemical character of water.________________________________ 41 Relation to the geology___________________________________ 46 Tables of basic data_______________________________________________ 51 Selected bibliography.___________________________________________ 77 Index______.__ ________________________________________ 79 IV CONTENTS ILLUSTKATIONS [All plates in pocket] PLATB 1. Map of Eureka area showing generalized geology and hydro- logic features. 2. Geologic sections of Eureka area. Page FIGURE 1. Index map showing report area_________________________ 4 2. Well-numbering system._______________________________ 5 3. Comparison of annual precipitation at Eureka and Scotia.__ 9 4. Summary of monthly precipitation at Eureka______________ 10 5. Water-level contour map of the Eel River valley, August 1952_ 24 6. Fluctuations of water levels in five wells in the Eel River valley________________________'_________ 33 7. Fluctuations of water levels in four wells near Arcata_______ 33 8. Fluctuations of water level in well 3N/1W-34J1_________ 34 9. Ground-water storage units in the Eel River valley _________ 36 10. Ground-water storage units in the Mad River valley________ 37 11. Relation of specific conductance to sum of determined con­ stituents. ___________________________________________ 42 12. Composition of representative ground waters from wellr in the Eureka area, 1952_______________________ 43 13. Distribution of chloride and iron concentrations in the Eel River valley, 1952_________________________ 44 14. Comparison of chloride concentrations in selected wells in the Eel River valley in August 1952 and August 1953________ 45 15. Partial log and chemical character of ground water during drilling of well 3N/1W-18K1___________________________ 48 TABLES TABLE 1. Stratigraphic units of the Eureka area. ___ ______________ 13 2. Estimated pumpage, in acre-feet, for irrigation in the Eureka area in 1952______________________.___ 30 3. Metered water consumption, in thousands of gallons, for the cities of Arcata and Fortuna, 1947-52__ _________________ 30 4. Estimated ground-water storage capacity of the alluvium, river- channel deposits, and lower terrace deposits of major ground- water basins in the Eureka area____________-______----__- 38 5. Range in chemical character of ground water in the Eureka area, 1951-53______________________________ 46 6. Descriptions of water wells in the Eureka area _______________ 52 7. Periodic water-level measurements in wells in the Eureka area__ 63 8. Chemical analyses of ground water in the Eureka area________ 69 9. Partial chemical analyses of ground water in the Eureka rrea___ 72 10. Chemical analyses of surface water in the Eureka area._______ 73 11. Selected drillers' logs of wells in the Eureka area____________ 74 GEOLOGY AND GROUND-WATER FEATURES OF THE EUREKA AREA, HUMBOLDT COUNTY, CALIFOFNIA By K. E. EVENSON ABSTRACT The U. S. Geological Survey, in cooperation with the California Department of Water Resources, made a reconnaissance investigation of the majci" ground- water basins in Humboldt County. The two principal basins are t^e coastal plain of the Eel River valley a triangular-shaped area, which is about 8 miles wide along the coast and extends inland for about 12 miles and tve Arcata plain, which is about 5 miles wide and lies betweeen the Mad Rive' and the north end of Humboldt Bay. The area investigated extends for about 34 miles along the coast and about 20 miles inland. The two principal streams in the area are the Eel River, near the south end of the area, and the Mad River, near the north end. Both discharpi directly into the Pacific Ocean. Minor streams that discharge into Humbold^ Bay are the Elk River and Jacoby, Freshwater, and Salmon Creeks. The average annual precipitation is about 40 inches. The mean arnual tem­ perature is 52° F, and the annual range in the mean monthly temperature Is about 10° F. Unconsolidated clay, silt, sand, and gravel 3,000 to 4,000 feet in total thick­ ness make up the dune sand, alluvium, terrace deposits, and Ho?kton and Carlotta formations of Ogle (1953). These deposits range in age fror* Pliocene to Recent and contain most of the ground water. Water-table conditions exist in the dune sand, alluvium, terrace deposits, and Pleistocene deposits throughout the area; confined conditions exist in the deposits of Pliocene to Pleisv<>cene age in the Eel River valley and in the Pleistocene deposits around the northern end of Humboldt Bay. Most of the water pumped is derived from unconflned alluvial deposits the alluvium of Recent age and the terrace deposits of Pleistocene age. Periodic water-level measurements, which were made in observation wells in the Eel River valley, on the Arcata plain, and in the area north of the Mad River, indicated an average decline of about 5 feet in water level" in each basin during the .irrigation season of 1952. These seasonal decl'nes were balanced by recoveries of water levels during the next winter, as in the other years of record; no appreciable difference was noted between water levels in observation wells in the spring of 1951 and the spring of 1955. Most of the ground water is used for irrigation and is distributed principally through various types of sprinkler systems. About 250 irrigation wcUs supply water to nearly 12,000 acres, which is used almost entirely as permanent pas­ ture. In 1952 the estimated pumpage of ground water for irrigation, industry, public supply, and domestic use totaled about 15,000 acre-feet. The tot^l ground- water discharge, both natural and pumped, from alluvial deposits in 1952 was 2 GEOLOGY AND GROUND WATER, EUREKA AREA, CALIF. about 25,000 acre-feet.