Geology of the Compacting Deposits in the Los Banos- Kettleman City Subsidence Area, California GEOLOGICAL SURVEY PROFESSIONAL PAPER 497-E Geology of the Compacting Deposits in the Los Banos- Kettleman City Subsidence Area, California By R. E. MILLER,). H. GREEN, and G: H. DAVIS MECH ANICS _ OF AQUIFER SYST FEF M S G BOLOGICAL SURVEY PROFESSIONAL PAPER 497-E Geology of the deposits undergoing compaction due to head decline, including source, type, physical character, and mode of deposition, and the hydrologic frameworé so developed UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 70-610408 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page , Geology-Continued .*.. =c. ans en El Geology of the tributary drainage area, ete.-Con. Page 1 Upper Tertiary and Quaternary deposits undif- Previous investigations........__......_______..._ 4 E13 Purpose of investigation and scope of report_____ _.. 4 Stratigraphy of the water-bearing deposits ________. 13 Electric-log interpretation..._..._..__..___.._..._ 5 Jacalitos Formation (Pliocene) ____________._._. 14 Acknowledgments....:.....-......_.-_-L._.......- 8 Etchegoin Formation (Pliocene) ____________-.- 16 Well-numbering system.=.=..._.-~.--s--«---.---..--. 8 San Joaquin Formation (Pliocene) __________-.- 20 san a= puk 8 Tulare Formation (Pliocene and Pleistocene) _.. 21 Geologic history and 8 Terrace deposits (Pleistocene) _______________- 33 Geology of the tributary drainage area, Diablo Range. 9 Alluvium (Pleistocene and Holocene) _______-.. 33 Jurassic and Cretaceous _. 9 SOR - Ae? o Prae l nea aide Pan o eae e ne a 33 Franciscan 10 | Hydrologic units in the ground-water reservoir.. 34 Ultramafic intrusive rocks-__--___-.____.. 10 Upper water-bearing 35 Cretaceous sedimentary 10 Lower water-bearing sone.._......._.___.___..__. 35 Lower Cretaceous sedimentary rocks 10 | Chemical character of the ground water- _____________._ 38 Upper Cretaceous sedimentary rocks.... 10 Waters of the upper water-bearing zone. .________.. 38 Significance of Mesozoic ___ 11 Streant WAbers:.cl.l__cc2c o ase 39 Lower Tertiary sedimentary rocks-_______-.-.-.- 11 Waters of the lower water-bearing zone____________ 39 Paleocene and Eocene marine sedimentary Saline water 40 12 -! References 41 Miocene deposite--...__..__..___..______. 12 { Index.. am 45 Prats 1. bo ILLUSTRATIONS [Plates are in pocket] Geologic map of the late Cenozoic deposits of the west border of the San Joaquin Valley in the LosBanos-Kettlemen City area, California. . Generalized geologic map of the Diablo Range tributary to the Los Banos-Kettleman City area, California. 3. Geologic section A-A4' from near Los Banos southeast toward Tulare Lake bed, Los Banos-Kettleman City area, California. 4. Geologic sections B-B' to E-E", Los Banos-Kettleman City area, California. 5. Composite logs of selected core holes, Los Banos-Kettleman City area, California. Fik Fraur® 1. Index map of central California showing location of repOrt E2 2. Map showing land subsidence, 1922-32 to 3 3. Location map of geologic sections and COre 6 4. Typical electric log with 1 2-. 8 5-7. Sections of strata in the: 5 Jacalitos cece nen ass na mick an mle 15 6: :Etchegoim snares sass 18 ": Tulare ~s ue h =& aa ma 22 8. Map showing thickness of alluvial-fan deposits derived from the Dmblo Range in the Tulare Formation below the Corcoran Clay ~ 26 9. Map showing thickness of alluvial-fan deposits derived from the Diablo Range above the Corcoran Clay Member of the Tulare ss 27 10. Map showing thickness of micaceous sand overlying the Corcoran Clay Member of the Tulare Formation... 29 11. Map showing thickness of the Corcoran Clay Member of the Tulare Formation-_____________-___-_-_-_---- 31 12. Map showing structure of the Corcoran Clay Member of the Tulare Formation_____________________.---- 32 13-15. Generalized sections: 13. A-A', showing HyUIOIOGIC UNIS. ans ~~ 35 14. B-B', C=C", and E-E' showing hydrologiG Re 36 15. B-B', C-C"', and E-E' showing yield factors of wells in relation to the depositional environment.. 37 III CONTENTS T A BLE S Page TABLE 1. Core holes in or near the Los Banos-Kettleman City E7 2. Generalized geologic units of the drainage area tributary to the Los Banos-Kettleman Cny nrea:..._...... 10 8. Areas of generalized geologic units within stream basing. 11 MECHANICS OF AQUIFER SYSTEMS GEOLOGY OF THE COMPACTING DEPOSITS IN THE LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA By R. E. Miuu®r, J. H. Greex, and G. H. Davis ABSTRACT The Los Banos-Kettleman City area includes 1,500 square miles on the central west side of the San Joaquin Valley, Calif., chiefly in western Fresno County. It is an agricultural area, ir- rigated chiefly by ground water. Intensive pumping has lowered the artesian head several hundred feet and has caused the water-bearing deposits to compact. By 1959 the resulting re- gional subsidence of the land surface exceeded 4 feet in most of the area and locally attained 20 feet. Superimposed on this regional subsidence was as much as 10-15 feet of localized sub- sidence due to hydrocompaction of moisture-deficient near-sur- face deposits, which affected at least 80 square miles. This is the largest known area of intensive land subsidence due to with- drawal of ground water. Therefore, the geology of the com- pacting deposits, including source, type, physical character, and thickness, is of primary interest in appraising the response of the sediments to change in effective stress. The fresh-water-bearing deposits of late Pliocene to Holocene age forming the ground-water reservoir in the Los Banos-Ket- tleman City area have been derived from both the Diablo Range to the west and the Sierra Nevada to the east." Rocks exposed in the tributary drainage area in the Diablo Range, which range in age from Jurassic to Pleistocene, shown on a generalized geologic map, are chiefly sandstone and mudstone. Unconsolidated to semiconsolidated sediments of éontinental, and, locally, of marine origin, which crop out along a relatively continuous strip 1-6 miles wide bordering the western flank of the subsiding area, were mapped for this report. They include the Jacalitos, Etchegoin, and San Joaquin Formations of Plio- cene age and the Tulare Formation of Pliocene and Pleistocene age. The principal aquifers occur within the alluvial and lacustrine deposits of the Tulare Formation, which underlies all of the Los Banos-Kettleman City area and ranges in subsurface thickness from a few hundred to more than 3,000 feet. The underlying formations of Pliocene age contain brackish or saline water, except in the central southwestern part of the area where fresh water occurs in the San Joaquin and Etchegoin Formations. In a series of subsurface maps and sections based on electric logs and core records, the Tulare Formation and overlying younger deposits are subdivided into alluvial-fan, flood-plain, * Principal source of deposits, where identified, is indicated as Diablo (derived from the Diablo Range) or Sierra (derived from the Sierra Nevada). deltaic, and lacustrine deposits and are identified as to source area-Sierra Nevada or Diablo Range. The one persistent map- pable subsurface stratigraphic unit is the Corcoran Clay Mem- ber of the Tulare Formation, a diatomaceous lacustrine clay 0-120 feet thick that underlies most of the project area and is the principal confining bed. Deposits derived from the Sierra Nevada extend far west of the modern axis of the San Joaquin Valley. The axis of the valley shifted laterally in Tulare time, in response to tectonic uplift in the mountains, warping in the valley, and climatic changes, which determined the relative proportion of sediments being contributed from the east and west. In pre-Corcoran time, Sierra flood-plain deposits extended a maximum of 13-17 miles west of the modern topographic axis; immediately after deposi- tion of the Corcoran-about 600,000 years ago-Sierra mica- ceous sands extended as much as 13 miles west. Subsequently, the axis gradually moved east to its modern position. In general, the deposits from the Sierra Nevada, which are mostly flood-plain deposits, are coarser, better sorted, and more permeable than those from the Diablo Range, which are mostly alluvial-fan deposits. The depositional history and the character of the deposits are primary factors in determining areal varia- tion in permeability and compaction characteristics of the water-bearing sediments in the Los Banos-Kettleman City area. The continental fresh-water-bearing deposits can be subdi- vided into two principal hydrologic units. The upper unit, termed the "upper water-bearing zone," extends from the land sur- face to the top of the Corcoran Clay Member at a depth ranging from 20 to 900 feet below the land surface. The lower unit is referred to as the "lower water-bearing zone." It is 600 to more than 2,000 feet thick and extends from the base of the Corcoran Clay Member down to the deposits containing the main saline water body. The chemical character of the ground water changes markedly with depth. The major changes with depth are a marked decrease in dissolved solids and an increase in the percent of sodium among the cations. INTRODUCTION The Los Banos-Kettleman City area of California, as referred to in this report, is that part of the west side of the San Joaquin Valley extending from Los Banos in Merced County, through western Fresno County, to Kettleman City in Kings County. As shown in figure 1, it is bounded on the west by the foothills of the Diablo E1 E2 MECHANICS OF AQUIFER SYSTEMS 122° 121° 120° 119° ; T tp yo. 04,\«1 Suisun 494\ Bay > f. MONTIEZUMA HILLS San Pablo M 38° |- Bay Carquinez , Strait 87° MONTEREY O C; BAY ye Z " Monterey EXPLANATION Boundary between SanJoaquin Valley alluvium and de- formed rocks Area of report 36° |- 0 20 40 MILES heet en reali nec TULARE LAKE BED % 1 FIGURE 1.-Index map of central California. Los Banos-Kettleman City area shown by diagonal ruling. Range, and on the east, by the trough of the San Joa- quin Valley. < When the first Spanish soldiers entered the valley in 1772, they found it populated with Indians and wild game. Since that time the changes imposed by man on the landscape have been primarily due to agriculture. The land has been tilled nearly to the edge of the foot- hills and irrigated with water chiefly pumped from deep wells but, in part, imported in canals; the principal crops grown in the Los Banos-Kettleman City area are grain, cotton, and alfalfa. Sheep graze in the Coast Ranges west of the valley. The climate is arid and the summers are very hot. This climatic condition combined with high mineral content of the ground water has discouraged any large-scale urban or industrial development in the area. Less than a dozen very small towns occupy this 1,500-square-mile area where the annual rainfall is from 6 to 8 inches. Large declines in artesian head in confined aquifers, due to the intensive pumping of ground water for irri- gation, had caused more than 2 feet of subsidence of the land surface throughout 1,200 square miles of the Los Banos-Kettleman City area as of 1959. Maximum sub- sidence of 20 feet had occurred west of Mendota; near Huron in the southern part of the area, maximum sub- sidence totaled 16 feet in 1959 (fig. 2). Between 1955 and 1959 the rate of land-surface subsidence ranged from 0.2 foot to 1.5 feet per year. Near-surface subsidence has resulted from hydrocompaction of moisture-deficient deposits above the water table in 82 square miles along the western border of the valley (Lofgren, 1960; Bull, 1964). This hydrocampaction, which is locally (fig. 2) superimposed on the more widespread compaction due to decline of head, has resulted in startling surface slumpage and very extensive damage to structures. Land subsidence in this area has been, and probably will con- tinue for some years to be, a serious problem in the design and maintenance of highways, oil pipelines, 37°00" 36°30 36°00' COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA 120°30' 120°00' e Los Banos @ ~. faz. rem __ Rif st _ _ ON w a 3 Firebaugh e t*" y \ G/O ~ -- Q? h *, 2 m} i_," P ‘/... Kerman ."\é’% A fl. - < ; E x." EXPLANATION | \3\\\ Nopointg)\ ~~ WWL 4 SSS 2... 3 > . Boundary of deformed rocks # \\\ > Y xE AX» Line of equal subsidence C." ts x." # \ Interval 2 feet. Compiled as sum of (1) comparison of 5’? 7¢ “\ \ \\/\3 o \ topographic mapping by U.S. Geological Survey in MG ( £ 3h \\ \ \ 1922-32 and 1955 (control date) and (2) leveling by F W X o\ & U.S. Coast and Geodetic Survey in 1955 (September- \\\,’; ~ \ \ \ November) and 1959 (October 1959 to January 1960); % //, y JN & - \ } controlled in part by 1943 leveling by U.S. Coast and 2 4 1, l \\ *C o\\\ I } * \ 1 I Geodetic Survey. / / #. 7 \ $\\z ae ‘ lt Westhaven j : Lal 4 , Boundary of area of near-surface o } x \\ Peo Dul \ subsidence as mapped in 1961 PB rpuensant < ~ \\\ M Coalinga @ \§\\\\\e LAKE 5 0 5 10 MILES BED TE 4.6 £216.20 .L... cnd Keitleman 7/4 City 120°30' 120°00' Base from U.S. Geological Survey Central Valley map, 1:250 000, 1958 FicuRrE 2.-Land subsidence, 1922-32 to 1959. E3 37°00° 36°30" 36°00° E4 powerlines, irrigation canals and ditches, and other large structures. However, increased understanding of the subsidence phenomenon has made it possible to cope with many of the subsidence problems. PREVIOUS INVESTIGATIONS Geologists first turned their attention to the Los Banos-Kettleman City area in the 1890's when the first oil wells were drilled in the vicinity of Coalinga. The earliest systematic geologic investigation was that of W. L. Watts (1894), who reported on the oil fields along the border of the San Joaquin Valley for the California State Mining Bureau. Since that time, many reports on the geology of the oil fields in, and adjacent to, the Los Banos-Kettleman City area have been written. Most of the work, however, has been concerned chiefly with the oil-bearing formations of Cretaceous and Tertiary age. The earliest published de- tailed geologic descriptions of subsurface Pliocene and Quaternary deposits are in papers on the Kettleman Hills oil field by Goudkoff (1934), Barbat and Gallo- way (1934) and Woodring, Stewart, and Richards (1940). The first detailed geologic studies in the area were by Arnold and Anderson (1910), who described and mapped the geology of the hills around Coalinga and a part of the Kettleman Hills. Anderson and Pack (1915) extended reconnaissance geologic mapping of the west- ern border of the San Joaquin Valley from the Coalinga area northward to Suisun Bay. Woodring, Stewart, and Richards (1940) enlarged upon the earlier work of Arnold and Anderson in their comprehensive report on the geology and paleontology of the Kettleman Hills. Their report contributed greatly to dating of the forma- tions exposed there. Work by later authors has been mostly detailed stud- ies of small areas. These studies include a report on the Moreno Formation at its type section on Moreno Gulch by Payne (1951), a report on the geology of the Ortiga- lita Peak quadrangle by Briggs (1953), and a report on the geology of Tumey and Panoche Hills by Schoell- hamer and Kinney (1953). The areas covered by these reports are shown in the index to geologic mapping (pl. 2). The rapid growth of irrigation on the central west side of the San Joaquin Valley during and after World War II greatly increased the rate of ground-water with- drawal from the late Cenozoic water-bearing deposits. This increase in withdrawal caused a rapid decline in water levels, and an investigation of possible overdraft was made by the U.S. Geological Survey in cooperation with the California Department of Water Resources (Davis and Poland, 1957). In the fieldwork for this MECHANICS OF AQUIFER SYSTEMS investigation, which began in 1950, about 700 drillers' logs and electric logs were collected ; these data formed the basis for a general description of the water-bearing deposits throughout most of the area covered in this report. During 1951 and 1952, the U.S. Bureau of Reclama- tion drilled 64 core holes in the San Joaquin Valley as part of their ground-water and canal studies. Twelve of these core holes are in the Los Banos-Kettleman City area. A paper by Frink and Kues (1954) described some of the late Tertiary and Quaternary stratigraphy of the San Joaquin Valley as interpreted from the core- hole studies. Their paper was the first to describe the wide extent and hydrologic importance of the Cor- coran Clay Member of the Tulare Formation. PURPOSE OF INVESTIGATION AND SCOPE OF REPORT Previous geologic investigations along the west border of the San Joaquin Valley were concerned primarily with petroleum development and were directed mainly at the stratigraphy and structure of marine deposits of Pliocene age and older. Hydrologic investigations, al- though they dealt with the compacting deposits, were directed mainly at evaluating the water resources of the area. By 1954, pronounced subsidence of the land surface in most of the Los Banos-Kettleman City area and in two other extensive areas in the valley resulted in the forma- tion of an Inter-Agency Committee on Land Subsidence in the San Joaquin Valley for the purpose of planning and coordinating the study of this phenomenon. The committee recommended (1955) a comprehensive in- vestigation of the extent, magnitude, causes, and pos- sible remedies for the subsidence. As one result of the Inter-Agency planning, the U.S. Geological Survey undertook intensive studies of sub- sidence due to water-level decline in the San Joaquin Valley. These studies are being made in cooperation with the California Department of Water Resources. Poland and Davis (1956) summarized the available information on subsidence in the Los Banos-Kettleman City area as of the start of the investigation. Ireland (1962) prepared an inventory and description of wells, and Bull (1961, 1964) has described extent, causes, and mechanics of near-surface subsidence in the Los Banos- Kettleman City area. Areas of active and substantial land subsidence afford an unusual opportunity to study the compaction of sedi- ments in response to increase in applied stress that can be measured. In 1956, therefore, the Survey also began a companion federally financed research investigation ; it is directed toward determining the principles con- trolling the deformation (compaction or expansion) COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA of aquifer systems resulting from change in effective stress (grain-to-grain load), caused by change in in- ternal fiuid pressure. This research study on the mechanics of aquifer systems is under the direction of J. F. Poland. This report is one product of the Federal research program. It describes the geology of the deposits that are undergoing compaction in the Los Banos-Kettleman City area and includes discussions of stratigraphy, lithology, source, environment of deposition, structure, and geologic history. The report also describes briefly the hydrologic framework of the compacting deposits and the chemical quality of the ground waters. Geologic mapping of the water-bearing deposits ex- posed along the western border of the valley is shown on plate 1. The description of the subsurface geology is supported by electric-log sections and by maps show- ing extent, configuration, and thickness of various im- portant geologic units in the water-bearing section. The data presented herein furnish the basis for study of the relationship between the physical character and depositional environment of the different types of the continental sediments and their relative compaction in response to the increased effective stress caused by the decline in artesian head. Other reports in this series describe the physical and hydrologic properties of the water-bearing deposits (Johnson and others, 1968), their particle sizes and clay minerals (Meade, 1967), and the factors that in- fluence change in pore volume and compaction under increasing effective overburden load (Meade, 1968). Several short papers describing methods of study and selected findings have been published while the investi- gation was in progress (Lofgren, 1961; Meade, 1961a, b; Miller, 1961; Poland, 1960, 1961; Poland and Even- son, 1966). The analysis and interpretation of subsurface geo!- ogy was done by R. E. Miller from data available prior to 1963. The surface geologic mapping was done in 1957 by J. H. Green, assisted by W. A. Cochran. A manuscript describing the subsurface geology, hydrol- ogy, and geochemistry of the ground waters was writ- ten by R. E. Miller; a companion manuscript written by J. H. Green descrlbed the stratigraphy of the ex- posed rocks. These two manuscripts subsequently were revised and combined by G. H. Davis in this report. The geologic map (pl. 1) included in this report shows the outcrop areas of the unconsolidated and semi- consolidated formations of Pliocene and Pleistocene age and the outlines of the moderately to poorly permeable alluvial soils that border the foothills. The Etchegoin and Jacalitos Formations are differentiated, and the Tulare Formation is distinguished from the terrace de- E5 posits. Geologic sections measured at eight locations are presented in graphic form to illustrate the lithologic character of the late Tertiary and Quaternary deposits as exposed at the land surface (figs. 5-7). In the areas mapped in detail by earlier workers, their geologic mapping was adopted in most part with little or no modification. This was done for mapping in the Kettleman Hills (Woodring and others, 1940) , the map- ping in the Tumey and Panoche Hills by Schoellhamer and Kinney (1953), and the mapping in the Ortigalita Peak quadrangle (Briggs, 1953). The principal modi- fication, discussed under the Tulare Formation, involved the reassignment of Briggs' Oro Loma Formation be- tween Little Panoche and Ortigalita Creeks to the Tulare Formation on the basis of evidence developed during 1961-64. The reconnaissance mapping was done by J. H. Green and W. A. Cochran in July-November 1957. Aerial photographs aided immensely in this work. The usual procedure for mapping was to determine formation boundaries by inspection in the field and then to extend them on the photographs. Many repetitions of this process, with additional detailed field inspections and measurements at selected locations, allowed mapping of a large area in the relatively short period of fieldwork. The interpretation of the subsurface geology was based largely on interpretation of electric logs of water wells in conjunction with stratigraphic information from exploratory core holes. As part of the Inter-Agency Committee's activity during 1957 and 1958, four core holes were drilled in the Los Banos-Kettleman City area. Composite logs of these holes are presented on plate 5. About 500 electric logs and several hundred drillers' logs of water wells collected to June 1961, and more than 400 single-point electric logs of shallow explora- tion holes drilled in the San Joaquin Valley by the Geochemical Surveys of Dallas, Tex., were utilized in. the present study. Lithologic and stratigraphic data from 31 core holes in or near the Los Banos-Kettleman . City area (table 1) were used in preparing this report. Stratigraphic interpretations of the subsurface geology are shown by a series of four transverse and one longi- tudinal sections (fig. 3). ELECTRIC-LOG INTERPRETATION Electric logs of boreholes in alluvial sediments seek to measure and record two quantities. The first is the variations, in the borehole, of natural electrical currents that flow between clay beds and more permeable beds wherever such beds are in contact. The mud column in the borehole and the adjacent sediments constitute an electrical resistance, and flow of current through this E6 MECHANICS OF AQUIFER SYSTEMS R. 10 E. 11 12 13 120°30' - 14 15 16 #laorts wax)?“ { | Madera \_ i an N 13.8 179 [WV-{7,0 I 2 8 Pus j I MIE: " Ep CJA | [~, % Alluvium 3° *% sani % nfua ; Creek _ - an gay soe £3 ER "o 4 Cra! 8 & (oH I Tulare Formation Fivj Points § San Joaquin Formation 150 L Etchegoin Formation i: 270, lal f ae " Jacalitos Formation 56) | 33 oS fe or! § 137021 169 3 Mg“ ar are a 1 ig | 19 8 o28 HBN a 19r € ] f $s Sedimentary rocks esthaven ___ (| say| _ ___| E 3 undifferentiated l @ (3 / - Stratford | 20 Alinement of geologic section , e A 3 Sections are shown in figures 18-15 4 3 and on plates 8 and 4 a_ ~- -+-] | l Well for which electric log is shown TULARE 21 on geologic sections | I LAKE L991, Core hole shown on geologic f BED x8 sections or referred to in text City | s. 36°00 36°00° Base from U.S. Geological Survey Central Geology chiefly by J. H. Green, 1957 Valley map, 1:250 000, 1958 FIGURE 3.-Location of geologic sections and core holes. COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA TABLE 1.-Core holes in or near the Los Banos-Kettleman City area [Locations of core holes shown in figure 3] Core hole Year Depth Drilled by- drilled _ (feet) 12/12-16H1...... 1957 1,005 Inter-Agency Committee on Land Subsidence in the San Joaquin Valley. 14/13-11D1....._. 1957 1,500 Do. 16/15-34N1.-...... 1958 - 2, 000 Do. 19/17-22J1, 2_._._. 1957 2, 203 Do. 10/14-8B1.-...__. 1952 1,002 U.S. Bureau of Reclamation. 11/11<2J1_..."... 1952 600 Do. 11/11-22Q1....._. 1952 598 Do. 11/15-33P1...._.. 1952 850 Do. 1952 500 Do. 11/18-8Q1....... 1952 810 , Do. 1952 430 Do. 12/12-25D1....._. 1952 420 Do. 12/17-8G1._...__. 1952 500 Do. 12/18-13R1...... 1952 700 Do. 13/15-35BE1.._.._._._. 1952 785 Do. 13/16-201._._..... 1952 750 U.S. Bureau of Reclamation. 14/15-25H1...... 1952 705 Do. 15/12-28Q1...... 1952 850 Do. 1952 800 Do. 15/16-12C1.-._.._. 1952 733 Do. 15/16-17L1...... 1952 800 Do. 15/16-28A1....._. 1952 800 Do. 17/16-30A2...._. 1952 1, 500 Do. 20/18-13C....... 1936 3,501 Seaboard Oil Corp. of Delaware. 19/18-150.__.._._._ 1929 1,022 Shell Oil Co. 19/18-24R..___.._. 1929 - 2, 559 Do. 19/18-26H______. 1929 - 3, 071 Do. 19/18-27N....... 1929 - 2, 242 Do. 19/19-17P......_. 1929 - 3, 835 Do. 1929 - 3, 607 Do. 20/18-11A. ..... 1929 _ 1, 881 Do. NoTE.-In determining the source areas of the deposits, the authors are indebted to Ira E. Klein, of the U.S. Bureau of Reclamation, for his petrographic analysis of many of the core samples. resistance causes a potential change equal to the pro- duct of the magnitudes of the resistance and the cur- rent. The driving potential that causes the currents to circulate is called a spontaneous or self potential. The record of variations of this potential in millivolts is the "S. P. curve" of the electric log. The second quantity that the electric log seeks to measure is the electrical resistivity of the strata penetrated by the borehole, generally expressed in ohm- meters (ohm-m*/m). This measurement is commonly done by what is known as the three-electrode method, in which one current electrode is placed at the surface, and the other current electrode and two potential elec- trodes variously spaced on a mandrel or "sonde" are lowered into the borehole. The distance between the potential electrodes is called the pickup span, which is generally small compared with the distance between the borehole current electrode and the midpoint be- tween the potential electrodes which is commonly called the electrode spacing of the arrangement. The greater the electrode spacing, the deeper the penetration of the current into the beds forming the walls of the bore- hole. Resistivity curves on electric logs are generally ET made using two or more different electrode spacings. The purpose of this method, in part, is to make pos- sible a determination of the depth of the invasion of the drilling-mud filtrate into the beds adjacent to the borehole. This can only be done in permeable forma- tions, however, and in addition, the mud resistivity, borehole diameter, and bed thickness must be known. In the more heterogeneous alluvial sediments, only the relative amount of drilling-mud-filtrate invasion can be determined. This is done by noting the differ- ences in resistivity recorded for the same stratum by resistivity curves made with different electrode spac- ings. If the drilling mud has a lower restivity than the pore water in the formation, then the resistivity re- corded by the shorter electrode spacing is lower than that recorded by the longer spacing and the radius of the drilling-mud-filtrate invasion is greater. If the drilling-mud filtrate has a higher resistivity than the pore water, the reverse relationship occurs. The depth of the mud-filtrate invasion is sometimes an indicator of the relative permeability of the bed invaded, be- cause, in beds composed of similar sediments, the greater the permeability, the greater the amount of mud -filtrate penetration. This criterion can only be used as a rough indicator, however, and is not always dependable be- cause other factors are involved, such as variations in hole diameter, thickness of the bed in relation to the electrode spacings, and the difference in head between the drilling mud and the formation water. The type of sediments forming alluvial strata is re- flected by their spontaneous potential and resistivity as shown in figure 4. Clays generally give a maximum deflection to the right on the spontaneous-potential curve and have a low resistivity on the resistivity curve. Fresh-water sands and gravels give a deflection to the left on the spontaneous-potential curve and have a high resistivity on the resistivity curve. The greater the amount of clay and silt present in a sand, the lower the resistivity. If a bed contains brackish water, it gen- erally gives a large deflection to the left on the spon- taneous-potential curve and has a low resistivity. The type of alluvial sediments present in the bed then has to be approximately by the relative amount of drilling- mud invasion, assuming that greater invasion would occur in sands than in clays. More detailed information on electric-log interpretation can be found in many texts on the subject. The electric logs included on geologic sections in this report show only two curves. These two are the spontaneous-potential curve on the left and the short spacing ("short normal") resistivity curve on the right. Because of the small scale of the sections, it was not practicable to show the longer spacing ("long nor- E8 TYPICAL ELECTRIC LOG WITH INTERPRETATION |SELF-POTENTIAL _ RESISTIVITY REMARKS s | interbedded sand, silt, and clay indi- ts cated by moderate deflection of the self-potential and resistivity curves /—Clay or shale beds indicated by small self-potential and resisitiv- s- ity deflections JY t_) Fresh-water sand beds separated by silt and clay strata. Fresh-water sand typically has moderate self- potential and high resistivity values Sand beds containing slightly saline water interbedded with silt and clay strata, indicated by large self- potential and moderate resistivity deflections containing brackish or salt water, indicated by high self-potential and low resistivity values s 5 g 'Thin-bedded sand, silt, and clay b | EXPLANATION 3 Sand Clay Silt Sand and silt FicurE 4.-Typical electric log with interpretation. From Davis and Poland (1957, pl. 30). mal") resistivity curve on the geologic sections; but this second resistivity curve also was used in study and interpretation of the electric logs. ACKNOWLEDGMENTS The writers are grateful for the whole-hearted co- operation and material aid received from other public agencies participating in the Inter-Agency investiga- tion, from private firms, and from individuals in the San Joaquin Valley. Special thanks are due to Ira E. Klein, geologist, Bureau of Reclamation, whose petro- . graphic studies of many of the core sample furnished part of the basis for interpretations of the source of the deposits; to Geochemical Surveys Inc., of Dallas, Tex., who supplied electric logs of some 400 explora- tory holes drilled by them; to the California Division of Highways for supplying excellent low-altitude aerial photographs of the western border of the valley, which were invaluable in the geologic mapping; to Griffin Inc., for permission to drill core holes on their prop- erty ; and to the Pacific Gas & Electric Co., for supply- ing information on well yields and pumpage. WELL-NUMBERING SYSTEM The well-numbering system used in this report is the one used by the Geological Survey in California and MECHANICS OF AQUIFER SYSTEMS by the California Department of Water Resources. It shows the locations of wells according to the rectangu- lar system for the subdivision of public land. For ex- ample, in the number 14/15-18E1, which was assigned to a well 2%, miles south of Mendota, the part of the number preceding the slash indicates the township (T. 14 S8.) ; the number following the slash, the range (R. 15 E.); the digits following the hyphen, the section (see. 18) ; and the letter following the section number, the 40-acre subdivision of the section as shown in the accompanying diagram. @lg |a!) g ro-! -!: | tsl -| -(35 A I J R O| =| o| a Within each 40-acre tract the wells are numbered serially, as indicated by the final digit of the number. Thus, well 14/15-18E2 is the second well to be listed in the SW14 of the NW14 of see. 18. As all of the Los Banos-Kettleman City area is south and east of the Mount Diablo base and meridian, the foregoing abbrevi- ation of the township and range is sufficient. Explora- tion test holes and oil wells have not been assigned final digits. GEOLOGY GEOLOGIC HISTORY AND STRUCTURE The San Joaquin Valley is a great structural down- ways between the tilted block of the Sierra Nevada on the east and the complexly folded and faulted Coast Ranges on the west. The geologic history and develop- ment of the valley is intimately related to events in the bordering mountains; hence, geologic studies in the mountains are most helpful in unraveling the geology of the valley. The Sierra Nevada rises from an altitude of 500 feet along the east border of the San Joaquin Valley to more than 14,000 feet in a distance of about 60 miles. The range may be visualized as a much-dissected tilted pla- teau, uplifted along its eastern flank and depressed along its western flank, where it is overlain by sedimen- tary deposits of the San Joaquin Valley. The crystalline complex of the Sierra Nevada con- sists of metamorphosed shale, sandstone, limestone, and chert, intruded by plutonic rocks that range in composi- tion from peridotite to granite. The bulk of the rocks of the range, however, are of granitic composition. Sparsely scattered fossils found in the metasediments COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA indicate marine deposition during the Paleozoic Era and in the Triassic and Jurassic Periods. Potassium- argon dating of the intrusive rocks (Curtis and others, 1958; Kistler and others, 1965) suggests three intrusive episodes: Early Jurassic, Late Jurassic, and Late Cretaceous time. Beneath the San Joaquin Valley, crystalline base- ment rocks similar to those exposed in the Sierra Ne- vada are overlain by a wedge of sediments, partly of marine origin, that thickens westward. The full thick- ness of these rocks has not been penetrated by drilling, but geophysical and other indirect evidence suggests that the Sierra Nevada block extends westward to the flanks of the Coast Ranges (Davis and others, 1959, p. 41). The oldest beds known from drilling in the Los Banos-Kettleman City area are of Late Cretaceous age. Marine sediments of Early Cretaceous age, however, are exposed in the Diablo Range to the west and may extend a short distance beneath the San Joaquin Valley along its western border. The Diablo Range (the most easterly of the Coast Ranges) forms the western border of the San Joaquin Valley. In a general sense, the structure of this range is a broad anticline whose eastern monoclinal limb dips beneath the valley. The exposed core of the range is formed by complexly folded and contorted sedimentary and igneous rocks of the Franciscan Formation. Less deformed sedimentary strata exposed along the western border of the valley and folded during the uplift of the Coast Ranges range in age from Late Cretaceous to Quaternary. Although broadly anticlinal, the Diablo Range is characterized by lesser folds that trend obliquely to the range and pass beneath the valley. In general, the struc- tural complexity along the west flank of the Los Banos, Kettleman City area increases southward. For example, the Kettleman Hills is the surface expression of one of these oblique-trending anticlinal folds. During the Cretaceous and throughout early Tertiary time, the Los Banos-Kettleman City area was the site of marine deposition. From Miocene time onward, depo- sition was mainly nonmarine in the northern part of the area, while marine deposition continued in the southern part until late in Pliocene time. The youngest marine deposits, which are extensively exposed along the southwestern border of the area, are sedimentary rocks of the Etchegoin and San Joaquin Formations, of middle and late Pliocene age, respectively. The Plio- cene marine deposits grade northward into nonmarine deposits. At the north edge of the area, the youngest exposed marine deposits are in the San Pablo Forma- tion of Miocene age. EQ GEOLOGY OF THE TRIBUTARY DRAINAGE AREA, DIABLO RANGE Beneath the Los Banos-Kettleman City area, pre- dominantly well-sorted sandy sediments from the Sierra Nevada interfinger with predominantly poorly sorted silty and clayey sediments from the Coast Range. Con- tinental deposits of Pliocene and Pleistocene age, and, to a lesser extent, Pliocene marine sediments, together with overlying Holocene alluvium, constitute the ground-water reservoir of the Los Banos-Kettleman City area. . The geology of the tributary drainage area in the Diablo Range to the west is directly pertinent to this investigation for several reasons. First, this tributary area is the source of more than half of the deposits that constitute the ground-water reservoir. Second, the geo- logic history of the tributary mountain area is an aid in deciphering that of the valley deposits. Third, the fine- grained deposits of the ground-water reservoir, which are derived chiefly from the Diablo Range source area, are the ones most subject to compaction. For these sev- eral reasons, the source areas in the Diablo Range are described in some detail on following pages. Plate 2 presents a highly generalized picture of the geologic units that underlie the drainage basins of the west border of the San Joaquin Valley between latitude 36°N. and 37°N.-virtually the west border of the Los Banos-Kettleman City area. The geologic units have been combined into six broad categories as shown in table 2. - The formational units listed are those given in the principal sources of the mapping as shown in the index to plate 2-namely, Arnold and Anderson, 1910; Anderson and Pack, 1915; Woodring and others, 1940; Schoellhamer and Kinney, 1953; Briggs, 1953; and the California Division of Mines, 1958 (Santa Cruz sheet). The general description of the geology of the drain- age area tributary to the Los Banos-Kettleman City area is based on the same sources as plate 2. Specific references have largely been omitted for the sake of - simplicity. Formational names and ages used in the discussion are in accord with the currently accepted nomenclature of the U.S. Geological Survey. JURASSIC AND CRETACEOUS ROCKS In can readily be seen from plate 2 that rocks of the oldest generalized unit, those of Jurassic and Creta- ceous age, are common in the tributary drainage basins in the northern part of the area. Rocks of this unit are not common in the southern part of the area where marine rocks of Cretaceous and Tertiary age predomi- nate in the drainage basins. The areas occupied by the different geologic units within 13 of the largest drain- E10 Tapur 2.-Generalized geologic units of the drainage area tributary to the Los Banos-Keitleman City area Generalized geologic unit _ Symbol Formations and age on pl. 2 Qal _ Alluvium (Pleistocene and Holocene). Undifferentiated QTu Alluvium (Pleistocene and continental Holocene), terrace deposits deposits. (Pleistocene), and Tulare Formation (Pliocene and Pleistocene). Continental and QT - Terrace deposits (Pleistocene); Tulare Formation (Pliocene and Pleistocene) ; San Joaquin, Etchegoin, and Jacalitos Formations (Pliocene). marine sedimentary deposits of late Tertiary and Quaternary age. Marine sedimentary Tu and volcanic rocks of early Tertiary age. San Pablo, Temblor, Santa Margarita, and Vaqueros Formations (Miocene) ; Monterey Shale (Miocene) ; Quien Sabe Volcanics of Taliaferro (1949) (Miocene?) ; Kreyenhagen Formation (Eocene and Oligocene?) ; Domengine Sandstone, Yokut sandstone of White, (1940), Avenal Sandstone, and Tesla Formation (Eocene) ; Lodo Formation (Paleocene and Eocene); Laguna Seca Formation of Payne (1951) (Paleocene) ; and Martinez Formation (Paleocene). Marine sedimentary Ku rocks of Cretaceous age. Moreno Formation (Upper Cretaceous and Paleocene?) ; Panoche Formation (Upper _ Cretaceous); Wisenor Forma- tion of Briggs (1953) (Lower Cretaceous). KJu Franciscan Formation and associated ultramafic intru- sive rocks (Jurassic and Cretaceous). Marine sedimentary and volcanic rocks of Jurassic and Cretaceous age and associated ultra- mafic instrusive rocks. age basins are given in table-3 (modified from Davis, 1961, table 1, p. BT). Because most of the materials eroded from these basins have been deposited on allu- vial fans, there has been little mixing of erosional debris from drainage basins underlain by differing lithologies. FRANCISCAN FORMATION The Franciscan Formation, which forms the core of the Diablo Range, is most extensively exposed in the northern part of the area shown on plate 2, particularly in the drainage areas between Los Banos and Little Panoche Creeks. It underlies 26-81 percent of these four drainage areas (table 3). Its maximum thickness is unknown as neither the top nor base of the formation MECHANICS OF AQUIFER SYSTEMS has been recognized, but Briggs (1953, p. 11) estimates that at least 20,000 feet of the Franciscan is exposed near Ortigalita Peak. The Franciscan of this area consists predominantly of thin-bedded and massive gray wacke sandstone, dark slaty shale, and siltstone. Other common rock types in- clude bedded chert and mafic volcanic rocks (sometimes lumped under the general term "greenstone"). Less common rock types include limestone, glaucophane schist, and actinolite schist. ULTRAMAFIC INTRUSIVE ROCKS Ultramafic rocks intrusive into the Franciscan have been noted in many places. Most of these are narrow bodies of small extent, although one such body under- lies more than 35 square miles in T. 18 S., Rs. 12 and 13 E. The ultramafic rocks are commonly termed ser- pentine, because they have been almost completely altered to minerals of the serpentine group. In addi- tion, hornblende-quartz gabbro has been reported in the northern part of the area by Briggs (1953, p. 17). CRETACEOUS SEDIMENTARY ROCKS LOWER CRETACEOUS SEDIMENTARY ROCKS Lower Cretaceous sedimentary rocks unconformably underlie Upper Cretaceous strata north of Little Panoche Valley in sees. 8 and 17, T. 13 S., R. 10 E. (Briggs, 1953, pl. 1). At least 1,800 feet of dark shale and thin hard carbonaceous sandstone extends for 2 miles between the basal conglomerate of the Panoche Formation and rocks of the Franciscan Formation, with which they are in fault contact on the west. These Lower Cretaceous strata have been named the Wisenor Formation by Briggs (1953, p. 20). UPPER CRETACEOUS SEDIMENTARY ROCKS The thickest and most extensively exposed strati- graphic unit in the areas tributary to the Los Banos- Kettleman City area is the Panoche Formation of Late | Cretaceous age. This unit forms a nearly continuous belt roughly 6 miles or more wide that extends virtually uninterrupted nearly the entire length of the area. The thickness ranges from about 8,000 feet north of Coalinga to 30,000 feet north of Little Panoche Valley where the base and top of the unit are both exposed (Briggs, 1953, p. 24). Except where it overlies Lower Creta- ceous rocks, the Panoche is in fault contact with the Franciscan Formation along its western contact. In the southern part of the area the Panoche con- sists predominantly of massive sandstone, flaggy sand- stone, coarse conglomerate, siltstone, and mudstone. North of Panoche Creek, the Panoche is generally finer, COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA E11 TABLE 3.-Areas ! of generalized geologic units within stream basins [Modified from Davis, 1961, p. B7] Area, in percent, occupied by indicated geologic unit Drainage Marine sedi- - Marine sedi- - Continental Drainage basin area (square _ Franciscan Ultramafic mentary mentary deposits of miles) Formation intrusive rocks of rocks of Tertiary and rocks Cretaceous Tertiary age - Quaternary age ago Los sukie tige s 132 81 0 16 3 0 Salt (Merced COUNtY)--....--..---.-.«@.«.--.z«e=-s--=cc.u=%~ 26 26 0 55 0 19 ...s != nl _ {jm - l l ee.. 60 43 0 33 0 24 Little an abner ss 103 41 0 25 0 34 PaNOCKC-.._.... ccc? ece 298 17 0 26 42 15 Cantus... .n... oen s an 48 0 13 52 35 0 Salt (Fresno 25 0 0 68 32 0 ape -o 11 0 0 59 41 0 Los Gatog....__. : s air. dalle rns ins 127 0 6 84 10 0 ~ = bs gi cn 110 3 0 34 59 4 saas in fe ans cn e aps = 60 34 0 5 61 0 s- 47 5 0 40 50 5 CANO: - 20 0 0 19 65 16 1 Areas and percentages based on them are approximate; determined by planimeter from "Geologic map of California" (Jenkins, 1938; Kundert, 1955). and, although massive fine concretionary sandstone forms an important part of the unit, dark mudstone with thin beds of fine sandstone predominates. Overlying the Panoche with little, if any, unconform- ity, is the Moreno Formation, which includes the young- est Cretaceous rocks and probably beds of Paleocene age. The Moreno ranges in thickness from 1,000 to about 2,500 feet. The Moreno is characterized by purplish or maroon organic mudstone. Much of the mudstone is diatoma- ceous and is white where weathered. Massive concre- tionary sandstone identical to that of the Panoche Formation locally makes up a substantial part of the Moreno, but the most important constituent after the organic deposits is mudstone. SIGNIFICANCE OF MESOZOIC ROCKS Underlying more than half of the drainage basins tributary to the western slope of the San Joaquin Valley in the Los Banos-Kettleman City area, and the steepest parts of those drainage basins, the rocks of Mesozoic age are the predominant source of sediment of the west- side streams. These rocks are more than 50,000 feet thick in places and consist predominantly of clastic sedi- ments-chiefly feldspathic sandstone and mudstone, although mafic and ultramafic igneous rocks are promi- nent in the Franciscan sequence and organic sediments are important in the uppermost Cretaceous deposits. The type of material eroded from the various source rocks influences the lithology, mode and rate of deposi- tion, and compactibility of the materials deposited in the San Joaquin Valley. For example, Meade (1967) concluded in his studies of the sediments from the Little Panoche Creek basin that mixed-layer montmorillonite- illite and illite seem to be derived largely from rocks of the Franciscan Formation (p. C22, C73). In contrast. he found that the clay minerals derived from the marine sedimentary rocks of Cretaceous and Tertiary age are predominantly montmorillonite. Such differences in clay mineralogy directly affect the compactability of the sediments that are subject to increased effective stress resulting from artesian-head decline. The different types of rocks also have a profound influence on the chemical character of the stream waters of the area, as shown by Davis (1961, p. B20-B21). The ultramafic rocks supply abundant magnesium, and the mudstones and shales account for large sulfate con- centrations in the waters. LOWER TERTIARY SEDIMENTARY ROCKS The marine sedimentary rocks of early Tertiary age, as the term is used in this report (pl. 2; table 2), include all the rocks of Paleocene, Eocene, Oligocene, and Mio- cene age. In the northern part of the area especially, some sedimentary deposits laid down in brackish water and some continental deposits are included in this unit. As compared to the Mesozoic rocks, the post-Oligocene rocks are characterized by rapid changes in lithology over short distances and by a greater proportion of or- ganic deposits. As shown on plate 2, the lower Tertiary deposits form a narrow, discontinuous ribbon of out- crops flanking the San Joaquin Valley north of Panoche Creek. They are thicker and more extensively exposed south of Panoche Creek, especially along the flanks of the Vallecitos syncline south of Panoche Valley, and in the drainage basins of Warthan and Jacalitos Creeks southwest of Coalinga. The large exposure of lower Tertiary rocks shown in the northwest corner of the area consists of the Quien Sabe Volcanics of Taliaferro (Leith, 1949). These vol- E12 canic rocks consist of about 4,000 feet of andesite and basalt flows, and sediments, including agglomerate, con- glomerate, and tuffaceous sandstone, intruded by rhyolite and andesite. The age of the volcanic rocks has not been determined, but, on the basis of evidence from other areas in the Coast Ranges. Leith concluded that the Quien Sabe Volcanics was of Miocene age. The marine sedimentary rocks of early Tertiary ago are similar in many respects to the Cretaceous sedimen- tary rocks. Arkosic sandstone, commonly containing as much as 50 percent feldspar, and sandy or silty shale, commonly micaceous, make up most of the lower Ter- tiary section. In parts of the area, however, organic siliceous shale of the Kreyenhagen Formation makes up fully half of the lower Tertiary section. PALEOCENE AND EOCENE MARINE SEDIMENTARY ROCKS Between the organic siliceous Moreno Formation (Upper Cretaceous and Paleocene?) and the organic siliceous Kreyenhagen Formation (Eocene and Oligo- cene?) are clastic marine sedimentary rocks of Paleo- cene and Eocene age. In most of the area a sequence of dark clay shale with fine sandy beds rests conformably on the Moreno. This unit, the Lodo Formation, is ex- posed from Panoche Creek south to the Coalinga anti- cline. Locally, especially in the upper basins of Cantua Creek and Arroyo Hondo, the Lodo contains a massive concretionary sandstone member. The Lodo ranges in thickness from about 1,000 feet north of Coalinga to as much as 5,000 feet in the upper basin of Arroyo Hondo. North of the Fresno-Merced County line similar dark clay shale about 1,200 feet thick exposed along the west border of the San Joaquin Valley has been called the Laguna Seca Formation by Payne (1951). Overlying the shale of the Lodo Formation and rest- ing directly on Cretaceous rocks in the Panoche Hills is a light-yellow to white quartzose sandstone unit 50- 50 feet thick. The sandstone is interbedded with highly colored shale, carbonaceous clay, clay shale, and pebble beds. This distinctive lithology, which generally is in- terpreted as indicating tropical weathering in Eocene time, is known variously as the Tejon Formation, Domengine Sandstone, Yokut Sandstone of White (1940), and the Telsa Formation. Southwest of Coalinga the Kreyenhagen Formation is underlain by an Eocene sandstone (the Avenal Sand- stone) about 500 feet thick that rests directly on Upper Cretaceous rocks. Overlying the clastic sedimentary rocks of Eocene age throughout the area is a highly organic siliceous marine shale, the Kreyenhagen Formation, locally of Eocene and Oligocene(?) age. In addition to the or- ganic shale, the Kreyenhagen also contains sandstone MECHANICS OF AQUIFER SYSTEMS near the base and is cut by many sandstone dikes. The Kreyenhagen is as much as 2,000 feet thick north of Cantua Creek but thins to about 700 feet in Merced County. The Kreyenhagen is extensively exposed in the basins of Arroyo Ciervo and Arroyo Hondo, and frag- ments of the distinctive shale are ubiquitous on the Hol- ocene alluvial fans of these streams in the San Joaquin Valley. The Kreyenhagen is particularly important as a marker, especially in the northern part of the area and beneath the valley, where it not only is of distinctive lithology but also is the youngest extensive marine de- posit. The overlying Miocene deposits, although marine in part, are in part subaerial and are therefore difficult to trace on the surface and in the subsurface. The marine Kreyenhagen Formation where it under- lies the fresh-water-bearing deposits on geologic see- tions A4-4' and B-B' (pls. 3, 4) is about 700-800 feet thick. At the nearest outcrop north of Panoche Hills (Briggs, 1953, p. 41-44), the Kreyenhagen is 700 feet thick, the basal part consisting primarily of a brown sandy shale and white laminated sandstone, overlain by more than 600 feet of white-weathering diatomite and radiolarite. Seven miles northeast of this outcrop, on longitudinal geologic section A-4' (pl. 3), the top of the Kreyenhagen Formation is at a depth of 2,800- 3,200 feet. Opposite the Panoche Hills the dip of the formation increases southward; beneath Tulare Lake bed, 45 miles to the south, electric logs of deep oil ex- ploration holes show its top to be at a depth below 11,000 feet. The Kreyenhagen Formation is unconform- ably overlain by Miocene marine and nonmarine strata, except in surface exposures in the Panoche Creek area (Schoellhamer and Kinney, 1953) where it is over- lapped by the Tulare Formation (Pliocene and Pleistocene). MIOCENE DEPOSITS The Miocene deposits along the west border of the Los Banos-Kettleman City area are marked by great changes in thickness and lithology along their strike. In the southern part of the area-south of Coalinga and at Kettleman Hills-the Miocene is represented by thick marine shales and sandstones. North of Coalinga and extending to Panoche Creek the section is pre- dominantly marine sandstone with interbedded diato- maceous shale. North of the Fresno-Merced County line the Miocene is represented by a thin sequence of tuf- faceous, partly nonmarine sandstone, gravel, and clay. Wells in the Kettleman Hills penetrate some 4,000 feet of Miocene strata consisting of 500 feet of the Reef Ridge Shale, a soft silty shale with some interbedded volcanic sandstone; 1,500 feet of the McLure Shale Member of the Monterey Shale, a brown porcelaneous COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA organic mudstone; and 2,000 feet of the Temblor For- mation, predominantly dirty sandstones and inter- bedded shales. Only 20 miles northwest along strike from Kettleman Hills, the Miocene section exposed at the north end of Anticline Ridge consists of about 1,200 feet of pre- dominantly sandstone. The upper 550 feet, the Santa Margarita Formation, is a fine-grained, locally pebbly, brown sandstone with some calcareous reef-forming beds. The lower 650 feet is the Temblor Formation, chiefly soft gray to blue sandstone interbedded with diatomaceous siltstone and shale. Between Anticline Ridge and Cantua Creek the upper part of the Temblor consists of the Big Blue Serpentinous Member, a shale characterized by a high content of serpentine flakes which give it a distinctive blue color. Between Panoche Creek and the Fresno-Merced County line, the Miocene beds are overlapped by younger deposits. North of the county line the Miocene section consists of the San Pablo Formation, which rests unconformably on the Kreyenhagen Formation. The San Pablo varies in thickness from less than 100 to 400 feet and consists of volcanic gravel, sand, and clay. It is characterized by irregularly colored red, yellow, and green tuffaceous deposits. Locally, marine fossils are found in the San Pablo, but much of it is of fresh water or subaerial deposition. The subsurface geologic information available was insufficient to differentiate the Miocene formations that have been mapped in the foothills along the western boundary of the Los Banos-Kettleman City area on the electric logs of the geologic sections. They are shown, therefore, as an undifferentiated unit overlying the Kreyenhagen Formation. In the southern part of the area, where the undiffer- entiated Miocene deposits underlie the fresh-water- bearing deposits, the section is primarily marine. There, it is 3,000-4,000 feet thick, and its top is at a depth of 6,000-7,000 feet. In the northern part of the area, the subsurface Miocene section is primarily of continental deposition, 700-800 feet thick, and its top is at a depth of 1,900-2,000 feet. UPPER TERTIARY AND QUATERNARY DEPOSITS UNDIFFERENTIATED In the drainage basins tributary to the Los Banos, Kettleman City area are many isolated bodies of con- tinental deposits of late Tertiary and Quaternary age. Rocks of this age flanking the San Joaquin Valley have been mapped (pl. 1) as part of this investigation, but time and funds did not permit study of presumably equivalent deposits farther back in the Coast Ranges. Accordingly, these deposits, which include terrace de- E13 posits capping the older rocks as well as valley fill in the Vallecitos, Panoche Valley, and lesser valleys, have been treated on plate 2 as undifferentiated continental deposits of Pliocene to Holocene age. STRATIGRAPHY OF THE WATER-BEARING DEPOSITS The fresh-water-bearing deposits forming the ground-water reservoir in the Los Banos-Kettleman City area are restricted to late Pliocene and younger formations. The principal aquifers occur within the alluvial and lacustrine deposits of the Tulare Forma- tion of Pliocene and Pleistocene age. The underlying formations of Pliocene age contain brackish or saline water, except in the central southwestern part of the area where fresh-water-bearing strata occur in the San Joaquin Formation and in the upper part of the Etchegoin Formation. No fresh water is known to occur in the Jacalitos Formation or underlying strata. Surface and subsurface geologic studies made as part of this investigation were focused on the fresh-water- bearing deposits because compaction of these deposits due to withdrawal of ground water was presumed to be the major cause of the land subsidence. Unconsolidated to semiconsolidated deposits of Plio- cene and Pleistocene age which crop out along a rela- tively continuous strip 1-6 miles wide bordering the western flank of the project area were mapped for this report. They include the Jacalitos, Etchegoin, San Joaquin, and Tulare Formations, and terrace deposits. These strata are chiefly continental but, locally, of marine origin. The surface extent of each of these for- mations is shown on plate 1; they are shown jointly as one unit, "Continental and marine sedimentary de- posits," on the generalized geologic map (pl. 2). In general, the older of these Pliocene and Pleisto- cene formations are more consolidated than the younger units. Silt, sand, and sandy silt strata comprise the major part of the exposed section; true clay is rare. Sandstone, gravel, and conglomerate are relatively com- mon, and their presence is usually marked by strong topographic relief. Good exposures are uncommon, owing to the relatively unconsolidated character of the deposits. Slumpage, weathering, and soil formation also contribute to the difficulty of finding fresh expo- sures. Generally, deep stream cuts, roadcuts, and back slopes of hills provide the best outcrops. Liithologic characteristics change parallel to the strike of the beds as well as normal to it. This feature, coupled with the lack of good exposures, makes long- distance correlations impractical. Extensive use of aerial photographs, in part, helped to alleviate this problem. E14 In the following descriptions of the surface geology, the Jacalitos, Etchegoin, San Joaquin, and Tulare For- mations are described from south to north. Measured geologic sections are presented in the text in the same order. In order to show the character, source and environ- ment of deposition, and the relationship of the strata forming the aquifer systems in the Los Banos-Kettle- man City area, five geologic sections based on drill-log, core-hole, and electric-log data are presented on plates 3 and 4. The location of these sections is shown in figure 3. The land-surface elevation datum used on all the cross sections in this report is taken from the 1922- 32 series of U.S. Geological Survey topographic maps. It was not considered practical to compensate for eleva- tion changes caused by compaction and to adjust the land-surface datum on any of the geologic sections or on the structure map because of the subsidence. The land-surface datums of the individual core logs and elec- tric logs used in this report are from the period 1929- 1961; so the approximate maximum error that could have been introduced by land-surface subsidence can be determined from the map shown in figure 2. Generalized composite logs of four core holes, drilled as part of the program of the Inter-Agency Commit- tee on Land Subsidence, are presented on plate 5. JACALITOS FORMATION (PLIOCENE) The Jacalitos Formation was named by Arnold and Anderson (1908) for its characteristic exposures near Jacalitos Creek. According to Arnold (1909, p. 23), The formation may be roughly distinguished as that portion of the series between the shale of the Santa Margarita(?) below and the major beds of blue sand that characterize the lower part of the formation above it (the Etchegoin) through- out the district. The Jacalitos, however, includes a great thick- ness of blue sand 'beds at its summit in the southeastern part of the Kreyenhagen Hills. EXTENT The Jacalitos is the oldest formation mapped for this report. It crops out discontinuously from the southern end of the San Joaquin Valley to a point about 4 miles north of Arroyo Hondo. Plate 1 shows the extent of the formation as mapped in this investigation-from Anticline Ridge north about 23 miles to 1 mile north of Arroyo Ciervo. The average width of surface ex- posure of the Jacalitos in this area is less than 1 mile. In general, the outcrop width decreases from about a mile near the junction of State Highway 33 and the Coalinga-Fresno Road to less than a quarter of a mile at Arroyo Ciervo, north of which it is overlapped by younger deposits of the Etchegoin Formation. The predominantly fine-grained sedimentary rock MECHANICS OF AQUIFER SYSTEMS comprising the Jacalitos Formation greatly influence its topographic development. Strike valleys, formed between more resistant strata above and below, charac- terize the major part of the outcrop area near Oilfields and near Arroyo Hondo. Elsewhere, the more consoli- dated sandy rocks of the Jacalitos resist erosion equally as well as the younger deposits above, but not nearly so well as the older rocks below. Therefore, the surface outcrops of the Jacalitos generally are considerably lower than those of the older rocks to the west. LITHOLOGY The Jacalitos Formation consists mainly of banded red, green, and gray silt and sandy silt beds and only minor amounts of sandstone and gravel. When seen from the West, particularly in the late afternoon or evening sun, the color banding of the silt is very notice- able and in places very outstanding. Measured sections of the Jacalitos Formation are shown in figure 5. A section spanning the full outcrop of the Jacalitos (fig. 5A, section a to a') was measured 3.5 miles south of Salt Creek. From near the town of Oilfields north to Salt Creek the upper part of the formation contains a blue sand- stone similar to those found in the overlying Etchegoin Formation. Logically, this sandstone might be included with lithologically similar materials above. Arnold and Anderson (1910, p. 114), however, defined the base of the Etchegoin Formation as the @Zycymeris fossil zone, which in this area lies above the lowest blue sandstone. That definition was followed for this investigation. Below the sandstone, and continuing to the base of the Jacalitos Formation, is an alternating series of red and gray silt interbedded with sandstone and gravel. The basal unit of the formation in this area generally is a deep red silt, but, locally, a fossiliferous sandy gravel marks the base. Fossils found in the Jacalitos generally are waterworn and broken, indicative of reworking by streams. Opalized wood fragments are common, includ- ing remnants of large logs or tree trunks. Between Salt and Cantua Creeks, the top of the Jaca- litos is taken as the top of the bed just beneath the lowest blue sandstone. In a section measured 0.3 mile south of Cantua Creek (fig. 5B, section b""' to b"'"'), the top is an olive sand. The blue sandstone found in the Jacalitos farther south does not extend into this area, nor does the zone. The red silt found at the base to the south grades northward into drab gray and tan silt. With the gradational color change, the basal member becomes more sandy in the vicinity of Salt Creek. At Cantua Creek, the basal member is taken as the first gray silt overlying fossiliferous Miocene gravel and sandstone. COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA Red and gray EXPLANATION Blue Red and gray Sand f= Blue Silt "ches Red set and Gravel ere? Shale Brown and blue FEET! it r- 0 =- Green Brown |- 100 Brown Sandstone Red and gray Z Conglomerate Red and gray - 200 VERTICAL SCALE FiGURE 5.-Sections of strata in the Jacalitos Formation, A. Section a-a', strata exposed near Martinez Creek, sec. 20, T. 18 S., R. 15 E. B. Section b'''-b''"'', strata exposed near Cantua Creek, sec. 2, T, 18 S., R. 14 E. North of Cantua Creek, the Jacalitos consists prin- cipally of dull-green, gray, and tan slightly sandy silt. The color banding, so conspicuous farther south, is sub- dued here, owing to lesser amounts of contrasting red silt in the section. Gravel and sandstone are present in small amounts. The base of the formation is marked by a slightly gravelly gray to tan sand or sandstone. Opal- ized wood fragments were observed but not in amounts comparable to the area farther south. About 3 miles north of Arroyo Hondo, the coarse gravelly sand at the base of the Jacalitos fills root or worm holes that ex- tend into the underlying Miocene strata. E15 THICKNESS, MODE OF ORIGIN, AND STRATIGRAPHIC RELATIONS The exposed section of the Jacalitos Formation thins progressively from a stratigraphic thickness of more than 1,000 feet, near the intersection of State Highway 33 and the Coalinga-Fresno Road, to nothing about 4 miles north of Arroyo Hondo where it is overlapped by the Etchegoin Formation. Massive, thick sections of silt suggest the possible marine origin of most of the Jacalitos Formation. Minor amounts of crossbedded sandstone indicate that at least part of the formation is of deltaic origin. The presence of a number of bones and teeth of unidentified terrestrial animals, found in see. 13, T. 19 S., R. 15 E., indicates continental deposition at that locality. Angular unconformities are not apparent between the Jacalitos Formation and either the overlying or underlying formations in this area. Aerial photographs, however, show that each unit in turn overlaps the next older formation, indicating that disconformities prob- ably exist between them. Other evidence of a discon- formable contact at the base of the Jacalitos Formation is the presence of fossil wood in the basal conglomerates. The Jacalitos Formation is generally considered to be of Pliocene age. Woodring and others (1940, p. 103) state, The assignment of the Jacalitos, Etchegoin, and San Joaquin Formations to the Pliocene is now generally accepted. The ma- rine faunas of these formations have a Pliocene aspect in terms of the succession of Tertiary faunas on the Pacific Coast. The vertebrate evidence now known is not opposed to this assignment. SUBSURFACE EXTENT In the subsurface of the Los Banos-Kettleman City area approximately south of a line extending from Arroyo Hondo to the town of Cantua Creek, electric logs indicate that possibly as much as 500 feet of con- tinental deposits of the Jacalitos Formation overlies the Miocene section. In the subsurface at Kettleman Hills, Goudkoff (1934, p. 440) differentiated the Jacali- tos into seven zones on the bases of faunal and lithologic evidence and noted a distinct break in deposition at the base. The relation of the subsurface Jacalitos to the surface section is illustrated on plate 4. On geologic section C-C" the Jacalitos, which is 375 feet thick where it crops out, is shown dipping 18° toward the valley. On section D-D', parallel to C-C' and about 8 miles southeast, the Jacalitos dips 33° and is about 1,800 feet thick. Electric logs of oil exploration holes indicate that in the San Joaquin Valley proper to the east, the top of the Jacali- E16 tos Formation is at a maximum depth of slightly more than 4,000 feet. ETCHEGOIN FORMATION (PLIOCENE) The Etchegoin Formation was named by F. M. An- derson (1905, p. 178) for its exposure near the old Etchegoin Ranch in NW14 sec. 1, T. 19 S., R. 15 E. Arnold and R. E. Anderson (1910, p. 114) defined the Etchegoin Formation as the succession of beds of sand, gravel, and clay, in part in- durated, occurring in the oilfield northeast of Coalinga above the base of the hill-forming sandstone beds referred to for con- venience as the @lycymeris zone, and in the Kettleman Hills below the fresh-water beds described as the base of the Tulare Formation. They did not attempt to define the top of the formation in the hills north of Coalinga owing to the "indefinite- ness of the line between the Etchegoin and the Tulare there." In the Kettleman Hills, Woodring and others (1940, p. 28) placed the Etchegoin below the San Joa- quin Formation, whose base was drawn at the base of the Cascajo Conglomerate Member. South of State Highway 198 on Anticline Ridge the contact between the Tulare and Etchegoin is indefinite, but to the north, the contact is relatively easy to delineate with the use of aerial photographs. On photographs, features such as topographic expression, color (contrasts of dark and light), and overlap of one formation on the other helped to delimit the two formations. EXTENT The Etchegoin Formation is exposed discontinuously in the foothills from the southern end of the San Joaquin Valley to a point about 2 miles north of Panoche Creek. Where mapped for this investigation, its outcrop forms a band that averages slightly more than 1 mile in width. The basal part of the formation is not exposed in the Kettleman Hills or on the southern part of Anticline Ridge, where erosion has failed to cut through to the base. North of the Coalinga-Fresno Road, the uppermost part is not exposed because of over- lap by the Tulare Formation. LITHOLOGY In the North Dome of Kettleman Hills, the exposed Etchegoin strata consist chiefly of brown silty sand and sandy silt with lenses of blue sandstone. About 6 miles north of Coalinga, the Etchegoin, the base of which is marked by the fossil zone, consists of beds of compact coarse and fine bluish-gray silty sandstone alternating with zones of pebbly sand, fine gray sand, silt, and clay. The clay increases upward in the section (Arnold and Anderson, 1910, p. 117). Measured sections of strata in the Etchegoin Forma- MECHANICS OF AQUIFER SYSTEMS tion at six places between Anticline Ridge and Tumey Gulch are shown in figure 6 (4-F'). Two of these sec- tions (fig. 64, B), both of which span the full exposed thickness of the Etchegoin Formation, illustrate its lithologic character between Anticline Ridge and the Coalinga-Fresno Road. Here, the Etchegoin is pre- dominantly gray, brown, and red silt and sandy silt, with thinner, but massive, beds of brown and blue sandstone. Between the Coalinga-Fresno Road and Cantua Creek, the Etchegoin Formation is characterized by beds of massive blue sandstone and banded sandy silt. Near Cantua Creek, the blue sandstone grades into brown sandstone interbedded with light-brown, tan, and gray silt (fig. 6C) ; blue sandstone is not found north of Cantua Creek in the Etchegoin Formation. From the Coalinga area northward to about 3 miles north of the Coalinga-Fresno Road, the base of the Etchegoin is marked by the @!lycymeris zone; this zone can be traced as far north as NW 14 see. 35, T. 18 S., R. 15 E. North of there to Salt Creek, the base is taken as the base of the blue sandstone that lies directly over the @lycymeris zone farther south. Between Salt and Cantua Creeks, the base is taken as the bottom of the lowest persistent blue sandstone. Just south of Cantua Creek, the Etchegoin can be divided into three lithologic units. A section measured 0.3 mile southeast of Cantua Creek (fig. 6C) illustrates the threefold lithologic subdivision in that area. The upper unit is mostly yellow to light-tan silt with thin stringers of gravel. Below this lies a middle unit of brown and blue sandstone and gray to reddish-gray silt, with blue sandstone at the top and base. The lower unit consists predominantly of gray silt with red and tan banding. Between Cantua Creek and Arroyo Hondo, the see- tion consists chiefly of sandy silt with relatively thin lenses of sandstone, gravel, and silty sand. The silt beds display prominent color banding of red, tan, brown, and gray. The sandstone and gravel are usually gray or grayish brown. Definite evidence of overlap of the Etchegoin by the Tulare Formation is present north of Cantua Creek; therefore, the base of the Tulare was used as the contact between the two formations. The Etchegoin characteristically contains an exten- sive basal gravel and sandstone between Cantua Creek and Arroyo Hondo. Just north of Cantua Creek this basal bed consists of interbedded gravel and gravelly sandstone about 20 feet thick containing cobbles as much as 6 inches in diameter. This bed thickens northward and, in the vicinity of Arroyo Hondo, is about 80 feet thick. A section measured across the full outcrop of the Etchegoin 0.1 mile southeast of Arroyo Hondo (fig. COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA 6D) shows this basal gravel which there includes two interbeds of sandy silt. In many places the basal gravel contains a large amount of secondary gypsum in the form of crack and cavity fillings. The lithologic composition of gravel throughout the Etchegoin Formation is fairly constant. Fragments consist mostly of fine-grained igneous and metamorphic rocks, white quartz, chert, and jasper. Less common constituents are fragments of older resistant sandstone and shale, fossils reworked from Miocene strata, and concretions from Cretaceous sandstone. From Arroyo Hondo northwest about 6 miles to a point in the hills opposite Panoche Junction, the Etche- goin becomes more gravelly and sandy. The upper part is predominantly banded silt but contains much more sand and sandstone than farther south. The basal gravel thickens, and, in sec. 14, makes up about a quarter of the formation thickness, as indicated in section #"-F"' (fig. 6). Between Panoche Junction and Tumey Gulch, the Tulare Formation progressively overlaps and conceals the upper Etchegoin strata. Silt and sandy silt still persist as the major constituents of the Etchegoin, but the proportion of sandy material is greater than farther south. The basal part of the Etchegoin grades from gravel near Panoche Junction to sandy silt near Tumey Gulch. (See fig. 67.) Secondary gypsum is very common in this lower part and also is some of the upper coarse- grained beds. Also, many of the coarse-grained beds contain fossilized wood fragments. Red and gray colors still predominate. Some of the silt beds in the lower part of the Etchegoin display very bright and contrast- ing color bands. Color differences of red and gray sedi- ments are attributed by many geologists to variation in conditions prevailing at the time of deposition-that is, red is inferred to indicate oxidizing conditions at the time of deposition, and gray, reducing conditions. However, some of the silts in the Etchegoin seem to be developing their red color at present. Specimens of the red silt taken from below the surface have a mottled gray and red pattern, possibly indicating active oxida- tion of the gray material at, or very near, the surface. Near Panoche Creek, the Etchegoin Formation is ex- posed only in a very narrow discontinuous strip; all but the lowest part is overlapped by the Tulare. The northernmost exposure is about 2 miles north of Panoche Creek. There, the base of the formation con- sists of pebble and cobble conglomerate with a reddish- brown dirty sandy matrix. Cobbles of glaucophane schist as large as 6 inches in diameter are common in the conglomerate. This basal conglomerate grades up- ward into a pebble conglomerate of the same general compisiton. Overlying this conglomerate is a yellow- E17 brown friable arkosic sandstone, a sequence of greenish- gray clayey siltstone and sandstone, and a crossbedded arkosic sandstone, the highest exposed bed. THICKNESS, MODE OF ORIGIN, AND STRATIGRAPHIC RELATIONS The exposed thickness of the Etchegoin is not constant because of the unconformable contact at the base and progressive overlap of the Tulare Formation at the top. Measured sections at six localities (fig. 6) indicate that the exposed Etchegoin thins from south to north. At State Highway 198 the thickness exceeds 2,000 feet, but near Tumey Gulch, 30 miles northwest, it is less than 500 feet, and near Panoche Creek, it is only a few tens of feet. The Etchegoin Formation is partly marine and partly fluviatile and lacustrine in origin. Marine fossils are absent throughout much of the formation north of Anti- cline Ridge but are abundant in the Kettleman Hills (Woodring and others, 1940, p. 55). North of Anticline Ridge, many of the sandstone and gravel beds contain fossilized bones of terrestrial animals and are doubtless of continental origin. Rock constituents of the clastic sediments indicate that the source of the Etchegoin was the older rocks of the Diablo Range farther west. Angular discordance between the Etchegoin and Jaca- litos Formations is not discernible in the field, and the formations appear conformable in individual outcrops. However, the regional overlap of the younger upon the older shows that an unconformity does exist between the two. The Tulare Formation appears to be conforma- ble upon the Etchegoin in the southern part of the area. North of Cantua Creek, however, aerial photographs show overlap of some of the upper Etchegoin beds by the Tulare. At Tumey Gulch, there is a measurable un- conformity between the two units. Woodring and others (1940, p. 103) assigned the Etchegoin Formation to the Pliocene on the basis of marine invertebrate and nonmarine vertebrate fossils. SUBSURFACE EXTENT The Etchegoin Formation underlies the fresh-water- bearing deposits of the San Joaquin and Tulare Forma- tions throughout most of the Los Banos-Kettleman City area. In the west-central part of the Los Banos-Kettle- man City area, the upper part of the Etchegoin Forma- tion is fresh-water bearing (pl. 4). Several wells near the foothills and a few very deep wells (3,000-3,800 ft) in the valley proper south and southwest of the town of Cantua Creek tap the thin sand layers in the upper part of the Etchegoin. However, its depth of more than 3,000 feet beneath most of the valley prevents it from being considered as an important source of water for irrigation wells. E18 MECHANICS OF AQUIFER SYSTEMS C nmr: Light y+. gray Brown Gray | d . Brown White Yellow Gray Greenish gray Reddish wats gray Blue Gray Light gray Gray grey White Greenish gray Brown Light gray Red and gray Gray Light brown and iron stained Gray Gray Aliant Gray brown Gray Gray Tan wee. Glycymeris zone Red and green Tan Blue FEET Gray 0 Blue Light ray € Glycymeris zone Brown Gray 100 VERTICAL _ Iron-stained SCALE FicurE 6.-Sections of strata in the Etchegoin Formation. A. Section c-c,. strata exposed along State Highway 198, see. 30, T. 19 S., R. 16 E. and secs, 25 and 26, T. 19 S., R. 15 E. B. Section d-d', strata exposed along Coalinga-Fresna Road, sec. 7, T. 19 S., R. 16 E. and sec. 12, T. 19 S., R. 15 E. C. Section b'"'-Db''', strata exposed near Cantua Creek, sec. 35, T. 17 S., R. 14 E. and sec. 2, T. 18 S., R. 14 E. COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA E19 D Gray Yellow Yellow Red Yellow Gray Yellow Brown Gray Light grayish Light Greenish tan yellow gray Gypsum Yellow 3 Greenish gray F tBolue Yellow Light tan Greenish gray gray; gypsum and some silicified bones Light Light olive 1 > Gray 129). Bluish gray Yellow Tan Red< Variegated Gray; bone fragments Dark gray Blue Reddish and yellowish tan Gray Light tan ight gra Bluish gray Lfg ay Ti: _to and brown ight sy gbuyfidant Gray Dark gypsum brown a m Blue 3 Tan to reddish M i d d l e u n i t L o w er Brown Gray Reddish gray Greenish gray Gray 0 a %o 0% % ;® D. Section e'-e'' strata exposed near Arroyo Hondo, sees. 9 and 10, T. 17 S., R. 14 E. E. Section f'-f'", strata exposed near Panoche Junction, sees. 14 and 23, T. 16 S., R. 13 E. F. Section g'-g"', strata exposed near Tumey Gulch, SW¥% NEZ, see. 1, T. 16 S., R. 12 E. E20 The Etchegoin is differentiated near the western end of three of the transverse geologic sections (pl. 4). How- ever, it is not differentiated beneath most of the valley proper because of lack of subsurface stratigraphic infor- mation. On the basis of electric logs alone, the Etche- goin cannot be reliably distinguished from the underlying and overlying deposits, which in much of the area are lithologically similar to the Etchegoin. SAN JOAQUIN FORMATION (PLIOCENE) EXTENT The San Joaquin Formation, which is extensively exposed at Kettleman Hills and underlies the southern part of the Los Banos-Kettleman City area, contains the uppermost marine strata in the San Joaquin Valley. F. M. Anderson (1905) first described the "San Joaquin clays" from the Kettleman Hills, but he did not desig- nate a type locality. Barbat and Galloway (1934) pre- sented the first definitive paper on the "San Joaquin Clay," including the first designation of a type section and a type locality for the formation. Woodring and others (1940, p. 27) changed the name to San Joaquin Formation and suggested a section along Arroyo Hondo in Kettleman Hills as a standard section. In this report, the San Joaquin is distinguished only in the Kettleman Hills, as mapped by Woodring and others (1940), and in the subsurface. On Anticline Ridge, the upper part of what is mapped as Etchegoin on plate 1 may be equivalent to the San Joaquin Formation of the Kettle- man Hills. There is, however, no readily distinguishable lithologic basis for separation. A detailed study to try to resolve this problem was not within the scope of this field mapping. LITHOLOGY The most apparent lithologic feature of the San Joaquin Formation as exposed on Kettleman Hills is the predominance of fine-grained materials-silty sandstone, silt, and clay. On weathered surfaces the unit appears to consist mostly of clay, but fresh expo- sures show that silt and silty sandstone make up much of the formation. Many beds show pronounced litho- logic changes along the strike. However, the basal stra- tum of the formation, the Caseajo Conglomerate Mem- ber, was mapped by Woodring and others (1940) over a large part of the Kettleman Hills. The San Joaquin Formation is of mixed continental and marine deposition. Much of the fine material ap- pears to be nonmarine, and the remains of fresh-water shells and land plants have been found in some of them. Interbedded sandstones and conglomerates contain marine fossils. Thus, the San Joaquin Formation was probably deposited during a time of fluctuating sea level. MECHANICS OF AQUIFER SYSTEMS THICKNESS AND STRATIGRAPHIC RELATIONS The San Joaquin Formation is 1,200-1,800 feet thick where it is exposed on the flanks of Kettleman Hills (Woodring and others, 1940, p. 28). In the Guijarral Hills, where it is concealed beneath the Tulare Forma- tion, the San Joaquin Formation consists of sand, clay, and conglomerate and is 1,700 feet thick (Hunter, 1951, p. 15). Kaplow (1942, p. 22) concluded that, on Anti- cline Ridge along State Highway 198, exposures of clay with sand streaks, 1,570 feet thick should be assigned to the San Joaquin. No angular unconformities or major disconformities are recognized at either the base or the top of the San Joaquin in the Kettleman Hills. This fact suggests that the Etchegoin, San Joaquin, and Tulare Formations of the Kettleman Hills were laid down during a time of relatively continuous deposition. However, north of Cantua Creek where distinct unconformities mark the contacts between the Jacalitos, Etchegoin, and Tulare Formations, folding and erosion evidently interrupted the depositional sequence. Thus, it seems that deforma- tion in the Kettleman Hills began somewhat later than that in the foothills north of Cantua Creek. Woodring and others (1940, p. 103) assigned the San Joaquin Formation to the upper part of the Pliocene on the basis of vertebrate and marine invertebrate fossils. SUBSURFACE EXTENT In the Los Banos-Kettleman City area, the upper- most stratum in which the pelecypod / ya is recognized, has generally been taken as the top of the San Joaquin Formation. This so-called upper {ya zone was cored in several exploratory holes drilled in the vicinity of Westhaven in 1929 by the Shell Oil Co." By correlating this lithologic horizon on electric logs, the San Joaquin Formation has been differentiated from the overlying Tulare Formation in the southern part of geologic section A-4' (pl. 3). The 500-700 feet of fresh-water- bearing sand and interbedded clay underlying the Tulare Formation and indicated as littoral or estuarine deposits on the southern part of geologic section A-A' are considered to be a shoreline phase of the San Joa- quin Formation. Many deep water wells in the south- western part of the Los Banos-Kettleman City area are perforated in these strata, which are highly permeable, and are presently an excellent source of water. (See pl. 4, sections D-D', E-£".) Here, the deposits tenta- tively assigned to the San Joaquin Formation are much coarser and more permeable than those on Kettle- man Hills. 2 Shell Oil Co., 1929, "Results of Core Drilling on the Boston Land Co. Property," unpublished report. COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA TULARE FORMATION (PLIOCENE AND PLEISTOCENE) The alluvial deposits forming the Tulare Formation were first described by W. L. Watts (1894, p. 55, 67) and later assigned the name Tulare Formation by F. M. Anderson (1905, p. 181-182). No type locality was designated for the Tulare Formation by Anderson, but the Kettleman Hills have been regarded generally as the type region, and Woodring has proposed the east side of northern North Dome on La Ceja as the type locality (Woodring and others, 1940, p. 13). Woodring placed the base of the Tulare just above the youngest widespread marine deposit constituting the upper Mya zone of the San Joaquin Formation. The Tulare con- formably overlies the San Joaquin Formation in the Kettleman Hills, but, where exposed elsewhere in the Diablo Range, it rests unconformably on Pliocene and older formations. The top of the Tulare Formation by definition is the boundary between the uppermost de- formed or tilted strata and the overlying alluvium, which can be mapped with fair accuracy along most of the outcrop of the Tulare as shown on plate 1. SURFACE EXTENT The Tulare Formation extends almost continuously from the southeast to the northwest edge of the area shown on plate 1. Its outcrop averages less than 1 mile in width and at only a few places exceeds 1 mile. Nota- ble exceptions are in the Guijarral Hills, between Tumey Gulch and Panoche Creek, along Little Panoche Creek, and in the vicinity of 'Ortigalita Creek where broad outcrops result from gentle dips in the Tulare. In addition to the narrow strip that borders the foot- hills, the Tulare also caps some isolated hills north of Anticline Ridge, but most of the individual exposures are too small to show on plate 1. At one time the Tulare may have formed a broad blanket across most of the present foothill area. In the North Dome of Kettleman Hills, the Tulare consists principally of sand, much of which is silty, pebbly, and crossbedded; it contains some gravel, ap- parently laid down as stream deposits. The lower part contains some thin-bedded fine sediments that are inter- preted as lake deposits. In the Kreyenhagen, Jacalitos, and Guijarral Hills, the exposed Tulare is predomi- nantly coarse gravel. Lag gravels which probably are remnants of high depositional terraces, are found scattered over hilltops underlain by the Etchegoin and Jacalitos Formations from near Domengine Creek north to Arroyo Ciervo. Individual exposures are not large enough to map and at some places consist only of a few cobbles or boulders. Lithologically, the rock constituents are about the same as those in gravels of the Tulare Formation and older E21 Pliocene shown on plate 1. Boulders, however, are as much as 3 feet in diameter. The occurrence of these cobble and boulder gravels suggests that they once were laterally extensive and later were largely removed by erosion. Their distribu- tion and stratigraphic position are similar to that of the Tulare Formation in the Panoche Hills, suggesting a possible correlation with the Tulare; however, a definite correlation is not practicable. On Anticline Ridge, the contact between the Tulare and underlying deposits here included in the Etchegoin Formation is difficult to locate on the ground, and the contact shown on plate 1 was delineated on aerial photo- graphs on the basis of soil and vegetation differences. North of this area, the base of the Tulare is generally recognizable on both the ground and aerial photographs. At most places, the uppermost exposed part of the Tulare may be differentiated easily from the overlying alluvium by angular discordance. Where the discord- ance is small, the relatively more consolidated Tulare generally is more resistant to erosion and can be distinguished from the alluvium by its more pronounced topographic expression. LITHOLOGY From Anticline Ridge to Cantua Creek the Tulare Formation consists of beds of poorly sorted sand, gravel, and silt with a few interbedded lenses of well- indurated sandstone and siltstone. The basal zone, where fine grained, generally is somewhat limy. In much of this area the basal zone consists of coarse gravel or gravel and sandstone. The coarse basal sedi- ments commonly contain many secondary gypsum veins. Conspicuous dip slopes, generally formed on the more resistant lower members of the Tulare, are found in several places between Domengine and Cantua Creeks. Deposits supporting these slopes locally contain sand- stone concretions, as large as 2 feet in diameter, reworked from Cretaceous rocks to the west. Measured sections of strata in the Tulare Formation at seven places between Cantua and Little Panoche Creeks are shown in figure 7 (4-@). Section b-b' (fig. TA) illustrates the lithologic character of the Tulare Formation as exposed on the south flank of Cantua Creek valley. Between Cantua Creek and Arroyo Hondo the base of the Tulare is marked by a layer of locally concretion- ary - well-indurated - light-grayish-brown - sandstone about 15-20 feet thick. At several places north of Cantua Creek, the basal sandstone is overlain by a bed of hard reddish-tan marl. This lower marl is not found at Arroyo Hondo but is common near the base of the Calcareous Tan Yellow Yellow Marl; bone Yellow fragments Brownish gray Tan to brown; '~ concretions E 駢 Red Joe > Light tan to grayish tan - Olive green to 5 greenish gray FEET 0 100 VERTICAL SCALE FiGurE 7.-Sections of strata in the Tulare Formation. . Section b-Db', strata exposed near Cantua Creek, secs. 35 and 36, T. 17 S., R. 14 E. . Section e-e', strata exposed near Arroyo Hondo, secs. 3 and 10, T. 17 S., R. 14 E. . Section strata exposed near Panoche Junction, sees. 12-14, T. 16 S., R. 18 E. . Section g-g', strata exposed near Tumey Gulch, see. 31, T. 15 S., R. 13 E., sec. 6, T. 16 S., R. 13 E., and sec. 1, T. 16 S, R 12 E. . Section A-h', strata in upper part of Tulare Formation exposed near Little Panoche Creek, SE NW %, sec. 21, T. 13 S., R. 11 E. N- 'A W i MECHANICS OF AQUIFER SYSTEMS Tulare farther north. The remainder of the formation is predominantly sandy silt containing thin stringers of gravel and sandstone. Section e-e' (fig. 7B) shows the lithology of the Tulare Formation exposed along the south side of Arroyo Hondo. Between Arroyo Hondo and Panoche Junction the basal part of the Tulare Formation becomes gravelly (fig. 7C) and commonly contains cobbles as large as 6 inches in diameter. The gravel constituents are about the same as those of gravels in the Etchegoin-igneous and metamorphic rocks, quartzite, chert, white quartz, siliceous shale, and large oyster shells reworked from the Miocene strata. Abundant secondary gypsum fills the interstitial openings in the gravel. Above the base the formation consists of poorly consolidated inter- bedded sandy and gravelly silt, as shown by section $-f' (fig. 7C) of the Tulare Formation near Panoche Junction. In part, this silt is moderately to highly calcareous. Between Panoche Junction and Tumey Gulch the coarse basal bed of the Tulare Formation thickens and grades into a light-tan silty gravel and sand (fig. TD). Gravel constituents are the same as described above, but they also include olivine-basalt and sandstone fragments. Strata in the upper part of the section, par- ticularly the uppermost exposed layer, appear to con- tain a large amount of gypsite. It is uncertain whether the gypsite is within the Tulare Formation or is an evaporite deposited on the slightly eroded Tulare sur- face, and therefore it is not included in the measured section shown in figure 7D. In the Tumey and Panoche Hills, the Tulare Forma- tion consists of clayey and siltly sandstone and siltstone interbedded with pebble conglomerate and unconsoli- dated sand. The conglomerate beds are lenticular and grade laterally into sandstone. The gravel fragments are mostly of igneous and volcanic rocks, shale chips, and glaucophane schist; in addition, the basal con- glomerate contains fragments of limy brown sandstone. 'The basal gravel grades northward into finer mate- rial until, at Little Panoche Creek, the basal zone is about 90 percent marl or marly silt with thin gravel stringers. The gravels are predominantly igneous and metamorphic rock fragments, but, locally, they con- tain sandstone concretions as large as 3 feet in diameter reworked 'from Cretaceous rocks. Gypsite is common, but as farther south, its exact age and its position in the F. Section h''-h''', strata in middle part of Tulare Formation exposed near Little Panoche Creek, NEY SW %, sec. 20, T. 13 S., R. 11 E. G. Section A'''"'-h'''"', strata in lower part of Tulare Formation exposed near Little Panoche Creek, NEY, NW %, sec. 31, T. 13 S., R. 11 E. COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA section are somewhat in doubt. 'At most places, however, the gypsite appears to be either in the uppermost ex- posed Tulare or to be an evaporite deposited on a slightly eroded Tulare surface. The columnar sections of figure 7Z-G show the lithologic character of strata in the upper, middle, and lower parts, respectively, of the Tulare Formation near Little Panoche Creek. In his report on the Ortigalita Peak quadrangle, Briggs (1953, p. 46) assigned the name Oro Loma For- mation to a narrow unit of continental deposits exposed along the front of the Laguna Seca Hills, extending northwest for about 6 miles nearly to Ortigalita Creek and dipping at angles as much as 40° under the allu- vium. He concluded that these beds were lithologically and structurally distinct from, and older than, relatively flat-lying deposits to the south near Little Panoche Creek, which he mapped as Tulare Formation. In 1961 the Bureau of Reclamation drilled several core holes in connection with foundation studies for a pumping plant for the San Luis project about 3 miles south of Ortigalita Creek and about a quarter of a mile from the foothills. A diatomaceous silty clay 30-40 feet thick penetrated in these test holes has been identified as the Corcoran Clay Member of the Tulare Formation, on the basis of the presence of diatoms, lithologic similar- ity, and the known subsurface occurrence of the Cor- coran Clay Member to the east (I. E. Klein, U.S. Bur. Reclamation, written commun., May 1962). The core holes also were the basis for extension of the Corcoran to the outcrop of a gray silty clay in the foothills dip- ping 30°%-50° toward the valley (Carpenter, 1965), which had been mapped by Briggs (1953, p. 47) as the uppermost unit of his Oro Loma Formation. Where ex- posed, the gray silty clay is underlain conformably by several hundred feet of reddish-gray gravel, silty sand, and silt, stratigraphically above the San Pablo Forma- tion. The gray silty clay (Corcoran Clay Member) and the underlying gravelly deposits are therefore shown in the Tulare Formation on plate 1. The steeply dipping Tulare along the front of the Laguna Seca Hills appears to be unconformable with gently dipping beds to the south near Little Panoche Creek and to the north near Ortigalita Creek, which were mapped by Briggs as Tulare Formation and have been so mapped on plate 1. Working out 'the detailed field relations was not practicable within the scope of this study, but, evidently, beds of different ages sepa- rated by an unconformity are included in the Tulare Formation from Little Panoche Creek to Ortigalita Creek as mapped on plate 1. THICKNESS AND STRATIGRAPHIC RELATIONS The exposed Tulare Formation ranges widely in thickness. On the west side of North Dome in the E23 Kettleman Hills, the maximum exposed thickness is about 2,600 feet. North of Coalinga, the thickness in measured sections (fig. 7) does not exceed 350 feet and in most places is less than 300 feet. The exposed Tulare consists mainly of alluvium de- posited on the post-Etchegoin erosion surface. How- ever, calcareous beds and clay strata of considerable lateral extent indicate that locally it is of lacustrine origin. The processes of deposition probably were similar to those that currently are forming alluvial-fan, flood-plain, and lake-bed deposits on the west side and in the trough of the San Joaquin Valley. In the southern part of the area, the Tulare appears to rest conformably on the San Joaquin and Etchegoin Formations. North of Cantua Creek, aerial photo- graphs show definite evidence of overlap of the Tulare on the Etchegoin, although this relationship is not obvi- ous on the ground. Numerous strata of the Etchegoin, indistinguishable on the ground but traceable on aerial photographs, are progressively overlapped to the north- ward by the Tulare. From the vicinity of Tumey Gulch northward, angular discordance between the Etchegoin and Tulare Formations is apparent in the field and in- dicates pronounced pre-Tulare deformation. As already noted in the discussion of the Tulare in the Laguna Seca Hills, some deformation evidently occurred there during Tulare time. Furthermore, the steep dip of the Tulare beds along the front of these hills demonstrates pronounced post-Tulare deformation. South of the Tumey Gulch area, all exposed sections of the Tulare are tilted, suggesting post-Tulare folding in that area also. The age of the Tulare Formation has been a subject of disagreement among geologists for many years and it is still in dispute. The dispute involves also the posi- tion of the Pliocene-Pleistocene boundary in the Coast Ranges and the geomorphic development of the present topography of the Sierra Nevada. Discussion of these problems is beyond the scope of this report; however, direct evidence on the age of the Tulare is pertinent. Direct evidence on the age of the Tulare in and near the study area includes a fresh-water molluscan fauna in the basal part of the Tulare exposed at Kettleman Hills, which has also been cored at several points in the San Joaquin Valley; diatom floras from the basal part of the Tulare Formation exposed at Kettleman Hills and from the Corcoran Clay Member of the Tulare Forma- tion cored at many places in the valley ; potassium-argon dating of a rhyolitic ash bed exposed near Friant which has been correlated with volcanic ash just overlying the Corcoran Clay Member; and fossil mammal bones ex- cavated from the Corcoran Clay Member in the San Luis project canal section of the California Aqueduct in 1964. E24 According to Woodring and others (1940, p. 104), the lower part of the Tulare Formation in Kettleman Hills contains the largest fossil fauna of fresh-water mollusks known on the Pacific coast. On the basis of study of this fossil assemblage (p. 22-26), Woodring concluded (p. 104) that "assignment to the upper Pliocene is consist- ent with the character of the fauna." Dwight Taylor (oral commun., 1963), who has studied the fresh-water mollusks from the Tulare, con- cluded that- the fresh-water mollusks indicate that the basal Tulare in the Kettleman Hills is equivalent to the lower part of the Santa Clara Formation of the Santa Clara Valley and to some part of the Tehama Formation of the Sacramento Valley. On the basis of present knowledge, it is convenient to assign this se- quence to the Pliocene. In the upper part of the Tulare, near Little Panoche Creek, he concluded that fossils suggest a Pleistocene age (written commun., January 1962). K. E. Lohman (1938) assigned the basal Tulare to the Pliocene on the basis of diatom studies. Diatom floras studied by Lohman from the Corcoran Clay Mem- ber (report on referred fossils, February 1954) resemble the assemblage from the basal Tulare much more than they do numerous Pleistocene collections from the Western States (oral commun., 1963). From this, Lohman concluded that at the youngest the Corcoran is probably no later than early Pleistocene. A volcanic ash exposed near Friant in eastern Fresno County and correlated with volcanic ash just overlying the Corcoran Clay Member was dated at 600,000+ 20,000 years by G. B. Dalrymple (in Janda, 1965). The potassium-argon date demonstrated that the upper part of the Tulare Formation is of Pleistocene age. In 1964, fossil mammal bones were recovered by Bureau of Reclamation geologists from the Corcoran Clay Member during excavation of the San Luis project canal section of the California Aqueduct (Carpenter, 1965, p. 143). These bones were found about 5 miles southeast of the Dos Amigos pumping plant, in NW 14, sec. 28, T. 12 S., R. 11 E., at a depth of 25-30 feet below the land surface (R. E. Trefzger, oral commun., Au- gust 1967). The assemblage, which included remains of mammoths, camels, and Z#'quus, has been examined by Dr. J. E. Mawby ; he reported (written commun., July 1967, to J. F. Poland) that the mammoths identify the age of the Corcoran Clay Member as Irvingtonian or younger. According to the Holmes (1965) time scale, the Pleistocene Epoch began 2-3 million years ago. If vol- canic ash beds just overlying the Corcoran Clay Mem- ber are about 600,000 years old, and the Corcoran is of Irvingtonian (middle Pleistocene) age, then all of the Tulare above the Corcoran Clay Member, the Cor- MECHANICS OF AQUIFER SYSTEMS coran, and at least part of the Tulare beneath the Cor- coran is of Pleistocene age. As shown on geologic section A-A' (pl. 3), the part of the Tulare Formation under- lying the Corcoran Clay Member attains a thickness of 2,500 feet near Tulare Lake bed (south end of section A-A'). A substantial part of this 2,500 feet of pre- Corcoran Tulare doubtless is of early Pleistocene age, but data are not available to define the position of the Pliocene-Pleistocene boundary in these strata. SUBSURFACE CHARACTER In the subsurface, sediments derived from the Diablo Range interfinger with, and grade into, sediments de- rived from the Sierra Nevada. The eastern source arkosic sediments may be equivalent to part of the Kern River Formation of Diepenbrock (1983), which is exposed in the foothills adjacent to the southeastern part of the San Joaquin Valley. However, no attempt was made to assign an eastern boundary to the Tulare Formation on the geologic sections. The Tulare Formation consists of deposits laid down in a fresh-water environment, and it underlies all of the Los Banos-Kettleman City area. As discussed above, it crops out nearly continuously along the eastern slope of the Diablo Range where it is poorly to moderately consolidated. The top of the Tulare Formation in the subsurface in the Los Banos-Kettleman City area is not definable because the boundary between the uppermost tilted strata and the overlying alluvium in the outcrop area is a feature that cannot be recognized in wells in the San Joaquin Valley. In fact, beneath most of the Los Banos-Kettleman City area, the deposits between the Corcoran Clay Member and the land surface presuma- bly are conformable and thus the criterion used at the outcrop does not even exist beneath most of the valley area. Furthermore, these deposits, which are as much as 900 feet thick, are almost entirely of alluvial-fan and flood-plain origin. Although the topographic axis migrated eastward during post-Corcoran time, as shown by the gradual eastern extension of Diablo Range source materials, there is no marked change in physi- cal character or other criterion that can be related to the top of the uppermost tilted beds that define the top of the Tulare in the foothills. For purposes of defining thicknesses in this report, the depth to the top of the Tulare Formation is arbitrarily assumed to increase eastward from a featheredge at the foothills to about 200 feet below the land surface beneath the present valley axis. Obviously, a top so arbitrarily defined in no sense represents a time line. The subsurface thickness of the Tulare Formation ranges from more than 3,000 feet in the southern part COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA of the Los Banos-Kettleman City area to less than 800 feet locally in the northern part of the area. Thus, the subsurface thickness is much greater than the thick- ness in the outcrop area to the west. The Los Banos-Kettleman City area has been pre- dominantly a region of rapid and nearly continuous deposition during late Tertiary and Quaternary time. Consequently, the fresh-water-bearing sediments un- derlying the valley floor have undergone little weather- ing and reworking. Analysis of core samples indicates that very little discernible alteration has taken place in the clay minerals since their deposition (Meade, 1967, p. C6). Accordingly, oxidized sediments can gen- erally be assumed to be representative of subaerial deposition and reduced deposits indicative of subaque- ous deposition. In its subsurface extent, the Tulare Formation has been subdivided on the basis of drill-log and electric- log correlations and petrographic analysis of core sam- ples, into deposits representing four different types of continental deposition. These include alluvial-fan, flood-plain, deltaic, and lacustrine deposits, as shown in the geologic sections (pls. 3, 4) and the core-hole logs (pl. 5). Criteria that were used to identify the types of deposits have been summarized by Meade (1967, table 2). The distribution and poorly sorted character of the highly oxidized deposits underlying the alluvial slopes near the west border of the valley suggest that such deposits accumulated under subaerial conditions similar to those prevailing on the present-day alluvial fans, and therefore they are designated alluvial-fan deposits. Similarly, the lenticular and interfingering reduced fine- to coarse-grained fluvial deposits in the trough of the valley are designated as flood-plain de- posits, implying that they were deposited on the ancient river flood plain. This general term, "flood-plain de- posit," embraces channel, overbank, natural levee, back-swamp, and point-bar deposits, most of which cannot be differentiated in the subsurface. The lacus- trine deposits, where fossil evidence is lacking, are dif- ferentiated from the flood-plain deposits by their high clay content, indicative of a still-water environment, the highly reduced nature of the sediments, and their homogeneity and stratigraphic continuity as indicated by electric logs and drill logs. A few extensive, but thin, beds of well-sorted sand, associated with the fine- grained lacustrine silty clay beds, also have been identi- fied as of lacustrine origin. ALLUVIAL-FAN DEPOSITS The alluvial-fan deposits of the Tulare Formation in the Los Banos-Kettleman City area are derived chiefly from source areas in the Diablo Range. (For source E25 criteria, see Meade, 1967, p. C5.) They consist mainly of poorly sorted silt, clay, and fine to medium sand. The alluvial-fan deposits of Panoche and Los Gatos Creeks are the coarsest; they contain a few layers of medium to coarse sand, with some gravel. Although most of the material presumably was laid down by intermittent streams, boulder deposits suggest mudflow origin for parts of the deposits. The alluvial-fan deposits adjacent to the Diablo Range foothills can éasily be recognized in well cuttings or cores by their yellowish-brown to brown color. They are calcareous and gypsiferous and locally contain'small calcareous concretions, fragments of ser- pentine, glaucophane schist, siliceous shale, chert, and jasper derived from older rocks to the west. The bulk of the alluvial-fan deposits from the Diablo Range probably was laid down in post-Corcoran time. Prior to the deposition of the lacustrine Corcoran Clay Member, the ancestral Los Gatos Creek fan extended 18-22 miles east from the present western edge of the valley. (See fig. 8; pl. 4, geologic section £Z-Z".) 'After the deposition of the Corcoran Clay Member, the Los Gatos fan again expanded 18-22 miles eastward from the western edge of the valley (fig. 9). However, the post-Corcoran alluvial-fan deposits that extend north- eastward from the western border of the valley in the central part of the Los Banos-Kettleman City area are generally more extensive than the older pre-Corcoran alluvial-fan deposits. The Panoche Creek fan in the northern part of the Los Banos-Kettleman City area is one of the largest modern alluvial fans on the west side of the San Joaquin Valley, extending 18 miles across the valley floor from the western edge of the valley. However, prior to the deposition of the Corcoran Clay Member, an alluvial fan of western source extended several miles east of the present axis of the valley. The top of a layer as much as 50 feet thick consisting of oxidized deposits derived from the Diablo Range was cored below the Corcoran Clay Member at depths below land surface of 687 and 591 feet, respectively, in Bureau of Reclama- tion core holes 13/15-35E1 (pl. 4) and 13/16-2C1. A well-developed soil profile has been recognized at the top of the western source materials. Water wells in the area from near Mendota to the edge of the Panoche Hills commonly bottom in western source oxidized deposits. The uppermost layer of these deposits probably is a soil horizon because it is com- monly described in drillers' logs as being red or pink. The location of wells in this area that bottom in such oxidized deposits are plotted in figure 8. These deposits are interpreted as having been laid down on an alluvial fan that extended from the Panoche Hills east across the present valley trough in pre-Corcoran time. E26 120°30' MECHANICS OF AQUIFER SYSTEMS 120°00' Z. » 3" Los Banos A 2 37°00° / ~ Pres#O_... River.. / ~>. - ays; "x tas ~*~ Madera! RS- 0 0 P 3 a vaan s s Mendota Fresno® 4 2 o $ Fam» Kerman (0) f; d . G 1s § 3 ® bas % 3 ¢ % \ 6. ® P : AC *% * (of). EXPLANATION Zflvoo sely &; 0% % 36°30 |- ILLS Go Z Boundary of deformed rocks go,» C 2 *% O \2 400 --- Five Points \4 Line of equal thickness of alluvial-fan deposits that occur in the Tulare Formation below the Corcoran Clay Member; dashed where approxi- mate. Interval 200 feet Control point from electric log or core log 0 Location of driller's log or core log for well that entered, but generally did not pass through, oxidized sediments occurring in the Tulare Formation below the Corcoran Approximate boundary of alluvial-fan deposits derived from the Diablo Range that occur in the Tulare Formation below the Corcoran Clay Member Approximate western boundary of the Corcoran Clay Member of the Tulare Formation 5 0 5 10 MILES Io l 222 EL L 36°00" A PLEASANT Coalinga % VALLEY 120°30' Base from U.S. Geological Survey Central Valley map, 1:250 000, 1958 €, maf wa 120°00' tratford TULARE LAKE BED 37°00" 36° 30° Kettleman City 36°00" FIGURE 8.-Thickness of alluvial-fan deposits derived from the Diablo Range in the Tulare Formation below the Corcoran Clay Member. COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA E27 120°30" 120°00 Z. " 37°00" 37°90° bs 36° 30° 36°30 EXPLANATION ®°° LTW Boundary of deformed rocks 4 200- -- Line of equal thickness, of alluvial-fan deposits that occur above the Corcoran Clay Member of the Tulare Formation; dashed where approxi- mate. Interval 100 feet g Approximate western boundary of the Corcoran Clay Member of the Tulare Formation \\' # AYA ~ z - \\-YVestha.vén m & / z 1 Control point from electric log or core log // $21} Huron, + \\ : A sags \ «B . C + ke g," yee the PLEASANT ys ’/:°0 Y Z+ Coalinga @ + r—Qfi/ VALLEY 32 * gig TULARE - 3 LAKE BED 5 0 5 10 MILES La acacia _d ___] Kettleman City 36°00 36°00" 120°30" 120°00' Compiled by R. E. Miller Base from U.S. Geological Survey Central Valley map, 1:250 000, 1958 FicurE 9.-Thickness of alluvial-fan deposits derived from the Diablo Range above the Corcoran Clay Member of the Tulare Formation. / E28 The alluvial-fan deposits underlying the western slope between Cantua Creek and Anticline Ridge gen- erally are finer grained and less permeable than similar deposits to the northwest or southeast. The alluvial-fan deposits derived from the Diablo Range are of relatively low permeability and, for this reason, where such de- posits form the bulk of the Tulare Formation, irriga- tion wells in parts of the area are drilled as deep as 2,500-3,800 feet to tap more permeable aquifers in the underlying San Joaquin and Etchegoin Formations. (See pl. 4, geologic sections C-C", D-D'.) Alluvial-fan deposits derived from the Sierra Nevada that extend subsurface into the northern part of the Los Banos-Kettleman 'City area (pl. 4, geologic section B-2') are composed chiefly of fine to medium- grained micaceous granitic sand and varying amounts of silt and clay. The color of these deposits ranges from gray to brown. Where the clay content is low, alluvial- fan deposits derived from the Sierra Nevada are moderately permeable and yield adequate water to irri- gation wells. FLOOD-PLAIN DEPOSITS The term "flood-plain deposit" is used in the present report in a broad sense to include all reduced fluvial deposits laid down in the valley trough area. The flood-plain deposits derived from the Sierra Nevada as described from core samples generally con- sist of gray micaceous or arkosic sand with interbedded micaceous sandy silt and clay layers ranging in color from olive brown to greenish blue. The sands generally are subangular to subrounded and have a moderate to high permeability. As shown by the geologic sections, these deposits are extensive below the Corcoran Clay Member in the area west of Fresno Slough. The thick- ness and areal extent of micaceous sands derived from the Sierra Nevada that overlie the Corcoran Clay Mem- ber are shown in figure 10. This unit, which consists primarily of flood-plain deposits, includes just above the Corcoran a zone up to 200 feet thick containing varying amounts, up to 89 percent by weight, of rhyolitic vol- canic glass and pumice fragments (pl. 3, geologic sec- tion A-A4'; pl. 4, The approximate west- ern boundary of these volcanic deposits is shown in figure 10. The micaceous sands, which form the bulk of the flood-plain deposits from the Sierra Nevada, are highly permeable and yield water freely. In fact, from Tran- quillity to the Kings River and for several miles west, most of the irrigation wells tap the micaceous sand above the Corcoran Clay Member. In parts of the Fresno Slough area, however, the water in the flood-plain de- posits both above and below the Corcoran has such a MECHANICS OF AQUIFER SYSTEMS high mineral content that it is not satisfactory for domestic or irrigation use. (See pl. 4, geologic sections B-B', C-C'.) The flood-plain deposits derived chiefly from the Diablo Range generally have low to moderate perme- abilities. They generally are greenish gray to greenish black and are characterized by an abundance of andesit- ic and basaltic detritus. Locally, they contain moderate amounts of serpentine, chert, and other rock fragments derived from older rocks in the Diablo Range. They are also slightly to moderately micaceous, in contrast to the generally nonmicaceous character of the alluvial- fan deposits derived from the Diablo Range. Most of the western-source flood-plain deposits are found in the northern half of the Los Banos-Kettleman City area. Modern near-surface deposits laid down in flood basins by overflow of the San Joaquin and Kings Rivers in the level central floor of the valley consist largely of impervious clay and clay adobe with a texture that ranges from medium to heavy (Davis and others, 1959, p. 27, pl. 29, basin soils). In contrast, the flood-plain de- posits of the Tulare Formation are coarser and contain little clay, indicating that the depositional environ- ment was different from the present regime. The com- parative coarseness of flood-plain sediments in the Tulare suggests that streams that deposited them were more competent than the modern streams of the same areas. The relatively low clay content of the flood- plain deposits indicates excellent sorting. DELTAIC DEPOSITS Thick beds of medium to coarse well-sorted sand in the Tulare Formation in the southern part of the Los Banos-Kettleman City area are interpreted as deltaic deposits of extensive lakes. These deposits consist pri- marily of bluish- or greenish-gray angular and sub- angular medium- to coarse-grained arkosic sand with a high biotite mica content. Crossbedding and deposi- tional dips of 10°-40° and numerous carbonaceous layers are reported in core descriptions of these de- posits. Deltaic deposits are differentiated on geologic sections 4-4" and Z-" (pls. 3, 4). At the east end of geologic section Z-", sandy deposits beneath the Cor- coran Clay Member, presumably of deltaic origin, are 2,000 feet thick. (See well 19/20-32R.) Where tapped by wells, these thick sands yield abundant water. LACUSTRINE DEPOSITS The basal deposits of the Tulare Formation in the southern and central parts of the Los Banos-Kettleman City area and nearly all the deposits underlying the modern Tulare Lake bed consist of clay, silt, and sand COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA 120°30' 120°00' E29 C Los Banos 20 YG 37°00' w 4 yo 36 $2 A g + EXPLANATION se (- WWW Boundary of deformed rocks 300 --- Line of equal thickness of micaceous sand derived from the Sierra Nevada; dashed where approximate. Interval 100 feet Approximate western boundary of zone of rhyo- litic volcanic glass and ash within the micaceous sand Eastern boundary of Corcoran Clay Member Extent of water of high NaCl content in mica- ceous sand overlying the Corcoran Clay Member « Control point, from electric log or core hole 5 0 5 10 MILES hobo oon 00, i000 ents 37°00" Fresno 36°30 36°00° 120°30' Base from U.S. Geological Survey Central Valley map, 1:250 000, 1958 FiGURE 10.-Thickness of micaceous sand overlying the Corcoran Clay Member of the Tulare Formation. 411-341 0O-71--38 Westhaven yG Z 53:6” \v)’ rM * Tucare f LAKE €» Are. Kettleman _ BED s / irp +O5 Ma» 36°00 120°00' E30 commonly containing lacustrine fossils. These deposits are more homogeneous than the flood-plain deposits and generally are fine grained, except where intermixed with deltaic sands derived from the Sierra Nevada. The lacustrine sediments usually are strongly reduced, which accounts for their greenish or bluish color, and carbonaceous clay and peat layers are common. Thin oxidized layers found in parts of this sequence are generally yellowish brown to reddish orange. As shown on geologic sections A-4 ' and Z-Z" (pls. 3, 4), at least three extensive lake expansions since the retreat of the late Pliocene sea are recorded in the sub- surface deposits in the southern part of the Los Banos Kettleman City area. The initial lake in the basin is represented by the basal Tulare sediments, which con- sist of 400-500 feet of sandy lacustrine and deltaic de- posits. Core holes drilled by the Shell Oil Co.: in the vicinity of Westhaven indicate that these deposits con- tain abundant fossils of Ammicole and other fresh- water lacustrine fauna. Analyses of water from this interval and electric logs indicate that the water in these lacustrine deposits is now very brackish. On the west flank of North Dome where the Tulare Formation is well exposed, Woodring and others (1940, p. 22) noted small oysters and mussels in a sandstone 1,636 feet above the base of the formation and upward to the top of the measured section through a thickness of 322 feet of sandstone and conglomerate. About 1,300 'feet of apparently nonfossiliferous poorly bedded and crossbedded yellowish to brownish-gray sandstone con- taining conglomerate lenses and a few interbedded silt layers separate this fossiliferous zone from the upper- most Ammicola zone in the lower part of the Tulare Formation. The fossiliferous zone described by Wood- ring in the uppermost exposed Tulare Formation on North Dome represents a second major lake phase. A lacustrine deposit is found at a similar position in the subsurface northeast of North Dome. It is shown at the south end of geologic section A-A' (pl. 3) 1,200-1,600 feet above the base of the Tulare Formation. This de- posit is about 100 feet thick, and in core holes 20/18- 11A and 19/18-24R (pl. 4) where samples of it were recovered from depths of 1,151-1,160 feet and 1,039- 1,050 feet, respectively, ostracodes, Ammicola, and fish remains were reported. The third and largest lake is represented by the diatomaceous Corcoran Clay Member of the Tulare Formation, which at core hole 20/18-6B is separated from deposits of the second lake phase by 800 feet of western-source alluvium. Additional lacustrine deposits of lesser extent and thickness have been mapped by Croft (1968) between ® Shell Oil Co., 1929, "Results of Core Drilling on the Boston Land Co. Property," unpublished report. MECHANICS OF AQUIFER SYSTEMS the Corcoran and land surface in the vicinity of Tu- lare Lake. A lacustrine clay about 30 feet thick, 250 feet above the Corcoran, and 250 feet below the land sur- face, is shown at the eastern end of section Z-Z" (pl. 4). This unit has been designated the C clay by Croft. CORCORAN CLAY MEMBER A widespread diatomaceous clay stratum, first named as a separate formation by Frink and Kues (1954, p. 2357-2370), was redefined as the Corcoran Clay Mem- ber of the Tulare Formation by Davis (in Inter-Agency Committee, 1968, p. 120). The Corcoran Clay Member extends beneath the entire Los Banos-Kettleman City area, except in a narrow zone adjacent to the hills in the southern part of the area where, as shown in figure 11 and geologic section Z-£Z" (pl. 4), it grades into the surrounding deposits. The Corcoran Clay Member is the principal confin- ing layer for the artesian system throughout a large part of the San Joaquin Valley. The Corcoran is of very low permeability (Davis and others, 1964, p. 88), and in 1960 the difference in head in aquifers above and below the Corcoran locally was as much as 200 feet. The Corcoran Clay Member was deposited in a fresh- water lake 10-40 miles wide and more than 200 miles long (Davis and others, 1959, p. 77; pl. 14). The longi- tudinal axis of the lake in which the clay was deposited was about 5-10 miles west of the present topographic axis of the valley. The maximum known thickness of the Corcoran Clay Member in the Los Banos-Kettle- man City area is 120 feet, at a place 5 miles northeast of the mouth of Panoche Creek, and beneath Tulare Lake bed. At both places, thickness is based on electric- log interpretation. As shown in figure 11, the thickness exceeds 100 feet in several localities. Along the west edge of the valley adjacent to Monocline Ridge and the Ciervo Hills, the Corcoran is less than 20 feet thick. Its exact western extent is difficult to delineate because, as it thins, it bifurcates and its sand and silt content gradu- ally increase until it cannot be distinguished in electric logs from littoral sands that occur along its western edge. The Corcoran is generally reduced and is greenish blue, except locally along the western border of the Los Banos-Kettleman City area where it has been uplifted and has been partially oxidized to brown or red. Adjacent to the Panoche and Tumey Hills, the Cor- coran is 30-80 feet thick. At core hole 15/12-23Q1 (pl. 4), on the east flank of the Tumey Hills, 35 feet, the lower 10 feet of which is diatomaceous, has been assigned to the Corcoran Clay Member. From Tumey Hills northward in the Los Banos, Kettleman City area, the western edge of the Corcoran Clay Member has been uplifted (fig. 12). Fine dark silty 37°00" 36°30° 36°00° COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA 120°30' 120°00" Wa. \Y. | / éirebaugh Fresno. \ I I EXPLANATION LWW Boundary of deformed rocks 20- -- Line of equal thickness of the Corcoran Clay Member; dashed where approximate. Interval 20 feet Approximate boundary of Corcoran Clay Member Control point from electric log or core log Note: Where Corcoran Clay Member bifurcates, only the thickness stratum is represented 5 0 5 10 MILES Lingey so 101... . dio k ean crane) ¢ PLEASANT oalinga VALLEY 120°30' Base from U.S. Geological Survey Central Valley map, 1:250 000, 1958 FIGURE 11.-Thickness of the Corcoran Clay Member of the Tulare Formation. E31 37°00° 36°30 36°00° E32 37°00" 36°30" 36°00° MECHANICS OF AQUIFER SYSTEMS 120°30' 120°00" Ay el w RR an Nk */ ¢, An * EXPLANATION "op, Boundary of deformed rocks -----200 --- Structure contour Shows altitude of top of Corcoran Clay Member of the Tulare Formation. Dashed where approzimate. Con- tour interval 50 feet below mean sea level and 100 feet above mean sea level. Prepared from data available as of 1962 0,0 + 4 Control point from electric log or core log ¥ Approximate boundary of upper clay stratum of Corcoran Clay Member Approximate boundary of lower clay stratum | # of Corcoran Clay Member where upper clay // layer is absent & Area where lacustrine sand deposits along the western margin of the Corcoran Clay Member are in excess of 100 feet in thickness. 5 0 5 10 MILES Ln erd ,,, te men cud 8, < C& *, ¥ **, @ 0 -] PL NT * Coalinga % VALLEY £2" 37°00" 36°30" 36°00" 120°30' Base from U.S. Geological Survey Central Valley map, 1:250 000, 1958 FieurE 12.-Structure of the Corcoran Clay Member of the Tulare Formation. 120°00' COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA material exposed at an altitude of 500 feet in a roadcut at the north end of the Panoche Hills where Little Panoche Creek enters the San Joaquin Valley may represent the Corcoran. The material consists of two grayish-green silt strata; the upper, about 1 foot thick, and the lower, 4 feet thick. The upper stratum is over- lain by about 90 feet of ill-sorted red alluvial detritus ranging from silt to cobble conglomerate. Separating the two reduced silt strata is 6-8 feet of sand and gravel. The material underlying the lower silt is poorly ex- posed, but it appears to consist of intermixed sand and gravel. The silt strata are exposed intermittently for more than a quarter of a mile in the roadcut and indi- cate a slight anticlinal upwarp. The silt appears to be nondiatomaceous and contains many subrounded peb- bles and sand grains indicating a probable nearshore lake environment. Where the Corcoran Clay Member is known in the subsurface 2% miles east of this outcrop, it is 25 feet thick. At that point, the Corcoran is 320 feet lower in altitude than the exposure described, but is rising about 110 feet per mile toward the west at a gradually increasing rate. Lithologic similarity, strati- graphic position, and the fact that in this part of the San Joaquin Valley the Corcoran is the uppermost reduced deposit, strongly suggest correlation of the lacustrine silt exposed at the mouth of Little Panoche Creek with the Corcoran. A few miles to the northwest, the outcrop of the Con- coran Clay Member along the east edge of the Laguna Seca Hills has been described (p. E23). TERRACE DEPOSITS (PLEISTOCENE) Stream-terrace deposits, obviously older than the present flood plains, are found along nearly all the streams, but only along the north sides of Cantua and Panoche Creeks are they sufficiently extensive to be shown on plate 1. The deposits are similar to some of the coarser materials in the underlying Pliocene and Pleistocene formations. They consist principally of gravel containnig boulders to about 2 feet in diameter in a matrix of sand and silt. Thickness commonly ranges between 2 and 20 feet. The terrace deposit mapped along Cantua Creek evi- dently was laid down by the creek when its erosional and load-carrying capabilities were much greater than at present. The deposit appears to be flat lying, or nearly so, and thus is uncon'formable on, and younger than, the Tulare. As the terrace deposits are younger than the Tulare but older than the alluvial deposits now laid down in the stream channel, they are presumed to be of Pleistocene age. 411-341 0O-71--4 E33 ALLUVIUM (PLEISTOCENE AND HOLOCENE) For practical purposes, the entire post-Tulare section in the San Joaquin Valley is grouped in this report into a single unit-alluvium-which includes stream-laid and still-water deposits ranging in age from Pleistocene to Holocene. As the Tulare Formation is defined (p. E21) as the uppermost deformed or tilted strata, the valley alluvium can readily be distinguished from the Tulare along most of the west border of the area. Be- neath the San Joaquin Valley, however, this distinc- tion is virtually meaningless because the Tulare and the overlying alluvium are conformable. The thickness of the post-Tulare alluvium is not known because the top of the Tulare Formation cannot be identified in the valley. An indicated on page E23, for purposes of defining thickness in this report the depth to the top of the Tulare Formation is arbitrarily assumed to increase eastward from a featheredge at the foothills to about 200 feet below the land surface beneath the present valley axis. Under this arbitrary assumption, the thickness of the post-Tulare alluvium ranges from 0 to about 200 feet. The lithology of the alluvium is similar to that of the underlying deposits of the Tulare; it consists of sand, silt, clay, and minor gravel laid down as alluvial fans and on flood plains. Poorly sorted alluvial-fan deposits 'from the Diablo Range generally predominate, except in the eastern part of the area, which is underlain chiefly by well-sorted micaceous sands derived from the Sierra Nevada, and by fine-grained basin deposits near the surface. soms The alluvium at the land surface near the west border of the valley has been subdivided on plate 1 mainly on the basis of soil-profile development. Soil surveys of the U.S. Department of Agriculture (Harradine and others, 1952, 1956) were used to delineate the soil types. The valley soils in the area of plate 1 that are characterized by profile development include the Panthill, Lost Hills, and Ortigalita soil series. In the area mapped, only the Panoche soil series is characterized by a lack of pro- file development. Other factors being equal, the degree of profile de- velopment could be taken as a measure of relative age of the soils. However, the characteristics of the soil at a given place depend also on such variable factors as (1) the lithology of the source material, (2) the en- vironment in which the soil was deposited and the cli- mate since deposition, (3) plant and animal life in the soil, and (4) relief and drainage. These variables in the area mapped are very complex. As a result, the E34 two classes of soil-profile development indicated by plate 1 are at best poor indicators of younger and older surfaces. The division of the surface alluvium into the two classes is useful as a rough measure of relative perme- ability to influent seepage. The Panoche soils are per- meable to moderately permeable; the others (Panhill series and older) are in general only moderately to poorly permeable. HYDROLOGIC UNITS IN THE GROUND-WATER RESERVOIR The geologic maps and sections in this report show that the subsurface geology of the fresh-water-bearing deposits is highly complex when the deposits are differentiated with respect to source, environment of deposition, and, in part, lithologic character. Fortu- nately, the hydrologic units are not so complex in their gross features relating to occurrence and movement of ground water. As pointed out by Davis and Poland (1957, p. 421), a generalized threefold subdivision of the fresh-water-bearing deposits can be made as follows : An upper unit extending from the land surface to the top of the relatively impervious Corcoran Clay Mem- ber (diatomaceous clay) at a depth ranging from 10 to 900 feet below the land surface; the Corcoran Clay Member, ranging in thickness from a featheredge to 120 feet, which separates waters of substantially different chemical quality; and a lower unit 100 to more than 2,000 feet thick that extends down ito the deposits con- taining the main saline water body. The saturated part of the uper unit they referred to as the upper water- bearing zone, and the lower unit, as the lower water- bearing zone. As shown by the electric logs on the geologic sections and by core-hole logs, the fresh-water-bearing deposits in the Los Banos-Kettleman City area are heterogene- ous, as would be expected from their environments of deposition, and they display rapid variation in texture and permeability, especially in the vertical direction. Beds or lenses of sand are separated by strata of silt and clay of low permeability. If an aquifer is defined as a permeable deposit that will yield water to wells, the entire lower zone can be considered an aquifer in a broad sense. On the other hand, the permeable sand units can be considered as aquifers, separated hydraulically in varying degree by the finer grained less permeable interbeds of silt and clay. Silt and clay, especially the latter, are much more MECHANICS OF AQUIFER SYSTEMS compressible than sand under load, such as that applied when artesian head declines. Therefore, it is important in study of subsidence problems and the compaction of deposits under increased effective stress to differentiate between a water-bearing unit that is composed entirely of coarse material, such as clean sand and gravel, and one that contains many fine-grained interbeds of silt and clay. For purposes of differentiation in the studies of compaction and subsidence, a water-bearing unit characterized by approximate hydraulic continuity but that contains many fine-grained interbeds is termed an aquifer system. Thus, under this definition, the lower water-bearing zone is a confined aquifer system. A simplified picture of the hydrologic units that con- stitute the ground-water reservoir is presented in four generalized sections to show the principal geologic con- trols and the two hydrologic units-the semiconfined aquifer system of the upper zone and the confined aqui- fer system of the lower zone. These sections (figs. 13, 14) coincide with the detailed geologic sections of plates 3 and 4, and are identified by the same letters. The depth of wells tapping the ground-water reser- voir generally decreases from west to east and ranges from as much as 3,800 feet in the southwestern part of the area along the west border of the valley to less than 200 feet near Fresno Slough. In the western and cen- tral parts of the area, most wells tap both the upper and lower water-bearing zones, although many tap only the lower zone. The deepest wells are in the western part of the area south of Panoche Creek, because the average permeability of the aquifer systems is low. In order to obtain the locally required 1,000-2,000 gallons per min- ute for irrigation, wells must tap a thicker saturated section and are drilled through thick alluvial-fan de- posits of generally low permeability to reach more per- meable underlying flood-plain and deltaic deposits. In the eastern part of the area from Tranquillity south to the Kings River, in the reach where the thickness of the highly permeable Sierra micaceous sand above the Cor- coran exceeds 300 feet and the water is of good quality (fig. 10), most wells tap only the upper zone. Here, the average depth of wells is 400-600 feet. The yield factor * (Poland, 1959, p. 32), which is an approximate measure of the average permeability of the water-bearing material tapped by a well, is shown in figure 15 to be highest for shallow wells which tap only the flood-plain deposits (Sierra micaceous sand) in the upper water-bearing zone (section C-C"). The wells with the lowest yield factor are generally those which tap mainly alluvial-fan deposits. Specific capacity (gallons per minute per foot of drawdown X 100). 4 ¥iela factor = Perforated casing interval, in feet COMPACTING DEPOSITS, LOS BANOS-KETTLEMAN CITY SUBSIDENCE AREA, CALIFORNIA E35 NoXIH soUTH A A 800' - 2 sls Ss S Fal 5:2 Cantggwgfeek g? Sa Water tabley \‘Ji ; § ___ Psa __ ~- o nsmeaton SEA LEVEL -L-.-__._._._ (principal confining bed) 800' — 1600' - 2400' -] //// 3200 - 0 10 20 MILES VERTICAL SCALE GREATLY EXAGGERATED 4000" m z mess 2 =-- s __ . 1 Ls " agt .~. -_ __ Piezometric surface ZZ/J/ZZZZZZ—[Z—[j7Z/f/ Easzzzl’agzz May 1960 Corcoran Clay Member \ Tulare | (Upper zone) (Lower zone) CONFINED Sue SYSTEM L4 d won ._ Formatic Ck. E- (s W aw f/ff//‘ Saline water body FicUurE 13.-Generalized section A-A', showing hydrologic units. See figure 3 for location of section. UPPER WATER-BEARING ZONE The upper water-bearing zone has a water table, and, locally, the water is unconfined. In general, however, the ground water in this zone is semiconfined to con- fined. Under conditions of pumping draft, head differ- entials of 100-200 feet or more have developed between the water table and the water levels in wells tapping the base of this zone just above the Corcoran Clay Member. Hence, confinement is known to be substantial in some parts of the area, and, in general, it increases with depth ; but in places where the deposits are more coarse grained and have greater vertical permeability, differ- ences in head are not great. This upper zone thus con- tains a number of semiconfined aquifers, with the degree of confinement varying from place to place. Considered as a unit, this upper zone is termed a semi- confined aquifer system in this report. Most of the more than 1,000 active irrigation wells that furnish the bulk of the irrigation supply in the Los Banos-Kettleman City area are perforated in the lower part of the upper zone as well as in the lower zone. However, in most of the area, the low permeability of 'the alluvial-fan deposits, and, locally in the eastern part, the poor water quality in the more permeable Sierra flood-plain deposits precludes the upper zone as a sole source of irrigation water. In an area about 5 miles wide along Fresno Slough, however, from Tranquillity southeast to the Kings River, wells tapping the upper zone yield water of adequate quantity and good quality for irrigation. The temperature of the water from these wells ranges from 65° to 75°F (fig. 15). Most of this supply is from permeable micaceous sand 200-500 feet thick that overlies the Corcoran Clay Member. LOWER WATER-BEARING ZONE The lower water-bearing zone is effectively confined by the Corcoran Clay Member (figs. 11, 12), except locally in the southwestern part of the Los Banos, Kettleman City area where the Corcoran Clay Member is absent, and confinement is poor or lacking. This lower zone is the principal source of ground water for irriga- tion in the Los Banos-Kettleman City area, and Davis and Poland (1957, p. 432) estimated that it supplies T5- 80 percent of the pumpage. Much of the water presently (1966) being produced from the lower zone is pore water that is being squeezed out of the fine-grained clayey sediments (aquitards) by compaction of the aquifer system due to decline in artesian head. The temperature of the water produced from wells tapping only the lower water-bearing zone ranges from about 80° to 90°F, except where water is drawn from the permeable deposits below the Tulare Formation. In E36 1200' 800' 400" SEA LEVEL 400" 8oo' 1200' 1600" 2000" MECHANICS OF AQUIFER SYSTEMS Tumey B Hills # * Fresno Slough _AQUIFER SYSTEM _ CONFINED AQUIFER SYSTEM ~ é &. _n -_- f Were __ SEMICONFINED T> gm"? : oJ, surface May 1960 Corcoran Cla (Lower zone) Base of fresh water 7 mad f m T" j "Zone of brackish water 7 (UPDET 2008) won css Mfi Member (principal con WWW : xfifilflw‘ Saline water body 1200 - goo" - 400" - SEA LeveL - 400' - 8oo' - 1200' - 1600' - 2000 - 2400" - 2800' - 1200' 800" - 400" - SEA LEVEL 7 400' - 800' - 1200' - 1600' - 2000" - 2400" - 2800' - C; F 4 A € z \ Water tables, ", te "__ __ unr o ro Hie nels rami rs une reared recs pact é y .. £. SEMICONFINED AQUIFER _ , _. _. -- - -y$%Zz -_- -*- \\a;fitzg;gxéfgg\§$m “(gong |. . uous Barri s ages goss ace mm mes cem om J.. } Camer Senitarter WIP P as ¢/\ . f l: Vial” Tu:::::: Zita" 7 K S4 o aline water body %// sut m: Zé//// Se a ~JAnticline 5 Ridge \ é /\\ aT: j;j:flfilt'.ble_- a --> SE Micontrimen mlFE—R (eter rie E'fibnflglzz.clay=;£::<; o +- | é \\ Piezometric, art-fab?— € ;—=: ----- 33555” ———————— z—on;;2:: ———————— ;_ %///// 2x T ree emotes, % \\... c. .0. ifelse 22 4s - cher eels 17 Echegoin Ranch............... £ 16 Extent, Etchegoin Formation...............- 16 Jacalitos 14 San Joaquin Formation..................~ 20 F M8 29... 01. ALL ete ous 12 Ficldwork.... 2.0.0.3... LDU ACL rede vel 4,5 Flood-plain deposits, Sierra Nevada.......... 28, 35 Tulsre 25, 28 Fossils, fresh-water, in saline water body... .. 41 Jacalitos Formation...................... 14 mammal bones, Corcoran Clay Member of Tulare Formation.............. 28, 24 marine, Etchegoin Formation, Kettleman Mills: es.: . 2:00 us nes 17 San Joaquin Formation.............. 20 San Pablo Formation.... 13 Tulsre Formation.................... 23, 24, 80 Franciscan Formation............._.._...... 9, 10,11 Fresh-water-bearing deposits, Etchegoin .s 18, 17 San Joaquin Formation................... 18 subsurface geology... * $4 Tulare Formation............. Peet 18 Fresh-water mollusks, Tulare Formation. .... #4 28, 34, 35, 39, 40, 41 ._ 28, 24 Frink/ J.. W i tited... ssl. c.. eu lulls 30 a Geochemical Surveys of Dallas, Tex_......... 5 Geologic history.. 8 Geologic mapping, water-bearing deposits... . 5 Page Geologic . csc... E1} Geologic units of drainage area tributary to Los Banos-Kettleman City area...... 10 tributary drainage area, Diablo Range.... 9 Glycymeris fossil zone, Etchegoin Formation.. 14, 16 Goudkoff, P. P., 15 88 Ground-water reservoir, hydrologic units. ..... 84 Ground-water withdrawal from Cenozoic water-bearing deposits............ 4 20, 21 Gypsite..... 28 Oslo roe 17, 22 ¥en... re 21 H Holmes, Arthur, cited........................ 24 Hornblende-quartz gabbro..................-- 10 Hydrocompaction of moisture-deficient de- posits above water table.......... U Hydrologic units in ground-water reservoir. .. $4 + Tilite. : :=: (cc ALL ARU ITL cc nects bem 11 Inter-Agency Committee on Land Subsidence in the San Joaquin Valley...... 4,5, 14 11... :c... . lise 1 Trrigation.......... 2, 4 WOS serve nc device ee ia rears . 28, 35, 88 J Jacalitos Creek drainage basin.............-.- 14 Jacalitos Formation........... 5,14 blue sandstone............ 14 opalized wood fragments 14,15 Jacalitos Hills..:.....;..___.....- 21 JurASSIC ..... ccc. nece. 9 K Kaplow, E. J., cited........._...._.._.._....- 20 Kern River Formation. . 24 Ketteman Hills.................. 4, 5, 9, 15, 16, 20, 21 20 fossils, in Tulare Formation.-........--.-- 28,84 marine, in Etchegoin Formation...... 17 Welle. .-. .R... 00.1 ere dusan ences 12 Kings 28, 35 Kreyenhagen Formation, thickness..........- 18 Kreyenhagen Hills............__..........--- 21 Kues, H. A., tited........_._...._.........--- 30 L Lacustrine deposits, Tulare Form ation.. 21, 25, £8, 40 Laguna Seca Formation..............-------- 12 Laguna Seca Hills..................---------- 23, 33 Lakes in subsurface deposits...............--- 80 Land-surface subsidence, problems...... ..- 8,4 E45 E46 Page Lithology, Etchegoin Formation............. E16 Jacalitos Formation........ 14 San Joaquin Formation.................. 20 TFuolare Formation--c«-.....:..._..._._-.. #1 Little Panoche Creek. 21, 22, 23, 33, 38 igsolved solids.. cs. 89 Little Panoche Creek basin................... 11 Location of area.............. 1 Lodo Formation, thickness................... 18 Logs OP CONG 14 Lohman, K. E., cited.......... 24 Los Banos Creek, dissolved solids.... .. 89 Los Gatos Creek, alluvial-fan deposits.... 25, 40 dissolved solids................... 39 Lost Hills soil series............ 33 Lower Cretaceous sedimentary. .... <+ +130 Lower Tertiary sedimentary rocks............ 11 Lower water-bearing zone, chemical character. 89 . .L... 89 M McLure Shale Member of Monterey Shale... 12 Magnesium, concentrations in upper water- 38 in ultramafic 11 Marine deposits-......:................ --. 9, 1% Mawby, J. E., 24 Meade, R. H: 11, 25, 38 Measured sections, Etchegoin Formation.... 16,17 Jacalitos Formation...................... 14 'Tulsre #1 ..-: ao vibe accel 25, 89, 40 Mesozoic rocks, significance.................. 11 Micaceous sands, Sierra Nevada.............. 33 Sierra Nevada, water-bearing............. 28, 39 «z-» 0202. chen 18 Mode of origin, Etchegoin Formation.... 17 Monocline Ridge. 30 Monterey Shale, McLure Shale Member. .... 12 MontmoriHonibe...1. .. . 11, 38 Montmorillonite-illite........................ 11 Moreno Formation........................s 4,11,18 Moreno ities 4 Mudstone, Moreno Formation... .... 11 Myra zone, San Joaquin Formation........... 20, 21 N North Dome of Kettleman Hills........ 16, 21, 23, 30 North Dome on La Ceja............_......... 21 0 .. eres -n i r aie ian ad 14 Opalized wood fragments, Jacalitos Forma- cs. ries reverse avi 14,15 Origin, Jacalitos Formation................... 15 Oro Loma Formation........... 5, 28 . .. os colle. 21, 28 Ortigalita Peak quadrangle..._...._.....__... 4, 5, 28 Ortigalits soil gorieg.200. . .l. cros 33 r Paleocene marine sedimentary rocks.......... 18 Fanoche ...l. 38 alluvial-fan deposits. .. . 25 dissolved solids....... 89 Fanoche Formation-. .. ..... 10 Fanocthe Hills...;-.-.;.... ;-. 4, 5, 12, 21, 22, 25, 30, 33 Panoche soil series... Fanoche . 13 Poland, J. F.; cifed.:s.....00.00000.002....00. 34 Previous investigations. 4 Purpose of investigation............___.____._. 4 Q, R Quien Sabe Volcanio8......._...cc.........._. 11 Rainfall, annual.... 2 Reconnaissance mapping..................... 6 INDEX Page Reef Ridge Shale.. E12 Rhyolitic ash 28 8 Saline water body...... 40 fresh-water foggilg.....-...c-:..lc.l...c... 41 San Joaquin Clay................. 20 San Joaquin Formation......... - 9,20 Cascajo Conglomerate Member........... 20 fresh-water-bearing strata................. 18 marine fossils. ...... 20 MYG LONG.... c cece n be vee 20, 21 cious. Cool Le es 20 San Joaquin (town) - - - 40, 41 San Josquin 28 San Jooguih 4, 5, 11, 12, 13, 15, 20, 23, 25, 30, 33, 38, 39 structure........ F 8 water-level decline. $ 4 San LUls PrOJOCL... . -.. cooll l 28, 24 San Pablo Formation, marine deposits of Mio- ONO BLEC- .. .. .ca 9 fO88Ilg. -.. .. Jr. as 13 Santa Margarita Formation.................. 13 SCODS Of FODOrE . 1 Sir col core ence 4 Sections, showing principal geologic controls and hydrologic units.............. $4 strata of Etchegoin Formation. strata of Jacalitos Formation............. 14 Sedimentary rocks, Cretaceous............... 10 lower Tertiary.... ...... " 11 Serpentine. =c 10 Shell Oil Co.. -.. 20, 30 Sierra Nevada......... alluvial-fan deposits.. ....... 28 crystalline complex.. % 8 flood-plain deposits..........._._.._..._.... 28, 35 SAIS. . -.. ...s oak -n 33 water-bearing micaceous sands. Sodium 40 in saline water body..........._........_. 40 Sodium concentrations in ground water.... 38, 39, 40 338 Stratigraphic relations, Etchegoin Formation. 17 Jacalitos Formation...................... 15 San Joaquin Formation.................. 20 Tulare Formation....................-... 23 Stratigraphy of the water-bearing deposits.. .. 18 Stream basins, areas of generalized geologic unite Within.....2c............._. H Stream waters, chemical character. 89 SHUHOVUTRE - ..- cellos alc Perea ren sceentih 8 Subsurface character, Tulare Formation.... #4 Subsurface deposits, lakes...................- 30 Subsurface extent, Etchegoin Formation.... .. 17 Jacalitos Formation...................... 15 San Joaquin Formation................... 20 Subsurface geology, fresh-water bearing de- . (L.. e ccie as $4 InferDrefAHON. . .=. . ofc ss 5 Sulfate concentrations in upper water-bearing BONG. . . LIT cok ch seen c iui 38 Surface extent, Tulare Formation............. A1 T Taylor, Dwight, quoted..:......:..........>. 24 TPejon Formation. ..... 12 Telsa FormatIOn.....~ ...... 12 Temblor ci-. 18 Big Blue Serptinous Member............. 18 Temperature, water from wells in lower water- Dearing 2016.. .... .%. $5, 88 water from wells in upper water-bearing 8010.1; esses 85 Terrace deposits, stream...................... 83 Thickness, Corcoran Clay Member of Tulare 80, 84 Etchegoin Formation..................... 17 Thickness-Continued Page Jacalitos Formation............ E15 Kreyenhagen Formation. . y 12 Lodo Formation.................c....l... 18% Moreno Formation....................... 11 FPsnoche Formation...................._. 10 San Joaquin Formation................... 20 Tulare Formation......;................. 28 2001000000 eal in cc lees 35 Trefsger, B. E., cited.... 24 Tulare Formation................. 5, 16, 17, 20, 21, 41 alluvial-fan deposits..............___.___. 25 LONG.... . .: fei ss 30 Corcoran Clay Member...._..... 4, 25, 80, 34, 35 fossil mammal bones.................. 23, 84 deltaic deposite...=................ - 28, 40 diatom floras... .. . 28, 44 flood-plain deposits. - 25,28 21. 04 .s Shave ce 30 fresh-water-bearing deposits_ Mo hs 18 lacustrine deposits......_.__...._... 21, 25, 28, 40 unconformity between Etchegoin Forma- eee eae nevr 17 Lake ls}. 12, 28, 30 Tumey ... .... ..2.. .... cele. ass 17, 23 Pumey GAI 4, 5, 22, 30 U Ultramafic intrusive rocks, Franciscan Forma- 11. oo - an ond Sak rate 10 Ultramafic rocks, magnesium... ... 11 Upper Cretaceous sedimentary rocks......... 10 Upper Tertiary and Quaternary deposits un- differentiatedi................../. 18 Upper water-bearing zone, chemical character. 38 WATS. oe AIE. civ 38 U.S. Bureau of Reclamation............. 4, 28, 24, 25 v YVallecitO® .Z. ;...... 11 Vallecitos Valley.. £ 13 Yelns, 21 Volcanic ash overlying Corcoran Clay Mem- ber of Tulare Formation.......... 28, 24 w, Y Warthan Creek, dissolved solids............~. 89 drainage basin... ~. f 11 Water-bearing deposits, geologic mapping... 5 .: SX lsc 18 Water-bearing micaceous sands, Sierra Ne- . c_... o. is 28, 39 Water-bearing zone, lower. 34, 35, 39 1JOWery, WAberS. ;.. ._. 89 S. RIL occ 34, 35, 39 WHLOTE L ...l 38 Waters, lower water-bearing zone......._..... 89 upper water-bearing zone................- 38 Well-numbering system.. ...........-- 8 Wells, chemical changes in water samples...... 41 deep, chemical character................~- 40 Etchegoin Formation.... 17 ground-water reservoir. . $4 irrigation............ 28, 35, 38 Kettleman Hills.. . 1% lower water-bearing zone... .............. 34, 40 observation................ 88 San Joaquin Formation..............-..- 20 upper water-bearing zone.............. 34, 35, 40 WBLOT SL.: ITIL. Westhaven...... White, R. T., cited.. Yokut Sandstone.................... U. S. GOVERNMENT PRINTING OFFICE : 1971 O - 411-341 > cUMNs Department | _ 3 - f- Mar (i988 | - wp _ usmw ___ i gus UNIVERSITY OF CALIEORN]A f Land Subsidence in the Santa Clara Valley, California, as of 1982 By J.F. POLAND and R.L. IRELAND M FEC HA N IL CS O F A Q U I' FE RK $ -¥ 'S T- EOM 8 U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 497-F A history of land subsidence in the Santa Clara Valley from 1916 to 1982 caused by water-level decline UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988 DEPARTMENT OF THE INTERIOR DONALD PAUL HODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging-in-Publication Data Poland, J.F. (Joseph Fairfield), 1908- Land subsidence in the Santa Clara Valley, California, as of 1982. (Mechanics of aquifer systems) (U.S. Geological Survey Professional Paper 497-F) Bibliography Supt. of Does. No.: I 19.16:497-F 1. Subsidences (earth movements)-California-Santa Clara Valley (San Benito County and Santa Clara County). I. Ireland, R.L. II. Series. III. Series: U.S. Geological Survey Professional Paper 497-F. QE7T5.P9 No. 497-F 557.72 s 87-600268 [QE600.3. U6] [551.353] For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 CONTENTS Page Abstract --- - --- F1 | Hydrology-Continued Introduction -- 1 Recovery of artesian head, 1967-80 - - - - --- --- -- Location and general features- - - - --- --- --- -- 1:1: Land subsidence ~~ - -- .~~ == ba wa Leb arm ~~~ Scope of study and purpose of report - - - - -- --- -- 6 History of leveling control - ---------=------ Well-numbering system - - - - --- --- --- 3 Extent and magnitude of subsidence --- --- --- -- Acknowledgments - - - - - - - --- --- 3 Economic and social impacts - -- -- -- -----~-~ -- Annotated bibliography of reports by U.S. Geological Survey Monitoring of compaction and change in head --- -- --- AUtROrS --= --- -==- -- 8 Measurement of compaction --- --- --- - - - - - --= -==- 5 Analysis of stresses causing subsidence - - - --- --- - Hydrology --- --- 14 Example of stress-strain graph --- --- --- Rainfall - - - -- --- 14 | Computer simulation of aquifer-system compaction - -- -- - Ground-water pumpage - - - - --- --- --- 14 | Compaction-subsidence ratio - - - --- --- --- --- -- Surface-water imports --- --- ------------ 14 |. Computer plots of field records - - - --- --- --- --- ~- Decline of artesian head, 1916-66 - - --- --- --- -- 14 'I Selected referendées"- @- «--== m=«« «~~~ 4 ses ILLUSTRATIONS FIGURE 1. Generalized geologic map of north Santa Clara County --- --- --- --- 2. Geologic section A-A' from Alviso southeast to Edenvale Hills =- --- --- --- =-- -=- 3. Geologic section B-B' from Los Altos east to Milpitag- - --- --- --- --- 4. Geologic section C-C' from near Los Gatos northeast to Alum Rock --- --- -- --- --- 5. Composite log of core hole 6S/2W-24C7 in Sunnyvale =- --- - --- 6. Composite log of core hole TS/1E-16C6 in San Jose - - --- --- --- 7-12. Graphs showing: 7. Consolidation-test curves for samples from core hole 6§/2ZW-24C07 --- - --- --- 8. Consolidation-test curves for samples from core hole TS/IE-1606 --- --- --- 9. Cumulative departure of rainfall at San Jose from the seasonal mean for the 106-year period 1874-75 to .. tal c e a- cannon t aims - als plein ain aln nie migo mo 10. Ground-water pumpage in north Santa Clara County, 1915-80 - - --- --- --------------_-_--_-- 11. Surface-water imports to north Santa Clara County, 1955-80 --- --- --- 12. Artesian-head change in San Jose in response to rainfall, pumpage, and water imports --- --- --- --- -- 13-17. Maps showing: 13. Generalized water-level contours for spring and summer, 1915, north Santa Clara County - --- --- --- --- 14. Change in water level, 1915-67, north Santa Clara County-- --- --- --- 15. Network of level lines in the San Jose subsidence area; initial numbering of level lines --- --- -- 16. Network of level lines in the San Jose subsidence area; numbering of level lines revised to three digits in the late 1950's rns n m meine me ol ie mole hume on me ml in me melon me Tmn bn an me an inc lan ae nlin eline e ae 17. Times and extent of leveling in the San Jose subsidence area --- --- --- --- 18. Graph showing artesian-head change and land subsidence, San JOS@- - - --- --- --- --- 19-21. Maps showing: 19. Land subsidence from 1934 to 1960, north Santa Clara County --- C algle a « - 20. Land subsidence from 1960 to 1967, north Santa Clara County --- -- --- --- 21. Land subsidence from 1934 to 1967, north Santa Clara County -------------------------- 22. Profiles of land subsidence, D-D', Redwood City to Coyote, 1912-69 - - --- --- 23. Profiles of land subsidence, E-E"', Mountain View to Milpitas, 1983-67 - -- --- --- 24. Profiles of land subsidence, F-F"', Los Gatos to Alum Rock Park, 1984-69 --- -- 25. Diagram of recording extensometer installations --- --- --- --- 26-30. Graphs showing: 26. Elastic response of multiple extensometers at the Sunnyvale site 6§/2W-24C, 1981-82 - - - - - - - --- 27. Measured annual compaction in wells 1,000 ft deep in Sunnyvale and San Jose --- --- --- 28. Stress change and compaction, San JOSe Site --- -- --- --- 29. Simulation of compaction based on water-level data for well 7S/1E-7R1 (1915-74) and on subsidence measured at bench mark PT -- --- --- --- o aoe a a a ion e anime mera Nalo has fos oe a The TBE ol (ie oo an an iim he 30. Compaction/subsidence ratios versus depth at extensometer wells in north Santa Clara County --- --- --- - II 10 11 12 13 15 15 18 20 21 22 28 25 29 40 41 48 45 IV CONTENTS FiGuURES 31-48. Computer plots showing: 31. Hydrograph, change in applied stress, compaction, subsidence, and stress-strain relationship, 6S/1W-23E1-- F 48 TABLE mP» to fo - 32. Hydrograph, change in applied stress, compaction, and stress-compaction relationship, 6S/2W-24C4 --- - - 33. Hydrograph and change in applied stress, 6S/2W-25C1; compaction and stress-compaction relationship, 6S/2W-2404 - - ___ 22222222222 R2 R2 RRR R2 RRR RE R R R _ R R _ ___ ece ccs 34. Hydrograph, change in applied stress, compaction, and stress-compaction relationship, 6S/2W-24C3 --- - - 35. Hydrograph and change in applied stress, 6S/2W-25C1; compaction and stress-compaction relationship, 6S/2W-2408- - -_- __ 222222222222 R2 R2 R2 R2 R2 R2 RRR RR R R R ___ _ _ _ ___ _ ___ 36. Hydrograph and change in applied stress, 6S/2W-24C4; compaction and stress-compaction relationship, 6S/2W-2403 and 6§/2W-2404 - - - - -- _- -e 22222222222 R22 RRR R2 RRR R _E _ _ ~ 37. Hydrograph and change in applied stress, 6S/2W-25C1; compaction and stress-compaction relationship, 6S/2W-2403 and 6§/2W-2404 - - - --- ee 2222222222222 2 R2 RR RRR RR __ ~ 38. Hydrograph and change in applied stress, 6S/2W-24C7; compaction, subsidence, and stress-compaction relationship, 6S/2W-2403 and 6§/2W-2407 - --- --- _-_ __ _E ~ 39. Hydrograph, change in applied stress, compaction, subsidence, and stress-compaction relationship, TS/1E-9D2- - --- -_- R22 R2 RER R _E _R RRR eR eR eR eRe _E ece c cece c_ ece 40. Hydrograph, change in applied stress, compaction, subsidence, and stress-strain relationship, 78/1E-16C5 - - 41. Hydrograph and change in applied stress, 7S/1E-16C5; compaction, subsidence, and stress-strain relation- ship, --- RRR RRR RRR R _ R E ___ ~~ 42. Hydrograph, compaction, and subsidence, TS/IE-16C6-11- - - - --- 43. Hydrograph and compaction, 6S/ZW-24C08 --- --- 44. Hydrograph and compaction, 6§/ZW-24C04 --- --- _-_. ~ 45. Hydrograph and compaction, 6S/ZW-24C07 --- --- 46. Hydrograph and compaction, TS/IE-16C05 - -- --- 47. Hydrograph 7S/1E-16C5; compaction TS/LE-16C11 --- --- 48. Hydrograph and compaction, TS/1IE-16C11 --- --- --- TABLES Ground-water pumpage, north Santa Clara County, 1915-80 --- -- Surface-water imports to north Santa Clara County, 1955-80 --- Annual compaction at compaction-measuring sites in north Santa Clara County =- --- --- Values of parameters used for simulating observed compaction at selected sites in north Santa Clara County --- --- Compaction versus subsidence for periods of leveling in north Santa Clara County --- --- --- Wells for which records are included in figures 81-42 - --- --- CONVERSION FACTORS The inch-pound system of units is used in this report. For readers who prefer the International System of Units (S1), the conversion factors for the terms used are listed below: Multiply By To obtain acre 4047 m* (square meter) acre-ft (acre-foot) 1283 m* (cubic meter) ft (foot) 0.3048 m (meter) gal/min (gallons per minute) 003785 m/min (cubic meters per minute) (gal/min)/ft (gallons per minute per foot) 207 (L/s)/m (liters per second per meter) in. (inch) 2.54 cm (centimeter) mi (mile) 1.609 km (kilometer) mi (square mile) 2.590 km (square kilometer) National Geodetic Vertical Datum of 1929 (NGVD of 1929); A geodetic datum derived from a general ad- justment of the first-order level nets of both the United States and Canada, formerly called mean sea level. NGVD of 1929 is referred to as sea level in this report. Page 49 50 51 52 53 54 55 56 57 58 59 59 59 60 60 60 60 Page F16 19 38 MECHANICS OF AQUIFER SYSTEMS LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 By J.F. Poranp and R.L. IrELaAND ABSTRACT From 1916 to 1966 in the San Jose area of the Santa Clara Valley, California, generally deficient rainfall and runoff was accompanied by a fourfold increase in withdrawals of ground water. In response, the artesian head declined 180 to 220 feet. As a direct result of the artesian- head decline, the land surface subsided as much as 12.7 feet in San Jose, due to the compaction of the fine-grained compressible confining beds and interbeds as their pore pressures decreased. The subsidence resulted in flooding of lands bordering the southern part of San Francisco Bay, and the compaction of the sediments caused compressional failure of well casings in several hundred water wells. The gross costs of subsidence to date are estimated to be $30 to $40 million. The recovery of artesian head since 1967 has been substantial. In downtown San Jose, the artesian head recovered 70 to 100 feet in the 8 years to 1975. Recovery of water levels was due to a fivefold increase in surface-water imports from 1965 to 1975, favorable local water supply, decreased withdrawal, and increased recharge. In 1960, the U.S. Geological Survey installed extensometers in core- holes 1,000 feet deep in San Jose and Sunnyvale. Measurements obtained from these extensometers demonstrate the marked decrease in annual compaction of the confined aquifer system in response to the major head recovery since 1967. In San Jose, for example, the annual compaction decreased from about 1 foot in 1961 to 0.24 foot in 1967 and to 0.01 foot in 1973. Net expansion (land-surface rebound) of 0.02 foot occurred in 1974. INTRODUCTION LOCATION AND GENERAL FEATURES The Santa Clara Valley is a long, narrow structural trough that extends about 90 mi southeastward from San Francisco. San Francisco Bay occupies much of its north- ern one-third. The valley is bounded on the southwest by the Santa Cruz Mountains and on the northeast by the Diablo Range (fig. 1). The San Andreas fault system is a few miles southwest of the valley, and the Hayward fault borders the valley on the northeast. Both fault systems are active. Land subsidence occurs in the central one-third of the valley in an area of intensive ground-water development. This report discusses only this densely populated central one-third of the valley, which extends southeastward about 30 mi from Redwood City and Niles to Coyote, at the bedrock narrows about 10 mi southeast of downtown San Jose. The subsidence area is almost wholly in Santa Clara County. Southeast of Coyote Hills, the subsidence area extends into Alameda County, and north of Palo Alto it extends into San Mateo County (fig. 1). Santa Clara. County extends 30 mi southeast of Coyote. Ground water is pumped from wells in this area. There- fore, to avoid confusion, the project area is defined as north Santa Clara County when clarification is needed. For example, tables of ground-water pumpage and surface-water imports listed in this report are for north Santa Clara County, as indicated by their titles. Minor subsidence also has occurred in the Hollister area (not shown). It is reported that as of the late 1960's, sub- sidence of 1 to 2 ft had occurred at bench marks in Hollister (T.H. Rogers, Woodward-Clyde Consultants, oral commun., November 1983.) However, Hollister is in San Benito County, 10 mi south of the south boundary of Santa Clara County, and thus this subsidence is not discussed further in this report. SCOPE OF STUDY AND PURPOSE OF REPORT Since the late 1950's the U.S. Geological Survey has carried on a modest study of land subsidence in the Santa Clara Valley, financed by Federal funds for study of the mechanics of aquifer systems. The study has been similar to concurrent studies of land subsidence in the San Joaquin Valley (Poland and others, 1975; Ireland and others, 1984), but on a much smaller scale. The principal field activities of the program have been twofold. First, in 1960 the Geological Survey drilled core holes at the centers of subsidence in San Jose and Sunnyvale. They were drilled to a depth of 1,000 ft-the maximum depth tapped by most water wells as of 1960. Cores were tested in the laboratory for physical and hydrologic properties and for clay-mineral analysis. Results have been released F1 F2 in several publications (Johnson and others, 1968; Meade, 1967). Second, in 1960 extensometers (compaction recorders) were installed in the 1,000-ft core holes and in nearby satellite holes in order to measure the compaction or ex- pansion of the sediments in that depth range and com- pare it with change in artesian head and with subsidence in the same time interval. Aquifer-system compaction and expansion and water-level change (change in applied stress) have been measured for 22 years. The change in MECHANICS OF AQUIFER SYSTEMS artesian head was monitored by the Geological Survey, and subsidence was monitored by the National Geodetic Survey. These records from 1960 to 1980 are included in full in this report as computer-plotted stress-strain or stress-compaction relationships (see figs. 31-42). The Geological Survey terminated measurements of water level and of compaction or expansion at the end of 1982. Measurements of these data for the 3 years 1980-82, inclusive, have also been included in this report (table 3; figs. 48-48). R1 E 121°45° R26 0 ® - O A DUMBARTON BRIDGE \ 37° |_ 15" w o 4 5 KILOMETERS 5 MILES | | 1 A I EXPLANATION | IAIIuvium and bay deposits aa -* «| Santa Clara Formation and assoc- iated deposits Consolidated rocks -----Fault-Dashed where approx- imate, dotted where concealed A ___A 'Trace of geologic section- See figures 2-4 Types of observation wells and iden- tification numbers Water level - 6M 1 o 23E1 Extensometer (listed in tables) © Well and (or) extensometer x" ' Bench mark and number - Z ~ EDENVALE E ¢ HILLS ’///////// Guadal Russo” W // Lexington Reservoir FIGURE 1.-Generalized geologic map of north Santa Clara County. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F3 In addition to the principal field activities, development of a one-dimensional mathematical model that calculates idealized aquifer-system compaction and expansion was a highly significant accomplishment. The model has been applied to observed water-level fluctuations and to the resulting observed transient compaction and expansion behavior of a total thickness interval at several sites in the Santa Clara Valley (Helm, 1977). The principal purposes of this report are (1) to present a summary of measured land subsidence through 1982, including the overall extent and magnitude; (2) to report the measured annual compaction and water-level change from 1960 through 1982 at extensometer sites; (8) to show the relationship between water-level change (stress change), measured compaction, and subsidence, chiefly by use of computer plots of Geological Survey field data; (4) to record the yearly pumpage of ground water in north Santa Clara County from 1915 to 1980; and (5) to report the yearly surface-water imports from 1955 to 1980 via the Hetch Hetchy and South Bay Aqueducts. Reports and papers published to date on various aspects of the Geological Survey study in the Santa Clara Valley have been published in several different sources. There- fore, to assist the interested reader, this report includes a brief annotated bibliography of published reports pre- pared by Geological Survey authors as a result of these studies. WELL-NUMBERING SYSTEM The well-numbering system used in California by the U.S. Geological Survey and the State of California shows the locations of wells according to the rectangular system for the subdivision of public land. That part of the number preceding the slash (as in 78/1E-1606) indicates the township (T. 7 S.); the number following the slash is the range (R. 1 E.); the digit following the hyphen is the see- tion (sec. 16); and the letter following the section number indicates the 40-acre subdivision of the section. - Within each 40-acre tract the wells are numbered serially, as indicated by the final digit. In this report, wells are referenced to the Mount Diablo base and meridian; all wells are south of the base but are both east and west of the meridian. ACKNOWLEDGMENTS We acknowledge the cooperation of Federal, State, and local agencies, private companies, and individuals. All leveling data used in the preparation of the subsidence maps and graphs and in calculating magnitude and rates of subsidence were by the National Geodetic Survey (formerly the U.S. Coast and Geodetic Survey). Water- level data utilized in this report were chiefly from field measurements by the Geological Survey, but the Santa Clara Valley Water District was most helpful in supply- ing records of ground-water levels from its well-measur- ing programs. The California Division of Highways and the San Jose Water Works granted permission to drill core holes and maintain compaction-measuring equipment on their properties. Core descriptions in the field were by W.B. Bull, J.H. Green, R.L. Klausing, R.H. Meade, G.A. Miller, and F.S. Riley (all of the Geological Survey). J. H. Green prepared figures 2, 3, and 4 (geologic sections), figures 5 and 6 (com- posite logs of core holes), and figure 19 (land subsidence from 1934-60). ANNOTATED BIBLIOGRAPHY OF REPORTS BY U.S. GEOLOGICAL SURVEY AUTHORS 1962, Poland, J.F., and Green, J.H., Subsidence in the Santa Clara Valley, California-A progress report: U.S. Geological Survey Water-Supply Paper 1619-C, 16 p. By maps and profiles, this report illustrates the sub- sidence that had occurred by 1954; bench mark P7 in San Jose had subsided 7.75 feet. The first complete survey of the bench-mark network was in 1934. Sub- sidence maps are included for 1934-54, 1940-54, and 1948-54. 1962, Green, J. H., Compaction of the aquifer system and land subsidence in the Santa Clara Valley, California: U.S. Geological Survey Professional Paper 450-D, p. 175-178. Results of laboratory tests on the compres- sibility of fine-grained cores from two 1,000-ft core holes and records of the fluctuation of artesian head since 1915 were used to compute the compaction of the con- fined aquifer system up to the 1960 releveling of the bench-mark network. Computed compaction was in general agreement with actual subsidence, but the pro- cedure is highly subjective when applied to such hetero- geneous deposits. 1964, Green, J. H., The effect of artesian-pressure decline on confined aquifer systems and its relation to land sub- sidence: U.S. Geological Survey Water-Supply Paper 1779-T, 11 p. This report summarizes the use of one- dimensional consolidation tests on cores and known declines of artesian head to compute compaction of fine- grained clayey beds. It also describes the use of void ratio values derived from one-dimensional consolidation tests to compute change in porosity in response to change in effective stress. 1967, Meade, R.H., Petrology of sediments underlying areas of land subsidence in central California: U.S. Geological Survey Professional Paper 497-C, 83 p. This paper describes petrologic characteristics that influence F4 compaction of water-bearing sediments in the San Joaquin and Santa Clara Valleys, including particle size, clay minerals, and associated ions. The analytical pro- cedures used in the clay-mineral studies are discussed. In addition, particle-size data for cored sediments in the Santa Clara Valley are tabulated, as are clay minerals and associated ions from fine-grained cored sediments and from fine-grained surface sediments (see p. 38-45 and 63-78). Montmorillonite is the dominant clay mineral, comprising between 5 and 25 percent of the sediments, depending on the general fineness of their particle size. Calcium is the dominant exchangeable cation. 1968, Johnson, A.I., Moston, R.P., and Morris, D.A., Physical and hydrologic properties of water-bearing deposits in subsiding areas in central California: U.S. Geological Survey Professional Paper 497-A, 71 p. To provide information on the water-bearing deposits in the areas of maximum subsidence (in San Jose and in Sunnyvale), two core holes were drilled in the Santa Clara Valley. In all, 87 samples from these core holes were tested by the Geological Survey for physical and hydrologic properties, and 21 samples were tested by the U.S. Bureau of Reclamation for engineering prop- erties, including one-dimensional consolidation tests. The report presents core-hole logs and laboratory data in tabular and graphic form, describes methods of laboratory analysis, and shows interrelationships of some of the physical and hydrologic properties. For a summary of the results of laboratory analyses, see p. 43-45. 1968, Meade, R.H., Compaction of sediments underlying areas of land subsidence in central California: U.S. Geological Survey Professional Paper 497-D, 39 p. A study, partly statistical, of the factors that influence the pore volume and fabric of water-bearing sediments com- pacted by effective overburden loads ranging from 40 to 1,000 lb/in2. Paper includes summary of pertinent previous studies that identify these factors and that in- dicate the nature and degree of their influence on com- paction processes (p. 3-14). 1969, Poland, J.F., and Davis, G.H., Land subsidence due to the withdrawal of fluids: Geological Society of America, Reviews in Engineering Geology, v. 2, p. 187-269. A review of the known (1963) examples of appreciable land subsidence due to fluid withdrawal throughout the world, with a brief examination of the principles involved in the compaction of sediments and of aquifer systems as a result of increased effective stress. Special emphasis is given to subsidence studies in the San Joaquin (p. 238-252) and Santa Clara (p. 252-262) Valleys and to the Wilmington oil field (p. 200-214) in the Los Angeles and Long Beach Harbor area. MECHANICS OF AQUIFER SYSTEMS 1969, Poland, J.F., Land subsidence and aquifer-system compaction, Santa Clara Valley, California, USA: in Tison, L.J., ed., Land subsidence, v. 1, International Association of Scientific Hydrology Publication 88, (is now International Association of Hydrological Sci- ences), p. 285-292. Intensive withdrawal of ground water from the confined aquifer system, 800 ft thick, in the San Jose area of the Santa Clara Valley has drawn down the artesian head as much as 220 ft since 1915. Resulting land subsidence, which began about 1916, was 12.7 ft in 1967. Report includes graphs of measured compaction, water-level change, and sub- sidence to 1969 in Sunnyvale and San Jose, log-log plots of compressibility of fine-grained samples from the Sunnyvale core hole, and a map of land subsidence from 1934 to 1967. 1972, Poland, J.F., Lofgren, B.E., and Riley, F.S., Glossary of selected terms useful in studies of the mechanics of aquifer systems and land subsidence due to fluid withdrawal: U.S. Geological Survey Water- Supply Paper 2025, 9 p. The glossary defines 25 terms as they are used in Geological Survey research reports concerned with the mechanics of stressed aquifer systems and of land subsidence. Most are terms that have appeared in engineering or hydrologic literature, but several have been introduced as a result of the Survey's studies. 1973, Webster, D.A., Map showing areas bordering the southern part of San Francisco Bay where a high water table may adversely affect land use: U.S. Geological Survey Miscellaneous Field Studies Map MF-530, 1 sheet, scale 1:125,000. Map presents general informa- tion about the depth to the top of the saturated zone (water table), shown in four depth zones 0-5, 5-10, 10-20, and >20 ft below land surface. Depth zones are based on data obtained from more than 1,000 soil borings made for foundation engineering studies. The problems caused by a shallow water table are also discussed. 1977, Helm, D.C., Estimating parameters of compacting fine-grained interbeds within a confined aquifer system by a one-dimensional simulation of field observations: International Association of Hydrological Sciences, International Symposium on Land Subsidence, 2d, Anaheim, California, December 1976, Publication 121, p. 145-156. A one-dimensional mathematical model that calculates idealized aquifer-system compaction and ex- pansion has been applied to observed water-level flue- tuations and to the resulting observed transient compaction-and-expansion behavior of a total thickness interval at several sites in the Santa Clara Valley. For established values of total cumulative thickness of fine- grained interbeds (aquitards) within the confined aquifer system, the weighted average thickness of these inter- LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 beds, and the initial distribution of preconsolidation pressure, it is demonstrated that carefully evaluated values of the vertical components of hydraulic conduc- tivity and nonrecoverable compressibility can be used to predict aquifer-system behavior with reasonable accuracy over periods of several decades. The paper includes plots of simulated compaction based on meas- ured water level and compaction data at eight sites in the Santa Clara Valley for periods of record ranging from 12 to 59 years. 1977, Poland, J.F., Land subsidence stopped by artesian- head recovery, Santa Clara Valley, California: Inter- national Association of Hydrological Sciences, Inter- national Symposium on Land Subsidence, 2d, Anaheim, California, December 1976, Publication 121, p. 124-1832. From 1916 to 1966, generally deficient rainfall and runoff was accompanied by a fourfold increase in withdrawals of ground water. In response, the artesian head declined 180 to 220 ft, causing the land surface to subside as much as 12.7 ft in San Jose, due to com- paction of the fine-grained compressible aquitards as the pore pressures decreased. From 1967 to 1975 the artesian head recovered 70 to 100 ft. This water-level recovery was due to a fivefold increase in surface-water imports from 1965 to 1975, favorable local water supply, decreased withdrawal, and increased recharge. Exten- someters installed in 1960 to measure change in thick- ness of the confined system demonstrated the marked decrease in annual compaction in response to the major head recovery. In San Jose, the annual compaction decreased from about 1 ft in 1961 to 0.01 ft in 19783. 1978, Helm, D.C., Field verification of a one-dimensional mathematical model for transient compaction and ex- pansion of a confined aquifer system: in Verification of mathematical and physical models in hydraulic en- gineering: American Society of Civil Engineers, Pro- ceedings of Specialty Conference, College Park, Maryland, p. 189-195. Land subsidence due to ground- water withdrawal from a confined aquifer system is an expression at land surface of net compaction (vertical consolidation) at depth of compressible layers within the system. Water-level fluctuations within coarse-grained aquifers produce stress changes on the upper and lower boundaries of slow-draining aquitards. Within a con- fined system, any lag in compactive response to such a load increase is usually ascribed to slow vertical drainage from the aquitards. The emphasis of this paper is threefold: First, the author describes the trial-and- error method used to find vertical hydraulic conduc- tivity, K', and nonrecoverable specific storage, Si; second, the values of these parameters so estimated are listed in table 1; and finally, based on these values, predictions of critical stress and ultimate compaction values are presented. F5 HYDROGEOLOGY A generalized geologic map of north Santa Clara County (the central part of the Santa Clara Valley) is shown in figure 1. The map was compiled chiefly from geologic maps prepared by Jennings and Burnett (San Francisco sheet, 1961), Rogers (San Jose sheet, 1966), and Dibblee (Palo Alto 15-minute quadrangle, 1966). The consolidated rocks, shown as a single unit on the map, range in age from Jurassic to Pliocene; they consist principally of con- solidated sedimentary rocks but also include substantial areas of metamorphic rocks-the greenstones of the Fran- ciscan Formation, which are probably metamorphosed submarine basalt flows (Dibblee, 1966). These rocks are highly compressed but yield small quantities of water to domestic wells from fractures induced by tensional and compressional forces. Except for the two major regional faults-the San An- dreas and Hayward faults-no attempt has been made to include faults on this generalized map because detailed geologic mapping was beyond the scope of the study. For more geologic detail, in addition to the sources cited, the reader is referred to a geologic map published by the California Department of Water Resources (1967, pl. 3). That map shows subsea contours on the buried surface of rocks of the Franciscan Formation for much of the _ valley. From the Dumbarton Bridge southeast to Sunny- vale, the buried surface plunges from 300 to 3,000 ft below sea level. The Santa Clara Formation of Pliocene and Pleistocene age unconformably overlies the consolidated rocks and is exposed intermittently along both flanks of the valley. Dibblee (1966) designated a type area as the exposures between Saratoga and Stevens Creeks, with a type sec- tion as exposed in Stevens Creek. About 2,200 ft of the Santa Clara Formation is exposed in the type area. Where exposed, the formation consists of semiconsolidated conglomerate, sandstone, siltstone, and claystone. The conglomerate and sandstone are poorly sorted and have a fine-grained matrix; thus the formation has a low permeability and, where exposed or at shallow depth, yields only small to moderate quantities of water to wells, rarely enough for irrigation purposes. Along the western border of the valley, the Santa Clara Formation was warped and folded during the last uplift of the Santa Cruz Mountains. Dips of 25° to 35° are com- mon. Beneath the valley the formation may be undis- turbed and in part conformable with overlying beds. In his map of the Palo Alto 15-minute quadrangle, Dibblee (1966) discriminated a geologic unit overlying the Santa Clara Formation that he calls "older alluvium." The only extensive outcrop covers about 4 mi? in the Saratoga area. He described the unit as stream-laid gravel com- posed of cobbles and pebbles in a matrix of sand and silt, F6 derived from adjacent hills, generally undeformed, dis- sected where elevated, as much as 50 ft exposed, and age presumably late Pleistocene. Because this unit has been mapped only on the west side of the valley and is of little importance in water supply, its outcrop area has been combined with that of the Santa Clara Formation in the stipple pattern of figure 1. Unconsolidated alluvium and bay deposits of clay, silt, sand, and gravel of late Pleistocene and Holocene age overlie the Santa Clara Formation and associated deposits; their upper surface forms the valley floor. Well logs indicate that permeable alluvial deposits attain a thickness of 1,000 ft or more in the valley trough. Wells range in depth from 200 to 1,200 ft (California Depart- ment of Water Resources, 1967, pl. 4). The deeper wells probably tap the upper part of the Santa Clara Forma- tion, although the contact with the overlying alluvium and bay deposits has not been distinguished in well logs because of the lithologic similarity. Coarse-grained deposits predominate in the alluvial-fan and stream-channel deposits near the valley margins, where the stream gradients are steeper. The proportion of clay and silt layers increases bayward. For example, a well-log section extending 12 mi northward from Camp- bell to Alviso (Tolman and Poland, 1940, fig. 3) shows that to a depth of 500 ft the cumulative thickness of clay layers in the deposits increases from 25 percent near Campbell to 80 percent near Alviso. Well yields in the valley range from 300 to 2,500 gallons per minute (gal/min), and the specific capacity [(gal/min)/ft drawdown] ranges from 10 near the valley margin to 70 in mid-valley, exceeding 300 in both San Jose and Santa Clara (California Department of Water Resources, 1967, pl. 6). Geologic sections A-A ' (fig. 2), B-B' (fig. 3), and C-C" (fig. 4) illustrate the general nature of the alluvial water- bearing deposits that underlie the valley floor. Fine- grained materials such as clay, silt, and sandy clay, which retard the vertical movement of confined ground water, constitute the major part of the valley fill near the bay (figs. 2, 3). Sand and gravel occur in lesser amounts near the bay, but they are more abundant near the valley margins, where locally they are predominant. None of the distinctive layers or lenses can be traced laterally for more than a mile or two. Inspection of the three figures in- dicates that the well-log section B-B' (fig. 3), which traverses mostly lowland areas near the bay, contains a preponderance of clay. On the other hand, sections A-A' and C-C" (figs. 2, 4) traverse chiefly upland areas, and many of the well logs indicate a preponderance of coarse- grained material. In the central two-thirds of the valley below a depth of 150 to 200 ft, ground water is confined. The confinement extends northward from the southern part of San Jose MECHANICS OF AQUIFER SYSTEMS to Palo Alto and Milpitas and beneath the bay. In much of the area of confinement, wells more than 200 ft deep flowed in the early years of urban development (see fig. 13). The confined aquifer system is as much as 800 ft thick. Around the valley margins, ground water is generally unconfined, and most of the natural recharge to the ground-water reservoir percolates from stream channels crossing alluvial-fan deposits. The confining member overlying the confined aquifer system has a thickness of 150 to 200 ft (see fig. 3, central part; also see fig. 5). Although predominantly composed of clay and silt, it also contains some channel fillings and lenses of permeable sand and gravel. This confining member supports a shallow water table distinguished by an irregular surface. As of 1965-70, the shallow water table overlying much of the confined system was less than 30 ft below the land surface (Webster, 1973). At least near the bay, the shallow water table did not fluctuate ap- preciably during the period of prolonged artesian-head decline terminating in 1966, indicating little change of stress in the shallow confining member. In 1960, the Geological Survey drilled core holes 1,000 ft deep at the two centers of subsidence: in Sunnyvale (well 68/2W-2407) and in San Jose (well 78/1E-16C6). An electric log was obtained for each core hole after coring was completed. Graphic logs and generalized lithologic descriptions were prepared from the geologists' logs made at the drill site, supplemented by interpretation of the electric log in zones not cored or of poor recovery. These three elements were combined to give a composite log for each core hole (figs. 5, 6). The depths of the samples tested also were plotted on the composite logs. In all, 87 samples from these core holes were tested by the Geological Survey in the laboratory for physical and hydrologic properties, including particle-size distribution, specific gravity of solids, dry unit weight, porosity and void ratio, hydraulic conductivity (normal and parallel to - bedding), and Atterberg limits (Johnson and others, 1968, p. A1 and tables 5 and 6). Compressibility characteristics of fine-grained com- pressible layers (aquitards) can be obtained by making one-dimensional consolidation tests of "undisturbed" fine- grained cores in the laboratory. As one phase of the research on compaction of the aquifer system, laboratory consolidation tests were made by the U.S. Bureau of Reclamation on 21 selected fine-grained cores from the two core holes (see sample depth and number in composite log). Properties tested included the compression index, C,, a measure of the nonlinear compressibility of the sam- ple, and the coefficient of consolidation, C,,, a measure of the time rate of consolidation. Complete results of these laboratory tests have been published (Johnson and others, 1968, tables 8 and 9, and figs. 12 and 21¢). The 21 samples tested spanned a depth range from 141 to 958 ft below LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 FT land surface. The range of the compression index, C,, was | consolidation-test curves for the 11 samples from core hole small compared with the range in the San Joaquin Valley: | 6S/2W-24C7 and the 10 samples from core hole the maximum value was 0.33, the minimum was 0.13, and | 78/1E-16C6 are shown in figures 7 and 8. the mean was 0.24. Of the 21 samples, 15 had C,, values The plot of void ratio against the logarithm of load falling between 0.20 and 0.30. This suggests that the | (effective stress) is known as the e-log p plot. The com- nonlinear compressibility characteristics of the aquitards | pression index, C,,, representing the compressibility of the in the confined aquifer system do not vary widely. The | sample, can be obtained graphically from the e-log p FA NW a §'§ SE ALVISO ‘3 § AGNEW SAN JOSE 8 6 EDENVALE "C = won; 9 ta 39] - 6 ou 6 reeta 0 § § _> ay sigs A 300 7 e - § o A 9 0 , 9 .a " SSF .- $14 3 a. © & 2 y 8 (40. wo od e M <4 o:}; .- 1 - C a B» T < 1 uw - u = S »cof '~ «"~ 398 o J § F & i C "8 iy S =s ""a, C «Rll a. = a aw. a a T0 m \ w:" T" :y 3 W u m i Yo u a an " l y $ "| i s 2 a 0 D n ] $ I 1 bess? fp CP LC -/ wos &. 2 555 5 9°.) s g m f -Water % - § A* f HS 5 g i gif $. - ~ ' § 6 5 > ~ * £ < SEA gra _- _ a E B LEVEL |Z 100 Nii q: h n a F #18, L is Ie e |- ;‘=_.__‘;‘ g EXPLANATION Sand 500 |= C [ ilt *> 600 - ind gravel ® & ravel 700 - f Cla-y kw;— 800 - Cleve aand | See figure 1 for location gnzy'grsaavnel' of section mar 900 - 0 1 2 3 4 5 KILOMETERS EARCH a I 1 M o AS Il ; ITs 1 0 1 2 3 4 5 MILES FIGURE 2.-Geologic section A-A ' from Alviso southeast to Edenvale Hills. ALVISO MILPITAS MECHANICS OF AQUIFER SYSTEMS LOS ALTOS F8 u & .6 8 0 pote ~ s = & o t 11 Awmhom a1wis -LNZL-MLIS9 -ing $% l1z1i-mi/sg -]} s yee 10403 ewer = miso <4. & TZMLL-ML/S9 - LNLL-miL/Sg -f | Zd401-mi/sg -! sealy sanjoponey -I GH OSIATWMITIA NLW -- 2 y LEZ AVMHOIH Lv91-mL/sg -| m» Zr8L-mL/sg -) ad l gd toin tet Zag -II; LyE 1-mz/so -|! 101 AymHoim sm NU¢N|>>N\w\oI.R 3409) LZDbZ-MZ/S9 "~ /| 1392Z-me/Ss9 - ill 32217 suanary __L1LT-MT/S9 - Z8 AVMHOIM m. iwcz-mz/iso - 1% / 4}: ; Kf recut | 18 :.\..fl i Kalas € 9 = 3 - 8 a x o & 6 ~ o o 2 a Fg = o o w SEA LEVEL 100 4 200 ~ 300 47 400 7 500 7 600 4 700 - 800 7 900 - 5 MILES 1 5 KILOMETERS FIGURE 3.-Geologic section B-B' from Los Altos east to Milpitas. 1000 FQ LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 NE Cl ALUM ROCK 101 AwMHOIH 'S' ZWGP-31/SL - yaa17 -2TQO6-3V/SL |_‘ } hfiia-h- Water f level, azary adnjppong -' 44-3 LISL - ____n+._.u.mfl LUPZ-ML/SL - [ |\___ LY9Z-ML/SL t_"_ somo so7 -- L19Z-ML/SL - LISE-MIL/SL NOmM|>>§Mh/| Lhpe-mi/sc -/] =-- ZObE-ML/SL { / See figure 1 for location of section See figure 2 for explanation SW FEET 300 7 © 100 4 600 7 700 7 800 4 900 J 1000 1 5 KILOMETERS ~- 5 MILES FIGURE 4.-Geologic section C-C' from near Los Gatos northeast to Alum Rock. F10 MECHANICS OF AQUIFER SYSTEMS SPONTANEOUS RESISTIVITY GENERALIZED LiTROLOGIC SAMPLE NUMBER GRAPHIC DESCRIPTION 2 20121711 ohms m Im LOG (from core descriptions, drilling user ' uses _m’_‘o +3 AM=16 in. 50 “on performance, and electric logs) 0 500 f- 60 CAL 10 0-150 Clay, silty, sandy, and gravelly. Olive to blue. g Calcareous nodules 23 1255 -£ - |- 60 Cal 20 150-185 Clay. Greenish gray to olive. Calcareous nodules 23 L256 -L >_ 185-215 Gravel, clayey, silty, and sandy. Greenish gray 23 L258 -+ 256-318 Clay, silty, sandy, and gravelly. Greenish gray to olive brown. Calcareous nodules 23 1257 -+ =< % 318-328 Gravel, sandy - 60 CAL 30 23 1259 -f L 328-415 Clay and silt, sandy. Olive gray -to yellowish brown. Calcareous nodules 415-434 Sand, gravelly and . silty. Olive brown to yellow brown rrr 23 L262 —«L 60 CAL 40 23 L263 - Tort F 131 265 -L 678-742 Clay, silty. Greenish gray i- 60 CAL 50 t aaa tr " ms - 752-802 Clay, silty. Dark greenish gray to olive gray. a Calcareous nodules. Gastropod shells at 755-760 ft | a* _| 802-814 Sand, lr'lr'r'o'on gr [3.0mm clayey silt. Olive gray - _ 814-839 Sit, clayey and sandy. Olive gray. Calcareous @ gravely. Yellowish brown - 60 CAL 23 L267 -L e - 900 -- 45-1000 Clay, silty and sandy. Greenish gray to olive brown. F Calcareous nodules f 23 1269 -+ - 60 CAL 69 1000 _ [M 434-506 Clay, silty, and sandy . Olive gray to yellow brown. Calcareous nodules 506-516 Gravel 516-536 Clay, silty, sandy, and gravelly. Olive gray to yellowish brown. Calcareous nodules SQ-SH Sand, silty and clayey. Yellow brown to gray 547-678 Clay and silt, sandy. Dark greenish gray to olive brown "U.S. Bureau of Reclamation Prepared by J. H. Green FiGurE 5.-Composite log of core hole 6S/2W-24C7 in Sunnyvale. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 SAMPLE NUMBER SPONTANEOUS RESISTIVITY GRAPHIC GENERALIZED LITHOLOGIC POTENTIAL ohms m*/m LOG i Diismflllgn ys I 5 millivolts AM~16 in. rom core descriptions, M USBR uses sr 50] FEET performance, and electric logs) minds ( 500 0-70 - Clay and silt 70-75 Clay, gravelly and sandy. Greenish gray to yellowish brown. Wood at 73 ft 100 -> 75-148 Gravel, sandy and clayey 148-214 Clay and slit, sandy. Greenish gray to olive brown. Gravel at 172-174 ft -_— 60 CAL 70 200 214-246 Clay, sity and sandy. Greenish gray to yelowish f brown. Plant remains at 230-231 ft, gravel i fl at 240-241 ft |- 246-290 Gravel, sandy and clayey. Rock fragments as large as 3 in. a==~ "290-303 Clay, sitty, sandy, and gravelly. Light olive 23 1272 4- gray - , clayey gravelly. ate brown & &. to dark yellowish brown 231273 -. 326-390 Clay, silty, sandy, and gravelly. Greenish gray 23 L275 -I- 60 CAL 80 calan -+ 23 L279 -+ - 23 L280 -+- |- f- 60 CAL 90 23 L282 - 23 1283 -L .. 23 284 4 go car ge Mh iaa A WWWWMWWM 1000 to olive gray. Calcareous 390-426 Sand and gravel. Sand is pale olive to yellowish brown. Calcareous 7426-438 Clay and sit, sandy. Yellowish brown. Cal- careous 438-473 Gravel, sandy and silty. Moderate brown 473-512 Silt and clay, sandy. Grayish red to moderate olive brown. Carbonaceous, calcareous 512-528 Gravel. Rock fragments as large as 2.5 in. 528-583 Sit and clay, sandy. Bluish gray to yellowish brown. Calcareous. Carbonaceous - at 530-531 ft, gravel at 546-550 ft 583-670 Cemented gravel, gravel, and sand 670-706 Sitt, clayey, sandy, and gravelly. Olive brown to yellowish brown. Calcareous 706-722 Clay and gravel. Yellowish brown 748-785 Gravel, sandy, and silty. Sitt at 756-759 ft 785-817 Sitt and clay, sandy and gravelly. Dark bluish gray to yellowish brown 817-834 Gravel and sand, silty and clayey 834-855 Sit and sand, clayey and gravelly. Olive n gray to olive brow 855-865 Gravel 865-897 Sit and clay Rock fragments as large as 2 in., sift at 903-906 ft 929-973 Sit and clay, sandy. Yellowish brown to olive. Sand or gravelly sand at 964-967 ft 'U.S. Bureau of Reclamation FiGuRE 6.-Composite log of core hole 7TS/1E-16C6 in San Jose. Prepared by J. H. Green FIL F12 MECHANICS OF AQUIFER SYSTEMS SAMPLE DEPTH 141 FEET 6.70 SAMPLE DEPTH 437 FEET 0.60 |- 0 . 50 0.40 |- 0. 30 0. 60 0. 50 - 0. 40 |- 0. 30 0 . 20 0. 80 0.70 0.80 I T \| 0.60 0 . 50 0. 40 0.30 0.80 VOID RATIO, e 0.70 0.60 0. 50 0. 40 0.30 SAMPLE DEPTH 865 FEET 0.70 0.60 0.50 0.40 0.30 0 1 10 100 1000 0.70 0.60 0 . 50 0 . 40 0 1 10 100 1000 10,000 LOAD, IN POUNDS PER SQUARE INCH FIGURE 7.-Consolidation-test curves for samples from core hole 68/2W-24C7. Sample depths are in feet below land surface. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 curve: It is the slope of the straight-line portion of the loading curve or its dashed extension. Note that several points were obtained on the rebound as well as the loading branch of the curve in order to compare void-ratio in- creases due to unloading. Based on a study of the cores recovered from the two core holes, Meade (1967, table 1 and p. 39-43) described VOID RATIO, e 0.70 0 . 40 |- 0.70 f 0.50 '- 0. 30 |- SAMPLE DEPTH 233 FEET SAMPLE DEPTH 354 FEET 0.60 | | 0.50 |- &_ REBOUND 0.30 | 0.60 |- 0 . 40 |- 0.20 | I Curve | £ 0 1 10 100 1000 LOAD, IN POUNDS PER SQUARE INCH FiGURE 8.-Consolidation-test curves for samples from core hole 7S/1E-16C6. Sample depths are in feet below land surface. 10,000 F13 the types of deposits encountered to the 1,000-ft depth as nonmarine and mostly alluvial, with possibly a few lacustrine deposits at depths below 700 ft. Although both core holes are near San Francisco Bay (the Sunnyvale hole is only 3 mi from the bay), Meade reported that neither core contained sediments that could be recognized as estuarine. He listed several pieces of evidence indicating 0.60 0 . 50 0.40 0.30 0.20 0.60 0 . 50 0. 40 0. 30 0.60 0 . 50 0.40 0.30 0.20 0.60 0 . 50 0. 40 0.30 0.70 0.60 0.50 0. 40 o SAMPLE DEPTH 554 FEET SAMPLE DEPTH 937 FEET 100 1000 10, 000 F14 the absence of estuarine sediments, including a complete lack of marine or estuarine fossils. It is of interest to note that at the Dumbarton Bridge crossing of San Francisco Bay, 9 mi northwest of the Sunnyvale core hole, Atwater and others (1977, pl. 1, cross section C-C") found two intervals of estuarine deposits above a depth of 180 ft, respectively 0 to 60 ft and 120 to 160 ft below sea level and each about 6 mi wide. Their study of late Quaternary depositional history is based on detailed examination of sediments from 18 boreholes at three San Francisco Bay toll crossings (Bay Bridge, San Mateo Bridge, and Dumbarton Bridge). Three geologic cross sections show detailed descriptions of samples to a maximum depth of 200 ft below present sea level. Emphasis is on the estuarine deposits. X-ray diffraction studies of 20 samples from the two core holes indicate that montmorillonite composes about 7O percent of the clay-mineral assemblage in these deposits. Other constituents are chlorite (20 percent) and illite (5 to 10 percent) (Meade, 1967, p. 44, fig. 33, and tables 14 and 15). Montmorillonite is the most compres- sible of the clay minerals. HYDROLOGY RAINFALL Precipitation that falls within the drainage basin is the ultimate source of all local ground water. The rainfall at San Jose has developed definite trends in the past 100 years (fig. 9). A plot of the cumulative departure of rain- fall at San Jose from the seasonal mean for the period of record clearly defines these trends. The rainfall record for San Jose began in 1874-75. For the 106-year period to 1979-80, the seasonal mean rainfall (July 1 to June 30) was 14.13 in. From about 1890 to about 1915 the generally rising curve defined by the yearly points indicates that the cumulative surplus exceeded the cumulative deficiency by about 55 in. Thus, the average yearly surplus in this wet 25-year period exceeded the seasonal mean by about 2 in. On the other hand, for the 50 years from about 1916 to about 1966 the declining curve defined by the yearly points indicates that the cumulative deficiency exceeded the cumulative surplus by about 60 in. Thus, the average yearly deficiency in the 50-year dry period was below the seasonal mean by about 1.2 in. 'The cumulative departure curve is determined by calculating the seasonal mean for a period of record, calculating each season's departure (plus or minus) from that mean, and then summing those departures. Thus, the first season had a defi- ciency of 6 in. and the second season had a surplus of 5 in., resulting in a cumulative deficiency of 1 in. for the first two seasons. MECHANICS OF AQUIFER SYSTEMS GROUND-WATER PUMPAGE The intensive development of irrigated agriculture in the valley began about 1900. Tibbetts and Kieffer (1921, pl. 7) reported that the number of irrigation wells in north Santa Clara County increased from 115 in 1890 to 1,590 in 1920. 1920 1,590 1890 115 1900 235 1910 440 Year Wells Agricultural pumpage increased from about 40,000 acre- ft/yr in 1915-20 to a maximum of 103,000 acre-ft/yr in 1945-50 (fig. 10, table 1). After 1945, population pres- sures caused a great transition of land use from agricul- tural to urban and industrial development. By 1970-75 most of the orchards had been replaced by houses, and agricultural pumpage had decreased to 20,000 acre-ft/yr. Municipal and industrial pumpage, on the other hand, in- creased from 22,000 acre-ft/yr in 1940-45 to 131,000 acre- ft/yr in 1970-75. Total pumpage (fig. 10, table 1) increased nearly fourfold from 1915-20 to 1960-65-from 49,000 to 185,000 acre-ft/yr-but then decreased 19 percent to 150,000 acre-ft/yr by 1970-75 in response to a rapid in- crease in surface-water imports. SURFACE-WATER IMPORTS The import of surface water to Santa Clara County began about 1940 when San Francisco began selling sur- face water imported from Hetch Hetchy Reservoir in the Sierra Nevada to several municipalities. This import in- creased from 6,000 acre-ft in 1955 to 12,000 acre-ft in 1960 and to about 50,000 acre-ft in the 1970's (fig. 11, table 2). Imports before 1955 are not known. Surface water imported from the Central Valley through the State's South Bay Aqueduct first became available in 1965; during the 1970's, deliveries through the aqueduct exceeded 100,000 acre-ft four different years (table 2, fig. 11). Unused imported water was recharged to the ground- water reservoir through stream channels and percolation ponds. The yearly quantity diverted to channels (stippled segment of yearly bars, fig. 11) in the 15 years has aver- aged about 40,000 acre-ft and represents about 48 per- cent of the total import from the South Bay Aqueduct. DECLINE OF ARTESIAN HEAD, 1916-66 In the spring of 1916, the artesian head in index well 7S/1E-7R1 in San Jose stood 12 ft above the land surface (fig. 12). At that time there were only about 1,000 irriga- tion wells in north Santa Clara County. The cumulative departure graph of rainfall at San Jose (fig. 9) shows that F15 LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 2 SEASONAL YEAR JULY 1 TO JUNE 30) I$ 14.13 INCHES (AVERAGE RAINFALL FOR 106 SEASONS "L. I 60 I =] o Co l= SHIN! NI 'NV3W TVNOSY3S 3HL WOYJ IYNLMYVdI0 40 19 40 1960 1980 1920 YEAR 1900 FIGURE 9.-Cumulative departure of rainfall at San Jose from the seasonal mean for the 106-year period 1874-75 to 1979-80. (Data from 1880 1860 U.S. Weather Bureau and National Weather Service.) ”(waxy Ammwww ////// \ ,/ § /”///M// XX in //// \ /, ans N MUNICIPAL AND INDUSTRIAL 200 o y m - 1331-3%49V 10 SONVSNOHL NI 1960 1970 1980 1950 YEAR FIGURE 10.-Ground-water pumpage in north Santa Clara County, 1915-80. 1930 1940 1920 F16 MECHANICS OF AQUIFER SYSTEMS TABLE 1.-Ground-water pumpage, north Santa Clara County, 1915-80, in acre-feet [From 1915 to 1966 agricultural pumpage was estimated by the Santa Clara Valley Water District from agricultural power sales of Pacific Gas and Electric Company and is reported by fiscal year. To 1966 municipal and industrial pumpage is listed by calendar year; municipal pumpage is metered, industrial is estimated. Since 1966 all pumj is metered and is reported here by fiscal year July 1-June 30. Industrial gum e was estimated as follows: 1915-34, 5,000 acre-ft/yr; 1935-43, 10,000 acre-ft/yr; 1944-50, 15,000 acre-ft/yr; 1951-60, 20,000 acre- yr; 1961-66, 22,000 acre-ft/yr) Municipal Agricultural Total. Sex" Yearly - 5-year average and Yearly - 5-year average industrial 1915-16 22,800 8,600 31,400 1916 31,500 9,200 40 , 700 1917 41,300 9,800 51,100 1918 45,500 10,700 56,200 1919-20 56,000 39,420 10,200 66 , 200 49,120 1920-21 63,000 10,800 73,800 1921 54,600 10, 500 65,100 1922 56,700 10,700 67,400 1923 97,500 10,800 108, 300 1924-25 82,500 70,860 14,700 97,200 82,360 1925-26 76,000 12,600 88 , 600 1926 74,000 12,500 86,500 1927 90,000 12,000 102,000 1928 118,000 12,700 130,700 1929-30 102,000 92,000 15,400 117,400 105,040 1930-31 122,000 14,600 136,600 1931 84,000 17,000 101,000 1932 104,000 14,400 118,400 1933 108,000 14,900 122,900 1934-35 56,000 94,800 15,100 71,100 110,000 1935-36 68 , 100 18,900 87,000 1936 63,700 19,800 83,500 1937 61,400 20,100 81,500 1938 77,600 20,200 97,800 1939-40 73,000 68,760 22,100 95,100 88 , 980 1940-41 72,600 20,700 93,300 1941 84,000 20,000 104,000 1942 97,600 18,700 116,300 1943 117,900 19,600 137,500 1944-45 96,100 93,640 33,500 129,600 116,140 1945-46 100,800 34 , 200 135,000 1946 104,900 36,400 141,300 1947 114,100 38, 200 152,300 1948 98, 200 41,600 139,800 1949 95,700 102,740 44 , 200 139,900 141,600 1950-51 84,000 49,500 133,500 1951 81,100 46,600 127,700 1952 95,700 50,700 146,400 1953 92,500 52,700 145,200 1954 121,800 95,020 55,600 177,400 146,040 1955-56 90, 200 64,900 155,100 1956 94 , 300 66,100 160,400 1957 78,600 77,100 155,700 1958 102,600 79,800 182,400 1959 90,000 91,140 93,200 183,200 167 , 360 LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F17 TABLE 1.-Ground-water pumpage, north Santa Clara County, 1915-80, in acre-feet-Continued Sear Agricultural Muzzzlpal Total Yearly 5-year average {industrial Yearly 5-year average 1960-61 84,800 106,400 191,200 1961 63,400 121,300 184,700 1962 54,400 119,400 173,800 1963 76,200 109,700 185,900 1964-65 57,200 67,200 131,400 188,600 184,840 1965-66 40, 200 122,300 162,500 1966-67 29,800 140,100 155,390 1967-68 35,400 139,200 174,630 1968-69 28,600 136,670 165,270 1969-70 29,320 32,660 126,040 155,360 162,630 1970-71 23,710 124,500 148,210 1971 24,090 142,390 166, 480 1972 17,450 137,820 155,270 1973 15,940 129,125 145,060 1974-75 16,903 19,620 120,526 137,430 150,490 1975-76 20,036 148,764 168,800 1976-77 16,714 136, 329 153,043 1977-78 11,702 115,581 127,283 1978-79 12,027 137,678 149,705 1979-80 9,793 14,050 139,764 149,557 149, 680 1980-81 9,568 151,558 161,126 1916 was the end of a wet period beginning about 1890. Hunt (1940) reported that in 1912, 29 percent of the valley lands were irrigated, but that by 1920, 67 percent were irrigated, including 90 percent of the orchards; nearly all of these lands were irrigated with ground water from wells. By the autumn of 1966, the head in well 78/1E-6M1 in San Jose was about 210 ft below land surface (fig. 12).2 The principal factors in this major 50-year decline of about 220 ft are shown in figure 12. The upper line is a replot (fig. 9) of the cumulative departure, in inches, from 1910 to 1980 of the seasonal rainfall at San Jose from the seasonal mean for the 106-year period since 1874-75. Ex- cept for the 6-year wet period 1936-42, the departure in the 50 years from 1916 to 1966 was substantially negative, and the cumulative departure represents a cumulative deficiency of 60 in. *The record of depth to water in index well 7S/1E-7R1 extends from 1915 to date. However, during the last two decades the artesian head in this well has been higher than the head in nearby representative deep wells, such as well 7S/1E-6M1 (803 ft deep). Accordingly, the composite hydrograph of figure 12 represents the artesian head in well TR1 to 1959 and the head in well 6M1 from 1959 to 1980. The bottom graph of figure 12 shows the estimated total ground-water pumpage for the 65-year period 1915-80; the plot is similar to figure 10 except that the increase in pumpage is plotted downward to reflect its influence on the artesian head in the index wells. Estimates from 1915 to 1965 are based chiefly on electric-power consump- tion for agricultural use and are graphed as 5-year averages; since then, virtually all pumpage has been metered. The 50-year decline in artesian head plainly was caused by generally deficient rainfall and constantly increasing pumping draft. The curve of artesian-head decline con- forms reasonably well with the cumulative departure curve of the seasonal rainfall at San Jose. Water levels in a relatively full ground-water basin at the end of the prolonged wet period beginning in 1890 are shown in figure 13. The water-level contours are generalized from plate XIV of Clark (1924), which was drawn from measurements of depth to water in wells in the spring and summer of 1915. Both figures 13 and 14 are maps prepared by P.R. Wood and K.S. Muir (U.S. Geological Survey, written commun., June 1972). Clark's area of artesian flow as of 1915 (from pl. XIV) and his "boundary of former area of artesian flow" (from pl. XV) F18 are both shown in figure 13. Obviously the confined aquifer system must extend beyond Clark's "former area of artesian flow."" The boundary between confined and free ground-water conditions is not easily determined or recognized in parts of the Santa Clara Valley. In this report, however, the 1-ft subsidence line of 1934-67 (fig. 21) is considered to be a general approximation of the boundary of the confined area, and accordingly it is plotted in figure 13. It is of interest to note that the California Department of Water Resources (1967, p. 85 and pl. 11) defined the boundary of the confined aquifer system as the boundary of their San Jose subarea. That boundary agrees in general with the 1-ft subsidence line of 1934-67 (fig. 21), except near Oak Hill and Penitencia Creek. In general, the water-level contours of figure 13 are assumed to represent a free water table near the valley margins and the potentiometric surface of the confined aquifer system in the central area included within the 1-ft subsidence line. The water-level contours by 1915 had not yet been distorted appreciably from the conditions that prevailed before man began the steady increase in ground- water withdrawal. The water-level contours indicate a 200 | l [ Lu u u u, 150 O3 soUTH BAY < AQUEDUCT u. Used directly [e») w o E < w 8 100 C SOUTH BAY E- AQUEDUCT < Diverted to channels - M oc O a. 3 at: 50 < m [«») F- HETCH HETCHY AQuUEDUCT 0 1950 1960 1970 1980 YEAR FIGURE 11.-Surface-water imports to north Santa Clara County, 1955-80. MECHANICS OF AQUIFER SYSTEMS generally northwesterly movement of ground water toward San Francisco Bay in 1915. In the San Jose area, the water levels in wells ranged from 60 to 100 ft above sea level, and artesian wells were still flowing in down- town San Jose. By 1967, after a half century of exploitation, water levels in wells had been drawn down below sea level in much of the ground-water basin. The hydraulic gradient toward San Francisco Bay in wells tapping the confined system had been reversed, and movement was now toward large cones of pumping depression as much as 200 ft below 1915 levels, surrounding heavily pumped municipal well fields. In central San Jose, the artesian head of 1967 was 160 to 180 ft below 1915 levels (fig. 14). In part of the confined aquifer system in 1967, water levels in wells had been drawn down below the base of the confining member, which near the bay is 150 to 200 ft below the land surface. Therefore, it is not practical to draw a boundary between water table and confined con- ditions as of 1967 on the basis of figure 14. RECOVERY OF ARTESIAN HEAD, 1967-80 The recovery of water level since the middle 1960's has been substantial. By 1975, the spring high-water level at index well 78/1E-6M1 (fig. 12) was 60 ft higher than in 1966 and about equal to the 1985 level. Subsequent recovery was affected by the drought of 1976 and 1977, but the high level of 1980 was still 60 feet higher than the 1963-66 lows. From 1958 through 1982, the Geological Survey measured depth to water in well 78/1E-16C5 at the 12th and Martha Street well field of the San Jose Water Works. This well is 908 ft deep and is about 1.5 mi east of well 78/1E-7R1 (fig. 1). The record of depth to water in well 78/1E-16C5 is shown from 1958 through 1979 in figure 414 and from 1980 through 1982 in figure 474. The recovery of artesian head in this index well from the 1966 low to the 1978 low was about 80 ft. This major recovery of artesian head was due to several factors, including increased imports of surface water, favorable local water supply, decreased pumpage, and in- creased recharge (fig. 12). The most important factor was the increase in imports. The import of surface water to Santa Clara County began in about 1940. As shown by table 2, by 1966-67 yearly import through the Hetch Hetchy and South Bay Aqueducts was 36,000 and 32,000 acre-ft, respectively. By 1979-80, total import was about 158,000 acre-ft, con- siderably more than double the import of 1966-67. The average seasonal rainfall at San Jose was above normal in the 14-year period 1966-80. The cumulative departure graph (fig. 9) indicates a positive increase of about 15 in. in the 14 years. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F19 TABLE 2.-Surface-water imports to north Santa Clara County, 1955-80, in acre-feet per fiscal year [Data from Santa Clara Valley Water District; total imports rounded to 5 acre-ft] South Bay Aqueduct Year Hetch Hetchy Piyartsd to lTotal (July 1-June 30) Aqueduct Total channels imports 1955-56 5,965 1956 6, 300 1957 7,445 1958 9,690 1959-60 12,300 1960-61 12,765 1961 15,578 1962 22,970 1963 24,072 1964-65 29,536 495 495 30,030 1965-66 33,572 29,680 29,680 63,250 1966 35,784 31,785 31,480 67,570 1967 39,902 63,032 55,213 102,935 1968 41,675 57,663 46,466 99,340 1969-70 47,203 773234 38,072 124,435 1970-71 45,288 88,486 44,024 133,775 1971 49,744 92,432 43,596 142,175 1972 48,890 92,582 47,586 141,470 1973 49,467 86,565 41,076 136,030 1974-75 53,273 104,052 36,196 157,325 1975-76 5845229 118,692 52,607 176,920 1976 47,657 89,693 29,318 137,350 1977 38,052 79,776 20,126 11745830 1978 49,434 105,107 41,308 154,540 1979-80 51,806 105,868 35,628 15745675 The average yearly pumpage of ground water, which reached a peak of about 185,000 acre-ft in 1960-65, decreased to about 150,000 acre-ft in 1970-75 and 1975-80 (table 1). A principal reason for this 19-percent decrease is the tax on ground-water pumpage applied since 1964 for water extracted from the ground-water basin. In 1970-71, for example, the ground-water tax was levied at $8 per acre-ft for ground water extracted for agricultural purposes and at $29 per acre-ft for ground water extracted for other uses. For water delivered on the surface in lieu of extraction, the cost was $10.50 per acre-ft for water used for agriculture and $31.50 per acre- ft for water used for other purposes. The economic ad- vantage of using surface water where available is obvious when one considers the cost of ground-water extraction in addition to the tax. Local agencies have been working since the 1980's to obtain water supplies adequate to stop the ground-water overdraft and raise the artesian head. Their program has involved (1) salvage of flood waters from local streams that would otherwise waste to the bay, and (2) importa- tion of water from outside the valley. In 1985-36, five storage dams were built on local streams to provide deten- tion reservoirs with combined storage capacity of about 50,000 acre-ft, to retain flood waters, and to permit con- trolled releases to increase streambed percolation (Hunt, 1940). The storage capacity of detention reservoirs was increased to 144,000 acre-ft by the early 1950's (Califor- nia State Water Resources Board, 1955, p. 51). Recharge from stream channels and percolation ponds to the ground-water reservoir has been augmented since 1965 by water from the South Bay Aqueduct that could not be delivered directly to the user. The quantity diverted to recharge areas in the 15 years has averaged about 40,000 acre-ft per year and represents 48 percent of the total import from the South Bay Aqueduct. (See stippled segment of yearly bars, fig. 11, and upper right graph, fig. 12). MECHANICS OF AQUIFER SYSTEMS F20 13341-3849V 10 sONVSNnOHL NI 'L4OdWI 13341-349V 10 SsONVSNnOHL NI '39VIWNd 3IV4i4NS ONVI MO138 '1334 NI OL H1d30 O07 o i «- UVIA OS61 'squodut pug 'adeduwnd 03 ut asop wey ut adueyo peoy-ueisau1y-'Z] THNODIL Ov6L O€E61 0261 0161 OOL |- O i | elorA 091 - LW9-31/SZL 44m; OTL |- 08 - oS OOL ost elorA STI3NNYVHO H3SN OL LOnd3nov Avg HLNOS olf L¥/L-31/SZL 773M dVIH NVISIIUYV Lonag3nov AHOLJH HDLFH aoeyins pug 7] T1TVINIVY Op of OC OL OL OC o€ Op 0861 01 S/81 401 NV3W 1VNOSVY3S 'S3HIN! NI '3HNLYV430 JAMLYVINWNI T171V4INIVH LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F21 LAND SUBSIDENCE In 1919, a line of first-order levels was run southward f from San Jose. This leveling revealed subsidence of 0.4 ft at San Jose (fig. 22, bench mark P7). The first relevel- The first precise leveling of bench marks within the sub- | ing early in 1932 showed subsidence since 1912 ranging siding area in Santa Clara County was carried out in 1912 | from 0.35 ft in Palo Alto (bench mark I7) to 3.66 ft in San on a line from Bingham, Utah, to San Francisco through | Jose. More extensive leveling early in 1983 confirmed the Niles, San Jose, and Redwood City. This initial line and | subsidence and provided additional control on its extent. HISTORY OF LEVELING CONTROL all subsequent leveling described in this report were ac- As a result of the great scientific interest in this regional complished by the National Geodetic Survey (formerly the | subsidence, and through the joint efforts of A.L. Day, C.F. U.S. Coast and Geodetic Survey). Tolman, and the National Geodetic Survey (Tolman and 121945" R 2 6 EXPLANATION E] Alluvium and bay deposits Santa Clara Formation and associated deposits m Consolidated rocks - Fault-Dashed where approx- imate, dotted where con- cealed - --- Boundary of area of artesian flow, 1915. (Data from Clark, 1924, Plate XIV) --- --- Boundary of former area of artesian flow (pre-1915). (Data from Clark, 1924, plate XV). 3 Approximate boundary of pres- sure area (Line of 1 foot sub- sidence, 1934-67) where uncertain uy 3 SK 10--Water-level contour -General: ized contour on the water table in the recharge area and on the potentiometric surface of the confined aquifer system in the con- fined area. Dashed where approximately located. Con- tour interval 10 and 20 feet. Datum is sea level. Contours generalized from Clark, 924, plate XIV- 1 41244 ock 7 w @ - @ w - 37° 15° Reservoir _|_ 30" $) R" C.. P p ) pesar) V y P PLexington _ Guadalupe // | /7// ~, A | Reservoir Reservoir Y LS FIGURE 13.-Generalized water-level contours for spring and summer, 1915, north Santa Clara County. $10... .-. a | 1. 2-3". :4/ "BMILES | I l % j 7 :.'_.l: o ( # 1 2 3 4 5 KILOMETERS | F22 Poland, 1940, p. 29), an extensive network was laid out in 1983 to determine by periodic releveling the extent, magnitude, and rate of subsidence. The extent of the network is shown in figures 15 and 16. Initially numbered with single or double digits (fig. 15), the lines were renumbered by the National Geodetic Survey in the late 1950's using three-digit numbers (fig. 16). The network was completely leveled for the first time in the spring of 1934. The total length of survey lines composing this bench-mark net is about 250 mi. As shown in figure 15, level line 1 extends from Morgan Hill north- MECHANICS OF AQUIFER SYSTEMS westward to San Jose and then northward along the east side of San Francisco Bay past Niles. Line 2 extends along the west side of the bay from San Jose northwestward past Redwood City. Three transverse lines (8, 18, and 9) extend southwestward across the San Andreas fault, and three (1, 4, and 6) extend eastward across the Hayward fault. The times and extent of leveling of the net are shown in figure 17. Heavy lines drawn on the screened back- ground define the leveling accomplished in a designated year, which may range from a single line to complete 121°45° R2 E I 0 & - 37° 7 w @ - 37° 15 5 KILOMETERS | 0 5 MILES 12 2. "Xx EXPLANATION Alluvium and bay deposits Santa Clara Formation and associated deposits Consolidated rocks -- Fault-Dashed where approximate, dotted where concealed ---20 -= Line of equal water-level change, 1915-67-Dashed where approx- imate. Interval 20 feet r //////////.':'?//A> Reservoir Reservoir FrGurRE 14.-Change in water level, 1915-67, north Santa Clara County. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 coverage of the net, as in 1954 and 1960. In 1956, the National Geodetic Survey published a chronologic com- pilation of adjusted elevations, in feet, through 1954 for all bench marks in the network (U.S. Coast and Geodetic Survey, 1956). Since the late 1950's, the primary control for identify- ing bench-mark elevations is the National Geodetic Survey's 30-minute quadrangle (for example, see parts of National Geodetic Survey quadrangles 371221, 371222, 371213, and 371214 in figure 16). Almost all the network is in National Geodetic Survey quadrangles 371213 and 122° 15" F23 371222. When requesting bench-mark elevations in sub- siding areas from the National Geodetic Survey, one should specify quadrangle, line number, and year or years of leveling. EXTENT AND MAGNITUDE OF SUBSIDENCE The subsidence record for bench mark P7 in San Jose is plotted in figure 18, together with the fluctuation of artesian head in nearby index well 7S/1E-7R1-6M1 taken from figure 12. The black dots on the subsidence curve 122° 00° 121° 45" I I EXPLANATION Bedrock -.. Fault-Dashed where approxi- mate, short dash where infer- red, dotted where concealed Number of level line City Airport 37° 30° 6 a ‘ (Z Cy Q 1 ,/ Q PV 37°15" |- Re 10 KILOMETERS 10 MILES % Morgan Hill © | FIGURE 15.-Network of level lines in the San Jose subsidence area; initial numbering of level lines. F24 indicate times of bench-mark surveys. The fluctuation of artesian head represents the change in stress on the aquifer system, and the subsidence is the resulting strain. Subsidence at bench mark P7 began about 1916 and was 5.4 ft by 1988. From 19838 to 1947, subsidence stopped during a period of artesian-head recovery but resumed in 1947 coincident with a rapidly declining head. It at- tained its fastest average rate in 1960-63 (0.7 ft/yr). By 1967 the bench mark had subsided 12.67 ft. Releveling of bench mark P7 in 1969 showed a further small increase in subsidence to 12.88 ft. 122 15 MECHANICS OF AQUIFER SYSTEMS Maps showing lines of equal subsidence for the periods 1934-54, 1948-54, and 1940-54 have been published earlier (Poland and Green, 1962, figs. 4, 5, and 6). Three additional subsidence maps are included in this report. They show subsidence from 1934 to 1960 (fig. 19), sub- sidence from 1960 to 1967 (fig. 20), and overall subsidence from 1934 to 1967 (fig. 21). To date (1984), 1967 was the last year of releveling of the bench-mark network. From 1934 to 1960, maximum subsidence exceeded 5 ft at centers in San Jose and Sunnyvale (fig. 19). In that period subsidence beneath the bay tidelands ranged from 122° 00° 121°45 371221 I EXPLANATION Bedrock G00 ------=* Fault-Dashed where approxi- mate, short dash where infer- red, dotted where concealed 103 371221 110 Quadrangle numbers (National Geodetic Survey) Number of level line o City o Airport 371214 37° 30° 371222 T 37°15 10 KILOMETERS 10 MILES 1 371213 101 X Morgan Hill 3 | FIGURE 16.-Network of level lines in the San Jose subsidence area; numbering of level lines revised to three digits in the late 1950's. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F25 o> < a a I z |@W = |-3 = | -O T + C 5 c o & o fol CC & u 9 T x [®] € | z $ | & t 3 w a f > x/ al <2) 4 Sy s j C 8 $ 5 O C St = |Pm = |@2m - .< = = |- = T E T 5 7 §) $ §) § 4 & § | z § |. ¢. g 3 3 > th { o = £ 4 y bo & 4 a 2 N 3 a> { 8 3 Sl w @ s l I. t- r- § ONT M > =] = 58 E (SE < = |A = | -< E / I g C 2 c CC 6 5 m 2 fo w 5 &} § 3 5 y £ [est * $ A a \ 3 Ah-_4 wA Bz 26 ., ke 6 CC MECHANICS OF AQUIFER SYSTEMS F26 HOHVW-AHVAYH83:3 6E61 'panunuo)-'/1 ZHNDIL 6661 AHYNNYr - SE6l #380100 6E-8E61 SE61 - {£61 H38W3AON SE-LE6L II!tH uebsom IIH uebsop ( C Aud " .. -pApoompay IIH uebsop U38W3030°HOHV W LE6L W 9E61 3NNP"AVW SE6L IIH uebsopm IIH uebsop !H uebsom F27 LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 H38W3AON-H 380100 0961 ZHNDI LSnony 9§61 vS6L II!H uebsop A; uebaopy II!H ueBsom A7NF+AYV NNY Sv6L AVN-HOH VW Ov6eL HDHVW = 6661 H38W3AON Op-6E61 IIH uebaow \IH uebson MECHANICS OF AQUIFER SYSTEMS F28 L961 HIHVWN-AHVNH834 S961 AVW~HOHV W 6961 IH uebsom AHVNH834 £961 IIH uebaop AI A /J h (¢. aud ( AI uebs0p \ f 4 LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 1 to 3 ft. As of 1960, the area of subsidence lay wholly within the area of alluvium and bay deposits. From 1960 to 1967, maximum subsidence exceeded 3.5 ft in San Jose and Santa Clara (fig. 20) and at one bench mark in San Jose was 3.9 ft. The average rate of subsidence was 0.5 ft/yr, the most rapid rate of subsidence in any 7-year period. From 1934 to 1967, the National Geodetic Survey re- surveyed the network from "stable"" bedrock ties a dozen times to determine changes in altitude of the bench marks. During the 33-year period 1934-67, subsidence ranged from 2 to 5 ft under the bay and its tidelands to 8 ft in San Jose and Santa Clara (fig. 21). The volume of sub- sidence (pore-space reduction) planimetered from the 1934-67 subsidence map is about 500,000 acre-ft. If the ratio of the pre-1934 subsidence volume to the 1934-67 subsidence volume is assumed to be equal to the ratio of the pre-1934 subsidence of bench mark P7 to the 1934-67 subsidence of that bench mark, then the total subsidence volume from 1912 to 1967 is about 800,000 acre-ft. When a line of bench marks in a subsidence area has been releveled a number of times, one of the most infor- mative means of presenting subsidence information is to draw a series of subsidence profiles (figs. 22-24). Land-subsidence profiles along line D-D ' from Redwood City to Coyote from 1912 through 1969 are shown in F29 figure 22 (for location of line D-D', see fig. 21). The spring 1934 leveling was used as a reference base because it was the first complete leveling of the net. Subsidence before 1934 is plotted above the reference base, and subsidence after 1934 is shown below it. The marked increase in rate of subsidence after 1948 from Palo Alto to San Jose plain- ly is due to the increased decline of artesian head (fig. 18) in response to increased ground-water withdrawal (fig. 10). Note that from 1934 to 1967 maximum subsidence of 8.6 ft was near bench mark W111 3 mi northwest of bench mark P7; in addition, note that from 1934 to 1960 the greatest subsidence along line D-D' was 5.7 ft at bench mark J111 reset in Sunnyvale. Changes in the rate and magnitude of withdrawal and of artesian-head decline doubtless have caused much geographic variation in sub- sidence rate and magnitude with time. Profiles of land subsidence along transverse line E-E' from Mountain View to Milpitas from 1983 to 1967 (fig. 23) have a pattern similar to that of the profiles in figure 22. The rate of subsidence prior to 1948 is low com- pared with the great increase in the rate thereafter. Benchmark J111 reset is common to both lines D-D' and E-E"' ; from 1934 to 1967 it subsided 7.8 ft. Land-subsidence profiles along line F-F' from Los Gatos through San Jose to Alum Rock Park from 1934 to 1969 are displayed in figure 24. Bench mark 119 in San 40 I I I I I ARTESIAN HEAD [ WELL 78/1E-7R1 WELL 78/1E-6M1 9 us < < kas S 0 |- -] 40 & 2 Indicates time of s bench-mark survey z 2 - 80 & > a w. cc z (= u *|~ _ suesipence Bench mark P7 o 5 3 : fad a i- w luke fab & 6 - 160 H m a 3 dal 8% =ya00 5 < (=] i- 10 |- -| 240 & a. 4 Note: f=] Dotted segments show 12 |- author's interpretation - 280 | 1 | I | 1+ + see r® _ 1910 1920 1930 1940 1950 1960 1970 1980 YEAR FIGURE 18.-Artesian-head change and land subsidence, San Jose. F30 Jose is common to both line D-D' and F'-F"; it subsided 7.7 ft from 1934 to 1969 and was exceeded only by bench mark E176, which sank 8.7 ft in the same period. Although line F-F' crosses the concealed Hayward fault at Alum Rock, about 2.5 mi from the east end of the line, the relevelings from 1934-69 do not indicate any differen- tial displacement across the fault. ECONOMIC AND SOCIAL IMPACTS Subsidence has caused several major problems. Lands adjacent to San Francisco Bay have sunk 3 to 9 ft since 12215" I Amor s <7 « oen: © \ 0 1 2 3 4 5 KILOMETERS fo- opto 0 1 20 3. 4 L 122°00' MECHANICS OF AQUIFER SYSTEMS 1916, requiring construction and repeated raising of levees to restrain landward movement of the saline bay water as well as construction of flood-control levees near the bayward ends of the valley streams. The subsidence has affected stream channels in two ways: Channel grades crossing the subsidence bow! have been downwarped, and saline bay water has moved upstream. These changes tend to cause channel deposition near the bay and reduce chan- nel capacity, creating the need for higher levees. Intru- sion may occur where wells tapping shallow aquifers are pumped, inducing downward movement, especially through rusted well casings. 121945" T EXPLANATION D Alluvium and bay deposits Santa Clara Formation and o associated deposits NH Consolidated rocks --- --- Fault-Dashed where approx- imate, dotted where concealed _ --4-- Line of equal subsidence-Dashed where poorly controlled. Com- piled from leveling of National Geodetic Survey in May- - September 1934 and October- November 1960. Interval, in feet, is variable 9 & G z //////////////I - Compiled by J. H. Gnon‘ FIGURE 19.-Land subsidence from 1934 to 1960, north Santa Clara County. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 About 30 mi? of evaporation ponds from Palo Alto around the south end of the bay are used for salt produc- tion. Behind the landward chain of dikes bordering these ponds, at least 17 mi? of land lie below the highest tide level of 1967. Currently these lands are protected by the dikes and stream-channel levees, but they as well as the bay-front levees are considered inadequate. Extensive flooding of the Alviso area in March to April 1983 attests to the inadequacy of the stream-channel levees. By making use of the table of annual compaction (table 3) and the compaction-subsidence ratios for the 1,000-ft core holes (table 5), we can derive a rough estimate of the F31 subsidence that occurred from 1969 through 1982. The measured compaction at 68/2W-24C7 from 1969 through 1982 was 0.24 ft. If the ratio of compaction to subsidence for the 13-year period remained at 105 percent, the sub- sidence would be about 0.25 ft. The measured compac- tion at 7S/1E-16C11 from 1969 through 1982 (table 3) was 0.44 ft. If the ratio of compaction to subsidence for the 13-year period remained at 99 percent,the subsidence would also be 0.44 ft. These figures suggest that the sub- sidence for the 13-year period was on the order of half a foot at San Jose (16C11) and a quarter of a foot in Sunnyvale (2407). 122°15" 122°00' 121°45' T T a-. - < + EXPLANATION 37° |_ 0 1 2 3 4 5 KILOMETERS 0. A.. 2, 3~ 4 ~ 5 MMES 1 T G - < D Alluvium and bay deposits m Santa Clara Formation and associated deposits Consolidated rocks ------Fault-Dashed where approx- imate, dotted where concealed --0.1-Line of equal subsidence-Dashed where poorly controlled. Com- piled from leveling of National | Geodetic Survey in October- November 1960 and February- March 1967. Interval 0.5 and 0.1 foot Compiled by J. F. Poland FIGURE 20.-Land subsidence from 1960 to 1967, north Santa Clara County. F32 About $9 million of public funds had been spent to 1974 on flood-control levees to correct for subsidence effects, according to Lloyd Fowler, former Chief Engineer of the Santa Clara Valley Water District. In addition, the Leslie Salt Co. has spent an unknown but substantial amount maintaining levees on the 30 mi? of salt ponds to counter as much as 9 ft of subsidence in the Alviso area. Several hundred water-well casings have failed in vertical com- pression as a result of compaction of the sediments. The protrusion of well casings as much as 2 to 3 ft above land surface also has been observed (Tolman, 1937, p. 344). The cost of repair or replacement of such damaged wells has been estimated as at least $4 million (Roll, 1967). Including R 2 W rales < R 4 W 122°15" IT @ 37° 15" 0 1 2 3. 4 5 KILOMETERS 1 2003 4 5 MILES 122°00' MECHANICS OF AQUIFER SYSTEMS funds spent on maintaining the salt-pond levees, estab- lishing and resurveying the bench-mark net, repairing railroads, roads, and bridges, replacing or increasing the size of storm and sanitary sewers, installing drainage pumping plants, and making private engineering surveys, the direct costs of subsidence must have been at least $30 to $40 million to date. Fowler (1981) has estimated that the direct costs of subsidence, including the estimated cost of a proposed new levee system, all figured in 1979 dollars, would exceed $100 million. A major earthquake could cause failure of the bay- margin levees, which would result in the flooding of areas presently below sea level. The bay-margin levees were 1219%45' R2E EXPLANATION I: Alluvium and bay deposits Santa Clara Formation and associated deposits m Consolidated rocks ----~-Fault-Dashed where approx- imate, dotted where concealed R 1 W R 1 E ---2- Line of equal subsidence-Dash- ed where approximately located. Interval, in feet, is D D' variable Alignment of subsidence profiles- See figures 22-24 Li Core hole and number = Observation well and number 2 x Bench mark and number | ////////1,"f//fln ¢ w FIGURE 21.-Land subsidence from 1934 to 1967, north Santa Clara County. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 constructed of locally derived weak materials and were designed only to retain salt-pond water under static con- ditions (Rogers and Williams, 1974). The potential for such an earthquake poses a continuing threat to flooding of the estimated 17 mi? of land standing below the high-tide level of 1967. Such a threat has probably reduced the value of this land substantially compared with its value if it all still stood above sea level as it did in 1912. This decrease in land values should be included in the gross costs of subsidence. MONITORING OF COMPACTION AND CHANGE IN HEAD MEASUREMENT OF COMPACTION Two principal objectives of the Federal program on mechanics of aquifer systems are to determine the depth F33 interval in which compaction is occurring and to measure the magnitude and time distribution of the compaction where possible. Such information, together with periodic measurement of land subsidence as determined by spirit- level surveys to surface bench marks, is essential for determining the cause of subsidence and for monitoring the magnitude and the change in rate of subsidence. When coupled with measurement of water-level or head change in the stressed aquifer systems, these data supply the numbers required for stress-compaction or stress-strain analysis. The first extensometer (compaction recorder) in the Santa Clara Valley was installed in 1958 at well 68/1W- 23E1 in Agnew. In 1960, extensometers were installed in the cased core holes 1,000 ft deep at the centers of sub- sidence in San Jose (7TS/1E-16C6) and in Sunnyvale (68/2 W-2407), in two satellite holes in Sunnyvale (2403 and 2404), and in two unused water wells. They have D San Jose D' E atk 7] T sets o e- / E 4 |- Menlo & .'" All "s 4 ~ Park Sunnyvale #5 % Redwood Y - \9, City Palo /// NCG * |- Alto sg ty.. cf . C- $ > // Coyote 2 |- $548. "4 [ \ a 7— //// < a I5 Agl £ G uae cpg et 2 t g. & pa m ust NLE er ow: 1933 - Paa # /_____—— LT \‘/‘ :: $s 0L" ey A --f C- 1934 BASE | ° 1940 ts rd [-- 936 ==«--3=-C | _--p E T Sez _. \S\\ \/l//\’_\ +- [l _- 1969 z X M “9 [N-t~_ "82.0 srt ches: A} 95:5 f -I = u C| y* AN 7 "a 3) - a P | 8 N0.) { 1 2 3 1T --a ”I al w Dashed lines indicate Y* [- I no control between f : ;f 1956// C bench marks 0 2 I 4 |- N "Ii = $'. 1 f "Cp! || 3 Q)? \7 I o - 2 4 kilometers AAS e" I 23 fas s ) i 0 2 4 miles __ [> ft p In 6 }- g 06:9 74 / \ ll l A // > I e (x / " Note: All leveling 4,19 A to bench marks /~ by the National \ 8 |- Geodetic Survey § % @ FiGURE 22.-Profiles of land subsidence, D-D', Redwood City to Coyote, 1912-69. F34 IN FEET SUBSIDENCE, MECHANICS OF AQUIFER SYSTEMS n +s $ ' # x £ Mountain View E (C. Alviso g 2 Milpitas m E § co C 5 § f f $ so } E. *E! < 2. o %s Co 5 - £ co o > m s he ass $ ff f iC o 2 o o 0 o o | | | X o [o] 5 *X paras. $6. PRs _ |e ~1988 2 C 14 3 j c E s l & 3 9 ""s y* & .. /me | mee < ces ~ ecg a N 0 [ek 111 4 1934 BASE f fun as ien er me a BA y a / se ihr [sA i wo ~ F2 hig \§\'\93/ ** -a . C r-- \ \}9A9' a \ - L-- a h- \ t - e 2 |- 3 - |__] / \ o # § / m \ y C \ 7 \ ta iy " d p # g/ A- Pa /\ Je * / \ . F4 'd / -- \ -l 8 "4 F 4 4 0 \ S 1983) Y 6- / 2th / 1965 Me Note: Dashed lines [ys p indicate no leveling 4 \ / 7 - we # / A "4 Note: All leveling by the Q’Q-g/ o M 2 3 4 KiLOMeTERs National Geodetic Survey s L L__.__} i 1 y 1 o 1 2 3 4 MILES 8 FIGURE 23.-Profiles of land subsidence, E-E', Mountain View to Milpitas, 1933-67. & IN FEET SUBSIDENCE, Los Gatos m C177 -' 8177 - N177 LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 - W176 2 (NG - 2 3 4 KILOMETERS i P 1 é II! 4 MILES + us a, + s + > &C C C CC CC CC e 5 3 3 o o o San Jose « go é £ floJ 9 Svi -C I - g.1 ~ ef S £ s hs g <£ £5 £ -& €£:8 E 82g 5s = =o «- + «- < 5 id - 8 3 - & t & & t o- -* C& > |f 1934 BASE | § | Pats ¥ 6g t t ;| Lf ~- -p __ 1936 19 # ] 1 SA % £ I «2 Note: All leveling by the National Geodetic Survey F35 Alum Rock -~ L176 Park ® U179 FIGURE 24.-Profiles of land subsidence, F-F', Los Gatos to Alum Rock Park, 1934-69. F36 MECHANICS OF AQUIFER SYSTEMS recorded compaction or expansion of the confined aquifer Extensometers of two types are in cable type (fig. 254), an anchor weight is attached to the Core hole 7S/1E-16C6 was destroyed in 1969 during the | extensometer cable, lowered into the system for 22 years. construction of a freeway. It was replaced in 1969 by another 1,000-ft extensometer, well 78/1E-16C11. Sheaves mounted in teeter bar feria ~* Recorder _._ _> A use (fig. 25). In the well, and set below the bottom of the well casing. This anchor acts as a depth bench mark. The extensometer cable is maintained Compaction tape --_|| Counterweights ___ Steel table ----- - Clamp Bench mark --a Concrete :>-* ~ ths y-: slab. =~ Cable, 1/8-inch stainless steel, 1 x 19 stranded reverse lay Well casing 4 to 13 inches -Anchor weight, 200 to 300 pounds, in open ho le Extensometer pipe Extensometer pipe cemented in open hole FIGURE 25.-Recording extensometer installations. A, Anchored cable assembly. B, Pipe assembly. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F37 (ideally) under constant tension by a counterweight at the land surface. As the aquifer system compacts, an q equivalent length of cable appears to emerge from the b well; this movement is measured by a mechanical recorder \ attached to the compaction cable at land surface. In the a free-standing pipe extensometer (fig. 25B), the pipe is X \ \s lowered into the well and set below the bottom of the well \ casing. A mechanical recorder attached to the exten- \ \ b \ someter pipe measures the movement of the land surface § relative to the nonmoving pipe and thus measures the compaction or expansion of the aquifer system. The accuracy of the compaction record is dependent largely on the ability of the extensometer cable or pipe to maintain a constant length between the bottom-hole reference point and the above-ground reference point. Friction tends to develop between the extensometer cable or pipe and the deforming well casing, which shortens and moves downward in the grip of the compacting sediments. Because of its much greater cross section, the pipe is more competent than the cable to resist frictionally induced length changes. Therefore it generally produces a better record in typical wells of moderate depth, but other fac- tors may be involved in selecting the design for a specific site. When initally installed, all the extensometers were of the anchored-cable type. To reduce the friction problem | | | MARCH FEBRUARY 1982 F JANUARY DECEMBER NOVEMBER OCTOBER and increase the accuracy of measurement, the three L-? 1g é paired Sunnyvale extensometers (68/2W-2403, C4, and Y a) |= C7) and 78/1E-16C11 in San Jose were modified in the { # Well 16C11 has 6-in. casing, the other three have 4-in. casing. S The kind of field record being obtained in 1981 at the bs R multiple extensometer site at Sunnyvale (wells 68/2W- 2403, C4, and C7) is illustrated in figure 26. The com- (r paction was recorded on a chart with a vertical scale Xx S1 \ August 1981 early 1970's by replacing the anchored cable with a free- standing pipe of 1.5-in. diameter (fig. 25B) in the casing. \ ~ \ x 25 \ & JULY JUNE (compaction) of 10:1 and a horizontal scale of 10 days/in. j The compaction records from the three extensometers ~\\ & were traced on a common chart base for a 1-year period \ SS t from March 20, 1981, to March 26, 1982. The maximum FIGURE 26.-Elastic response of multiple extensometers at the Sunnyvale site 6S/2W-24C, 1981-82. compaction occurred on October 3, 1981. o [SX Compaction and expansion in feet [minus (-) indicates expansion] x C4 cs CT 3 Date (250 ft) (550 ft) (1,000 ft) 4/1/81 0 0 0 esyf Sy 10/3/81 0.015 0.061 0.076 yooss \\\ 3126/82 -.015 -.061 -.076 : g Net change f & from 4/1/81 CK to 3/26/82 0 0 0 Pso f R These compaction plots are of interest for two reasons. > 7 lg & | First, they illustrate the sensitivity of the recording f 6 % 1334 NI Ni 3INVHI F38 extensometers to very small changes in applied stress. Secondly, we can see from the plots in figure 26 that the measured compaction from April 1, 1981, to March 26, 1982, at the Sunnyvale site all occurred within the elastic range of stress; that is, no permanent deformation occurred in the aquifer systems.. Continuous or periodic water-level measurements are also necessary in a subsidence-monitoring program in order to define the cause-and-effect relationship of the subsidence process. Moreover, in order to produce reliable stress-strain or stress-compaction plots that can be utilized to derive storage and compressibility characteristics of the aquifer system, water-level measurements must repre- sent the average change in stress in the compacting inter- val being measured. At the Sunnyvale site, for example, wells 2404 (250-ft depth) and 24C3 (550-ft depth) are open-bottom blank casings drilled primarily as extensometers. Periodic water-level measurements have been made and are recorded in the computer plots of field records (figs. 32, 34, 36) and supplementary records of 1980-82 (figs. 43, 44). The hydrograph for the 250-ft well (2404) shows an annual fluctuation of about 50 ft and may be a fair representation of stress change for the confined depth interval from 200 to 250 ft (fig. 324). The hydrograph for the 550-ft well (2403), on the other hand, was very slug- gish from 1964-74 (fig. 344) and is not considered reliable as a measure of stress change in the depth interval 250 to 550 ft. The Geological Survey terminated field monitoring of compaction and water-level change on this study in January 1983. At that time, extensometers were in use in five wells at two compaction and water-level monitor- ing sites (wells 68/2W-2403, C4 and C7 in Sunnyvale and MECHANICS OF AQUIFER SYSTEMS wells 7S/1E-16C5 and C11 in San Jose; for location, see fig. 1). The five wells will continue to be monitored by the Santa Clara Valley Water District for compaction of the aquifer system and water-level change. The net annual compaction or expansion (negative com- paction) at each site for the entire period of record through 1982 is summarized in table 3, as are records of compaction or expansion in two additional depth inter- vals defined by multiple-depth installations. For example, at 6S/2W-24C, wells C3, C4, and C7 are respectively 550, 250, and 1,000 ft deep. The extensometer in well C7 records total compaction from land surface to the 1,000-ft depth, and the extensometer in C3 measures the com- paction from land surface to the 550-ft depth. By sub- tracting the compaction in C3 from that in C7, the compaction of the 550- to 1,000-ft depth interval is calculated. The marked decrease in the annual compaction in response to the substantial head recovery since 1966 is demonstrated graphically by the compaction records from the two deep extensometers in Sunnyvale and San Jose (fig. 27). The annual compaction in well 78/1E-1606-11 in San Jose decreased from about 1 ft in 1961 and 1962 to 0.24 ft in 1967 and to 0.01 ft in 1973. Net expansion (land-surface rebound) of 0.02 ft occurred in 1974. In 1976 the drought caused a sharp decline of artesian head (fig. 40), which in turn increased compaction to 0.11 ft at the San Jose site. In Sunnyvale, compaction of the aquifer system in well 2407 decreased from about 0.45 ft in 1961 to 0.04 ft in 1973; net expansion of 0.016 ft and 0.04 ft occurred in 1974 and 1975, respectively. The subsidence of surface bench marks from 1960 to 1967 (or 1969), plotted on the long-term compaction plots for wells 68/2W-2407 (fig. 38) and 78/1E-1606-11 (fig. TABLE 3.-Annual compaction at compaction- [In order to arrive at consistent sums, the amount of annual compaction is shown to 0.001 ft; however, many F Anchor Depth Start $". depth . of ©1060 - io6t 1967 1b6a. 1965» lope A967 number installed (feet) record (feet) 6§/1W-23B1--- | 425 ocsss aylofss O.isl 0.970 0.253 o.1M9 0.158 Q.las 0.145 0.027 68/2%-2404--- - 250 0-250 1/29/60 ipar - lose - i040 "bso oss" "gis ~.om.. .of -~ 530 ~ 1/29760 $200 2 sle.a tog tags. mias aos ~ 178" or0 ~24e3=-- - $50 0-550 _ 1/29/60 . boo - tems iss". mor t N22. - aos" -24C7--- 1,000 550-1,000 _ 6/30/60 ais " as:o" Gaga (14k Af6 -24G7--- 1,000 _ 0-1,000 - 6/30/60 case i330 "ware arage - els _ 605 0-605 _ 5/5/60 Toos ' 39s s ads: 1.047 605 Pegos. 1/14/65 .210 _ .200 .087 7S/1E-16C5--- 908 0-908 _ 8/16/60 - "corp: - .499 adomes.307 + 418 ° «226 ~l6ce-==. 1.000; : 0-1,000. " 6/30/60 loser t-0or ° 23090 1506 "410 477. .936 1,000 _ 0-1,000 _ 6/2/69 Record ends April 22, 1963 (equipment failure) 2Ssite abandoned May 1978 3C6 record ends June 2, 1969, and Cll starts on June 2, 1969 LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 41), demonstrates that the measured compaction to the 1,000-ft depth is approximately equal to the measured sub- sidence as determined by bench-mark surveys. The close agreement of the compaction and subsidence values at the Sunnyvale and San Jose sites is shown in table 5. At the San Jose site (1606), measured subsidence from October 1960 to May 1969 was 4.21 ft, and measured compaction for the same time period was 4.17 ft; thus the ratio of com- paction to subsidence was 99 percent, which means that all of the subsidence is due to the measured compaction to the 1,000-ft depth. ANALYSIS OF STRESSES CAUSING SUBSIDENCE Increase in effective stress (grain-to-grain load) is the cause of compaction of sediments. The withdrawal of water from wells reduces the head in the aquifers that are tapped and increases the effective stress borne by the aquifer matrix. The reader interested in a quantitative analysis of stresses causing subsidence is referred to Lofgren (1968) and to Poland and others (1975, p. 39-44). In summary, water-level fluctuations change effective stresses in the following two ways: (1) A rise of the water table provides buoyant support for the grains in the zone of the change, and a decline removes the buoyant support; these changes in gravitational stress are transmitted downward to all underlying deposits. (2) A change in posi- tion of either the water table or the artesian head, or both, may induce net vertical hydraulic gradients across con- fining or semiconfining beds and thereby produce a net seepage stress. The vertical normal component of this stress is algebraically additive to the gravitational stress that is transmitted downward to all underlying deposits. A change in effective stress results if the preexisting measuring sites in north Santa Clara County F39 seepage stress across the bed is altered in direction or magnitude. The change in applied stress within a confined aquifer system, due to changes in both the water table and the artesian head, may be summarized concisely (Poland and others, 1972, p. 6) as Apq = -(Are - AhyY¥3), where p, is the applied stress expressed in feet of water, h, is the head (assumed uniform) in the confined aquifer system, A, is the head in the overlying unconfined aquifer, and Y, is the average specific yield (expressed as a decimal fraction) in the interval of water-table fluctuation. EXAMPLE OF STRESS-STRAIN GRAPH Field measurements of compaction and correlative change in water level serve as continuous monitors of sub- sidence and indicators of the response of the system to change in applied stress. They also can be utilized to con- struct stress-compaction or stress-strain curves from which, under favorable conditions, one can derive storage and compressibility characteristics of the measured part of the aquifer system, as demonstrated by Riley (1969). Nineteen years (1960-79) of measured water-level change (well 78/1E-16C5) and compaction (well 7S/1E- 16C6-11) in San Jose are shown in figure 41, together with a computer plot of stress change versus strain. Well 16C5 is 908 ft deep, and compaction in well 16C6-11 is measured to 1,000 ft, spanning the full 800-ft thickness of the aquifer system from the 200- to the 1,000-ft depth. As the water levels at this San Jose site rose rapidly after 1967 (fig. measured yearly values are not accurate to less than a few hundredths of a foot. Minus (-) indicates expansion] Total foss . 1960) 1970 1977 ios i076 i977. tors. loro ~i980" idk. gas. hensured compaction (feet) 0.028 -0.022 -0.031 : 0 0.024 -0.021 -0.024 -0.012 0.043 0.018 -0.027 0.003 1.536 .009 0. - .044 -.027 }-.006 =.002' -.b05 ©.004«" - .003 -.003 -.005 -0.001 6.003 -0.005 .298 084 > -.008"£.032.. .0f8' -.0r3 -.016> lo>> =.o02 - :001 -.002 " =2005 1.103 {073% 021". .Oo0t =.012}.001 _ =:020 <~.022 : -.02 026 : ;001" -.002 '<.001 -.010 1.401 O92 .020 _.0l8 ".024. .o60 - -:0ve '" O25 -.oo8 . i023 ".O0f -=-.00%- .o08 =2001 1.573 165> ' +102 . .030° . .025 ~ .040 --.016 =.037 | 021 0 . *.007 7 : 013 - 2.948 .882 ® 038 . .0G10 ..007-. .057 - -.003% =-.015 -.:014": 043: 2.036 .693 " fO054 : .044 '- .106 ' .123%. 030 . ;.Q21. 1026 2.005 cros?" ' =.b27 88.080 : =:038 4.319 129" #1023 4.443 more i050 ~.007i.=.01t9 '.0olV ~ 11s" ';043. ".006. .o42 -.O>8 -.035 .439 F40 41A), the stress-strain curves obtained from the paired measurements of compaction and artesian head began to show seasonal expansion during the winter months when the water level was highest and the effective stress on the confined system was lowest (fig. 41D). These stress- strain loops can be used to obtain the compressibility of the confined system in the recoverable or elastic range of stresses (less than preconsolidation stress). The stress- strain curve for 1967-74 has been enlarged in figure 28. Depth to water is plotted increasing upward. Change in depth to water represents an average change in stress in all aquifers of the confined aquifer system tapped by well 16C5. The lower parts of the descending segments of the annual loops for the winters of 1967-68, 1969-70, and 1970-71 are approximately parallel, as shown by the dotted lines, indicating that the response is essentially elastic in both aquifers and aquitards when the depth to water is less than about 180 ft. The heavy dashed line drawn parallel to the dotted lines represents the average slope of the segments in the range of stresses less than preconsolidation stress. The reciprocal of the slope of this MECHANICS OF AQUIFER SYSTEMS line is the component of the storage coefficient attribut- able to elastic or recoverable deformation of the aquifer- system skeleton, S;,, and equals 1.5 x 10-8. The component of average specific storage due to elastic deformation, Sy,,, equals ft = 1.87 x 10-S/ft. If stresses are expressed in feet of water, and if y,, (the unit weight of water) equals unity, the average elastic com- pressibility of the aquifer system skeleton, az,, is equal numerically to Ss,. In these computations we have assumed that in the range of stresses less than preconsolidation stress, the compressibility of the aquitards and of the aquifers is the same. Therefore, the full thickness of the confined aquifer system, 800 ft, was used to derive the average specific storage component, S;;,,, in the elastic range of stress. COMPUTER SIMULATION OF AQUIFER-SYSTEM COMPACTION As stated by Helm (1978), land subsidence due to ground-water withdrawal from a confined aquifer system 5 f ae f § 1T: -t -T 3 SUNNYVALE WELL 6GS/2W-24C7 st J 1 tat -t ET -~ 17 COMPACTION, IN FEET WELLS 7$/1E-16C6 and C11 SAN JOSE 1962 1964 1966 1968 1970 1972 1974 1976 YEAR FIGURE 27.-Measured annual compaction in wells 1,000 ft deep in Sunnyvale and San Jose. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 is an expression at land surface of net compaction (ver- tical consolidation) at depth of compressible layers within the system. Water-level fluctuations within coarse-grained aquifers produce stress changes on the upper and lower boundaries of slow-draining aquitards (compressible fine- grained interbeds). Indirectly, irregular and cyclic pump- ing drawdowns generate complex loading and unloading stress patterns in the aquifer system, causing compaction and expansion of the aquitards. Within a confined system, any lag in compactive response to such a load increase is usually ascribed to slow vertical drainage from the aquitards. After water levels in coarse-grained material rise during a period of water-level recovery, it has been observed during the next cycle of declining water levels that nonrecoverable compaction is reinitiated before water levels reach their prior lowest level. Helm (1977) developed a one-dimensional mathematical model of vertical deformation based on a modification of Karl Terzaghi's consolidation theory; the model computes transient aquitard compaction and expansion due to arbi- trarily specified changes in effective stress within an FAl adjacent aquifer. This model has been applied by Helm (1977) to observed water-level fluctuations and to the resulting observed transient compaction-and-expansion behavior of the confined aquifer system at seven sites in the Santa Clara Valley. According to Helm, values for total cumulative thick- ness b'sy;p of fine-grained interbeds within the confined aquifer system, the weighted-average thickness b'equiy of these interbeds, recoverable vertical compressibility Si,, and the initial distribution of preconsolidation pressure P max (@, 0) must be approximated from field data in- dependently of any subsequent simulation process. Only values for vertical components of hydraulic conductivity K' and nonrecoverable compressibility Si,, are adjusted by trial-and-error to fit calculated-to-observed compaction history. The estimated values for K' at the sites studied range from 0.56 x 10-8 to 12.5 x 10-8 ft/d, those for Ssp, range from 1.4 x 10-4 to 13.1 x 10-4/ft, and those for S5, range from 2.2, x 10-8 to 15.8x 10=U/ft (table 4). For established values of b'sum , b' equiv» 204 P max (¢) 0), 340 T T T T 300 |- 260 220 180 DEPTH TO WATER, IN FEET 140 100 60 1 1 1 | 0 0.4 1.0 0.6 COMPACTION, IN FEET FiGuRE 28.-Stress change and compaction, San Jose site. Depth to water in well 7S/1E-16C5, and compaction in well 7S/1E-16C6-11. FA2 MECHANICS OF AQUIFER SYSTEMS TABLE 4.-Values of parameters used for simulating observed compaction at selected sites in north Santa Clara County [Modified from Helm (1977, table 1)] Period of record Estimated thickness Estimated values of parameters (years) (feet) Site of water-level M K' S' S' data Water-level Compaction Total Weighted £ 6 1 sku L4 1 ske 6 data data b" x10~ x10~ sum F day foot foot equiv 6S/1W-23E1l 1958-72 1958-72 189 15.1 1.18 1.4 7«2 6s/2wW-2403 1960-72 1960-72 225 18 56 13.1 3.96 68s 1960-72 1960-72 422 53.1 12.5 3.35 2.60 68s/2W-25C1 1960-72 1960-72 255 18 19 3.26 15.8 68s/2w-25C1 1921-74 1932-74 255 18 12 3.29 -- 7S/1E-7RL 1915-74 1916-74 477 18 1.87 2.29 -- 78/1E-9D2 1958-72 1960-63, 258 18 . 82 6.1 7.92 1965-72 7S/1E-16C5 1958-72 1960-72 477 18 3.28 2.3 2.2 Helm (1977, figs. 9, 10) demonstrated that carefully evaluated values of K' and S,, can be used to predict aquifer-system behavior with reasonable accuracy over periods of several decades. A good example of the simula- tion result for six decades of record using values listed in table 4 is shown in figure 29 (from Helm, 1977, fig. 10). COMPACTION-SUBSIDENCE RATIOS The amounts of measured compaction and measured subsidence at extensometer sites where leveling data are available are shown in table 5. The ratio of measured com- paction to measured subsidence, expressed as a percent- age, was computed for the period of record available. Percentages are sometimes erratic for short periods of control at some sites, as shown by table 5; some periods of measured compaction and leveling are combined to make the compaction/subsidence ratios more consistent, and some are not shown as a result of incomplete data or mechanical problems at the extensometer site. At extensometer site 68/2 the compaction/sub- sidence ratio for the full period of the leveling record (November 1960 to February 1967) increased from 11 per- cent for C4 (the 250-ft extensometer) to 50 percent for C3 (the 550-ft extensometer) and to 105 percent for C7 (the 1,000-ft extensometer). For the shorter periods between levelings, the ratio for 2403 was surprisingly consistent, whereas the ratio for 2404 was erratic. For extensometer 24C7, the measured compaction during each of the shorter periods exceeded the measured sub- sidence and averaged 105 percent for the six years to February 1967. The 5-percent excess is attributed to mechanical problems in recording the compaction. At extensometer site 7S/1E-16C5 (908 ft deep) the aquifer system is about 800-ft thick, from 200 to 1,000 ft below land surface. If the compaction potential was uniform with depth, the part measured by extensometer 16C5 would be 708/800, or 88 percent of the subsidence. Actually, for the 8.5 years from October 1960 to May 1969 the compaction measured at 16C5 equaled 87 percent of the subsidence. At extensometer site 7S/1E-16C6, the extensometer cable anchor was landed at the 1,000-ft depth, believed to be the bottom of the aquifer system. For the full 8.5-year period to May 1969, the measured compaction was equal to 99 percent of the subsidence, indicating that the anchor truly was landed at the base of the compact- ing system. f In the 13.5 years from May 1969 through 1982 the cu- mulative compaction at the two 1,000-ft extensometers, 6S/2W-24C7 in Sunnyvale and 78/1E-16C6-11 in San Jose, was 0.24 ft and 0.44 ft, respectively (table 3). Dur- ing the six years 1977 to 1982, inclusive, the cumulative compaction was very small, about 0.03 ft at 68/2 W-240C7 and 0.07 ft at 78/1E-160C6-11. & A.K. Williamson (U.S. Geological Survey, oral commun., 1981) noted an interesting relationship in the San Joaquin Valley between extensometer depth and the compaction- subsidence ratio (Ireland and others, 1984, p. 153 and fig. 67). We have plotted a similar figure for the few exten- someters in north Santa Clara County (fig. 30). Compac- tion/subsidence ratios based on the full period of available ,_ LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 records were used in preparing figure 30. Although there were only seven ratios to plot, they surveyed a wide range of extensometer depths: one was at shallow depth, three were at mid-depth (400 to 600 ft deep), and three were at full depth of the aquifer system (about 1,000 ft). All were centrally located within the confined system and at either of the two centers of maximum subsidence. Together, they defined a relatively "tight" curve, which indicates that all the compaction due to ground-water withdrawal occurs at depths between about 200 and 1,000 ft. Between these depths the compaction/subsidence ratio is shown to approximate a linear function of the logarithm of the depth. The least-squares regression equation of the function has an R-squared value of 0.95, which indicates that 95 percent of the variation of the ratio is explained by the equation, whereas 5 percent of its variation is ran- dom (or attributable to other factors not considered). On the basis of the relation shown in figure 30, a 300-ft extensometer in a subsidence area in the Santa Clara Valley would record approximately 18 percent of the total subsidence measured at the well site, and a 700-ft exten- someter would record approximately 72 percent of the total subsidence at the site. F43 COMPUTER PLOTS OF FIELD RECORDS The records of compaction and of depth to water in the extensometer wells or in nearby observation wells have been computerized on a daily basis, and computer plots of these records through 1979 are included here as figures 31-42. Graphs of subsidence of a surface bench mark located at the measuring site, determined by periodic instrumental surveys to a stable bench mark, are also in- cluded for the first part of the period of compaction measurements. (No bench-mark surveys have been made since 1969.) Site locations are shown in figure 1. The Geological Survey continued collecting field records of compaction and depth to water at these sites in the three years 1980-82 (figs. 43-48). Early in 1983 the opera- tion and maintenance of the principal sites was taken over by the Santa Clara Valley Water District. The computer program and extensometer and water- level data collected on this long-term (mechanics of aquifers) study on land subsidence are stored on computer tape Number 220691, type 6250BPI, at the U.S. Geo- logical Survey Information Services Division, Reston, Virginia. l.— z tt . 200 mommy mT - < u (G 600 Boundary stress # (H5 > 2 NM 7S/1E-7R1 w 5.9513800 (Sls tel t - bse et o [OSL tor t t ef gs orer £ t eff 11.14 _L. LLL J AM (Lat 1-1 & o T TJ PLI YT THI LJ L1 1-191 19 Tle fT 4 f TJ Telugu 1 4- T JLL FT Ts T T e Compaction 's 2 |- wl 3 - - - & - 4 [- [ it Observed < 5 /] az s =] 6 6 E) TF Calculated/ < m a o -l "£ ao O. SF 3 10 A 11k = 12 |- ‘ - 13 KL LS) tS 3 f Sp p p T TL 1p (3 4 LSA OLT ORE TSP [ p OI J Of L 111. i- L L | 1920 1930 1940 1950 1960 1970 FIGURE 29.-Simulation of compaction based on water-level data for well 7S/1E-7R1 (1915-74) and on subsidence measured at bench mark P7 (from Helm, 1977, fig. 10). FA44 MECHANICS OF AQUIFER SYSTEMS TABLE 5.-Compaction versus subsidence for periods of leveling in north Santa Clara County [Ratio of compaction/subsidence: value shown on total line is ratio for period of record] B £ Ratio of Extensometer Depth egik Dates of Subsidence Compaction compaction number (feet) $s leveling (feet) (feet) to subsidence number (percent) 68 /1W-23E1 425 A176 11/60-2/67 2.392 1.033 43 68 250 J111 11/60-2/63 . 807 .091 11 2/63-4/65 . 683 . 085 12 4/65-2/67 544 045 8 sare neat sels rs s 2.034 w22l 11 6s /2w-2403 550 J111 11/60-2/63 . 807 «414 51 2/63-4/65 . 683 341 50 4/65-2/67 544 267 49 Total. aa % s vis. 2.034 1.022 50 68 1,000 Jll 11/60-2/63 . 807 .845 105 2/63-4/65 . 683 ©1138 108 4/65-2/67 . 544 547 101 .r ir¥ a @a %> +1 rss aa 2.034 2.130 105 7S/1E-9D2 605 JG4 10/60-2/63 1.552 162 48 2/63-2/67 1.551 C) 2/67-5/69 - 230 118 51 7S/1E-16C5 908 JG2 10/60-2/63 1.919 1.677 87 2/63-3/67 1,923 - 1.604 83 3/67-5/69 366 365 100 TOCA... «+x «@ sizcs s 8 5% % 4.208 3.646 87 7S/1E-16C6 1,000 JG2 10/60-3/67 3.842 3.812 99 3/67-5/69 366 1363 99 TOLal. .s. «r sss s aos 4.208 #.175 99 'No extensometer data from 4/22/63 to 6/18/65. The primary purpose of including these records is to show graphically the measured compaction and sub- sidence at specific sites, and (so far as possible) the change in effective stress in the pertinent aquifers at these sites, as indicated by the hydrographs. Because of the confin- ing beds and multiple-aquifer/aquitard system, it is dif- ficult to obtain water-level measurements that specifically represent the average stress change for the interval in which compaction is being measured. Change in applied stress and stress-compaction or stress-strain relationships are plotted for figures 31-41. In these figures, compaction equals the change in thick- ness of the compacting interval, and strain refers to the compaction divided by the thickness of the compacting interval. As indicated in table 6, stress-strain relationships are shown for figure 31 (extensometer 68/1W-23E1) and for figures 40 and 41 at the San Jose core-hole site (extensometers 78/1E-16C05 and 1606-11, respectively). LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F45 120 I l & 100 |-- <-- o & RATIO (%) = 149(LOG1q DEPTH)-352 i- a L1 & 80 |-- = PH a 3 uud C a Lad o m co m in &" 60 -l +- a G < C < ol p33 o C& Laz o & ' "40 |-- =- mad < oc EXPLANATION ag! © extensometer we SHI 0 | 0 200 400 600 800 1000 1200 DEPTH OF EXTENSOMETER, IN FEET FicuRE 30.-Compaction/subsidence ratios versus depth at extensometer wells in north Santa Clara County. SELECTED REFERENCES California Department of Water Resources, 1967, Evaluation of ground- Atwater, B.F., Hedel, C.W., and Helley, E.J., 1977, Late Quaternary water resources, South San Francisco Bay, appendix A, Geology: depositional history, Holocene sea-level changes, and vertical crustal Bulletin 118-1, 153 p. movement, southern San Francisco Bay, California: U.S. Geological 1975, Evaluation of ground water resources, South San Fran- Survey Professional Paper 1014, p. 1-15. cisco Bay, v. 3, Northern Santa Clara County area: Bulletin 118-1, California State Water Resources Board, 1955, Santa Clara Valley 133 p. (contains 11 geologic sections, fault map, and 10 sheets of investigation: Bulletin 7, 154 p. subsurface deposits by depth intervals). F46 Clark, W.0., 1924, Ground water in Santa Clara Valley, California: U.S. Geological Survey Water-Supply Paper 519, 209 p. Dibblee, TW., 1966, Geologic map and sections of the Palo Alto 15-minute quadrangle, California: California Division of Mines and Geology, map sheet 8. : Fowler, L.C., 1981, Economic consequences of land surface sub- sidence: Journal of Irrigation and Drainage Division, Proceedings of the American Society of Civil Engineers, v. 107, no. IR2, p. 151-158. Green, J.H., 1962, Compaction of the aquifer system and land subsidence in the Santa Clara Valley, California: U.S. Geological Survey Pro- fessional Paper 450-D, p. 175-178. _____ 1964, The effect of artesian-pressure decline on confined aquifer systems and its relation to land subsidence: U.S. Geological Survey Water-Supply Paper 1779-T, 11 p. Helm, D.C., 1977, Estimating parameters of compacting fine-grained interbeds within a confined aquifer system by a one-dimensional simulation of field observations: International Association of Hydrological Sciences, International Symposium on Land Sub- sidence, 2d, Anaheim, California, December 1976, Publication 121, p. 145-156. ___ 1978, Field verification of a one-dimensional mathematical model for transient compaction and expansion of a confined aquifer system, in Verification of mathematical and physical models in hydraulic engineering: American Society of Civil Engineers, Proceedings of Specialty Conference, College Park, Maryland, p. 189-195. Hunt, G. W., 1940, Description and results of operation of the Santa Clara Valley Water Conservation District's project: American Geophysical Union Transactions, part 1, p. 13-32. Ireland, R.L., Poland, J.F., and Riley, F.S., 1984, Land subsidence in the San Joaquin Valley, California, as of 1980: U.S. Geological Survey Professional Paper 487-1, 93 p. Jennings, C.W., and Burnett, J.L., 1961, Geologic map of California, Olaf P. Jenkins, ed.: California Division of Mines and Geology, San Francisco sheet, scale 1:250,000. Johnson, A.I., Moston, R.P., and Morris, D.A., 1968, Physical and hydrologic properties of water-bearing deposits in subsiding areas in central California: U.S. Geological Survey Professional Paper 497-A, 71 p. Lofgren, B.E., 1968, Analysis of stresses causing land subsidence: U.S. Geological Survey Professional Paper 600-B, p. B219-B225. Meade, R.H., 1967, Petrology of sediments underlying areas of land sub- sidence in central California: U.S. Geological Survey Professional Paper 497-C, 83 p. 1968, Compaction of sediments underlying areas of land sub- sidence in central California: U.S. Geological Survey Professional Paper 497-D, 39 p. Poland, J.F., 1969, Land subsidence and aquifer-system compaction, Santa Clara Valley, California, USA, in Tison, L.J., ed., Land sub- sidence, v. 1: International Association of Scientific Hydrology (is now International Association of Hydrological Sciences) Publication 88, p. 285-292. _____ 1977, Land subsidence gtopped by artesian-head recovery, Santa Clara Valley, California: International Association of Hydro- logical Sciences, International Symposium on Land Subsidence, 2d, Anaheim, California, December 1976, Publication 121, p. 124-132. 1984, Case history No. 9.14, Santa Clara Valley, California, USA, in Poland, J.F., ed., Guidebook to studies of land subsidence due to ground-water withdrawal: United Nations Educational, MECHANICS OF AQUIFER SYSTEMS Scientific and Cultural Organization, 7 Place de Fontnoy, 75700 Paris, France, p. 279-290. Poland, J.F., and Davis, G.H., 1969, Land subsidence due to the withdrawal of fluids: Geological Society of America, Reviews in Engineering Geology, v. 2, p. 187-269. Poland, J.F., and Green, J.H., 1962, Subsidence in the Santa Clara Valley, California-A progress report: U.S. Geological Survey Water-Supply Paper 1619-C, p. C1-C16. Poland, J.F., Lofgren, B.E., Ireland, RL., and Pugh, R.G., 1975, Land subsidence in the San Joaquin Valley, California, as of 1972: U.S. Geological Survey Professional Paper 437-H, 78 p. Poland, J.F., Lofgren, B.E., and Riley, F.S., 1972, Glossary of selected terms useful in studies of the mechanics of aquifer systems and land subsidence due to fluid withdrawal: U.S. Geological Survey Water- Supply Paper 2025, 9 p. Riley, F.S., 1969, Analysis of borehole extensometer data from central California, in Tison, L. J., ed., Land subsidence, v. 2: International Association of Scientific Hydrology (is now International Associa- tion of Hydrological Sciences) Publication 89, p. 423-431. Rogers, TH., 1966, Geologic map of California, Olaf P. Jenkins, ed.: California Division of Mines and Geology, San Jose sheet, scale 1:250,000. Rogers, TH., and Williams, J. W., 1974, Potential seismic hazards in Santa Clara County, California: California Division of Mines and Geology, Special report 107, 39 p., 6 pl. Roll, J.R., 1967, Effect of subsidence on well fields: American Water Works Association Journal, v. 59, no. 1, p. 80-88. Santa Clara Valley Water Conservation District, 1964, Hydrologic data for north Santa Clara Valley (California), seasons of 1935-36 to 1960-61, v. 3, surface-water summary and ground-water fluctua- tion: Santa Clara Valley Water Conservation District, mimeo report, p. 828-1230. ___ 1967, Hydrologic data for north Santa Clara Valley (California), seasons of 1961-62 to 1965-66, v. 4, precipitation, evaporation, reservoir fluctuation, surface-water flow, surface-water summary, ground-water fluctuation, and ground-water quality: Santa Clara Valley Water Conservation District, mimeo report, p. 1231-1705. ___ 1977, Historical ground-water level data, 1924-1977: Santa Clara Valley Water District, mimeo report, 423 p. Tibbetts, F.H., and Kieffer, S.E., 1921, Report to Santa Clara Valley Water Conservation Committee on Santa Clara Valley Water Con- servation project: Santa Clara Valley Water Conservation District, unpublished typwritten report, 243 p. Tolman, C.F., 1937, Ground water: New York, McGraw-Hill, first edition, 593 p. _ Tolman, C.F., and Poland, J.F., 1940, Ground-water, salt-water infiltra- tion, and ground-surface recession in Santa Clara Valley, Santa Clara County, California: American Geophysical Union Transactions, pt. 1, p. 23-85. U.S. Bureau of Reclamation, 1961, Central Valley Project, San Felipe Division geology and ground-water resources appendix: U.S. Bureau of Reclamation, Geology Branch, Project Development Division, 118 p. U.S. Coast and Geodetic Survey, 1956, San Jose area, California, 1912-54 leveling (190A California); 42 p. (A compilation of adjusted elevations for all bench marks in the level network.) Webster, D.A., 1973, Map showing areas bordering the southern part of San Francisco Bay where a high water table may adversely affect land use: U.S. Geological Survey Miscellaneous Field Studies Map MF-530, scale 1:125,000. FIGURES 31-48; TABLE 6 F48 MECHANICS OF AQUIFER SYSTEMS -lm EG aw 0 © = 40 # Ew 80} -- o 120 € o § 160 E @ 200 & & 240 8 - CHANGE IN APPLIED STRESS, IN FEET OF WATER i: -0.5 £ # oo 7 = 05 00 & # 10 0.5 u 2 is 10 & 3 20 5 15 8 # 2s > f ye : S 30 25 a 1958 1959 1960 1961 1962 1963 1964 1965 96s 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 ig7g 1979 1980 C 200 s passt S% 160 7 a-" Ais bt Neo J’W‘ KW/AfiLX \\'~ {7 Ay *A v.‘)/\’ \,_1 ay /\\/ Tx y ‘k/ 120 |- ~". * yl ~* % y / 1 eA ~" \ 1961 zf 1962 1963 1964 ra e so . & f 1958 5/ 1959 £5 1960 J Stress-strain 40 0 a a a a _i a a a a i a a a 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 7510" STRAIN D FIGURE 31.-Hydrograph, change in applied stress, compaction, subsidence, and stress-strain relationship, 6§8/1W-23E1. A, Hydrograph of well 6S/1W-23E1, perforated 170-177, 244-255, 311-315, and 343-350 ft. B, Change in applied stress, water table assumed constant. C, Compac- tion to 425-ft depth at well 6S/1W-23E1 and subsidence of bench mark A176, 0.6 mi west. D, Stress change versus strain (225-ft thickness). CHANGE IN APPLIED STRESS, IN FEET OF WATER LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F49 sS588 o ho ho =a -a 4 o DEPTH TO WATER BELOW LAMD SURFACE, IN FEET o OF WATER @ rn c m 00 0 © STRESS, IN FEET CHANGE IN APPLIED =~ze8m in 0 in 0 in IN FEET COMPACTION, 1960 1961 1962 1963 1964 1965 1966 1967 1968 1ig69 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 C o o 120 80 40 00 0.1 0.2 0.3 0.4 COMPACTION, IN FEET D CHANGE IN APPLIED STRESS, IN FEET OF WATER FIGURE 32.-Hydrograph, change in applied stress, compaction, and stress-compaction relationship, 6S/2W-24C4. A, Hydrograph of well 6S/2W-24C4, depth 250 ft. B, Change in applied stress, water table assumed constant. C, Compaction to 250-ft depth at well 68/2W-24C4. D, Stress change versus compaction of deposits above 250-ft depth. F50 MECHANICS OF AQUIFER SYSTEMS 40 80 120 160 200 240 DEPTH TO WATER BELOW LAND SURFACE, IN FEET 40 80 120 160 200 stress CHANGE IN APPLIED STRESS, IN FEET OF WATER -0.5 0.0 0.5 1.0 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 C COMPACTION, IN FEET 120 Stress-compaction 80 40 0 0 01 06.2 20.3 0A COMPACTION, IN FEET D FicurE 33.-Hydrograph and change in applied stress, 6S/2W-25C1; compaction and stress-compaction relationship, 6S/2W-24C4. A, Hydrograph of well 68/2W-25C1, depth 500 ft. B, Change in applied stress, 6§/2W-25C1, water table assumed constant. C, Compaction to 250-ft depth at well 6S/2W-24C4. D, Stress change versus compaction of deposits above 250-ft depth. CHANGE IN APPLIED STRESS, IN'FEET OF WATER CHANGE IN APPLIED DEPTH TO WATER BELOW LAND SURFACE, IN FEET OF WATER STRESS, IN FEET COMPACTION, IN FEET LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F51 40 Bo 120 160 200 240 40 7 80 ; s stress 120 - 160 40 80 120 160 200 240 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1g71 1972 1973 1974 1975 1976 1977 1978 1979 1980 C 160 120 40 Stress-compaction 0 a al a a a a a a a a al 0 0.5 CTI 1.5 COMPACTION, IN FEET D CHANGE IN APPLIED STRESS, IN FEET OF WATER co o FicurE 34.-Hydrograph, change in applied stress, compaction, and stress-compaction relationship, 68/2W-2403. A, Hydrograph of well 68/2W-2403, depth 550 ft. B, Change in applied stress, water table assumed constant. C, Compaction to 550-ft depth at well 68/2W-24C3. D, Stress change versus compaction of deposits above 550-ft depth. F52 MECHANICS OF AQUIFER SYSTEMS 5 $$ . pe #$ i o$ 180 &g 200 & < 240 E S gn- 0 C&, 40 #&s 1s L - 200 & ¥ @ -0s <. OD *.. 05 a e 10 56 15 & 20 f & he 1960 _ 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 i971 1972 1973 1974 1975 ig7e 1977 1978 1979 1980 C y E., 120 = F $%. if C =S 40 Stress-compaction =E g! 0 a a a a a al a a R 4 < 0 0.5 1.0 1.5 5 COMPACTION, IN FEET D FiGUuRE 35.-Hydrograph and change in applied stress, 68/2 W-25C1; compaction and stress-compaction relationship, 6S/2W-24C3. A, Hydrograph of well 6S/2W-25C1, depth 500 ft. B, Change in applied stress, 68/2 W-25C1, water table assumed constant. C, Compaction to 550-ft depth at well 6§/2W-24C03. D, Stress change versus compaction of deposits above 550-ft depth. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F53 DEPTH TO WATER BELOW LAND SURFACE, IN FEET & a 0 co stress OF WATER no o STRESS, IN FEET 160 CHANGE IN APPLIED COMPACTION, IN FEET o o 6 in G in in 0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 COMPACTION, IN FEET 550 feet COMPACTION, IN FEET 5 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 i976 1977 1978 1979 1980 E 160 120 80 40 Stress-compaction CHANGE IN APPLIED STRESS, IN FEET OF WATER 0 0.2 0.4 0.6 0.8 1.0 1.2 COMPACTION, IN FEET F FiGurRE 36.-Hydrograph and change in applied stress, 6S/2W-2404; C, Compaction to 250-ft depth at well 68/2W-24C4. D, Compaction compaction and stress-compaction relationship, 6S/2W-24C3 and to 550-ft depth at well 6S/2W-24C3. E, Compaction in 250-550-ft depth 6S/2W-24C4. A, Hydrograph of well 6S/2W-24C4, depth 250 ft. B, interval. F, Stress change versus compaction of deposits from Change in applied stress, 6S/2W-24C4, water table assumed constant. 250-550-ft depth. F54 MECHANICS OF AQUIFER SYSTEMS # - 38 0 = _ 'D & 120 - & 160 a Z 200 E < 240 o - 2+ 0 §#& 0 < z E 80 =, % 120 82s 160 yp 200 & € m G s § a o & 3 [edi g £ & a o & -0.5 = - 0.0 5p i <% 10 35 15 o 2.0 2.5 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 E € a s 120 a & 80 &s ‘5 40 Stress-compaction E LH # a= o L o. a. a il a a a E 0 0.2 0.4 0.6 0.8 1.0 1.2 o COMPACTION, IN FEET F FiGURE 37.-Hydrograph and change in applied stress, 6S/2W-25C1; compaction and stress-compaction relationship, 6S/2W-24C3 and 6S/2W-24C4. A, Hydrograph of well 68/2W-25C1, depth 500 ft. B, Change in applied stress, 6S/2W-25C1, water table assumed constant. C, Compaction to 250-ft depth at well 6S/2W-24C4. D, Compaction to 550-ft depth at well 68/2W-24C3. E, Compaction in 250-550-ft depth interval. F, Stress change versus compac- tion of deposits from 250-550-ft depth. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F55b 40 80 120 160 200 240 DEPTH TO WATER BELOW LAND SURFACE, IN FEET 40 80 120 160 200 CHANGE IN APPLIED STRESS, IN FEET OF WATER -0.5 0.0 0.5 COMPACTION, IN FEET = in 0 in COMPACTION, IN FEET -0.5 0.0 0.5 1.0 1.5 2.0 COMPACTION, IN FEET 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 SUBSIDENCE, IN FEET 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1.0 1.2 14 1.6 1.8 € Sf ' _ *~. /" aa 3 ae 1 my I 2% so Es 25 40 Stress-compaction 3 $= ol- < 0 0.2 0.4 0.6 0.8 & COMPACTION, IN FEET FiGuURE 38.-Hydrograph and change in applied stress, 6S/2W-24C7; compaction, subsidence, and stress-compaction relationship, 6S/2W-24C3 and 6S/2W-24C7. A, Hydrograph of well 68/2W-24C7, perforated 807-851 and 880-903 ft. B, Change in applied stress, 6S/2W-24C7, water table assumed constant. C, Compaction to 550-ft depth at well 68/2W-2403. D, Compaction to 1,000-ft depth at well 6S/2W-24C7, and subsidence at bench mark J111, 400 ft southeast. E, Compaction in 550-1,000-ft depth interval. F', Stress change versus compaction of deposits from 550-1,000-ft depth. F56 MECHANICS OF AQUIFER SYSTEMS 40 80 120 160 200 240 280 DEPTH TO WATER BELOW LAND SURFACE, IN FEET 40 80 120 160 CHANGE IN APPLIED STRESS, IN FEET OF WATER COMPACTION, IN FEET 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 120 pecs Y v V\ 49 Stress-compaction CHANGE IN APPLIED STRESS, IN FEET OF WATER 0 0.1 0.2 0.3 O4 O05 O6 0.7 0.8 09 COMPACTION, IN FEET D FicurE 39.-Hydrograph, change in applied stress, compaction, sub- sidence, and stress-compaction relationship, 7TS/1E-9D2. A, Hydrograph of well 7S/1E-9D2, depth 605 ft. B, Change in applied stress, water table assumed constant. C, Compaction to 605-ft depth from May 1960 to April 1963 and from January 1965 to January 1978, C SUBSIDENCE, IN FEET 3 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 o 6 120 80 40 Stress-compaction CHANGE IN APPLIED STRESS, IN FEET OF WATER 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 COMPACTION, IN FEET € and subsidence of bench mark JG4 at well 7S/1E-9D2. D, Stress change versus compaction of deposits above 605-ft depth, May 1960 to April 1963. E, Stress change versus compaction of deposits above 605-ft depth, January 1965 to January 1968. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F57 Hm 58 a : E ud 200 = & 240 ; ® 280 E & 320 cH a - 0 Egg 40 <5; 80 Egg; 120 $25 160 200 o L § § * 1.0 € 15 E 2.0 % 2.5 & 3.0 3.5 4.0 .5 4 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 19ss 1970 1971 qg72 1973 1974 1975 1976 1977 i978 1979 1980 C Sy Y \i 0 5 10 15 20 25 30 35 40 45 STRAIN D FIGURE 40.-Hydrograph, change in applied stress, compaction, sub- 7S/1E-16C5 and subsidence of bench mark JG2, located in top of north- sidence, and stress-strain relationship, 7S/1E-16C5. A, Hydrograph east concrete curb of 12th Street, approximately 20 ft west of well of well 7S/1E-16C5, depth 908 ft. B, Change in applied stress, water TS/1E-16C5. D, Stress change versus strain (708-ft thickness). table assumed constant. C, Compaction to 908-ft depth at well CHANGE IN APPLIED STRESS, IN FEET OF WATER 63x 10° SUBSIDENCE, IN FEET F58 MECHANICS OF AQUIFER SYSTEMS H 38 a #2 120 # c 200 2 & 240 - m 280 E8 320 S s 0 2B. 4 so «*y 12 # 3&8 & 180 €E - 200 5 -0.5 0.0 0.5 x 10 0.0 #o15 05 ._ z= 20 10 & az 25 1.5 ; 2 :0 10 43 g 25 § & 40 30 & 8 45 35 8 5.0 40 a 5.5 4.5 6.0 5.0 1958 1959 1960 1961 1962 1963 1964 i965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 C Stress-strain CHANGE IN APPLIED STRESS, IN FEET OF WATER 0 5 10 15 20 25 30 35 40 45 50 55 60 63 x10°* STRAIN D FIGURE 41.-Hydrograph and change in applied stress, 7S/1E-16C5; mark JG3 from February 1963 to May 1969. (Bench mark JG2 is compaction, subsidence, and stress-strain relationship, 7S/1E-16C6-11. located in top of northeast concrete curb of 12th Street, approximately A, Hydrograph of well 7S/1E-16C5, depth 908 ft. B, Change in applied 20 ft west of well 7S/1E-16C5; bench mark JG3 is located approximate- stress, 7TS/1E-16C5, water table assumed constant. C, Compaction to ly 300 ft north of bench mark JG2.) D, Stress change versus strain 1,000-ft depth at well 7S/1E-16C6-11 (see fig. 42B) and subsidence (800-ft thickness). at bench mark JG2 from October 1960 to February 1963 and bench LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F59 40 80 120 160 200 240 280 LAND SURFACE, IN FEET DEPTH TO WATER BELOW -0.5 0.0 0.5 i 1.0 0.0 # ois 05 _ = 20 1.0 g # 25 1.5 a= 2 30 24 5 € :s 25 § 5 £ 4.0 30 a o 4.5 35 g 5.0 40 a 5.5 4.5 5.0 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 B FIGURE 42.-Hydrograph, compaction, and subsidence, 7S/1E-16C6-11. 1960 to February 1963 and bench mark JG3 from February 1963 to A, Hydrograph of well 7S/1E-16C11, perforated 551-571, 598-618, May 1969. (Bench mark JG2 is located in top of northeast concrete and 640-660 ft. B, Compaction to 1,000-ft depth at well 7S1E-16C6-11 curb of 12th Street, approximately 20 ft west of well 7S/1E-16C5; (7S/1E-16C6 from June 1960 to June 1969 and 78/1E-16C11 from June bench mark JG3 is located approximately 300 ft north of bench mark 1969 to January 1980) and subsidence at bench mark JG2 from October JG2.) 0 o-- 0 3 - Hydrogr'aph, 2403 g 5 Hydrograph, 2404 QH | 40 e <4 40 . } : ATT - $; s" . %4 a i' u 80 Bw so zé J §< & u. it 120 o § 120 22 - a To 160 E9 180 55 E u < 13 - A- 200 ppg ppg ag ba $000 54008 0404, 324520008103 4.3304 303448 41 3 30600040954 94-4 4 200 Lica 02025220 ] 00522303005 30403000 1 A A 1.1 room- 0.0 tg: "1.2 5 0.1 4 [rd 2 1.3 z 0.2 z Compaction, 0-550 feet z Compaction, 0-250 feet 6 1.4 ___ - 0 0.3 €ons & 0.4 g a 3 1.6 8 o.s 1.7 Lega cir: sie iranian sss A i 144 Lbi i Fay (er e" ~ . (oie th. 1980 1981 1982 1983 1980 1981 1982 1983 B B FicurE 43.-Hydrograph and compaction, 68/2W-24C3. A, Hydrograph | FIGURE 44.-Hydrograph and compaction, 68/2W-24C4. A, Hydrograph of well 68/2W-2403, depth 550 ft. B, Compaction to 550-ft depth at of well 68/2W-24C4, depth 250 ft. B, Compaction to 250-ft depth at well 6§/2W-2403. well 6§/2W-240C4. F60 40 8o 120 160 DEPTH TO WATER BELOW LAND SURFACE, IN FEET 2.6 2.7 2.8 2.9 3.0 COMPACTION, IN FEET 3.1 3.2 MECHANICS OF AQUIFER SYSTEMS mommy [t takes 1 A- Hydrograph, 24C7 torr omor tommy? tommy Compaction, 0-1000 feet m) C rse Dug agg ga a 1980 FIGURE 45.-Hydrograph and compaction, 6S/2W-24C7. A, Hydrograph of well 6S/2W-24C7, perforated 807-851 and 880-903 ft. B, Compac- tion to 1,000-ft depth at well 6S/2W-24C7. 40 Bo 120 160 200 240 DEPTH TO WATER BELOW LAND SURFACE, IN FEET 280 4.0 4.2 4.3 4.4 COMPACTION, IN FEET 4.5 4.6 mmmmmmmmmrt tom Hydrograph, 16CS5 prrrrrerr+rr pM ia ........... ........... momma -or mmm Compaction, 0-908 feet A aaa pg g a aa ia pa ga ga a a apa aa g a ga a a pag a pg gag a 1980 1981 1982 1983 FiGurRE 46. -Hydrograph and compaction, 7S/1E-16C5. A, Hydrograph of well 7S/1E-16C5, depth 908 ft. B, Compaction to 908-ft depth at well 7S/1E-16C5. 40 Bo 120 200 LAND SURFACE, IN FEET 240 DEPTH TO WATER BELOW 280 4.6 4.7 4.8 4.9 5.0 COMPACTION, IN FEET 5.1 5.2 160 | Hydrograph, 16C5 M L | N W T A Compaction, 0-1000 feet <_ AV’AV, 1980 1981 1982 1983 FIGURE 47.-Hydrograph 78/1E-16C5, and compaction 7S/1E-16C11. A, Hydrograph of well 7S/1E-16C5, depth 908 ft. B, Compaction to 1,000-ft depth at well 7S/1E-16C11. 40 80 160 200 DEPTH TO WATER BELOW LAND SURFACE, IN FEET 240 aaa 4.6 4.7 4.8 4.9 5.0 COMPACTION, IN FEET 5.1 5.2 mmr Hydrograph, 16C11 P Ase AR _o K/ pba g a ag a a tom Compaction, 0-1000 feet ........... ad a aaa aa a 1982 FiGURE 48.-Hydrograph and compaction, 7S/1E-16C11. A, Hydrograph of well 7S/1E-16C11, perforated 551-571, 598-618, and 640-660 ft. B, Compaction to 1,000-ft depth at well 7S/1E-16C11. LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 TABLE 6.-Wells for which records are included in figures 81-42 F61 Water-level 1 Well Type of recorder or Figure € YP - of well interval Remarks number - number extensometer observation (feet) (feet) well 31 Cable Recorder 425 170-177 Stress-strain_plot 244-255 for 225-ft interval. 311-315 343-350 32 - 6§8/2W-24C4 Cable Observation 250 -== Changed from cable to and pipe. pipe assembly in October 1973. 33 -2404 ---do--- ----do----- 250 --- -25C1 None ----do----- 500 unknown 34 -2403 Cable ----do----- 550 --- Changed from cable to and pipe. pipe assembly in October 1973. 35 -2403 ---do--- ----do----- 550 --- -25C1l None ----do----- 500 unknown | 36 -2404 Cable 250 es- | and pipe. | -2403 ---do--- ----do----- 550 f | 37 -24C4 =«-~dp-=<~ 250 | -2403 ---do--- ----do----- 550 kn | -25C1 None ----dg---_-- 500 unknown 38 -2403 Cable ----do----- 550 ~- | and pipe. | -2407 ---do--- ----do----- 1,000 807-851 Changed from cable to 880-903 pipe assembly in 0c4ober 1973. | 39 - 7S/1E-9D2 Cable Recorder 605 unknown | 40 -16C5 Cable ---do--- 908 unknown Stress-strain plot for 708-ft interval. 41 7S/1E-16C6-11 _ Cable 1,000 551-571 Stress-strain plot for and pipe. 598-618 800-ft interval. 640-660 J -16C5 Cable ---do--- 908 --- | 42 -16C6-11 Cablg ---do--- 1,000 e Changed from cable to and pipe. pipe assembly in April 1972. GPO 585-045/78029 we. 17 Z UVAY PG "s v. 497-Cr p LiBkARY _ Land-Surface Tilting Near W heeler Ridge, Southern San Joaquin Valley, California GEOLOGICAL SURVEY PROFESSIONAL PAPER 497-G Prepared in cooperation with the California Department i ages. qf Water Resources f/J’Z‘J Y OF km?“\ Jy ae 17 [ |_ U.s.S.D. Land-Surface Tilting Near Wheeler Ridge, Southern San Joaquin Valley, California By FRANCIS 5. RILEY MECHANICS OF AQUIFER SYSTEMS GEOLOGICAL SURVEY PROFESSIONAL PAPER 4+97-G Prepared in cooperation with the California Department of Water Resources UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 70 cents (paper cover) CONTENTS Page Page 1 2.120. Lee iene Lebe er re G1 | The tilt and compaction records .............................______.... 15 TnErOUUCUIOTL L ll. sc CO. ober 1 Characteristics of the GS-I tiltmeter record .......... 15 Statement of the problem .........................._____.__._____. 1 Characteristics of the GS-II compaction records .. 16 Purpose and scope of the tiltmeter program .......... 3 Characteristics of the GS-II tiltmeter record ........ 18 ACKnOWIE@MIGNES | .e. ideas els 8 Summary of tilt and compaction data ...................... 18 Description of the instrumentation ...... 3 Data from GS-I tiltmeter ......................__...._._. 19 Tiltmeter principles ...... 3 Data from GS-II tiltmeter ..................__.. 21 Tiltmeter construction ................................... 4 Data from GS-II compaction sensors .............. 22 Methods used to control temperature effects.... 7. | Data from spirit leveling 26 The GB-I tilimeter 10 | SUMIMATY : 0, 2212 ise coe Colan detest d fo. 28 The GS-IL installation onle 10 | Conclusions 200 A0 ce oie Adc ience ote 29 References cited .... AH 29 ILLUSTRATIONS Page PLATE 1. Map of Wheeler Ridge pumping-plant site and tilt profiles determined by spirit leveling ..........................._._.___.... In pocket FicurE 1. Map of southern San Joaquin Valley, showing location of Wheeler Ridge pumping-plant site and lines of equal land subsidence; 1957-G5 ._.... ...... 22. ::. Ten IH Sn reale cee nee ren nes ede dies dev dove nee eve re ae do Aah desde G2 2. diagram of recording . (hoch sin inin oue ibe v ae heshe? race ove sees vad Ive covet recede 4 9. Cutaway sketch of tiltmeter Measuring DOL .. ..... : di ive £. d ie le . i+ ce 5 4. Diagrammatic section of tiltmeter measuring pot, showing transducer mounting .... 6 5. Graph showing relationships of units of measurement Used in this F@DOTt eee enne neenee. 8 6. Aerial view southeastward along the aqueduct alinement, showing the pumping-plant site and tiltmeter sta- MON " 2. eA Hedden recast che s ths ene de be resets a rede eee an vede ans wade aet ered cle Ie 13 he Seabee t 3s s reads Crv 11 7. Aerial view northwestward along the aqueduct alinement, showing infiltration ponds and the GS-I and GS-II CiltmeLens -:. 002 A0 c chun d cati eave ice annal dds char ie ece idd ade nang 12 8. Diagrammatic sketch of compaction sensor and tiltmeter foundation, GS-II installation .. 13 9. Southwestern end of the GSN-IL tiltmeter (lime 2) 000 e. ones vede bees oue 14 10. Sketch showing 8 days of typical record, GS-I 15 11. Graphs of differential compaction, compaction, tilt, temperature, and barometric pressure at the GS-II instal- lation, December 19-22, 19065 :...... . ......1..0- 100.0 corey reais eni ede nos ne denk nev PC nh ede cee ene 17 12. Composite graph of tiltmeter and COMpPACtiION-S@MNSOF GAtA neenee nene ees 19 13. The GS-I tiltmeter record and graph of aquifer compaction at well 11N/21W-3B1 .......... 20 14. Graphs of temperature changes and indicated compaction, northern compaction S@NSOF ...... 22 15. Graphs of differential compaction and GS-II tiltmeter d@ta ee}. C 24 16. Graphs of subsidence of bench marks LS-8 and B1053 with respect to bench mark A1053 ......................_._....._.__. 26 III ert eon MECHANICS OF AQUIFER SYSTEMS LAND-SURFACE TILTING NEAR WHEELER RIDGE, sOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA By Francis S. Riury ABSTRACT Two continuous-recording liquid-level tiltmeters and three associated borehole extensometers recorded tilt at land sur- face and compaction in the upper 150 feet of alluvial-fan de- posits at the site of the future Wheeler Ridge pumping plant of the California Aqueduct. The location, at the southern end of the San Joaquin Valley, borders on a large bowl of active land subsidence caused by compaction of the confined aquifer system under the stress of artesian-head decline. It is in an area subject also to subsidence due to near-surface hydrocom- paction of moisture-deficient fan deposits. Lastly, it is an area of potential tectonic movement related to the historically ac- tive White Wolf fault. The instrumentation was intended to record tilt and, so far as practicable, to identify and furnish magnitudes of tilt related to specific causes. During the first summer of operation (1965), the tiltmeter, a one-directional instrument, showed an abrupt northwestward tilting toward the nearby valley areas of intense pumping and rapid artesian-head decline. The tilt record lagged the hydro- graph by about 6 weeks, but this delay was not unreasonable in view of the time required for artesian-head change to mi- grate laterally through the aquifer system. The magnitude of the northwesterly summer tilt was 46 microradians, or roughly half the annual rate of tilting that had been postulated on the basis of repeated spirit leveling surveys between 1960 and 1965. The second tiltmeter, a two-directional instrument, was not in operation during the 1965 pumping season; it began re- cording in October 1965 and recorded virtually stable condi- tions during the following autumn months. A very slow but steady background tilting (5 microradians per year in a di- rection about N. 55° E.) may be due to continuing uplift of the Wheeler Ridge anticline; Pleistocene gravels have been tilted 60° to the northeast only one-quarter mile south of the tiltmeter site. - From December 16, 1965, to March 2, 1966, water was pumped at about 500 gallons per minute into an infiltration pond 400 feet upslope from the tiltmeter site. The resulting hydrocompaction caused as much as 2.7 millimeters of differ- ential settlement at the pumping-plant site, completely over- whelming the more subtle tilting due to deep-seated aquifer compaction during the 1966 pumping seasons. Differences in magnitude and timing between the responses of the tiltmeters and compaction sensors indicate that significant susceptibility to hydrocompaction existed at depths greater than 150 feet. A special array of 24 bench marks installed within a radius of 2,400 feet from the pumping-plant site was leveled six times between August 1965 and September 1966. The areal pattern of tilting determined by the leveling agreed with the tiltmeter data in defining two principal periods of northward tilting per year; these periods coincided with the winter and summer irri- gation seasons. In 1966 the total northward tilt was 42 micro- radians. INTRODUCTION From March 26, 1965, to September 19, 1966, the U.S. Geological Survey operated a recording tiltmeter station near Wheeler Ridge, 24 miles south of Bakers- field, Calif. This report describes the installation and discusses the data obtained. STATEMENT OF THE PROBLEM The site of the future Wheeler Ridge pumping plant of the California Aqueduct at the north base of Wheeler Ridge (lat 35°01'54" N.; long 119°00'24" W.) is near the southern margin of a large bowl of active land sub- sidence at the south end of the San Joaquin Valley. The extent and the magnitude of the subsidence from 1957 to 1965 are indicated by the lines of equal subsi- dence in figure 1. The principal cause of subsidence is compaction of the confined aquifer system between depths of about 300-1,500 feet, because of withdrawal of large quantities of ground water for irrigation (Lof- gren, 1963, and oral commun., 1966). An additional contributing cause of subsidence along the southern border of the area is compaction of moisture-deficient low-density alluvial-fan deposits of Pleistocene and Holocene age through the action of percolating excess irrigation water. This process, known as hydrocompac- tion, occurs when highly porous, moderately clayey sediments lying above the water table are rewetted for the first time since deposition. The resulting weaken- ing of intergranular clay bonds permits partial collapse of the sediments under the existing overburden load. (For a discussion of the process of hydrocompaction, see Bull, 1961, p. B187-189.) Before the present investigation, test drilling by the California Department of Water Resources revealed that, at the pumping-plant site, the alluvial deposits G1 G2 MECHANICS OF AQUIFER SYSTEMS R. 26 E. R. 276: R.28 E. h. 29 E: T.B1S. C 460) LOCATION MAP \Grapu 1m ///// //W "" * a 22 w. compiled by EXPLANATION Ben E. Lofgren C] Contact ] % 5 % Line of equal subsidence, in feet Unconsolidated rocks Trace of White Wolf fault ont Dotted where concealed California Aqueduct boy Semiconsolidated rocks ——-£——> > Axis of anticline 7/1 Arrow indicates direction of plunge Consolidated rocks FIGURE 1.-Map of southern San Joaquin Valley, showing location of Wheeler Ridge pumping-plant site and lines of equal land subsidence, 1957-65. LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G3 were subject to hydrocompaction to a depth of at least 100 feet. Analysis of data from repeated spirit leveling by the U.S. Coast and Geodetic Survey and the California Department of Water Resources indicated that particu- larly intense differential subsidence, or tilt, has oc- curred near the site of the Wheeler Range pumping plant, as is shown by the close spacing of the lines of equal subsidence in figure 1. Since 1960 the area ap- parently has been subject to valleyward (northward) tilting at an average rate of roughly 100 microradians per year (0.01 ft per 100 ft year), a movement which, if continued, would result in about half a foot of differ- ential settlement across the 100-foot width of the plant in a 50-year period. However, because the nearest bench marks, A1053 and LS-8 (pl. 1), were 1,200 and 1,400 feet, respectively, from the site and did not closely bracket its location this estimate was consid- ered uncertain. Furthermore, the leveling data did not provide any means of discriminating among several possible causes of tilting, namely, deep-seated aquifer compaction, near-surface hydrocompaction, removal of fluids from nearby oil fields, and tectonic movement associated with the historically active White Wolf fault and the very youthful Wheeler Ridge anticline. PURPOSE AND SCOPE OF THE TILTMETER PROGRAM The Wheeler Ridge pumping-plant site afforded the U.S. Geological Survey an opportunity to measure the magnitude and time distribution of tilt in an area of aquifer deformation and possible tectonic movement, to identify the possible causes of tilt, and to advance tiltmeter techniques. Furthermore, the California De- partment of Water Resources was concerned that pos- sible tilting of the pumping-plant foundation over a 50-year period might cause mechanical problems and, for this reason, was willing to undertake the necessary preparation of the site. Accordingly, in March 1965, the Geological Survey installed a temporary contin- uous-recording one-directional tiltmeter on the center line of the pumping-plant site. Late in April, the equip- ment was converted to semipermanent status. In October 1965, more comprehensive instrumenta- tion was installed adjacent to the first tiltmeter. The new equipment, a two-directional tiltmeter linked to three ultrasensitive compaction sensors, was designed to determine the true direction and full magnitude of tilting and to distinguish between tilt of deep-seated origin and tilt due to differential hydrocompaction in the upper 150 feet of alluvial-fan deposits. The instrumentation and data obtained through January 1966 were discussed briefly in a progress re- port (Riley, 1966). The instruments were operated through September 19, 1966, when they had to be re- moved to make way for excavation of the pumping- plant intake channel and bowl. The present report describes the installation in some detail, discusses the principal problems, presents the basic data obtained, and relates the results to perti- nent features of the hydrologic environment. ACKNOWLEDGMENTS The tiltmeters were installed and operated through June 1966 under the Mechanics of Aquifers project, which is a part of the Survey's nationwide, federally supported research program. Continuation of opera- tions from July 1 to September 19, 1966, was made possible by financial cooperation between the Geolog- ical Survey and the California Department of Water Resources. The Department of Water Resources also furnished helpful advice in the design of the compac- tion sensors, was responsible for site preparation and construction of the compaction-sensor wells, and car- ried out a special program of precise spirit leveling. The writer wishes to acknowledge particularly the thoughtful assistance and unfailing cooperation of W. D. Fuqua and R. J. Akers, Project Geology Branch, Department of Water Resources, in planning the tilt- meter installation and coordinating the activities of the Department of Water Resources. Special thanks are also due Robert G. Pugh of the Mechanics of Aqui- fers project staff for his capable assistance in field op- erations and data reduction. DESCRIPTION OF THE INSTRUMENTATION Because of the unusual and, in some respects, unique aspects of the tiltmeters and compaction sensors em- ployed in the Wheeler Ridge studies, the following de- scription of the instrumentation is included to facili- tate the understanding and interpretation of the re- sults. TILTMETER PRINCIPLES The tiltmeters employed at the Wheeler Ridge sta- tion were of the liquid-level, or water-tube type, in which differential elevation changes between two (or more) points are measured by reference to a common liquid level. This principle is not new. Its modern em- ployment in high-precision instruments extends back at least as far as the earth-tide investigations of Michelson (1914) and Michelson and Gale (1919). Various forms of the device have been developed by a number of workers, notably Egedal and Fjeldstad (1937), Hagiwara (1947), Eaton (1959), and Bonch- kovsky and Skur'yat (1961). The automatic recording tiltmeters used at Wheeler Ridge were developed by the author (Riley, 1962) from an earlier manually operated instrument de- G4 MECHANICS OF AQUIFER SYSTEMS scribed by Riley and Davis (1960). The instruments were originally intended for use primarily in geotech- nical studies of relatively short duration, typically a few days or weeks. For this purpose the equipment should be reasonably portable, operable under widely varying ambient temperatures, and usable with min- imum site preparation. The tiltmeter described in this report differs from other similar instruments chiefly in the electromechanical system used to obtain the continuous record of tilt and in the techniques em- ployed to minimize and compensate for temperature effects. The tiltmeter consists of a pair of cylindrical meas- uring pots, partly filled with liquid and connected by a length-usually 50-200 feet-of liquid-filled hose (fig. 2). A second hose connects the closed air spaces TRANSDUCER EXCITATION 2:4 KHz, 5°V TILTMETER POTS connected so that differential liquid-level changes re- sulting from ground tilting are electrically additive, whereas parallel fluctuations due to temperature-in- duced volume changes are mutually canceling. Thus, the strip-chart trace constitutes a continuous record of the changes in elevation of one pot with respect to the other. Sensitivity is adjustable to a maximum (limited by amplifier noise) of 1 millimicron of ground move- ment per millimeter of pen displacement (an amplifi- cation of 10°), but no practical use has been found for this extreme level of sensitivity. TILTMETER CONSTRUCTION The basic design features of the tiltmeter measuring pot are illustrated in figures 3 and 4. The inner cylin- der within which the liquid-level changes are meas- OSCILLATOR AMPLIFIER and DEMODULATOR DUAL-COIL RECORDING GALVANOMETER above the liquid surface in the pots. Minute changes in the relative elevations of the pots appear as recip- rocal variations in the heights of the liquid columns in the pots. A float-actuated transducer in each pot con- verts the position of the liquid level above or below an adjustable arbitrary datum to an analogous elec- trical signal. The signals from both pots are fed to a dual-coil, center-zero, strip-chart recording milliameter, OSCILLATOR AMPLIFIER and DEMODULATOR AMPLIFIER OUTPUT #3V DGC | _> FIGURE 2.-Schematic diagram of recording tiltmeter. ured is 3.375 inches in diameter and 5.000 inches high. It is surrounded by an outer cylinder which serves as a water jacket whose purpose is to promote uniform temperatures in the cylinder walls and to minimize rates of change in response to changing ambient tem- peratures. The cylinders are mounted on a heavy tri- angular base plate equipped with three adjustable legs which permit leveling the instrument and adjusting its LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY . MICROMETER (C 1 coco lll T W\\ \ t innna! minim nnZRRRRRE trm \l T OCOL T G5 TRANSDUCER LEADS - V uA" gore AIR HOSE s WATER HOSE FiGurE 3.-Cutaway sketch of tiltmeter measuring pot. height to accommodate varying foundation conditions. The measuring pots are fabricated entirely from stain- less steel. The transducer used to measure changes in liquid level is a linear variable differential transformer that 373-386 O - 70 - 2 converts vertical motion of its movable part into an analogous electrical signal. The transducer consists of two mechanically separate elements: one, the fixed or reference element, contains the transformer coils; the other, the moving element, is a small core of ferromag- G6 MECHANICS OF AQUIFER SYSTEMS netic material which is free to move vertically within the coil assembly (fig. 4). The reference element, or coil assembly, is clamped in an adjustable plunger mounted in the pot lid. The vertical position of the plunger and coil assembly can be precisely adjusted by means of the large micrometer. The moving core is mounted in the center of an open-topped cylindrical float, which is weighted to sink close to the bottom of the pot. A Teflon washer at the bottom end of the core keeps it approximately centered within the bore of the coil assembly and also serves to center the float within the pot. As the trans- former is relatively insensitive to radial movements of SECONDARY WINDINGS ee Ae ‘ \'|~[_\\\ I iI mmoncx. mmm mi meee mec ime 2 CGLGLLLLLLLLLOCOOOOOOOOOOID their outputs are equal in amplitude but opposite in phase, and consequently self-canceling. Energy trans- fer from the primary to the two secondary coils is governed by the vertical position of the core. When the core is perfectly centered vertically, the output voltage is zero and the transducer is said to be at null. If the core is raised, the output voltage in the upper secon- dary is increased, while that in the lower secondary is decreased; the difference appears as a net output signal. If the core is lowered, the converse occurs. The direction of departure from null is defined by the phase relationship (either 0° or 180°) between the output and excitation wave forms. MICROMETER SPINDLE POT LID PRIMARY =-+7] WINDING m. FLOAT FiGURE 4.-Diagrammatic section of tiltmeter measuring pot, showing transducer mounting. the core, it is possible to make the washer slightly smaller in diameter than the bore of the coil assembly, thereby effectively eliminating friction between the moving core and the fixed coils. The transducer is excited by a 5-volt a-c electrical signal at 2.4 kilohertz; this signal is fed to the middle or primary coil of the transducer and is transferred by induction to the two secondary coils located above and below the primary. The secondary coils are wound and connected in series opposing so that, when energy is transferred into them equally from the primary coil, Several features make the differential transformer particularly attractive as a linear-displacement trans- ducer in this application. Paramount among these are the absence of friction between the moving and the fixed elements, and the negligibly small loading effects of the alternating-current field on the magnetic core. These properties enable the transducer to be actuated by extremely small buoyant forces applied to the float and therefore to respond to water-level changes of a few thousandths of a micron. Other advantages of the differential transformer are infinite resolution, ex- dell Brot rome memes LAND-SURFACE TILTING NEAR WHEELER tremely high sensitivity, good linearity, and accept- ably low temperature sensitivity. Finally, the stable null point provides a recoverable instrument datum that is unaffected by amplifier drift or other possible malfunctions in downstream stages of the electronics. A solid-state oscillator-amplifier (Sanborn Model 311) drives the primary winding of the differential transformer and also functions as the amplifier and phase-sensitive demodulator for the output signals from the secondary windings. Each transducer is driven by its own oscillator-am- plifier, and the d-c output (+3 volts) from each ampli- fier is fed to the dual-coil tilt recorder (Esterline-An- gus Model AW, range +1.0 milliampere) , as illustrated schematically in figure 2. The amplifier outputs are direct electrical analogs of the heights of the floats above or below the transducer null points, and the dif- ference between the outputs, measured by the dual- coil recorder, represents the differential elevation change of one measuring pot with respect to the other. It has been found useful to record also the output from each amplifier independently, as a check on the proper functioning of the entire system. For simplic- ity, these supplementary recorders are omitted from figure 2. For the Wheeler Ridge installation, commercial power (120 volts, 60 hertz) was brought in from a near- by pole line. Regulated voltage was supplied to all electronic components by a servo-operated variable autotransformer that stabilized line voltage within +1 volt. The tiltmeter recorders at Wheeler Ridge were usu- ally operated at a chart-drive rate of three-fourths of an inch per hour and a sensitivity of 200-300 microns for full-scale deflection. At those settings, the minimum detectable angular change was less than 0.1 micro- radian, or about 0.1 percent of the postulated annual tilt at the pumping-plant site. When accumulated tilting caused the pen to approach the edge of the re- corder chart, the instrument datum was reset by ad- justing the large reference micrometer (figs. 3 and 4), which, in turn, adjusted the height of the differential transformer. In this manner the record was shifted back toward the center of the chart, and a check was obtained on the instrument scale factor. Thus, the span of the recorder was offset by accurately deter- mined increments; in cases of large accumulative tilt, the ultimate range and accuracy of the instrument is limited by the range and accuracy of the micrometers. The first tiltmeter installed at Wheeler Ridge had 1- inch micrometers divided every 0.0001 inch (2.54 mi- crons). The second, a two-directional tiltmeter, had 25-millimeter micrometers bearing 2-micron divisions. With care, both types of micrometers can be read with RIDGE, SOUTHERN SAN JOAQUIN VALLEY GT a repeatability of plus or minus one-tenth of a scale division. The absolute accuracy of the micrometers, according to manufacturer's specifications, is one scale division. Figure 5 provides a convenient graphic comparison between the English and metric units used in this re- port and also facilitates conversion from units of differ- ential elevation change to angular units of tilt (micro- radians). METHODS USED TO CONTROL TEMPERATURE EFFECTS The principal source of error in tiltmeter measure- ments is change in temperature, which adversely af- fects the mechanical, fluid, and electronic components of the system. The part most sensitive to temperature change is the liquid-filled hose connecting the measur- ing pots. Transparent vinyl hoses of 54-inch inside diameter were used in order to facilitate checking for air bubbles. An experimentally determined solution of 31 percent methanol in distilled, de-aired water proved to have nearly the same expansivity as the hoses, within the range of temperatures usually encountered. Nevertheless, the hose lines, which normally are not buried, must be thermally ballasted and insulated to prevent severe short-term (period less than 30 min- utes) instability due to solar heating. At Wheeler Ridge the ballasting was accomplished by covering both the liquid and air hoses with a flattened plastic tube about 8 inches wide, containing slightly less than one gallon of water per lineal foot. The tiltmeter hoses and ballast tube (as well as electrical power and signal cables) were enclosed in a wrap of foil-backed fiberglass batting which was, in turn, wrapped in plas- tic film, covered with a second layer of fiberglass bat- ting, and finally covered with overlapping 4-foot lengths of 12-inch-diameter half-section steel culvert pipe. The large thermal mass contained within the insulation produced a nearly uniform and very slowly changing temperature environment for the hoses. In general, the diurnal temperature fluctuation in the hoses was 2° 4° Celsius, in contrast to a daily range of 40° or more on the unsheltered ground surface. Seasonally, the hose temperatures progressed slowly from a Decem- ber low of 7°C to a June high of 38°C. Although the insulation and ballast effectively min- imized short-term instability throughout the period of operation, some inconvenience resulted from the fact that the plastic film enclosing the inner layer of insula- tion was not a sealed vapor barrier. Consequently, under appropriate conditions of temperature and hu- midity, moisture condensed on the ballast tube and eventually accumulated in amounts sufficient to satu- rate the fiberglass batting beneath the tube. As nearly as could be determined, this had no significant effect G8 MECHANICS OF AQUIFER SYSTEMS on 3200 120 - 3000 E 2800 -45 2600 100 |- 110 - +40 [_- 100 - 2400 6 35 a [- i 30 rd | 0 2200 C [~ * 80 : 5 5 g H—25 é g w 5 R 80 |- © 70 - & z & ' |-20 § -| 2000 & o E © 3 a . |- ® 60-15 ~ 4 4 e ** u g ta 50 1800 g & < r: =I 3 > i- 40 -| £ 2a z “cg 1600 Z o 5 fale * -| 1400 @ = < < ~ a § j- 3 [ra 4200 '@ 3: |- % # - tie i o 2 40 |- a - 1000 L L w ws & o ____________________________ - 800 1 PR i Example: | 30 x 10-3 inch of differential elevation change -| 600 | equals 762 microns of differential elevation 20 f change equals 25 microradians of tilt, & | at a pot spacing of 100 feet. | -| 400 I | - | i -<1.:200 | | s § putt y 3 o t_ =t m c i- "18 0 20 40 60 80 100 TILT ANGLE, IN MICRORADIANS FIGURE 5.-Relationships of units of measurement used in this report. on the functioning of the tiltmeters. Despite the approximate equalization obtained be- tween hose and fluid expansivities, operating conven- ience requires a means of adjusting the height of the liquid columns in the pots to achieve optimum operat- ing levels and to compensate for the volume changes that accompany large temperature changes. Manual adjustment is provided by a micrometer-actuated ground-glass syringe connected to the midpoint of the hose line. Precisely metered volumes of liquid may be *~~@ LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G9 added or withdrawn from the tiltmeter system in order to test the response of the transducers and the hydro- dynamic symmetry of the hose line about its midpoint. The latter test is especially important as a means of detecting a density trap or accumulation of bubbles at some point in the hose. Such a condition constitutes an impedance to flow through the hose and causes a lag or, in severe cases, a permanently attenuated re- sponse in the measuring pot on the obstructed side of the midpoint. An impedance is reflected in an offset of the tilt record, which may be temporary or permanent depending on the nature of the obstruction. During the operations at Wheeler Ridge, the correct function- ing of the tiltmeters was routinely checked each time the instruments were serviced, by adding and sub- tracting fluid as described above. In addition to the provision for manual adjustment of fluid volume, the tiltmeters were equipped with au- tomatic volume controllers, which continuously com- pensated for temperature-induced changes in volume that would otherwise have driven the transducer sys- tems off scale. The volume controller consists of a thermally insulated, liquid-filled expansion chamber which is connected to the midpoint of the hose and which contains an electrical heating element. Power input to the heating element is controlled by a transistorized servoamplifier that responds to the out- put from the transducer amplifier at one end (desig- nated the "controlled" end) of the tiltmeter line. When the transducer core in the controlled pot is centered (at null), the output from its amplifier is zero, and the power input to the heater is maintained at a constant low level, sufficient to maintain the temperature in the expansion chamber about 10°C above the ambient air temperature. Heat input to the chamber equals heat loss through its walls, and no change in the volume of contained liquid occurs. If the liquid level in the con- trolled pot declines slightly, the servoamplifier responds by a greatly increased power input to the heater. Liquid in the chamber immediately expands into the hose and raises the level in the controlled pot to ap- proximately its nominal operating point. Conversely, a rise in liquid level in the controlled pot causes a re- duction in power input to the heating chamber so that its contained fluid cools, contracts, and withdraws water from the hose to correct the level in the pots. The net result of this arrangement is that liquid-level fluctuations due to temperature-induced changes in volume are almost entirely absorbed in the expansion chamber, and liquid-level changes due to tilting are forced to appear almost entirely in the uncontrolled pot at the other end of the hose line. At Wheeler Ridge, an expansion chamber of half-gallon capacity contain- ing a 75-watt heater proved satisfactory for compen- sating 100 feet of hose line. For simplicity, the manual and automatic volume controllers have been omitted from figure 2. The measuring pots and associated transducer am- plifiers were shielded from abrupt temperature change in small insulating shelters made of rigid polyure- thane foam panels, 3 inches thick. The daily fluctua- tion of air temperatures within the shelters did not usually exceed 2°C, and the daily fluctuation of liquid temperatures in the pots was about 1°. The seasonal fluctuation of temperatures inside the shelters was about 24°C for the air temperatures and 21°C for the pot temperatures. The shelters for the first tiltmeter at Wheeler Ridge were equipped with heaters, circulating fans, and thermostats capable of maintaining temperatures con- stant within 0.1°. Their use was discontinued, how- ever, when it became evident that small diurnal tem- perature fluctuations in the pots and amplifiers were of no significance at the tilt sensitivities being used. It was not considered feasible to maintain the shelters at the same temperature throughout the year, inas- much as this would have necessitated a setting of about 55°C, which, during the winter, would have re- sulted in a temperature gradient of more than 30°C between the pots and the adjacent hose. The use of cylindrical flat-bottomed floats, weighted to sink close to the bottoms of the pots, minimizes the sensitivity of the system to temperature-induced den- sity changes in the fluid columns in the pots. Because the sides of the floats are vertical, only the hydrostatic uplift on their bottom surfaces influences their posi- tions in the fluid columns. Identical floats require equal hydrostatic uplift and therefore come to rest on hydrostatic pressure surfaces having the same pres- sure value. That value (equal to the weight per unit area of the floats) is determined directly by the weight per unit area of liquid overlying the pressure surface and is not affected by thermally induced changes in the height of the liquid column above that surface. Because of the lack of static shear strength in the liquid, the pressure surfaces under no-flow conditions must be horizontal; that is, they parallel the gravita- tional equipotential surfaces passing through the in- strument. If the hose is perfectly level, all hydrostatic pressure surfaces in one end of the line will be continu- ous through the hose to the other end and will extend horizontally into the measuring pots at both ends. Thus, if the bottoms of the floats are opposite the hose- connection orifices and the hose line is level, floats resting on the same pressure surface will also rest on a single gravitational equipotential surface, regardless of density differences within the system. Any departure of the hose from the horizontal will truncate some of the pressure surfaces against the top and bottom of the hose and thus will restrict the verti- G10 cal range within which the floats can operate with as- surance of remaining on the same equipotential sur- face. If the sum of the largest upward and downward departures from level exceeds the inside diameter of the hose, there will be no continuous pressure surface throughout the instrument. Given this circumstance plus a nonuniform temperature environment and an imperfect match between hose and.fluid expansivities, thermally-induced changes in fluid volume can displace the hydrostatic-pressure surfaces differentially about either side of the low point in the hose line. The floats, although still resting on surfaces of the same pressure value, will no longer be on the same gravitational equi- potential surface, and therefore will not define an ac- curate horizontal datum. For this reason the hose must be almost exactly level if temperature effects are to be avoided. Measures taken to insure horizontality of the hoses in the Wheeler Ridge tiltmeters are de- scribed in the following section entitled "The GS-I tiltmeter." Within the constraints imposed by transducer mount- ing and operating requirements, the pots, lid assem- blies, and floats were designed to minimize relative movements between the core and coils of the trans- ducer caused by thermailly-induced dimension changes. For example, if the temperature rises uniformly within the entire measuring pot, upward displacement of the pot lid and micrometer head by thermal expansion of the pot walls is largely compensated by downward ex- pansion of the plunger within which the transducer coil assembly is clamped (fig. 4). According to the manufacturer, the maximum ther- mal drift of the transducer amplifier output is 30 milli- volts per 10°C, equivalent to only 0.15 microradian at the recording scale used. A field test, in which the thermostat and heaters in one of the pot-amplifier shelters were used to create a step increase of 4.5°C in shelter-air temperature, pro- duced no clearly discernible offset in the tilt record. In view of the low temperature sensitivity of the pot- transducer-amplifier systems and of the nearly paral- lel seasonal temperature fluctuations in the shelters, it is believed that errors due to temperature changes within the shelters were not significant at the recording scale used. The long-term temperature insensitivity of the en- tire tiltmeter system is demonstrated by the record obtained; this is discussed more fully in the section entitled "Data from the GS-II tiltmeter." THE GS-I TILTMETER The first tiltmeter at Wheeler Ridge, herein desig- nated GS-I, was laid out parallel to and about 25 feet southwest of the center line of the aqueduct and across MECHANICS OF AQUIFER SYSTEMS the long axis of the pumping plant (pl. 1). The aline- ment selected (N. 35° W.) is approximately normal to the contours of the alluvial fan; therefore, considerable excavation was required to provide the level surface nec- essary for the instrument. A trench, about 12 feet wide, 120 feet long, and 7 feet deep at the uphill end, was prepared by the Department of Water Resources, and two rectangular concrete pads, 2 feet wide by 4 feet long by 0.3 foot thick, were poured at a center spacing of 101 feet to serve as pot foundations. To minimize moisture changes in the soil and changes in pad thickness after the initial cure, polyethylene film was used as a liner for the forms and cover for the fresh concrete. A final hand leveling and grading of the surface on which the tiltmeter hose was to rest brought this line to within +0.02 foot of a horizontal grade in order to minimize the possibility of differential-density traps developing in the hose under nonuniform temperature conditions. Because the aluminum sheds intended to house the pots and recorders were not immediately available, small box covers were used for the pots and a truck was used to house the recorders. This installation, which began recording March 26, 1965, was damaged by storms and vandalism, so data were recorded only intermittently. The aluminum sheds were erected in mid-April, and during the remainder of the month the installation was upgraded to essentially final status. Useful data were recorded beginning May 1, 1965. THE GS-IL INSTALLATION In June 1965, the Department of Water Resources asked the Survey to consider the installation of a two- directional tiltmeter at the pumping-plant site. Such an instrument would permit determination of the true direction and full magnitude of tilting at the site. Ad- ditionally, it was desired that an entirely new function be incorporated into this installation-that of dis- tinguishing between deep-seated tilting and tilting due to differential compaction of the upper 150 feet of alluvial-fan deposits underlying the site. Because the pumping-plant foundation was to be set in an excava- tion 150 feet deep, only deep-seated tilting was of prac- tical interest in evaluating the stability of the foun- dation. Furthermore, the near-surface fan deposits along the aqueduct alinement near the pumping plant were being prewetted and precompacted (under their own weight) by means of a series of infiltration ponds designed to produce virtually all potential hydrocom- paction prior to aqueduct construction. If water from the ponds were to permeate the sediments beneath the tiltmeters, substantial hydrocompaction might be ex- pected, making it impossible to extract data on deep- & - x room germs LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G11 FIGURE 6.-Aerial view southeastward along the aqueduct alinement, showing the pumping-plant site and tiltmeter station on the alluvial-fan surface that ex- tends northward from the base of Wheeler Ridge. Rectangular infiltration ponds define the aqueduct alinement except at the site of the pumping plant and its intake channel. (Photographed May 1966.) seated tilting from the tiltmeter records unless inde- pendent measurements of hydrocompaction were avail- able. The aerial photographs of the pumping-plant site (figs. 6 and 7) show the ponds on either side of the tilt- meter station. Each pond contained a set of gravel- filled infiltration wells (usually 6-12 wells which were about 80 feet deep) to hasten penetration of water. Typically, during several months of continuous infil- tration at rates of a few hundred to more than 1,000 gallons per minute, the ponds subsided 2-6 feet, and an area of perceptible subsidence, accompanied by sur- face cracking, expanded to distances of 100-500 feet from the ponds as water moved downward and out- ward through the deposits. In figure 6, which is a view southeastward up the alluvial fan toward Wheeler Ridge, numerous concentric cracks may be seen sur- rounding the ponds in the foreground. In figure 7, MECHANICS OF AQUIFER SYSTEMS FIGURE 7.-Aerial view northwestward along the aqueduct alinement, showing infiltration ponds and the GS-I and GS-II tiltmeters. ( Photographed May 1966.) mmm reo gegen LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G13 which is a northwestward view, cracks are visible in the banks of the uphill ponds (in the foreground) and are evidenced by arcuate lines of vegetation intersect- ing the unpaved road in the lower left part of the pho- tograph. The trenches and aluminum sheds of the GS- I and GS-II tiltmeters are visible in the center of the photograph. The basic elements of a design to accomplish the desired goals of the second tiltmeter installation were worked out in a series of meetings attended by F. S. Riley of the Geological Survey and A. L. O'Neill, W. D. Fuqua, R. J. Akers, and R. B. Hoffman of the Depart- ment of Water Resources. Fundamentally, the design provided for linking a two-directional tiltmeter-em- ploying three interconnected measuring pots in an orthogonal isosceles array-to three compaction sen- sors installed in 150-foot dry wells. A compaction sen- sor is a borehole extensometer consisting of an invar tape suspended from the land surface and anchored to a subsurface bench mark at the bottom of the well; the tape is maintained at a constant tension by a coun- terweighted lever at the land surface and is electron- ically linked through a differential transformer to the reference micrometer of the adjacent tiltmeter pot. The output of the differential transformer is recorded for each of the three compaction sensors; these data can be used to subtract from the record of land-surface tilt any component due to differential compaction of the upper 150 feet of deposits beneath the three tilt- meter pots. Figure 8 is a simplified, diagrammatic sketch of this arrangement. There is no physical con- tact between the compaction sensor and the tiltmeter pot. If frictional contact between the invar tape and the well casing can be avoided, the resolution of the sensor is better than 1 micron. Early in July, the decision was made to proceed with the final design and construction of the second instal- lation, herein designated GS-II. It was agreed that the Department of Water Resources would be responsible for site preparation, including drilling the wells for the compaction sensors, and that the Geological Survey would be responsible for the design, acquisition, em- placement, and operation of the instrumentation. Line 1 of the GS-II tiltmeter was laid out in a trench parallel to, and about 50 feet southwest of, the GS-I tiltmeter. Line 2 was laid out approximately along a contour at right angles to line 1 and extended southwestward from the northwest end of line 1 (pl. 1). Each line was 100 feet long. A single measuring pot at the intersection of the two lines was common to both, The hose lines were constructed, ballasted, and insulated identically to those at the GS-I tiltmeter. The GS-II tiltmeter differed from the GS-I in the method of recording tilt. A dual-coil differential re- 373-386 O - 70 - 3 BALANCE BEAM COMPACTION TRANSDUCER MICROMETER COUNTER WEIGHT STEEL PIPE SET 12 FEET DEEP VERMICULITE GRANULES sa ge - ~ (( ecus Une Us j=t FIGURE 8.-Diagrammatic sketch of compaction sensor and tiltmeter foundation, GS-II installation. corder was not used; instead three individual recorders were used to graph the liquid level in each pot inde- pendently, and the volume controller was connected directly to the central or common pot at the north corner of the layout. In this manner, the liquid level in the common pot was held nearly constant, while the northwest-southeast component of tilting was recorded directly by the southeast pot and the northeast-south- west component by the southwest pot. A major difficulty in the construction of the com- paction sensing system was the drilling of the 150-foot wells at the ends of the tiltmeter lines. Prime require- ments for the wells were as follows: (1) they should be nearly plumb and of such diameter and straightness that the invar tape would not touch the well casing; (2) they should be drilled without wetting the de- posits, because wetting would cause mechanical in- stability of the dry, highly compactible formation; (3) they should provide firm, stable foundations for the G14 MECHANICS OF AQUIFER SYSTEMS subsurface bench marks to be set in their bottoms; (4) they should be cased to prevent sloughing of formation materials against the tape and anchor; (5) to the ex- tent feasible, the casings should be mechanically de- coupled from the formation so that any compaction in the upper part of the deposits would not transmit a downward thrust through the casings to the bench- mark foundations; (6) the drilling should be done in such a way as to minimize temperature changes in the formation next to the well bore. In consideration of the stringent requirements, it was decided to drill by the rotary method using com- pressed air to clear the cuttings from the hole. Because no reverse-rotary air rig was available, the air circu- lated down through the drillstem and up the annular space; with this arrangement the low velocity of the ris- ing air limited the hole diameter to a maximum of 9 inches. This method was used with the first hole, but progress was exceedingly slow and the hole could not be held straight. The two remaining holes were drilled with a hydraulic rotary rig; highly viscous drilling mud composed of diesel fuel and bentonite was used to prevent wetting the adjacent sediments. When the holes reached 147 feet, the mud was bailed out and the last 3 feet were drilled dry, using compressed air. This method worked well. The holes were cased with thin- walled 6-inch ducting, and the annuli between casings and well bores were backfilled with commercial vermic- ulite insulating granules. The subsurface bench marks, resembling huge double-headed scaffold nails (fig. 8), were attached to the end of the drill string and driven to refusal into the formation at the bottoms of the wells. The top of each bench mark, on which the tape anchor rested, was a machine-finished surface. When the drilling was completed, only the central (northern) one of the three wells was entirely satis- factory in terms of straightness and plumbness. The southeastern well, which was drilled with air, was so crooked that a light lowered from the surface disap- peared from view at a depth of about 100 feet. The southwestern well was less crooked, but the light dis- appeared in it, too, at a depth of about 130 feet. Be- cause there were neither funds nor time for redrilling, the installations were completed in spite of the fact that friction between the invar tape and the well cas- ing presumably would impair the operation of the southeastern and southwestern compaction sensors. The tiltmeter pots and above-ground components of the compaction sensors were mounted on steel trivets which were welded to the tops of three steel piers. The piers consisted of 2-inch pipes about 12 feet long that had been driven into the bottoms of 3-inch holes drilled 9 feet deep at the corners of 52-inch equilateral triangles centered about each well (fig. 8). The an- nuli were backfilled with vermiculite. Figure 9 shows Figure 9.-Southwestern end of the GS-II tiltmeter (line 2). The lid of the insulating shelter has been removed, revealing the trivet, measuring pot, compaction-sensor components, and transducer amplifiers. (For identifica- tion of parts, see figure 8.) a tiltmeter pot, compaction-sensor components, and transducer amplifiers mounted over the southwestern well and housed in a triangular insulating shelter made of foamed plastic. The compaction-tape anchors were steel cylinders, 5% inches in diameter and weighing about 75 pounds (fig. 8). To avoid overstressing the invar tapes, each anchor was lowered into position on a loop of steel cable which passed under the sheave attached to the top of the anchor. Subsequently, the lower end of the tape was attached to the cable, pulled down the well, and engaged in the latch at one end of the sheave bracket. This method of emplacement and attachment made it possible to position the anchor so that the lower end of the tape was near the "outside" of the inevitable bend in the well casing; thus, contact between tape and cas- ing at the "inside" of the bend was avoided entirely in the nearly straight northwestern well and minimized in the other two. With the same goal in view, the trivets and above- ground elements of the compaction sensors also were designed to permit maximum flexibility in positioning the tiltmeter pots and compaction equipment, so that the tapes could be brought out of the well at whatever position would minimize contact with the casings. The upper end of each invar tape was clamped in the top of a T-bar assembly 4 feet long, which hung about 3 feet down into the well from a knife-edged yoke at one end of an equal-arm astatic balance beam (figs. 8 and 9). At the other end of the balance beam was suspended a counterweight that maintained the Yili o m - ~ LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G15 --» SOUTHEAST DOWN MICRORADIANS | _- O = w n f | L/ 1K Ffifi” B is on $a H 44/04, /G/7, A \\ g ‘ Noy Oo fet. [~ "on // l vo Can, SAA HA R 0800 (--t I |-- er Rel " o H p- ad } NL] i. 04,108 mINSUS & lA i jflwz 400 LLL} lL ~~ l al a i I 1600 L-] t-} 2. |A ?\ N#% Oo AA N- C C Ing A ) o HAHN a w %, /L pp p p -- a"" aan. 35° SBN S 55 th *n 2892 28 gay "6 (eal FiGURE 10.-Reproduction of 8 days of typical record, GS-I tiltmeter. tape under the 20-pound tension specified by the man- ufacturer. The balance-beam support, or fulcrum, was bolted to the trivet. All suspensions were by hardened knife-edges and V-blocks of the type used in precision industrial balances. At the down-hole end of the T-bar, the invar tape was centered between the ends of a pair of nylon set screws. With the tape under tension, the set screws restrained the T-bar from tipping on its yoke but did not appreciably restrict vertical movement between the tape and the bottom of the T-bar due to differential thermal expansion. When compaction occurred within the upper 150 feet of sediments, the trivet at the land surface sub- sided, carrying down with it the tiltmeter pot and the fulcrum of the balance beam. The tape and T-bar, however, remained fixed with respect to the subsurface bench mark, and the compaction transducer sensed the lowering of the pot with respect to the fixed reference. To the observer at the surface, the effect was an ap- parent protrusion of the T-bar from the well, accom- panied, of course, by a tipping of the balance beam. THE TILT AND COMPACTION RECORDS The primary concern in evaluating the stability of the pumping-plant site is the long-term accumulative tilting measured in tens of microradians. However, short-term oscillatory tilting of smaller amplitude is of interest in evaluating the response characteristics and reliability of the instrument systems. Accordingly, both aspects of the tilt and compaction records are discussed. CHARACTERISTICS OF THE GS-I TILTMETER RECORD Typical diurnal and other short-term fluctuations in the GS-I tiltmeter record are illustrated in figure 10, in which 8 days of record in April 1966 have been re- traced on a single 24-hour length of recorder chart. The rapid and rather uniform southeasterly tilt that was occurring at the time separates the successive lines by about 1 microradian per day. It is apparent that the daily record is characterized by a fairly smooth repetitive pattern, well displayed on April 15, 19, and 22, upon which are superimposed small shorter-term fluctuations of varying duration and amplitude. The diurnal pattern is a somewhat dis- torted sinusoidal oscillation which had a peak (maxi- mum southeasterly tilt) at about 1000 Pacific Stand- ard Time, a trough at about 2200, and an amplitude (double) of about 0.7 microradian. The cause of the diurnal fluctuation has not been extensively investi- gated. Instrumental error, perhaps of thermal origin, has not been ruled out, although the fluctuation does not coincide in phase with any of the temperature G16 MECHANICS OF AQUIFER SYSTEMS cycles that have been recorded in the tiltmeter system and does not vary in amplitude with daily and seasonal weather changes. The fluctuation may represent real tilting related to the diurnal temperature cycle. The repetitive diurnal tilting cannot reasonably be attributed to tidal effects because it is about four times larger than the maximum theoretical earth tide and does not exhibit the strong semidiurnal component and regular progression characteristic of both earth tides and ocean-tide loading. Some of the short-term fluctuations are readily iden- tified when a cause-and-effect relationship can be ob- served as the record is being generated. Wind noise with an amplitude of 0.2-0.6 microradians is common during the summer, and the passage of small but vigor- ous whirlwinds, common on hot days, has been ob- served to cause "spikes" in the record of more than 3 microradians. Because the pot lids are not equipped with positive hermetic seals, it is not impossible that such large spikes were caused by the leakage of strong, transient barometric gradients into the pots. However, this probably is not a competent explanation for the more typical wind-induced fluctuations with "periods" of 3-15 minutes, because the very high impedance of the possible leakage paths, in contrast to the low im- pedance of the air line connecting the pots, minimizes the possibility of sustaining a significant internal air- pressure gradient between the pots. The winter record was characteristically less noisy than the summer, except during major storms, when substantial tilts-as much as 3 microradians-were re- corded over periods of several hours. The inherent viscous damping properties of the hose- fluid system sharply attenuate the response to oscilla- tions with frequencies higher than about 3 cycles per minute, with the result that the instrument is nearly immune to high-frequency noise from vehicular, seis- mic, or other sources. Longer-period seismic waves from major earthquakes as far away as Alaska, Chile, and Formosa were recorded on the Wheeler Ridge tilt- meters. The GS-I tiltmeter was approximately critic- ally damped and had a time constant of about 20 sec- onds without being subject to "ringing" or overshoot. For comprehensive discussions of the dynamic charac- teristics of liquid-level tiltmeter systems see Eaton (1959) and Bonchkovsky and Skur'yat (1961). Much of the GS-I record is characterized by a diur- nal departure during the daylight hours from the typi- cal sinusoidal fluctuation shown in figure 10. The de- parture consists of a rapid northwesterly tilting from about 1 hour after sunrise to about 1230 and moder- ately rapid southeasterly tilting from about 1230 to about 1 hour after sunset. The amplitude of the de- parture reached a maximum of about 7 microradians during June and July and a minimum of about 3 micro- radians in December and January. These diurnal and seasonal characteristics, together with the fact that the departure is subdued or almost absent on overcast days, suggest that it is directly related to the intensity of solar heating of the hose line, despite the fact that the fluctuation is not in phase with recorded tempera- ture change in the hose. The mechanism by which solar heating of the hose may, under some circum- stances, generate a spurious tilt is not fully understood. It may be caused by the development of density traps as the result of gradual segregation of warmer and cooler liquid in minor humps and sags in the hose. Ex- periment has shown that flushing the hose temporarily eliminates the spurious diurnal tilting but that it tends to build up again over a period of weeks. CHARACTERISTICS OF THE GS-II COMPACTION RECORDS Diurnal and other short-term fluctuations typically are of much smaller amplitude in the compaction rec- ords than in the tilt records. During the first 3 months of operation, when there were no nearby infiltration ponds in use to disturb the instruments, only two iden- tifiable factors-temperature and barometric pres- sure-exerted significant influence on the compaction sensors. The characteristics of the compaction records and their relation to temperature and barometric-pressure changes are illustrated in figure 11, in which 4 days of data in December 1965 have been replotted to conve- nient scales. This particular interval of record was selected because continuous records of temperature (in the northern instrument shelter) and barometric pres- sure were available and because significant barometric changes took place. The generally downward trend of the compaction records in figure 11 is due to the seasonal cooling trend (fig. 14), which causes a substantial shortening of the instrument piers. A detailed discussion of the effects of ambient temperature changes on the compaction sensors is presented in a later section dealing with the long-term compaction records. Of interest here is the fact that the diurnal temperature cycle is not strongly reflected in the compaction records. Inasmuch as the transducer-amplifier system in the compaction sensor is identical with that in the tiltmeter, and any dimen- sion changes in the tiltmeter pots would appear in the compaction record (fig. 8), the diurnal temperature response of the compaction sensors may be taken as the maximum limit for the temperature sensitivity of the electronic and mechanical elements of the tiltmeter system. Thus, the theoretically predicted low thermal sensitivity of the tiltmeter pots and transducer system is further confirmed by the compaction records. e 1 ___ alf Lt. reo e ~a * oue, s LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G17 ui EAR 53 : o 1 . - : : LJ Ste aC { mSE 51 |- * L gag? C. 1 1 1 1 1 1 - Egg 49 T I I I I I I LJ faw [7 isin l ngD 30.0 |- Record miss! 8 3] ": SSE ..... 2 EEZE 30.2 |- - cae g a 304 1 1 1 1 1 1 | |__ NORTH COMPACTION 1 1 | 1 1 1 1 I I I I T T T [_ soUTHWwEST COMPACTION § 1 1 I 1 1 1 i In } 20 microns yy l Z - @ [_ soutHEaAst comPActION 3 9 1 1 1 I 1 1 1 = Z _» I I - s 2 > . [ § 5 a |. soutHEast Pot Z {j 1 1 1 1 1 1 i w o [st -- ® & T T T T T T T | G > 3 [_NoRrTH POT , 1 i 1 f 1 1 1 & C - '_ ® < SsoUTHWEST POT _ 1 1 1 1 1 1 1 [~ _ NORTH COMPACTION MINUIS SOUTHWEST CEOMPACTION , j j 19 20 21 22 DECEMBER 1965 FIGURE 11.-Differential compaction, compaction, tilt, temperature, and barometric pressure at the GS-II installation, December 19-22, 1965. G18 Visual comparison of the barograph and compaction records demonstrates that the alluvial-fan deposits be- neath the site experience measurable changes in thick- ness in response to variations in atmospheric loading. The relationship is, however, neither direct nor simple. Large, rather long-term barometric changes accom- panying the passage of major weather systems have little or no effect, but small short-term fluctuations with rapid rates of change produce evident responses. For example, during the night of December 21-22, a distinctive series of barometric fluctuations caused definite but somewhat dissimilar responses in the three compaction records. A thorough analysis of the barometric responses of the compaction sensors is not within the scope of this investigation. The records seem to suggest, however, that the observed effects are time-dependent, rate- sensitive processes, in which atmospheric loading con- stitutes an effective stress on the deposits only to the extent that pore-pressure changes in the intergranular air cannot keep pace with barometric -pressure changes at land surface. For example, in the case of an abrupt increase in barometric pressure, significant movement of air into the deposits would occur until the inter- stitial pressure was built up to equilibrium with the increased barometric pressure. During this interval of downward flow, the pressure dissipated in viscous drag against the soil grains is accumulative downward with- in the solid skeleton of the deposit and constitutes an effective stress tending to compact the deposits. As pressure equilibrium is approached, the flow and re- sultant seepage stress approach zero, and the soil col- umn tends to rebound toward its normal thickness. On the other hand, large but gradual changes in baromet- ric pressure produce low flow rates, small seepage stresses, and minimal strains within the soil column. Under the circumstances postulated, the response of a column of unsaturated soil to a given rate of change of barometric pressure would be dependent pri- marily upon the vertical permeability, effective poros- ity, compressibility, thickness, and temperature of the deposits. All but the last two of these factors would be highly dependent on the lithology, mineralogy, and moisture content of the soil. Thus, at the Wheeler Ridge site, the exceedingly heterogeneous nature of the alluvial-fan deposits underlying the tiltmeter sta- tion should be expected to result in appreciable differ- ences in both phase lag and amplitude among the re- sponses of the three compaction sensors. This, indeed, seems to be the case. CHARACTERISTICS OF THE GS-II TILTMETER RECORD The diurnal and other short-term characteristics of the two-directional GS-II tiltmeter records are very MECHANICS OF AQUIFER SYSTEMS similar to those of the GS-I record. Minor differences in dynamic response characteristics probably are due to the tripartite pot connections and certain differences in plumbing fittings. The "normal" diurnal fluctuation in both lines is nearly identical in shape but somewhat smaller in the GS-II than in the GS-I tiltmeter. A spurious diurnal tilting presumably related to solar heating of the hose is also observed, especially in line 2, which often indicates a northeastward departure from the true tilt record during the daylight hours. Figure 11 illustrates, in addition to the compaction records, the records of liquid-level fluctuations in the three tiltmeter pots during the same 4-day period. The functioning of the automatic volume controller is dem- onstrated by the nearly straight-line record of the northern pot. The records for the southeastern and southwestern pots constitute approximations of the indicated tilt in those directions. (For precise tilt de- termination, the minor departures from null of the con- trolled northern record must be subtracted from each of the other two records.) Comparison with the barograph record again indi- cates that atmospheric pressure changes are a principal source of the minor irregularities characteristic of the tilt records. Comparison is complicated by the fact that the tiltmeters show only the differences in baro- metric response among the instrument piers. Therefore, in figure 11 the tilt records are compared with derived curves of differential compaction obtained by sub- tracting the northern compaction record from each of the other two. The comparison demonstrates that the tiltmeters are recording differential compaction and ex- pansion similar to, but of greater magnitude than, the fluctuations measured by the compaction sensors. Pre- sumably, the greater magnitude and certain differ- ences in phase may be taken to indicate that differen- tial effects of short-term barometric fluctuations ex- tend to depths considerably greater than the 150 feet measured by the compaction sensors. f The spurious daytime tilting indicated by the south- western pot shows up very clearly in the record as humps that bear no relation to the differential-compac- tion graph. SUMMARY OF TILT AND COMPACTION DATA The long-term tilt and indicated compaction meas- ured by all instruments throughout the life of the Wheeler Ridge installation are summarized in figure 12. This illustration was prepared by plotting for each day the 0600 hours point in the diurnal cycle of the tilt and compaction records. This procedure minimizes ex- traneous fluctuations due to thermal and barometric anomalies in the original records. Each graph was plot- ted in the original units of measurement-thousandths LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G19 tof 9g 77 1 3000 -aA40 1 | . Water input to ‘ 2800 e ca. pond 8-17 30 " he 2600 § § -20 |- 4 $ sano | ., "tg. a % f 2200 - § LJ F C a; J- 1800 _ z 10 i ¢ -| 1600 A &© 226 faf? G a 20 |- 5 fo? se = § se GS-I ¢ / be 2 d8 so |- 11200, 9 u _< Inch scale iG "14000 - 6 i ég 40 |- for GS-I 7 Micron scale 9 -E - 20 . J A fortmesI and 2 *~ -Llsop < § 5 9+ sio s & < A-. 50 |- C _. s rep -a * 600 I: d if 3 - so | as P: & & ‘ Apr. | May iJune ‘ July | Aug. a Sept. «lato ri- 1965 -i 200 a; u < I 36° . € Ca Le o _o wheeler Ripee oy | 3 K& _|- n - 200 & XC, PUMPING-PLANT € £2 0~ m ner aa el SE 2. SITE o 98 we u acs -| 400 T= © ps w 200 |- GS‘II et 7'- W i- -- CC /\>/\ 2 L t “l: /WJHL|NE pae iis co sud 600 g 34 Pi | = E25 p g) £ a a \ GS-4 | £ £8 soo |- BrN, fase C -) 800 2 5 3a" ~: SF Micron scale TILTMETER 9 P2... ol , | g s @ Wfi for compaction sensors | Z wa 200 - TILTMETERTE | 3 $8 _ [- AND COMPACTION \S o if? 400 |- RECORDERS 2 X54 ma 8g te: x 13 (<3 m Ist t __ __} claws. col ta rar % SE o 100 200 FEET {iy " | 8 & | i Memos. p 2, sol aj. cp lacs Cm ons alia ates aro Ne a Oct. | Nov. | Dec.| Jan. | Feb. | Mar. ; Apr. | May | June | July | Aug. | Sept.) 1965 1966 FIGURE 12.-Tiltmeter and compaction-sensor data, Wheeler Ridge, Calif. of an inch for the GS-I tiltmeter, and microns for the GS-II tiltmeter and compaction sensors. The two ver- tical scales on the illustration are comparable within 1.6 percent. The resolution of the graphs as originally plotted is about 5 microns (2 % 10 inch) or roughly 0.2 microradians. Data from GSI tiltmeter During its first 6 weeks of operation, the GS-I tilt- meter indicated almost stable conditions-small fluc- tuations of unknown origin superimposed upon a trend of slow southeastward tilting. From the middle of June 1965 until the end of August, however, a very rapid northwestward tilting was recorded, the northwestern pot subsiding a total of 55 y 10~ inch (4.6 % 10% foot) with respect to the southeastern pot. This 2%- month interval corresponds approximately to the sum- mer period of most intense ground-water pumping in the valley area immediately north of the site. The nearest well for which detailed water-level data are available is the Geological Survey's Lakeview test well, 1 1N/21W-3B1, which is 6.4 miles west-northwest of the site, in an area of concentrated pumping. The well is equipped with water-level and compaction re- corders. Its hydrograph (fig. 13) reflects the artesian head in the aquifers between the depths of 1,037 and 1,237 feet, which is the lower part of the principal pro- ducing zone. The artesian-head decline between April 26 and July 30, 1965, was 47 feet, and at the well, the resulting aquifer compaction between depths of about 300 and 1,477 feet was 0.25 foot during the same pe- riod (fig. 13). The similarity between the shapes of the hydro- graph and compaction graph (fig. 13) and the shape of the tilt record through the summer pumping season strongly suggests that the northwestward tilt is the re- sult of differential aquifer compaction, although the tilt record lags the hydrograph by about 6 weeks. This G20 MECHANICS OF AQUIFER SYSTEMS 0.80 "Fu- "{\ T I I I T T T T T T T T T T T T T T T yz 430 | > - AY Well depth: 1477 feet ets t. 440 |- \> 460 |- § 5 1.00 g? A \\ iz < z 470 |- bo g 105: 3% F § 1.10 88 480— \‘\ ydrograph J J [- e ¢ ° iis Eg hyprograpH anp GRaPH "\t, Isso # ~ 500 |- OF AQUIFER COMPACTION AT : T i t ai m i me ae e ao age oe a as up 1.20 -{ _ THE LAKEVIEW TEST WELL e--" y fol f avi tt: i 230 & / = s i § 25 10! H c §5 ' g Se 2°} f GA { *. oh f I WO 39 |- } E <3 4 2 E2 40 /- THE GS-4 TILTMETER RECORD $ bz 50] j ( 4 € iy. f ~y o so |- *~* *may 1 1 } | } | Jan. I Fob-i Maul Apr-lMaleunel July J] “Slant! Oct. LNomi Deaf Jami Feb.i Mani Apni May iJunoi July i Mayhem 1965 1966 FiGurRE 13.-The GS-I tiltmeter record and graph of aquifer compaction at well 11N/21W-3B1. delay is not unreasonable if one considers the time re- quired for significant head decline to migrate laterally from the areas of intensive pumping to the tiltmeter site. (The nearest irrigation well is almost a mile from the site.) Furthermore, local variations in agricultural practices may have produced appreciable time differ- ences between the pumping effects recorded at the test well and those that occurred in the irrigated areas closest to the tiltmeter site. The tilt recorded during the pumping season (55 % 10 inch or 46 microradians), if extrapolated north- westward toward the center of subsidence, would pro- duce much more subsidence than actually occurred, about 1.55 feet at the Lakeview test well, for example, instead of the 0.25 foot that was recorded. This situa- tion is in accord with the historical record of subsid- ence, which shows that differential subsidence, or tilt, has been particularly intense along the north base of Wheeler Ridge. (See fig. 1.) The intensification of tilt- ing close to the ridge presumably is due to profound seasonal steepening of the ground-water pressure sur- face in that area and perhaps also to a local decrease in compressibility of the sediments adjacent to the ridge. Both factors would be likely corollaries of the inferred geologic structure beneath the pumping-plant site. Pleistocene gravels with a northeasterly dip of 60° crop out in the north flank of Wheeler Ridge a quarter of a mile south of the pumping-plant site, and presum- ably extend beneath the valley floor with dips dimin- ishing rapidly northward. Because permeability across the bedding typically is much less than permeability parallel to the bedding, the dipping strata almost cer- tainly constitute partial barriers to ground-water move- ment; such barriers would cause steep hydraulic gra- dients and delayed transmission of head declines from the areas of concentrated pumping to the north. It is also possible that the up-arching of older, more indur- ated sediments near Wheeler Ridge into the depth range of artesian-head decline has effectively thinned the aquifer system and reduced the compressibility of this zone on the north flank of the anticline. Early in September 1965, ground-water pumping virtually ceased and artesian pressures began to re- cover rapidly. The compaction record from the Lake- view test well (fig. 13) suggests about 0.03 foot of ex- pansion of the aquifer system at the onset of rapid re- covery, followed by an interval of stability during the 4 succeeding months of water-level rise. The tilt record shows minor fluctuations after the first of September, but no change comparable to that which occurred during the pumping season. Early in October 1965, the failure of a differential transformer and certain mechanical problems necessi- tated partial dismantling of the GS-I tiltmeter. Dur- ing reassembly it was not possible to recover pre- cisely the preexisting instrument datum. At the time it was thought that the preexisting datum had been recovered within +0.002 inch. However, the trend of LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY the subsequent record suggests that the datum may have been offset by 0.004-0.008 inch in such a way as to indicate an. erroneously large subsidence of the northwest pot. During the heavy rains at the end of December, suf- ficient water seeped under the walls of the shelters to moisten the clayey soil surrounding and underlying the northwestern instrument pad at the GS-I tiltmeter. The moistened soil swelled rapidly and elevated the pad about 0.012 inch. Continuing cool, damp weather prevented significant drying of the soil during January 1966. At the end of January a storm flooded the south- eastern pad and caused an apparently equal amount of soil swell there; this swelling returned the tilt record to its former trend line. A rapid southeastward tilt began February 11 and continued through May, during which interval 98 x 10 inch of differential elevation change occurred. Evi- dence from the compaction records, discussed in a fol- lowing section, indicates that the large southeastward tilt was caused by hydrocompaction of deposits be- neath the southeastern pot foundation. The hydro- compaction resulted from lateral percolation of water from infiltration pond 8-17, 400 feet upslope. On June 10, the record reversed and began a rapid northwest- ward tilt which continued through July, totaling 47 % 10~ inch of differential elevation change. Finally, from July 30 until the end of the record (September 16), irregular but moderately rapid southeastward tilting caused 22 . 107 inch of differential elevation change. Although the northwestward tilting in June and July once again corresponds approximately to the pe- riod of most intensive draft on the ground-water reser- voir, the correlation between the tilt record and the hydrograph at Lakeview is much less impressive in 1966 than it was in 1965. This problem is discussed further in the "Summary" of this report. Data from GS-II tiltmeter Data from line 1 and line 2 of the GS-II tiltmeter (fig. 12) show that the site was nearly stable from Oc- tober through mid-December 1965. During that period the only consistent trend in the data was a slight northeastward tilting on line 2, which, in fact, con- tinued until April 1966, at an average rate of 12 mi- crons per month of differential elevation change. This observed trend seems to indicate that during the autumn period of no known aquifer or near-surface compaction, the GS-II tiltmeter record suggested a continuing "background" tilting of about 5 microra- dians per year in a direction about N. 55° E. Tectonic tilting in that direction and of such a magnitude (0.5 * The compaction-sensor curves in figure 12 are strongly influenced by tem- perature, as will be discussed in detail in the next section. G21 ft per 100 ft per 1,000 yrs) would not be inconsistent with what is known of the recent activity of the White Wolf fault and of the Pleistocene origin of the Wheeler Ridge anticline (Dibblee, 1954, p. 26, 27). The stability shown by line 1 from October through mid-December and by line 2 through mid-April is highly significant in that it clearly demonstrates the insensitivity of the tiltmeter system to seasonal tem- perature changes. From October to late December, the temperatures in the instrument shelters fell 17°C and the hose temperatures fell about 22°C. From late De- cember to mid-April the shelter temperatures rose 15°C and the hose temperatures rose 22°C. These changes encompassed 70 percent of the total annual temperature fluctuations in the shelters and hoses, but produced no discernible response in the tiltmeter records. On December 16, 1965, water was introduced into preconsolidation pond 8-17, 400 feet upslope from the southeast ends of the tiltmeters. On December 21, the graph of line 1 turned sharply upward, indicating that the southeastern pot was subsiding in relation to the other two. (In order to plot the northward tilting dur- ing the pumping season as a declining trend compar- able to the hydrograph and compaction record in figure 13, an arbitrary plotting convention that causes the relative subsidence of the southeastern pot to appear on the graph as a rising trend was adopted in laying out figure 12.) Relative subsidence of the southeastern pot continued at an average rate of 11 microns per day through January 7. From January 7 to March 1, the southeastern pot subsided at a diminishing rate that averaged 6 microns per day. Differential subsid- ence of the southeastern pot relative to the north pot from December 21 to March 1 was about 500 microns. On March 1, the southeastern pot began an accel- erated subsidence that rapidly attained a sustained maximum rate of 33 microns per day. On March 2, input of water to pond 8-17 ceased. The subsidence slowed in April, May, and June and finally ceased on July 6, after creating a total differential displacement of 2,530 microns since December 21. Between July 11 and July 29, there was rapid rela- tive subsidence of the northern pot in the amount of 490 microns, followed by a resumption of slow south- eastward tilting. Line 2 first departed from its well-established trend of very slow northeastward tilting (12 microns per month of relative subsidence of the northern pot) about April 1. Thereafter, northeastward tilting oc- curred at a more rapid rate; tilting accelerated notably in mid-May but gradually diminished through June, July, and August. Between April 1 and September 6, 1966, the northern pot subsided about 600 microns G22 with respect to the southwestern pot-a departure of about 500 microns from its previously established trend. For both lines 1 and 2, the interval of record between June 3 and July 18, 1966, is shown disconnected from the rest of the plot because of some uncertainty as to the precise relationship of the instrument datum dur- ing this interval to that existing before and after. The uncertainty, which may be as much as 100 microns, derives from the fact that the differential transformer in the northern pot was damaged by prolonged immer- sion during the latter part of May because of leakage of a valve on the fluid-supply reservoir. The damage and resulting offset in the instrument datum were not noticed until mid-July, when the transformer failed entirely and had to be replaced. Data from GS-II compaction sensors The long-term records of the compaction sensors (fig. 12) are dominated by two kinds of fluctuations- a seasonal oscillation apparently due to the tempera- ture cycle, and, in the case of the southeast sensor, a major downward departure from the temperature curve, due to hydrocompaction effects beneath the southeast trivet. The relationship between temperature and indicated compaction is illustrated in figure 14; this figure shows MECHANICS OF AQUIFER SYSTEMS book values of thermal-expansion coefficients yield an amplitude (double) of 130 microns for the seasonal dimension change in the above-ground components of the compaction sensor. Very few data were obtained on temperatures of the piers, but temperatures were recorded regularly at 7, 16, and 40 feet below land surface in the north compac- tion-sensor well. The relationship between the ampli- tude of seasonal temperature fluctuation and depth in the wells was found to be approximately exponential. Because several spot checks indicated that the temper- atures at depths of about 8 feet in the piers were gen- erally comparable to those recorded at 7 feet in the wells, the assumption has been made that the observed exponential relationship can be extrapolated to the piers. On the basis of this assumption, the value calcu- lated for the average seasonal temperature fluctuation for the 11 feet of buried pier is 13°C, and the resulting seasonal dimension change is about 500 microns. The total calculated dimension change for the piers plus the above-ground elements is therefore about 630 mi- crons. This amount is offset to a minor degree by the thermal response of the invar tape, which for the entire length of tape does not exceed 30 microns. Thus, it can be estimated from the properties and dimensions of the materials and the observed temperature fluctua- tions that approximately 600 microns of fluctuation in e {Temperature in north compaction well 7 feet below land surface TEMPERATURE, IN DEGREES FAHRENHEIT \\ e* ra o- sath -| 68 E Temperature in _ ues be +* 2 w north pot & § 200 |- -| 60 o & o o o £ a = 400 |- North compactionx. -| 52 E Z sensor xv < o as , 5 *"600 | St | pori. o | | | | | a Oct. Nov. I Dec. l Jan I Feb. Mar. Apr May June July 1 Aug. [ Sept. 1966 F1GURE 14.-Temperature changes and indicated compaction, northern compaction sensor. the northern compaction record and the temperatures measured in the northern tiltmeter pot and at a depth of 7 feet in the northern compaction sensor well, The close correspondence between the temperature and compaction records suggests that thermal expansion and contraction of the piers, trivets, tiltmeter pots, and transducer mounts may account for the seasonal fluc- tuation in the compaction records. Calculations based on the observed temperature range of 22°C and hand- the compaction record can be expected in response to the annual temperature cycle. This value compares fa- vorably with the 570 microns of fluctuation (a mini- mum value) recorded by the northern sensor and the 750 microns recorded by the southwestern sensor. Hindsight reveals that better temperature compen- sation of the compaction sensors could have been achieved if the invar tapes had been clamped at the bottom instead of at the top of the T-bar assembly. LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G23 (See fig. 8.) In the zone of maximum temperature fluc- tuation, this would have placed comparable materials (mostly steel pipe) in parallel, instead of invar in parallel with steel, which has a thermal expansion co- efficient about 30 times that of the invar. As far as can be determined, the indicated seasonal compaction and expansion recorded by the southwest- ern sensor during 11 months of operation are attribut- able almost entirely to thermally induced changes in dimension in the instrument and its piers. If the southwestern compaction record is accepted as the standard curve of temperature response for all three instruments, it is evident that the first well- defined departure from this curve appears in the south- eastern record early in January 1966 (fig. 12). At that time, an apparent expansion of the sediments beneath the southeastern trivet began, as shown by the rising trend of the record. Early in March, the rising trend was abruptly reversed and rapid compaction was re- corded through May, followed by slow compaction dur- ing the remainder of the record. The northern compaction record began a gradual but continuing downward departure from the tempera- ture curve in April, indicating that real compaction began at that time. (See fig. 12.) To minimize the effect of the temperature fluctua- tions and to facilitate a comparison of the compaction and tilt records, differential compaction plots (north minus southeast and north minus southwest) are pre- sented in figure 15. The apparent northward tilting shown by the differential compaction curves during November and December results from the fact that the northern compaction sensor recorded substantially more indicated compaction during this period than did the other two (fig. 12). This excessive indicated com- paction is not corroborated by the tiltmeter data and therefore cannot be attributed to changes in the near-surface elements of the equipment (piers, trivets, and measuring pots). It may simply reflect processes of thermal and mechanical stabilization of the sedi- ments surrounding the subsurface bench marks, follow- ing the disturbance created by drilling. The same ex- planation may be invoked to account for the modest divergence of the differential compaction plots during November and December. The downward trend of the north-minus-southeast graph (comparable to line 1 of the tiltmeter) during January and February suggests northwestward tilting at the time when line 1 of the tiltmeter was recording substantial southeastward tilting. Both phenomena are believed to be related to the influx of water to the sediments through pond 8-17, which was flooded con- tinuously from December 16 to March 2. In a previous progress report (Riley, 1966), it was tentatively con- cluded, on the basis of data available through January 1966, that the initial southeastward tilt recorded by the GS-II tiltmeter was due to the loading effect of the large mass of water (about 2,900 tons per day) being added to the deposits beneath the pond. However, the lack of a comparable response from the GS-I tiltmeter casts considerable doubt on this interpretation. In the light of later data and an improved understanding of the response characteristics of the compaction sensors, the following alternative interpretation is suggested. The principal movement of water from the infiltra- tion pond and wells (80 ft deep) is presumed to have been downward toward the water table; before flooding of the pond began, the water table was at an unknown depth, but greater than 250 feet (W. D. Fuqua, oral commun., June 1965). The writer postulates that some of the percolating water encountered a narrow, highly permeable stringer of gravel filling a former channel cut in sediments of much lower permeability. Moving along the channel as a perched ground-water body, this water was, in effect, "piped" downdip toward the tilt- meter site far ahead of the general advance of the wet- ted front surrounding the pond. Arriving beneath the southeastern end of the GS-II tiltmeter, at some depth appreciably greater than 150 feet, the water created a highly localized tongue of hydrocompaction whose gradual growth was recorded by the moderate southeastward tilting between December 21 and March 1. Because the hydrocompaction was initially restricted to a small body of sediment at considerable depth, its effect, in transmission to the surface, was spread later- ally and attenuated vertically by the cohesiveness and resulting "beam strength" of the dry overlying de- posits. Those deposits thus were placed in vertical tension above the region of actual compaction, and the subsurface bench mark subsided more than the trivet at land surface. Evidence tending to support this pos- tulate is found in the approximately 200 microns of expansion recorded by the southeastern compaction sensor between January 10 and March 1 (figs. 12 and 15). The differential subsidence of the southeastern trivet as recorded by the tiltmeter was about 500 mi- crons, so the total subsidence of the southeastern sub- surface bench mark relative to the north trivet was about 700 microns. Continuing growth of the bulb of wetted sediments beneath pond 8-17 evidently pushed the moisture front upward and outward past the southeastern sub- surface bench mark on March 2, as is shown by the sharp inflection in the differential-compaction graph * The existence of thin zones of very high permeability is demonstrated by the fact that intervals of severe mud loss were encountered in test holes drilled by the hydraulic rotary method immediately upslope from the tiltmeter site (W. D. Fuqua, oral commun., June 1965). G24 SOUTHWARD TILT -> DIFFERENTIAL ELEVATION CHANGE, IN MICRONS SOUTH DOWN --> DIFFERENTIAL COMPACTION, IN MICRONS 2600 2400 2200 2000 800 600 400 200 -200 -400 - 600 - 800 - 800 - 600 =400 -200 200 400 600 MECHANICS OF AQUIFER SYSTEMS I | | | | I | /‘/ = y M "\.~ LINE 2 -I “v7 Kaz ea al ..... __\_\_ R \ ire bel NORTH MINUS SOUTHWEST "o \[. + -I NORTH MINUS 50m 7 + R - .\N/ | | | | | Oct. I Nov. ll Dec. | Jan. 1 Feb. l Mar. I Apr. May June July Aug. Sept. 1965 1966 mm 15.-Differential compaction and GS-II tiltmeter data. oop eg iment e we com =: LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G25 (fig. 15). Thereafter, hydrocompaction between the subsurface bench marks and some unknown upper limit caused about 1,250 microns of differential com- paction in the upper 150 feet of sediments. If, as pre- viously stated, the indicated compaction record of the southwestern sensor (fig. 12) is taken as the standard temperature-response curve, then the total hydrocom- paction between the southeastern trivet and its sub- surface bench mark may be estimated at about 1,500 microns, on the basis of the departure of the indicated southeastern compaction record from the indicated southwestern compaction record, March to September 1966. (See fig. 12.) The north-minus-southwest differential-compaction graph (fig. 15) shows no indication of hydrocompac- tion effects until mid-April. Thereafter, a fairly con- stant rate of compaction beneath the northern trivet is indicated, with a total of about 300 microns attained by the end of the record. This amount constitutes 60 percent of the northeastward tilting (500 microns) re- corded on line 2 during the same period. A major, but indeterminate, part of the 200 microns of northeast- ward tilting that must be accounted for below the north subsurface bench mark probably is attributable to deep-seated differential aquifer compaction due to artesian-head decline. During the period of rapid hydrocompaction (mid- December through June), line 1 of the tiltmeter re- corded about 2,500 microns of differential subsidence beneath the southeastern trivet. Within the same pe- riod, the northern compaction sensor recorded about 200 microns of hydrocompaction. (See fig. 15.) Thus, the total subsidence of the southeastern trivet during this time was at least 2,700 microns. Data from spirit leveling (discussed in a following section) reveal that nearby areas outside the influence of hydrocompaction tilted toward the north during this period because of deep-seated aquifer compaction. This fact strongly suggests that the total hydrocompaction beneath the southeastern trivet was substantially more than 2,700 microns and that probably more than half of the total hydrocompaction occurred below 150 feet. In the preceding discussion, the compaction data have been taken at face value as indicative of actual hydrocompaction at the point of measurement. In the strictest sense, this implicit conclusion must be re- garded as an inference because, in the absence of an array of piezometers and soil-moisture probes, no direct information on the migration of water from pond 8-17 is available. The small magnitude of compaction at the pump- ing-plant site (about 3 millimeters) in contrast to the 1,080 millimeters (3.54 feet) of subsidence that oc- curred at pond 8-17 suggests that only a minute per- centage of the hydrocompactible deposits beneath the site was appreciably moistened. This, in turn, implies that only the outermost fringes of a highly irregular moisture front migrated through the sediments as far as the pumping-plant site. Alternatively, it might be argued that the apparent hydrocompaction at the site was due wholly or in part to a lateral transmission of strain from the area within 200 feet of the pond where nearly all the subsidence occurred. This argument assumes that the deposits possess a fairly high degree of tensile strength and thus are able to transmit laterally part of the centripetal pondward rotation that affected the area immediately surrounding the pond. No evidence of the required strength is available. On the contrary, the characteristic weakness of soils in tension is demonstrated by the numerous tension cracks that formed around the pond as the unwetted shallow deposits tipped toward the pond in response to differential hydrocompaction at greater depth. Cracks usually developed at radial intervals of 10-50 feet and had initial widths at the surface as small as 0.05 inch. Cracking had extended 215 feet from the pond by Feb- ruary 4, 1966, but not until mid-April did the cracks reach the maximum extent of 350 feet from the pond and 50 feet from the tiltmeters. The cracking demon- strates that the sediments could not withstand appre- ciable tensile strain and that stress was relieved by quasi-brittle failure rather than by plastic yielding. In addition, the cracks, extending down to unknown depths, served to isolate, at least partly, the area of major subsidence from outlying areas. Additional evidence in favor of direct hydrocompac- tion rather than the strain-transmission hypothesis may be inferred from the spatial and temporal distri- bution of hydrocompaction effects around pond 8-17. Spirit-level surveys indicate that subsidence around the pond diminished very abruptly beyond about 150 feet from the pond's northwestern margin. This sug- gests that the bulb of complete or nearly complete sat- uration never expanded beyond that distance. The leveling data also show (1) that by January 6, 1966, subsidence at the pond was 95 percent of the value achieved by the end of the flooding on March 2 and (2) that by April 15, subsidence within 100 feet of the pond was 90 percent of that attained by September 1966. In contrast, the compaction sensors recorded no compaction before early March, and the tiltmeters had by mid-April recorded only 65-75 percent of their maximum southeastward tilt. It should also be noted that the infiltration rate had stabilized by mid-Janu- ary at about 90,000 cubic feet per day. These facts suggest a slow but continuing lateral migration of cap- illary moisture beyond the limits of a bulb of satura- G26 MECHANICS OF AQUIFER SYSTEMS tion that had become essentially stabilized early in the hydrocompaction episode. The high degree of horizon- tal and vertical textural variability characteristic of the fan deposits insures a large range of capillary per- meabilities, which in turn implies a highly irregular moisture front, characterized by increasing irregularity at increasing distances from the pond. This conceptual model of the hydrocompaction process provides, in the writer's opinion, the most reasonable explanation of the facts available and is the basis for the interpretive statements and conclusions presented in this report. DATA FROM SPIRIT LEVELING Before the present investigation, information on tilt- ing in the immediate vicinity of the pumping-plant site was derived from a series of spirit-level surveys over bench marks A1053 and LS-8. (For locations of bench marks, see fig. 16.) The California Department [=) 8 LS-8 was radically affected by hydrocompaction that was caused by the flooding of adjacent preconsolida- tion ponds. Bench mark LS-8 was less than 40 feet from the edge of a field that was irrigated during the latter part of the 1950's and as recently as 1962. Therefore, the possibility of bench-mark subsidence due to near-sur- face hydrocompaction during this period must be con- sidered in evaluating its history. For this purpose, the differential elevation changes of bench mark B1053 with respect to A1053 are also shown in figure 16. Bench mark B1053 was 1.0 mile due west of LS-8 in a comparable geologic setting. The nearest irrigation was half a mile to the north and east, so hydrocompac- tion at this location can be ruled out. The subsidence history of LS-8 closely approximates that of B1053 and shows no significant departure correlating with cessa- tion of nearby irrigation in 1962. This fact indicates 1% I I I ; \' BENCH MARK B1053 0.20 |- BENCH MARK LS ¥ R. 20 W. o 8 [=) 8 -«<--NORTH DOWN DIFFERENTIAL ELEVATION CHANGE, IN FEET P 8 DEPTH TO WATER, IN FEET BELOW LAND SURFACE 8105 ‘NO - | & Reser * COMPACTION, IN FEET § [ Adjacent preconsolidation 0.80 0 _ 2000 4000 FEET ponds flooded fll llllllI||lllllllllllllllIllllllllll lllllllllllllllllllIlllllllllllllllllIIIIIllIlll 961 1962 1965 FigurE 16.-Subsidence of bench marks LS-8 and B1053 with respect to bench mark A1053. of Water Resources surveyed the bench marks an- nually from 1960 through 1965 and the U.S. Coast and Geodetic Survey leveled through the area in 1960, 1964, and twice in early 1965. The results of these surveys are plotted in figure 16, which shows the progressive subsidence of LS-8 with respect to A1053. LS-8, which is about 1,380 feet north of A1053, subsided at a nearly uniform rate (with respect to A1053) from 1960 through mid-1963, and at a somewhat reduced rate from mid-1963 through mid-1965. The northward tilting averaged 104 microradians per year (about 0.01 ft per 100 ft per yr) during the first period and 67 microradians per year during the second period. The average rate of north- ward tilt between April 1960 and August 1965 was about 90 microradians per year. No later data are usable because during September 1965, bench mark that local hydrocompaction did not affect LS-8 during the period shown. Data from the Lakeview test well (11N/21W-3B1), also plotted in figure 16, show continuing compaction of the confined aquifer system during the period of record (1963 through 1966). Although the compaction rate fluctuated in response to seasonal changes in head in the aquifer, the overall rate was approximately uni- form, as was the subsidence rate of LS-8 and B1053 during this period. In the light of the facts just presented, the tiltmeter data, and the detailed leveling data discussed in sub- sequent paragraphs, it is believed that the 1960-65 subsidence history of bench mark LS-8 is a reliable record of the effects of aquifer compaction at a point one-quarter mile northwest of the pumping-plant site. For the period 1963-65, the due northward tilting ESOS rn rain mim ege meier omni ~a - LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G27 near the pumping-plant site, as indicated by the sub- sidence of bench mark LS-8 relative to A1053, is ap- proximately defined by the empirical relationship T = 1.4C x 10% where T is the angular tilt expressed in microradians and C is the compaction of the aquifer system, in feet, measured at the Lakeview test well. During August 1965, after the seasonal character of the tilting had been demonstrated by the GS-I tilt- meter, the Department of Water Resources installed a special array of paired bench marks near the pumping- plant site (fig. A on pl. 1). Each pair consisted of a standard bench mark (brass cap in concrete pier) and an adjacent "deep-seated" pier of 1%4-inch pipe set about 15 feet into the ground. Ten pairs were set along the aqueduct centerline between preconsolidation ponds 8-17 and 8-9. Twelve pairs were established along a line approximately normal to the aqueduct be- tween preexisting bench marks A1053 and WR-18. The two lines intersected 380 feet northwest of the tiltmeter station. On August 30, 1965, a crew from the Department of Water Resources leveled over the bench marks for the first time, using high-precision equipment and techniques. Subsequent releveling was done on Octo- ber 6 and December 15, 1965, and on April 15, June 14, and September 13, 1966. The results of this work are presented on plate 1 in figures B and C as a series of tilt profiles, showing the changes in elevation of the deep-seated bench marks for each successive survey. The August 30, 1965, elevations were taken as the datum, and each profile represents the changes in ele- vations that have occurred since that date. All eleva- tions are relative to bench mark A1053, which was the starting point of the surveys and was arbitrarily con- sidered to be stable. The profiles show very clearly both the regional northward tilting due to deep-seated aquifer compac- tion during the winter and summer irrigation seasons and the highly localized effects of hydrocompaction around ponds 8-17 and 8-9. There is also a small but well-defined northeastward tilting during the fall, com- parable to that recorded by line 2 of the GS-II tilt- meter. The resolution of apparent tilts along the two pro- files into true tilts is shown by the vector diagram (fig. D on pl. 1) in which the lengths of the vectors are pro- portional to the angles of tilt in microradians. The vec- tor for the period August 30-December 15, 1965, is based upon the estimated average slopes of the entire profiles. Vectors for subsequent intervals are based on bench marks A1053, 1016, 1007A, and 1009A, which apparently are unaffected by hydrocompaction. The vectors should be regarded as approximate, because in some cases leveling errors of only 0.001 foot would pro- duce large changes in their direction and length. For example, a total leveling error of 0.001 foot between bench marks A1053 and 1016, 900 feet apart, would produce an angular error of 1.1 microradians. The same leveling error between 1007A and 1009A, 300 feet apart, would result in an angular error of 3.3 micro- radians. It is evident from the vector diagram that between August 30, 1965, and September 13, 1966, the tilt his- tory of the pumping-plant location (outside of hydro- compaction areas) was dominated by two major epi- sodes of northward tilt, corresponding approximately to the winter and summer irrigation seasons. Between December 15, 1965, and April 15, 1966, the tilt was 21 microradians in the direction N. 2° E.; and between June 14 and September 13, 1966, the tilt was 15 micro- radians in the direction N. 9° W. The minor north- northwestward tilting (3 microradians) during the spring of 1966 is poorly controlled because of the small elevation change and short profile available and must be considered very approximate. The modest north- eastward tilting (4.5 microradians) during the fall of 1965 is, on the other hand, well controlled by the long profile and probably is significant. As previously noted in the discussion of the tiltmeter data, this type of tilt- ing may be of tectonic origin. The total tilt from August 30, 1965, to September 13, 1966, as found by the addition of the vectors in fig- ure D on plate 1, is 42 microradians in the direction N. 1° B. The relative coarseness of the leveling data and the distances between the bench-mark grid and the tilt- meters preclude detailed comparisons between the two kinds of information. Nevertheless, a question nat- urally arises as to why northeasterly tilt on line 2 of GS-II was only 2 microradians during the winter irri- gation period (December 15, 1965, to April 15, 1966), while tilting along profile A-A' between bench marks A1053 and 1016A was 14 microradians. No definitive explanation can be given for this seeming anomaly. However, examination of figures B and C on plate 1 demonstrates that a considerable degree of irregularity is characteristic of the tilt profiles. Some of the irregu- larity presumably is due to minor leveling errors, but substantial changes in slope, greater than the probable range of error, occur from place to place along the pro- files. For example, between December 15, 1965, and April 15, 1966, the average tilt of the 2,020-foot profile segment between bench marks 1016¥ and 1022A, which includes the segment directly downslope from the tiltmeters, was only 3 microradians northeastward, while the segment A1053-1016A tilted 14 microra- dians, as noted above. Thus, the local irregularities in the leveling profiles and the rapid decrease in tilt with distance from the base of Wheeler Ridge indicate that G28 MECHANICS OF AQUIFER SYSTEMS small tilts measured over relatively short distances cannot be confidently extrapolated very far from the point of actual measurement. SUMMARY Two continuous-recording liquid-level tiltmeters were operated at land surface on the site of the future Wheeler Ridge pumping plant of the California Aque- duct. The location, at the southern end of the San Joaquin Valley, is at the margin of a large bowl of ac- tive land subsidence caused by compaction of the con- fined aquifer system under the stress of artesian-head decline; the site is also subject to subsidence due to hydrocompaction of moisture-deficient alluvial-fan de- posits. The first tiltmeter, designated GS-I, began record- ing in May 1965. Between mid-June and the end of August 1965, the GS-I tiltmeter recorded 46 micro- radians of valleyward tilting (0.0046 ft of differential elevation change between bases 100 ft apart). Between the end of April and the end of July, the Lakeview test-well installation recorded 47 feet of artesian-head decline and 0.25 foot of compaction in the artesian aquifer system. If a 6-week time lag is allowed for pumping effects to migrate laterally through the aqui- fer system, there is a very good apparent correlation between the record of the tiltmeter and the curves of head decline and aquifer compaction. The GS-I tiltmeter, mounted on thin concrete pads, is known to have been sensitive to changes in soil mois- ture and soil temperature, but the large summertime deflection of the tilt record does not correlate with any major change in these factors, nor does it correlate with flooding of infiltration ponds, construction activ- ity, or any other known phenomenon except artesian- head decline. Known major changes in soil moisture and temperature during the fall and winter produced much smaller deflections of the tilt record. Therefore, it is concluded that most, if not all, of the northwest- ward tilting recorded during the summer of 1965 is most reasonably attributable to differential aquifer- system compaction due to seasonal decline of artesian head. Although the one-directional GS-I tiltmeter meas- ured only the N. 35° W. component of tilting and al- most certainly did not record the full magnitude of valleyward tilt, the 46 microradians of tilt recorded dur- ing the summer pumping season constitutes about half the average annual tilt that had been postulated on the basis of repeated spirit leveling between nearby bench marks during the period 1960-65. It is reason- able to expect that a roughly comparable amount of tilt would have been recorded during the other yearly pumping period, the pre-irrigation season of late winter and early spring, had the tiltmeter been in operation at that time. The second tiltmeter, a two-directional instrument designated GS-II, began recording in October 1965, after the end of the summer pumping season. During the fall and early winter, it demonstrated that the site was essentially stable when artesian head was not being drawn down by pumping. The only significant long- term movement recorded during this period was a very slow background tilting of about 5 microradians per year in a direction about N. 55° E. This tilt may be of tectonic origin. The GS-II tiltmeter, mounted on piers set 9 feet deep, was relatively insensitive to changes in surficial soil conditions. The short-term ir- regularities in the tilt records may be largely attribut- able to differential responses of the subsurface mate- rials to changes in atmospheric loading. The three compaction sensors linked to the GS-II tiltmeter proved to be rather sensitive to temperature changes in the instrument piers. Nevertheless, the ef- fects of hydrocompaction resulting from infiltration of water beneath preconsolidation pond 8-17 are clearly discernible in the records of the southeastern and northern compaction sensors. As far as can be deter- - mined, the major long-term fluctuations in the south- western compaction record were due almost entirely to changes in temperature. The southeastern compaction sensor recorded about 1,500 microns of hydrocompaction within the upper 150 feet of deposits. Comparison of the compaction and tilt records indicates that at least 2,700 microns of hydrocompaction occurred beneath the southeastern trivet and that at least 44 percent of the total hydro- compaction occurred below a depth of 150 feet. The amount of subsidence due to hydrocompaction beneath the pumping-plant site was too small (2.7 mm) to be, in itself, of practical engineering significance. It should be noted, however, that the site was at the extreme fringe of the moisture front surrounding infiltration pond 8-17 and that the percentage of moistened de- posits beneath the pumping plant was probably very small. In view of the apparent susceptibility to hydro- compaction of the deposits below 150 feet, the possi- bility of substantial subsidence beneath the pumping plant, in the event of thorough wetting, cannot be ruled out. The northern compaction sensor recorded about 300 microns of hydrocompaction between the northern trivet and the subsurface bench mark at 150 feet, while the tiltmeter was measuring 500 microns of northeast- ward tilt. Because of the evidence that hydrocompac- tion may occur at depths greater than 150 feet, it is impossible to determine from the tilt and compaction data how much of the 200 microns of northeastward tilting that must be accounted for beneath the subsur- e o oi ii i age oromo rs mm a- LAND-SURFACE TILTING NEAR WHEELER RIDGE, SOUTHERN SAN JOAQUIN VALLEY G29 face bench mark is due to hydrocompaction and how much is due to deep-seated compaction of the artesian aquifer system. Discrepancies among the tilt, compaction, and level- ing data indicate that the irregular, prolonged, and unpredictable process of hydrocompaction increasingly influenced the data obtained at the site after Decem- ber 21, 1965, and, by late April 1966, dominated the records from all instruments except the southwestern compaction sensor. As soon as hydrocompaction be- neath the subsurface bench marks is indicated in the records, it becomes impossible to determine whether a given feature in the tilt record is attributable to hydro- compaction below the bench marks, mass loading, differential aquifer compaction, or tectonic movement. Furthermore, compaction in equal amounts beneath the subsurface bench marks at both ends of the tilt- meter line completely escapes detection by both the compaction sensors and the tiltmeter. For these rea- sons, the northward tilting recorded by the GS-I and GS-II tiltmeters during June and July 1966 cannot be definitely and quantitatively related to the summer head decline, although the effect of aquifer compaction is clearly demonstrated by the northward tilting of the bench-mark profiles outside the areas of hydrocompac- tion. For the same reasons, no firm interpretation can be made of the irregular southeastward tilting recorded during August and September 1966. CONCLUSIONS Interpretation of the mutually supporting data from the Lakeview test well and from the tiltmeters, com- paction sensors, and spirit leveling at the Wheeler Ridge pumping-plant site leads to the following prin- ._.cipal conclusions: 1. In the valley areas north of Wheeler Ridge, decline of artesian head during the winter and summer ir- rigation seasons causes two pulses per year of aqui- fer compaction, resulting in substantial annual land subsidence. _ 2. The cone of artesian-head decline evidently en- counters a partial ground-water barrier and prob- ably less compressible deposits as it expands sea- sonally into the steeply north-dipping strata on the flank of the Wheeler Ridge anticline. The re- sulting steep hydraulic (and compressibility?) gradients generate a narrow band of fairly intense differential subsidence, or tilt, along the north base of Wheeler Ridge, in the area of the pumping-plant site. 3. Tiltmeter data recorded during one episode of ar- tesian-head decline in the summer of 1965 support the estimate based on repeated spirit-level surveys between 1960 and 1965 that as much as 100 microradians (0.01 ft per 100 ft) of northward tilting occurs annually. From August 1965 to Sep- tember 1966, however, data from spirit leveling indicated only 42 microradians of northward tilt. 4. The tiltmeter data and the leveling indicate that nearly all the tilting is due to differential compac- tion of the artesian-aquifer system under the stress of seasonal pumping. 5. There is inconclusive evidence from both the tilt- meter and the leveling data that 5-10 percent of the observed northward tilting may be due to some other cause, possibly tectonic. 6. Pleistocene and Holocene alluvial-fan deposits be- neath the pumping-plant site apparently are sub- ject to at least a limited degree of hydrocompac- tion (collapse on wetting) to depths appreciably greater than 150 feet. f 7. Hydrocompaction may proceed in a highly irregular manner as water moves downward and outward from the infiltration ponds through the heteroge- neous alluvial-fan deposits. 8. The resulting bowl of local subsidence continues to expand for months after infiltration at the surface has ceased. REFERENCES CITED Bonchkovsky, V. F., and Skur'yat, A. N., 1961, The level vari- ometer LV: Akad. Nauk SSSR, Izv. Geofiz. Ser., p. 79-90. Bull, W. B., 1961, Causes and mechanics of near-surface sub- sidence in western Fresno County, California, in Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-B, p. B187-B189. Dibblee, T. W., 1954, Geology of the southeastern margin of the San Joaquin Valley, California, in Earthquakes in Kern County, California, during 1952: California Div. Mines Bull. 171, p. 23-34. Eaton, J. P., 1959, A portable water-tube: tiltmeter: - Seismol. ~ Soc. America Bull., v. 49, no. 4, p. 301-316. Egedal, J., and Fjeldstad, J. E., 1937, Observations of tidal motions of the earth's crust made at the Geophysical In- stitute. Bergen: Geofys. Publikasjoner, v. 11, no. 14. Hagiwara, T., 1947, Observations of changes in the inclination of the Earth's surface at Mt. Tsukuba: Earthquake Re- search Inst. Bull., Tokyo [Japan] Univ., v. 25, pts. 1-4, p. 27-32. Lofgren, B. E., 1963, Land subsidence in the Arvin-Maricopa area, California, in Short papers in geology and hydrol- ogy: U.S. Geol. Survey Prof. Paper 475-B, p. B171-B175. Michelson, A. A., 1914, Preliminary results of measurements of the rigidity of the earth: Astrophys. Jour., v. 39, no. 2. Michelson, A. A., and Gale, H. G., 1919, The rigidity of the Earth: Astrophys. Jour., v. 50, p. 330-345. Riley, F. S., 1962, An automatic recording liquid-level tilt- meter [abs.]: Am. Geophys. Union Trans., v. 43, no. 4, p. 427. 1966, Progress report on the U.S. Geological Survey tiltmeter station near Wheeler Ridge, California: U.S. Geol. Survey open-file report, 23 p., 7 figs. Riley, F. S., and Davis, S. N., 1960, A tiltmeter to measure sur- face subsidence around a pumping artesian well [abs.]: Jour. Geophys. Research, v. 65, no. 5, p. 1637. U. S. GOVERNMENT PRINTING OFFICE : 1970 O - 373-386 g- rma w wo commie!" -~ 1. Mk - ui _ n _ fff __ 20 omc ___ ~ __ #. ce tko a_ dh __ A __ Ahh ___ - M sds ~ diffs © 23 tks .> we? * Ake --- [FIK Ree - 5 "ll ._ HA. Mth, S q/lr UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY T.10 8. 37°00 NORTHERN PART 120°52'30" R. 10 E. Los Banos THATS A 52’30"\ PROFESSIONAL PAPER 497 -E PLATE | SsOUTHERN PART 120° R; 14 £. 36°30 36°30" EXPLANATION ~ Qal © $$ . g 3 Alluvium 27930" 2 Eq Qal, unconsolidated clay, silt, sand and gravel deposited on alluvial fans and SE wa at Rood plains of the present streams; permeable to moderately permeable; little < FS § or no soil-profile development P Qalp, parts of alluvial fans with moderately to poorly permeable surficial de- C posits. Soil-profile development is apparent in most places r E < J O Terrace deposits Unconsolidated gravel, sand, silt, and clay of old stream terraces above level of present stream valleys and flood plains; mapped only where extensive J Pleistocene ore 120°30' A Tulare Formation Unconsolidated to semiconsolidated continental deposits, chiefly poorly sorted silty materials containing lenses of gravel and sand; locally contains beds of U _- fossiliferous limestone, marly silt, and gypsite Pliocene and Pleistocene TERTIARY AND QUATERNARY ,- 120°52'30" R.:10 E. EXPLANATION Contact U D Fault U, upthrown side; D, downthrown side 20 Strike and dip of beds Acca Measured geologic section Sections are shown in figures 5-7 Base from U.S. Geological Survey Santa Cruz, 1956 45'\1; N % 3730" \ P T:16 5x x San Joaquin Formation 2230" 2230" Unconsolidated to semiconsolidated continental and marine deposits of silt, 5 clay, samd, sandstone, gravel, and conglomerate. Mapped only in Kettleman 0 Hills T. 18 S. T.18-6: R. 16 E. ® § |. ig Etchegoin Formation 37730" Ax Unconsolidated to semiconsolidated continental and marine deposits of sand- | ~a stone, sandy silt, gravel, and clay; locally contains beds of conglomerate and E calcareous gypsite. Upper part possibly equivalent to San Joaquin Formation < of Kettleman Hills - ce I Lu l— Jacalitos Formation Unconsolidated to semiconsolidated continental and marine deposits of sandy %., y e silt, sandstone, conglomerate, and clay 5230" s $ 4 < .S g Sedimentary rocks undifferentiated of 3 Unconsolidated to consolidated marine and continental deposits of sandstone, hal siliceous shale, clay shale, conglomerate, carbonaceous clay, sand, gravel, silt, and clay J T. 19 8. 1.19 8; H ina Ku O & G 15" Sedimentary rocks undifferentiated < Consolidated marine deposits of concretionary sandstone, siliceous shale, clay {a shale, and conglomerate 1d U 1. 13:5. Z APPROXIMATE MEAN DECLINATION, 1970 i T H \ T: 20 S. ga» ¢ f f 45 4 5 < ) /// T. 14 S. J T 7'30'' CRRT] [EA L-- N- ___] ] ed ___ _ [ Sue 7'30" 120°00' Qalp 1 ¢4 s /_\ A 22'30' N 37!30" R. 13 E: x T:22 %. Ip 0 f 36°00, 4 36QOO/ "42" 15'~ RIG E. R7 E. 730" R18 E:: :120°*00' R. 19 E INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D.C. 1971-W6e9360 Geology largely by J. H. Green and W. A. Cochran in 1957; in parts of Tumey and Panoche Hills chiefly after Schoellhamer and Kinney (1953); from Little Panoche Creek north, chiefly after Briggs (1953); in the Kettle- man Hills after Woodring, Stewart, and Richards (1940); and in the Coalinga area after Arnold and Anderson (1910). Contact of Qal and Qalp modified after U.S. Dept. of Agriculture Soil Surveys of the Los Banos, Mendota, and Coalinga areas SCALE 1:125 0060 2 0 2 4 6 8 10 MILES EEE ~ msr pm F j .......... 2 o 2 4 6 8 10 KILOMETERS e-- l | | |___ SEG 36°30 f 3730" R. 13 E. 120°30" GEOLOGIC MAP OF THE LATE CENOZOIC DEPOSITS OF THE WEST BORDER OF THE SAN JOAQUIN VALLEY IN THE LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA UNITED STATES DEPARTMENT OF THE INTERIOR ] PROFESSIONAL PAPER 497-E. GEOLOGICAL SURVEY ; PEATE 2 r 120°00' es R. 6 E. 12%" 18 R. 7 E. R. 8 E. 121°00' R. 9 E. R. 10 E. R. i! £. - 45' R. 12 E. R. 13 E. 30' R. 14 E. R. 15 E. 15". 8.16 £: R. 17 E. o AAF 37°00 j gry : $4 98 EXPLANATION y C. tits T. 11 S. a $ < & $ "4 % % r S f x3 's R < & § Alluvium S ( , 0 ® § § QTu # is: ~ ““““““““““ R as) Undifferentiated continental sedimentary deposits t Peco Ranch o y a < A; Silt, sand, gravel, and clay . f 3 FA T. 12 S #X rire s | t. 13 s. }—-ZII - (~ Cid 4. Z- I< al $"! & W _ < R. 6 E $ $ F:'y $T § - 0 if Continental and marine sedimentary R. deposits mapped in this investigation C Silt, sand, gravel, and clay J I | C J % Ranch * | § $ C. : |. yaw is - t.13 8 es anat re op T. 13%. g§ 3 ~E I 1" $ G < Marine sedimentary and volcanic rocks IT! as 7L wwwww 3 'e -* $ £ yore - Sandstone, shale, siltstone, and conglomerate 2 |- I pope C I 45" - ] ( 2. th [] 1 % 9 PROFESSIONAL PAPER 4 PLATES (@joy a109) Z'I0TII-E1/p1T IN61-61/0¢ MPZE-81/0Z aul Aqunogy sgury-ousa14 - | IUbe-81/07 (2104 2109) ogt-g1/oz INII-81/02 | INE-81/0Z eNEE-81/61 (@1oy 2109) g9-gt/oz |-- T19E-£1/61 IPE-LI/6B1T |---4 I I 861 A¥MmHOIHN 31.¥1S -I __ I t (@104 2109) z trzz-z 1/61 NONLO3S I TN6-£1/61 fiuuwmwwmwuNw IV9-£L1/61 Mei MSZT-91/8T TIE y-. WSI~-91/81I A-dit l Nooss JeE-91/ZI (ejoy 2109) NETI-ST/LT MII-SI/LT dE-§S1T/z21 gn NOILONS . . (@joy 2409) INPE-S1/91 yaa1q eunjure;y If CNLZE-S1/91T 106-S1/91 a91-S51/91 1JP2-PI/ST \\ - Eage-pI/51 (@10y 2109) THo-tt/sr | _-_ 8-8 INOZ-#1/¥PTI - [- 1800' |- 2000" |- 2200" |- 2400" |- 2600" |- 2800" |- 3000" |- 3200" 3400" H ya. EU-... ~ ‘ 3 . Alluvial-fan } op---- Corcoran Clay Member of the Tulare Formation "d 1952 water table M | ; J Approximate \ - - § - _deposits Tri sk | ZZ $x Lacustrine l | is -_ bmp 06 CCl f»? | | | f¢>fiyafgfr>>g%gzbweéfisfi>§<;szaé o l im, acustrin (Diablo) | ush WWa -- deposits ood-pla | ~ )a \ .mfivw \ %. 2 2 a pa I .. §§2 & bds | i c 0 a. zl \ © o @- C ~PMmn/. mo 21%駧¥> n t MARS PR ,L/ E | f i a 5 F. MW 3 a \_\ 0 \ i Mm 4. Fa _ € W \ _ \ 8 o \ § # £ * 5.6 f A * MBs § € . a $4 | € § & ¢ § .S ys £ J 48 / 5 A X- PM tihe. . AMs Juan t f vf 3 H o 7 2 & a C + +0 & >--- fe F 6 i. s & £ (gift/xii: é? N a... m .... c § f ®: W. _ 9 e o _ o E \ , "4 C ~ E m n \ & lflm ... + . F. | 6 z J & 2 a. * m 3 | 6 o ann g {gig 4 8 5 E sy ta E f it f a £ g.- + \\ i ... .... 0 \ x a ... iL & S & é; % g A l m *, a : 8 % " > a. iP * # U i . % bo * & coe E Pe] C % G e 6 6.2 & p 'C . & o c 1 a Oo *> 5 % $16 f c "g., 2 t se > 5p 2 f - s¢ % §. _ go 4 a s 0 0 8 f £ a ts.. 'T "% U o c.o \ m yr =z % c_ Fo] H o ~ p = { * :$ F 0 o 1 @ 2 & \ N us E p o 2 So, i K/€ P o * f 0 4 bg . "gC 2 *, y N . o 3 's T .C 0%. H a. a & ~ B F o lea = © o F & § T = % s ¢ Frefes -~. D g & me & * C T 2 = © & \ + n +# a in M & fe iP. G A \ & C & a 3 " & € a & 2 . u nger at" st ® o 9 w _. and w- .... ... U S Oto U i s 00 00 Formation t ' € e © Fis % T G lama [+] w O # = 3 & e § f .* $ & R @ $ g -. 1$ £ a co if; & éng rad o f C kte o 3 < a o jig le ag. .s d hls 8 | ¥ \ | V | x- --- | # || CS_ MM e.+|LA I € 81 G hm: 6 $$ §yl|. -> | x: \ | l sg », ¢.! e / 4 / / f [ WN>>J)\)>\\\s2\ll\i{<>\/éfa\§ f - plainer pation 422523 UV hea | © étéfiswfigé a? fiqi/E/ng Zéig fifvsiééij 2g} Pm l At : fl! nok 143“ ranna x§s+§ §§\é,}liéé deposits 2 (Diablo - git/xxx /> ros sa- ans w monts ts «11211.erij AEs . imam murs fej a CG & oe ye "f erry Ty Littoral (5?wa C CITY W!" yoy ~ - f y yal pel and Sierra) nin alt sto Ham _ silt "y pn P N ha Ms a [... } (Kgl'fi/E; ggr}f\f\hfl<fllx[€1§ emmy" as. CoN 3 & cC % (G s: o H ® A . P d; d A A? | Cr)‘}])\L, §>s€i haw rw" m (iii;fix\§ -_-_L__ AAH Y ru Z fr -~ a ne s tae n oe sew. eae % A % % a c- ~ i i 6 & a & F & & & & & p "y, # & i > i s o o £ i 09 e- « I I P 0 : M - .MJJHJ g o % and 0-30 ~0-10 154 f=) x n an a silt sand (Diablo) prov y éifiéfi I I I 1 I I nollo3s ~- a I * agxfi>ézsaeeiuxyxtfxw My | ( | I / Massiv *a. *a 0 *+, « & *. VSE-EI/Et mo wo Ne maim e Hn me hv nto fne faw b eX nee wie men fe wet rs w id at ce ws he o m fs men Approximate 1952 water table rk INIbRSL/SL |L----I-- |-! IYEI-ZT/ET I _ 1 I Set mg | l I 0 | i ('] 1 £ \! 8:11 a t I € |a W M I * «14 T r” ad I ~I La LW a f AJJ (ajoy 2109) IH9T-ZT/ZT |-- I I I | | | | | v M4\mw,_ I N6T-Z1/1q Diablo) ~- | £ ¢ fail F Spas s >. A $M NYA een hame fru) AJ flood-plain 's - Alluvial-fan deposits Cote alse fine-grained (Diablo) | | deposits / wl $51» L5< a)??? u £67 A AW at lino Luk GEOLOGIC SECTION A-A' FRON PA i o cie n'e SK Jx --- \ $ & \ I S > > S) > S oat 5 k © G m + A no n \ 0 : * iL . £ &. : & 1mm 5 «~ £ | e w T + 6 a < e 5- | o us m C 3 .C a. m, m bo (0 s | / 6 C C CG t A C k. L] o A " ol -o 0 o 0 o A aime ) Gatt carmen! TL+ w % s- tars f o. MPW meyt gm 4 w Ua et Wha) $4 58 M Ax. "y 3 AN; V \ \ a [ [ hia L| | o / , ) | | | A Woah w Ewfihz (Q $521 fizz? Ierzi j, . Lé/Kieif Fwy/xx * bugle s... imino m ram ity meo Ntini ae f te ~ aan o cr t as af ~-. f\ \ MEA .All aa") " noted "whi si ) NB Rik & l mege=subuy if zepgng?fif "AJU Ts. (32 - Wells _- § | | | / - CG a 4 U Polg v (. o o \ s aie | 6 © | 6 m o € =) & G o I C p C 4- m m | 2 E | c ke! I fe | a o | o 5 | E | : f C t for 5.0 x & © T | £ & I @ - I o 0 o + _ ld J > [ anna man '" o T a | @ a = | 2 o o | C B F. "3 w 'm 6 [ m E R | a WV C | | 3 | ~3 & Pig | | ve z I a s 19 (Bing (s PIX w | =] & © Iss I 0 = ce e | go | 0 0 3 |'8 a : E 4 € | 3 U I3 | A Suto A 's 1 | 8 2 2 ale 212. 5 1 & | LL |- 5 3 Shake 9 AL | $499 5s > lala Notre |; \| | <3 $ Mic aa hrd 8 | Anh > aaa e ait < e s | bo g & 1 2 w onle e ." ieee w. 0 E a _ 3. 1g 18 :; 2 m TT | (ajoy 3109) ITZ-II/TI o 8 0 m E -I (*> § A i 5 ~ | § | «& ¥ s o 2 (8. 4 ew m \ tis wn 0 2 o E € S L .= s af B f 2 5 IPX == § ois * g. to. {2 ts ' § ? 13 \| 6 | 3 © 2 o 0 | n 3 | - & | # ~ ~I 5 9 I "g o o | + & 3 5 . | 3 & o | is a, f= - © (Druin I3 M G A yrghn® a a & a ? +o "® | m | ea \ 5% s. ~* 3 | h \ E2 33 0 ~ 6 I 3 | £ f is .e C ® T o. 4 sais P | = S ( 7 £ Cig t Ar o f $'o t o P 0 6 \ f 5 LE &a 0 p .C \ I z o C \/ : a a. \ | an f % Y- 2 j $ 0 \ 0 C F A. ~ Au j fx | | | 7C, T | S FZ J | | = , - o 0 o a 8 S o = e. o o C 3 $ S + © 8 & g © r Q g o O - ) C C \ o O < < le m i M. d O o A c m m m 411-341 0 - 11 (In pocket) No, 3 __10 MILES ST TOWARD TULARE LAKE BED , CALIFORNIA _10 KILOMETERS SCALE 1:125 000 VERTICAL EXAGGERATION x26 Perrin nne BLE ECBCE A NEAR LOS BANOS SOUTHEA ¥ LOS BANOS-KETTLEMAN CITY AREA 200" 400' 600' 800' 1000! 200' 400! 600° 800' 1000' 1200' UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY SPONTANEOUS | RESISTIVITY POTENTIAL 2 -MILLIVOLTS+ (OHMS mzm) so bs 0 1s 30 GRAPHIC LOG GENERALIZED LITHOLOGIC DESCRIPTION T (from core descriptions, drilling performance, and electric logs) 1d e cael mp F o r m a t i o n F ; é . ( e------___- Tu 0-320 ft. Silt and clay, some sand m 0-320 ft. Alluvial-fan deposits (Diablo) Dusky-yellow to yellowish-brown, calcareous; pentine and siliceous shale, some glau- cophane ica scarce. Contains fragments of ser- 320 Olive-gray to greenish-gray, 320-352 ft. Sand A -350 ft. Flood-plain deposits (Sierra) micaceous ome wood fragments 352-379 ft. Clay, plastic 379-465 ft. Clay, plastic to brittle, massive 350-379 ft.Flood-plain deposits (Diablo) Greenish-gray to greenish-black; mica \ scarce 379- (Lacustrine deposit) Dark-greenish-gray, diatomaceous 465 ft. Corcoran Clay Member 465-513 ft. Clay, silty 513-558 ft. Sand, silty careous incrustations. Sands and : # gravels contain fragments of siliceous 558-568 ft. Clay, silty, plastic to loose shale, volcanic | basalt, .and 'valcanie 568-603 ft. Clay and sand andesite 603-690 ft. Clay, silty 690-714 ft. Sand, loose, massive 714-733 ft. Clay, silty, some sand 733-752 ft. Clay, silty, plastic to firm, massive 752-776 ft. Silt, sandy 776-828 ft. Sand and gravel 828-860 ft. Silt, sandy and clayey, massive 860-931 ft. Sand, fine to coarse; gravel and silt streaks; conglomerate below 905 ft. 931-1000 ft. Sand, poorly sorted 465-1000 ft. Flood-plain deposits (Diablo) Greenish-gray to greenish-black, slightly to moderately micaceous; occasional cal- CORE HOLE 12/12-16H I1 Note.-Principal source of de- posits, where identified, is indicated as Diablo (derived from the Diablo Range) or Sierra (derived from the Sierra Nevada) SPONTANEOUS | RESISTIVITY GRAPHIC GENERALIZED LITHOLOGIC DESCRIPTION POTENTIAL LOG (from core descriptions, drilling A performance, and electric logs) -MILLIVOLTS+ (OHMS M/M) 100 50 0 15 30 F o r m a t i o n T u I a re 0-120 ft. Sand and gravel; some clay and silt interbeds 120-299 ft. Sand, fine to coarse; some grav- el; clay and silt interbeds 299-321 ft. Sand and silt 321-345 ft. Clay 345-405 ft. Silt, sandy 405-447 ft. Silt and sandy 447-475 ft. Sand and silty sand 475-582 ft. Sand, silty, fine to medium 5é2—610 ft.Sand, fine to medium;some gravel 610-648 ft. Silt and sand 648-676 ft. Sand, fine to coarse; some gravel 676-730 ft. Sand, fine to coarse, massive 730-750 ft. Silt, massive, friable 750-780 ft. Sand, medium to coarse, massive 780-807 ft. Clay and silt; some sandy layers 807-840 ft. Sand and gravel, loose 840-880 ft. Clay, silty to sandy 880-912 ft. Clay, plastic 912-933 ft. Sand and gravel 933-952 ft. Clay and sandy clay 952-1034 ft. Sand, silty, loose to firm 1034-1077 ft. Sand and gravel 1077-1133 ft. Clay silty; some sand 1133-1248 ft. Sand, silty, loose to firm 1248-12é6 ft. Clay, silty 1286-1369 ft. Sand, fine to coarse; some gravel 1369-1435 t. Clay, silty 1435-1460 ft. Sand, fine to coarse 1460-1480 ft. Clay 1480-1640 ft. Sand, very fine to medium, silty, loose to firm | 1640-1792 ft. Silt and clay; massive clay- stone, some sand 0-670 ft. Alluvial-fan deposits (Diablo) Olive-brown to yellow-brown; some clays and silts dusky yellow. Most strata mod- erately to highly calcareous, containing fragments of fine-grained rocks includ- ing chert, jasper, quartz, and sandstone; some weathered mica is present 670-730 ft.Lacustrine deposits Olive-brown to bluish-gray, locally sorted 730-750 ft. Corcoran Clay Member Dark-bluish-gray; contains organic matter and some biotite 750-780 ft. Lacustrine deposits Dark-bluish-gray, locally well-sorted; con- tains some biotite 780-1790 ft. Alluvial-fan deposits (Diablo) Yellow to olive-brown, mostly yellowish: brown; occasional olive-gray layers and bluish-gray inclusions below 1342ft.; slightly to moderately calcareous; com- mon occurrence of fragments of fine- grained rocks, including chert, jasper, quartz, and some volcanic rocks. Gravels consist of pebbles and cobbles as much as 2 in. in diameter 1792-1998 ft. Sand, silt, siltstone, clay and claystone, interbedded i E : § E > f é § } 998-2023 ft. Siltstone and claystone 2023-2203 ft. Sand and siltstone well- indurated 1790-2203 ft. Deltaic deposits (Sierra) Blue-green to greenish-gray, noncalcareous to moderately calcareous; mica and quartz common. Much organic material including reed and grass remains, and wood fragments in zone from 1792- 2030ft. Shell fragments, including Litto- rina, Ammicola, and Fluminicola, at 2054 ft. coORrE HOLE 19/17-22.]1,:2 PROFESSIONAL PAPER 497-E PLATE 5 SPONTANEOUS | _ RESISTIVITY GRAPHIC GENERALIZED LITHOLOGIC DESCRIPTION POTENTIAL L (from core descriptions, drilling $ performance, and electric logs) - MILLIVOLTS+ (OHMS M/M) 200' 100 5|0 0 1's T 0-565 ft. Alluvial-fan deposits (Diablo) Dusky-yellow to yellowish-brown except for reduced interbeds below 558 ft; most strata calcareous and fragments of 200-415 ft. Sand, fine to very coarse; clay chert, jasper, serpentine, and black rock 4 and silt interbedded are common 400' 415-565 ft. Clay, silty; some sand and silt interbedded 565-575 ft. Corcoran Clay Member (lacus- trine deposit) Bluish-gray to dark-greenish-gray, carbon- - aceous 565-575 ft. Clay, silghtly silty sco 575-640 ft. Lacustrine deposits d C i Greenish-gray to dark-gray, well-sorted; 575-637 ft. Sand, fine to coarse contain rock fragments (notably ser- pentine) 637-700 ft. Clay, silty; some very fine to very coarse sand 640-980 ft. Alluvial-fan deposits (Diablo) Yellowish-brown to olive-brown with reduced 700-750 ft. Sand, silty to medium coarse; interbeds above 656 ft. and below 946 ft.; some clay and silt calcareous concretions and fragments - of chert, serpentine, and black rocks 750-772 ft. Clay, silty common. Some mica 772-795 ft. Sand, fine to coarse 800' 795-842 ft. Clay, firm, silty to sandy 842-895 ft. Sand, fine to medium; some clay and silt 895-907 ft. Clay, film 907-940 ft. Sand, silty to very coarse I 940-980 ft Clay, plastic to firm 1000' r ; % I 980-1470 ft. flood-plain deposits (predom- c f ; inantly Sierra) s 980-1130 fl'. Sand, fine to coarse; tg)rav§|l3j/ Gray to dark-greenish-gray noncalcareous ha near top; some thin hard interbedde to slightly calcareous; high mica and a clay and silt quartz content except from 990-1013 ft [J and 1231-1241 ft where chert, serpen- tine, and sandstone fragments are com- E mon. Carbonaceous from 1350-1354 ft ye | 1130-1200 ft. Siltstone and sandstone, cal- occasional crossbedding noted 0 cite cemented; some sand, silt, and u. clay 1200' 0 x f 7 1200-1375 ft. Silt, clayey to sandy; thin 3 sand and clay streaks interbedded - 1400' 1375-1465 ft. Sand silty to gravelly; some silt and clay; firm to hard 1470-1500 ft. Lacustrine depqsits 1465-1549 ft. Clay, firm to very firm; some Dark-greenish-gray to brownish-black; con- sand interbedded tain much organic material 1500-1770 ft.Flood-plain deposits (Sierra) Gray to greenish-gray; sands contain much 1600' mica and quartz; organic material pres- ent above 1524 ft and below 1710 ft 1549-1720 ft. Clay, firm to hard; some sand and silt interbedded /1 770-2000 ft. Lacustrine (?) deposits Dark-greenish-gray to greenish-black, de- 800' pending upon organic content; abundant 1800 carbonaceous material including root fragments and reeds from 1870-1875 ft. Sand below 1950 ft has blueish cast 1720-2000 ft. Clay, with some claystone; friable to firm; some sand ao ca _-] SPONTANEOUS | _ RESISTIVITY GRAPHIC GENERALIZED LITHOLOGIC DESCRIPTION POTENTIAL LOG (from core descriptions, drilling performance, and electric logs) -MILLIVOLTS+ (OHMS M?/M) so 2s o is 30 *I the 0-530 ft. Alluvial-fan deposits (Diablo) 0-110 ft. Sand and gravel Dus'ky-yellow to olive-brown, moderately to highly calcareous; chert and dark-rock fragments common 110-200 ft. Sand, fine to very fine; silt and clay interbeds 200' 200-270 ft. Clay, plastic; sand , fine T I 270-400 ft. Sand, fine to medium, some clay 400' I | 400-534 ft. Silt and sand, fine | 584-565 it. Silt: sandy 530-625 ft.Flood-plain deposits (Diablo) Olive-gray to dark-greenish-gray, nonmica- vel | 565-625 ft. Clay, plastic ceous I ; _ 625-700 ft. Corcoran Clay Member ‘ 625-675 ft. Clay, massive, plastic (lacustrine deposit) - Greenish-gray to blue-green, micaceous I 675-700 ft. Clay, silty and diatomaceous ma 7 A 700-900 ft. Flood-plain deposits (Sierra) e [NLL] 700-783 ft. Silt, sandy Greenish-gray to grayish-green; clays are o m1caceou§ and sands consist primarily of z quartz grains and mica. Some wood frag- 800' + 783-795 ft. Clay ments at about 844 ft, and plant remains s at 888 ft F 795-874 ft. Sand, fine, silty e 0 » it 874-899 ft. Clay, silty be 220 tt Rand, mediam to fine, silty 900-1270 ft. Flood-plain deposits (predom- 920-946 ft. Clay, well-indurated inantly Diablo) # 946-973 ft. Silt, clayey and sandy Greenish-gray to olive-brown; silghtly mica- £ ceous to nonmicaceous except from 1000' id 973-1001 ft. Clay silty to silt, massive 1000-1033 ft. where mica is abundant. l Chert and dark-rock fragments common 9 1001-1041 ft. Silt, sandy, and sand except where mica is abundant - _@-1056 ft. Clay | 1056-1127 ft. Silt, sandy, and sand 1127-1204 ft. Sand, coarse, loose, and gravel 1200' | 1204-1250 ft. Sand, medium, loose 1250-1348 ft. Sand, silty, loose to well. 1270-1350 ft. Alluvial-fan deposits (Diablo) ind: #ted Yellowish-brown to olive-gray; some cal- careous concretions; chert and rock frag- ments common ; f 1350-1480 ft. Lacustrine (?) deposits 1100" 1348-1455 ft_. Clay, silty with occasional Olive-gray to dark-greenish-gray; mica com- beds o_f silt and silty sand, mostly hard mon in sands but scarce in clays; wood and brittle fragments and other organic matter at 1481 ft 1455-1480 ft. Sand, fine to medium loose CORE HOLE 14/13-!101,2 COMPOSITE LOGS OF SELECTED CORE HOLES, LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA 411-341 O - 71 (In pocket) No. 5 PREPARED IN COOPERATION WITH THE PROFESSIONAL PAPER 497-G UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY CALIFORNIA DEPARTMENT OF WATER RESOURCES PLATE 1 A100 ft to bench mark LS-8 SK 695 Cs ¥ Tiltmeters | i ~: SE ; i .$ $2 "a Ait - $ a gz. 4T. s -an. 3 3 $4 3 B pono a- 17 § g § l > 5. 3 | 3 0 6 5 fig/903, 4 7 \Datum is August 30, 1965, eleéations ”Ky/h t t <-- "fi// .\./- % Ties: - sorce Suno suse s \\\ OCtOber 6v 1%5 -0.005 7 ea \.\ f- Dec. 15, 1 A -0.010 - $2 ad e Cy -=0.015 7 f 64qu CENTERLINE OF CALIFORNIA AQUEDUCT\' AX - 0.020 - (- . ><\ A1053 1014 1018 “DOM A 3 0s6 * June14 Al-@- -y ~ _- 1016 £. 590 0°5.-I vag - % > &= ~. a = -0.030 - [- 4 ide ul September 13, 1966>\ & 5 Z T -0.035 - f: O Z e 0.040 J- -V. " p- s Lu iud Ll -0.045 7 is §<\ —0050 y |- a «P ($9 As =-0.:055 ~ E @" 1510 +0 A >< © R A* Tiltmeter pot 5 >< 3 - 0.060 7 [= 1003 § $50 ® Gib») Qb Bench mark and number -0.065 - E- ¥. / —0.07OJ C. TILT PROFILES ALONG LINE B-B' [-< 0 200 400 FEET Qx Ponp| 8-17 ( ; * ly A CONTOUR INTERVAL 10 FEET DATUM IS MEAN SEA LEVEL ax " cx % > A. MAP SHOWING LOCATION OF TILTMETERS AND BENCH MARKS SW : NE g 3 r é G Sgctngn m" g ps I é E é 5 o 4 r- r- w- m U v4 «- +- m A < S > S S | 4 F C S 3 m S 3 ao 0 } } } . £ t t t t t + £- -t emic toe oct rege oe sal a INm is August 30, 1965, elevations ; \ BS mane, mt Col ud 2 0000 C22, 11000 0 0 hol for Col TOUT Sente (mages mee withe \7‘ \ / \ -0.005 - \-\ December 15, 1965 : f anol oal s October 6, 1965 & xs: fung. "4 \ ¥ ' : f FR. tr nae _s _. -0.010 - I \\\ 2. 2a t. tant g -=90.015 - ag ~0.020 - April 15, 1966>,/\\ C \\\\\\ Ca ‘//// \\ + \\ 4 > \ - 0025 Is s. px "- " es *A LJ - « E " \ '\ v \\\\ E _00304 '\\ 1/ \\\\ [- t ~ ,_ ,September 13, 1966 June 14, 1966 ~- nomas s- *i i ~<2C ~. .. 5 -~0.035 - Is i O rss. h * € #.. = -0:040 - ox. _ _ _8 = E os r as- a o Note: Bench mark numbers shown on map are for standard bench marks (brass % i 6 10 15 20 -0.045 - cap in concrete pier). Elevation changes shown on profiles are for adjacent \ |- 2 r o s $ I | "deep-seated" bench marks (1%-inch pipe set 15 feet into ground), designated f by suffix "A'": Elevation of bench mark A1053 has been arbitrarily held constant mt TILT SCALE, IN MICRORADIANS =0:050 - & \ g C Ar- Aug. 30, 1965-Dec. 15, 1965 {A' =0.055 - oa |- 1017 (ols lo19 1020 \ 1001 =- 0.060 - 'e z, = \ \ " \ \ =0.065. - C agin. oly |- D. VECTORS SHOWING DIRECTION AND . MAGNITUDE OF TILTING B. TILT PROFILES ALONG LINE A-A =0.070 -| | © MAP OF WHEELER RIDGE PUMPING-PLANT SITE AND TILT PROFILES DETERMINED BY SPIRIT LEVELING, 373 - 386 O - 70 (In pocket) SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA