Land Subsidence Due to

Ground-Water Withdrawal in the

Los Banos-Kettleman City Area,

California

Part 1. Changes in

The Hydrologic Environment

Conducive to Subsidence

GEOLOGICAL SURVEY PROFESSIONAL PAPER 437-E

Prepared in cooperation with the 

California Department of Water Resources
Land Subsidence Due to

Ground-Water Withdrawal in the

Los Banos-Kettleman City Area,

California

Part 1. Changes in

the Hydrologic Environment

Conducive to Subsidence

By WILLIAM B. BULL and RAYMOND E. MILLER

STUDIES OF LAND SUBSIDENCE

GEOLOGICAL SURVEY PROFESSIONAL PAPER437-E

Prepared in cooperation with the 

California Department of Water Resources

A description of the ground-water reservoir

and the great stress imposed on the aquifer system

by mans mining of ground water

UNITED STATES GOVERNMENT PRINTING OFFIC E , W ASH I N GTO N : 1 9 75
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Bull, William B. 1930-

Land subsidence due to ground-water withdrawal in the Los Banos-Kettleman City area, California.

(Studies of land subsidence) (Geological Survey Professional Paper 437-E-G)

Pt. 2 by W. B. Bull; pt. 3 by W. B. Bull and J. F. Poland.

Includes bibliographies and indexes.

CONTENTS: pt. 1. Changes in the hydrologic environment conducive to subsidence. pt. 2. Subsidence and compaction 

of deposits, [etc.]

Supt. of Docs. No.: I 19.16:437-E 

1. Subsidences (Earth movements) California San Joaquin Valley. 2. Aquifers California San Joaquin Valley. 3.

Water, Underground California San Joaquin Valley. I. Miller, Raymond E. II. Poland, Joseph Fairfield, 1908- III.

California. Dept. of Water Resources. IV. Title. V. Series. VI. Series: United States. Geological Survey. Professional

Paper 437-E-G. 

QE75.P9 No. 437-E-G [GB485.C2] 557.3'08s [551.3'5] 74-28239

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 024-001-02608
CONTENTS

Abstract _______________________________ El

Introduction _____________________________ 1

Inter-Agency Committee on Land Subsidence_______ 2

Cooperative and Federal subsidence programs ______ 6

Scope of field and laboratory work _____________ 6

Field program _________________ 6

Laboratory program _______________ 7

Purposes of report _________________________ 7

Acknowledgments ________________________ 8

Definitions__________________________ 8

Geographic setting ______________________ 8

Land subsidence ___________________________ 9

Compaction ___________________________ 9

Stresses tending to cause compaction ________________ 11

Description of the ground-water reservoir ___________ 12

General features _______________________ 12

Upper zone_____________________________ 14

Physical character ______________________ 17

Productivity ______________________ 17

Chemical character of water_______________ 17

Page

Description of the ground-water reservoir Continued

Corcoran Clay Member of the Tulare Formation _ ___ E19

Lower zone___________________________ 19

Physical and hydrologic character ___________ 23

Productivity ______________________ 25

Chemical character of water_______________ 29

Saline water body ___________________ 32

Natural flow system ________________________ 32

Changes in the hydrologic environment caused by man ___ 34

History of ground-water development ___________ 34

Trends in total ground-water pumpage _______ 36

Changes in ground-water levels ________________ 39

The water table ______________________ 39 

The upper-zone semiconfined to confined aquifer

system_________________.._______ 43

The lower-zone aquifer system______________ 45

Changes in the potentiometric surface ______ 46

Seasonal fluctuation of the potentiometric level-- 59

History of head decline _ ____________ _ 61

Summary and conclusions____ ________________ 65

References cited __________________________ 66

Index _____________________________ 69

ILLUSTRATIONS

Page

FIGURE 1-4. Maps showing

1. Principal areas of land subsidence in California due to ground-water withdrawal E3

2. Topographic features _____________________________ 4

3. The boundaries, bench marks, observation wells, compaction recorders, core holes, and lines of sections referred

to in this report_______________________________ - 5

4. Land subsidence, 1920-28 to 1966 ________________________________ 10

5. Graph showing subsidence and artesian-head decline near bench mark GWM59 ___ - H

6. Diagram of compaction-recorder installation _ ______ __ _ _ __ ___ _________ 11

7. Cross sections showing well-yield factors and depositional environments of the aquifer systems _ 13

8. Longitudinal section showing general hydrologic units ____________________ ___ 14

9. Cross sections showing general hydrologic units ________________________ __ 15

10-13. Maps showing

10. General variation in the amount of water pumped from the lower zone or its stratigraphic equivalent __ 16

11. Thickness and extent of the Sierra Sand overlying the Corcoran Clay Member of the Tulare Formation 18

12. Depth to the base of the Corcoran Clay Member of the Tulare Formation __ __ 20

13. Structure of the Corcoran Clay Member of the Tulare Formation __ ______ 21 

14. Graphs showing variation in the hydraulic continuity of the lower zone ___ __ 22 

15-19. Maps showing

15. Areas in which part of ground water is pumped from pre-Tulare deposits of Pliocene age _ 24

16. Yield factors and types of lower-zone deposits ____________________ 26

17. Thickness of the fresh-water-bearing deposits of the lower zone ______________ __ 28

18. Maximum thickness of the perforated interval of the lower zone _ ______ _________ _________- 30

19. Variation in dissolved solids of the lower-zone water ____________________ __ 31

III
IV CONTENTS

Page

FIGURE 20. Diagrams showing change in the natural-flow conditions in the central San Joaquin Valley ___ _________ E33

21. Map showing areas of early ground-water development_____________________________ ___ 35

22. ^Map showing increase in irrigated land ________________________________________ 37

23. Graph showing estimated ground-water pumpage, 1935-66 ____________________________ 38

24. Hydrographs of upper- and lower-zone piezometers at the Yearout site ____________________ 39

25. Map showing depth to shallow ground water, 1965_______________________________ _______- 41

26. Map showing change in depth to the water table, 1951-65 _______________________________________ 42

27-30. Hydrographs of

27. Wells perforated in the unconfined zone ____________________________________ 43

28. Upper-zone piezometers at 15/14-15E ______________________-_________________ 44

29. Wells perforated in the upper zone_____________________________________________ 44

30. Wells perforated in both the upper and lower zones _____________________________ 45

31. Water-level contours for the lower zone or its stratigraphic equivalent, 1926________________________ 47

32. Water-level contours for the lower water-bearing zone, 1943 ________________________________ 48

33. Minimum altitude of the potentiometric surface of the lower zone as of 1960_____________________________ 49

34. Map showing artesian head of the lower zone as of May 1960 ____________________ _________ 51

35. Water-level contours for the lower-water-bearing zone, December 1962 _________________________ 52

36. Generalized water-level icontours for the lower zone, December 1965' ________________ _________ 53

37-40. Graphs showing change in

37. Slope of the potentiometric surface of the lower zone southwest of Five Points, 1906-66 ______________ 54

38. Slope of the potentiometric surface of the lower zone southwest of Firebaugh, 1906-66 __ _ __ 54

39. Altitude of the lower-zone potentiometric surface, 1943-66, Tumey Hills to Mendota ____ _______ 55

40. Altitude of the lower-zone potentiometric surface, 1943-66, Anticline Ridge to Fresno Slough________ 56 

41-43. Maps showing

41. Decline in the altitude of the potentiometric surface of the lower zone, 1943-60 _____ _______ 57

42. Change in altitude of the lower-zone potentiometric surface between December 1962 and

December 1965 ____________________________________________________ 58

43. Seasonal decline in the altitude of the potentiometric surface of the lower zone, December 1965

to August 1966 ____________________________________________________ 60

44. Graph showing variation in seasonal fluctuation of water levels in lower-zone wells in the central part

of the Los Banos-Kettleman City area _____________-___ _ ___ -- 61

45. Long-term hydrographs of lower-zone wells __________________________ 62

46. Hydrograph of irrigation well tapping the Etchegoin and San Joaquin Formations ________ ____ 63

47. Diagram showing trends of lower-zone pumping levels _______________-__ ___ 64

TABLES

Page

TABLE 1. Relation of yield factors to types of upper-zone deposits _____________________________ _________ E17

2. Relation of yield factors to types of lower-zone deposits __________________________-___ 25

3. Estimated ground-water pumpage, 1935-66, Los Banos-Kettleman City area________ _______ 36
STUDIES OF LAND SUBSIDENCE

LAND SUBSIDENCE DUE TO GROUND-WATER WITHDRAWAL IN 

THE LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA

PART 1. CHANGES IN THE HYDRO LOGIC ENVIRONMENT 

CONDUCIVE TO SUBSIDENCE

By WILLIAM B. BULL and RAYMOND E. MILLER

ABSTRACT

About 500 to 2,000 feet of unconsolidated flood-plain, alluvial-fan, 

lacustrine, deltaic, and marine deposits are compacting at accelerated 

rates because of man's changes in the hydrologic environment in the 

west-central San Joaquin Valley. Ground-water pumping has increased the stresses tending to compact the deposits by as much as 50 

percent.

Three basic hydrologic units comprise the ground-water reservoir 

between Los Banos and Kettleman City. An upper-zone aquifer system, 100-900 feet thick, extends from the land surface to the top of the 

second unit. It is a lacustrine confining clay. The upper zone consists 

mainly of poorly permeable alluvial-fan deposits derived from the 

Diablo Range that contain semiconfined water of poor quality. Little 

water is pumped from the fan deposits; however, water of good quality 

is pumped from an extensive wedge of arkosic, micaceous sands. These 

sands are flood-plain deposits derived from the Sierra Nevada that 

extend 4-10 miles west of the valley trough along the full reach of the 

area.

The lacustrine aquiclude, the Corcoran Clay Member of the Tulare 

Formation, extends beneath the entire study area except for the 

southwestern part adjacent to the Diablo Range.

The third hydrologic unit, the confined aquifer system of the lower 

zone, supplies about three-fourths of the ground water pumped and is 

the zone in which 50-95 percent of the compaction causing the subsidence occurs. The lower zone consists mainly of flood-plain deposits in 

the northern part, alluvial-fan deposits in the southern part, and 

diverse continental to marine deposits in the central part of the area.

The thickness of the fresh-water bearing deposits and the perforated interval of the deposits below the Corcoran rarely are the same. 

Some wells that have sufficient yields bottom 1,000 feet above the 

base of the fresh water. In other areas, 3,000-foot wells obtain a 

sufficient yield only by withdrawing part of their water from deep 

brackish-water-bearing marine deposits.

The sodium-sulfate water of the lower zone indicates that the connate water has been flushed out of the marine and Sierra sands. 

Maximum concentrations of dissolved solids in the well water occur 

opposite the mouths of the two major streams and in the area of 

pumping from the marine sand.

Initially the lower-zone potentiometric surface sloped gently from 

the bordering mountains to the valley trough where it was more than 

20 feet above the land surface.

Agricultural development has resulted in more than a million 

acre-feet of water being pumped from the ground-water reservoir each 

year since 1951; has lowered the potentiometric surface as much as 

600 feet; has reversed an eastward gradient in the study area of 2-5 

feet per mile to a westward gradient of 30 feet per mile; and has caused 

water levels to decline below the base of the Corcoran adjacent to the 

Diablo Range.

The steep westward gradient of the lower-zone potentiometric surface has increased the recharge to the area. Pumpage stopped increasing in the early 1950's when most of the land had been developed. By 

the early 1960's, a rough balance between the amount of water being 

pumped from the lower zone and the amounts of water derived from 

compaction, recharge, and storage was obtained for most of the area. 

The potentio metric surface did not steepen further, and artesian-head 

decline ceased or decreased to rates of less than 5 feet per year in most 

of the area.

Applied stresses on the lower zone have been greatly increased by 

the large historic decline of artesian head but have not been affected 

appreciably by water-table changes. Water-table rises of as much as 

100 feet and declines of as much as 350 feet locally have caused large 

changes in applied stress on the upper-zone deposits. Water-table rise 

or decline causes little net change in applied stress on the lower zone 

because concurrent seepage stress changes more than offset the effects of buoyancy change and the effects of change in the stress condition of part of the contained water that occur when the degree of 

saturation is changed.

Change to a water-table condition below the Corcoran decreases the 

future rate of increase in applied stress from 1.0-0.8 foot of water per 

additional foot of lower-zone water-level decline.

INTRODUCTION

By increasing the stress tending to compact the unconsolidated deposits by as much as 50 percent, man has 

created what is believed to be the world's largest area of

El
E2 STUDIES OF LAND SUBSIDENCE

intense land subsidence in the west-central part of the 

San Joaquin Valley. Withdrawal of ground water for 

agriculture has caused more than 2,000 square miles to 

subside more than 1 foot. As of 1966, the area that had 

subsided more than 10 feet was 70 miles long and extended 500 square miles. Maximum subsidence was 26 

feet.

Water-level changes in the aquifer systems have increased the applied stresses on the deposits and have 

caused compaction of the aquifer systems. Detailed 

knowledge of the interrelations of water-level change, 

change in thickness of the aquifer system, and the concurrent changes in the altitude of the land surface is 

necessary for a more complete understanding of the 

mechanics of aquifer systems, compaction of sediments, 

and for the development of adequate criteria for the 

prediction of future land subsidence.

The hydrologic environment and the changes man 

has made in it to cause land subsidence which are the 

main topics of this paper will be presented for one of 

four major areas of intense land subsidence caused by 

ground-water withdrawal in California. The general 

location of the Los Banos-Kettleman City subsidence 

area, and its geographic relation to the three other 

subsidence areas is shown in figure 1.

The topographic and cultural features of the Los 

Banos-Kettleman City area and part of the area to the 

northeast of the study area of this paper are shown in 

figure 2. All the place names used in this paper also are 

shown in figure 2.

The boundaries of the Los Banos-Kettleman City 

study area and the lines of sections and profiles referred 

to in this paper are shown in figure 3. The boundary of 

deformed rocks at the edge of the Diablo Range foothills 

is the southwestern boundary of the study area, although small parts of the area of deformed rocks subsided 1-2 feet during the 1943-66 period. The southeastern boundary of the area is State Highway 41 on the 

northwest side of Tulare Lake bed between Kettleman 

City and Stratford. Small amounts of subsidence have 

occurred farther to the east between the Los BanosKettleman City and Tulare-Wasco subsidence areas 

(fig. 1). The northern boundary of the study area is State 

Highway 152 which passes through the town of Los 

Banos. The northeastern boundary, as originally 

defined (Inter-Agency Comm., 1958), for most aspects of 

this paper is the San Joaquin River, Fresno Slough, and 

the Kings River.

However, as much as 8 feet of subsidence has occurred 

east of the trough of the valley. Therefore, in discussions

of the amount and extent of subsidence, the 1-foot subsidence line shown in figure 4 provides a better 

definition of the eastern boundary of the system being 

affected by appreciable compaction. Geologic and hydrologic aspects east of the valley trough will be discussed also.

The effects of land subsidence have become increasingly costly in the study area, which is traversed by 

several canals of large capacity and low gradient. One 

canal, the San Luis Canal, is part of the California 

Aqueduct, which is the major canal for transporting 

water from areas of abundant water in northern 

California to areas needing water in the San Joaquin 

Valley and southern California. The amounts, rates, 

and distribution of subsidence pose serious problems in 

the construction and maintenance of the canals and 

their extensive distribution systems. Subsidence also 

poses problems for local water-distribution, sewage disposal, and drainage systems. A major drain just west of 

the present trough of the valley will be built to remove 

drainage water of poor quality and to assist in maintaining a salt balance. Another major expense resulting 

from subsidence is the damage that occurs to well casings as the sediments adjacent to the wells compact to 

cause compressional casing failures.

INTER-AGENCY COMMITTEE ON LAND SUBSIDENCE

As a result of the problems posed by subsidence, the 

Inter-Agency Committee on Land Subsidence in the 

San Joaquin Valley was formed in 1954 with J. F. Poland of the U.S. Geological Survey as its chairman. The 

purpose of the committee was to plan and coordinate a 

program that would provide information about the extent, magnitude, rates, and causes of the various types 

of land subsidence in the San Joaquin Valley (InterAgency Committee, 1958, p. 21). Other objectives of the 

program were to estimate future subsidence under assumed conditions and to suggest ways of alleviating 

subsidence. Representatives from the Geological Survey, U.S. Bureau of Reclamation, U.S. Coast and Geodetic Survey, (now National Geodetic Survey of the 

National Ocean Survey), U.S. Army Corps of Engineers. Soil Conservation Service, the California 

Department of Water Resources, California Division of 

Highways, University of California at Davis, and Stanford University composed this committee.

A proposed program of investigation was prepared by 

the Inter-Agency Committee (1955), and in 1958 a progress report on land-subsidence investigations in the San 

Joaquin Valley was published.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE 

122° 120° 118° 116°

E3

42C

40°

38°

36?

34°

100 MILES

Los Banos 

Kettleman City

area

Santa Clara Valleyarea

O

FIGURE 1. Principal areas of land subsidence in California due to ground-water withdrawal. Outline of Central Valley dashed; areas of major subsidence shaded black; areas of

lesser subsidence hachured.
E4 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00

_ A 

Tranquillity 0 \

\ o San Joaquin

EXPLANATION

.

Boundary of deformed 

rocks

San Luis Canal California 

Aqueduct

5 _____10_____15 MILES 

5 10 15 KILOMETRES

CONTOUR INTERVAL 40 FEET 

DATUM IS MEAN SEA LEVEL

36°30' 

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 2. Topographic features of the Los Banos-Kettleman City area.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

R. 10 E. 11 12 13 120°30' 14 15 16 17 120°00'

E5

37°00' E

36°30' -

36°00

Mendota

Merdota site

31N2.3

Tranq lillity/^ite

EXPLANATION

Boundary of deformed rocks

Boundary of the Los BanosKettleman City area

017P1

Core hole and well number

Compaction recorder; if more than one, 

number indicated inside symbol

Q16N1

Observation well and well number; if more 

than one, number indicated inside symbol

( ) i 22J1,2^

26N1U

esthayeng>35$i

Westhaven'site

Irrigation well from which water-level record has been obtained, and well number

X GWM59

Bench mark and number

Line of geologic section or hydrologic profile or section shown in succeeding illustrations

15 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 3. The boundaries, bench marks, observation wells, compaction recorders, core holes, and lines of sections referred to in this report.
E6 STUDIES OF LAND SUBSIDENCE

COOPERATIVE AND FEDERAL SUBSIDENCE PROGRAMS

One result of the inter-agency cooperation was the 

initiation in 1956 of an intensive study of land subsidence in the San Joaquin Valley, by the Geological 

Survey, in financial cooperation with the California 

Department of Water Resources. The objectives of the 

cooperative subsidence program, of which this report is 

one result, were to define the rate, magnitude, and extent of subsidence through a vertical-control measurement program; to determine the various causes of subsidence, and the depth intervals in which the compaction was occurring; to furnish criteria for the prediction 

of future subsidence; and to determine whether any part 

of the subsidence is reversible, and, if so, to what extent.

In 1956, the Geological Survey also began a federally 

financed investigation of the mechanics of aquifer systems: the fieldwork was concentrated chiefly in the San 

Joaquin and Santa Clara Valleys in California. It was 

recognized that those areas of active subsidence due to 

water-level change offered an unexcelled opportunity to 

study compaction of sediments in response to increase 

in effective stress. Objectives of the Federal program 

were to determine the principles controlling the change 

in aquifer-system thickness resulting from change in 

grain-to-grain load, and to appraise the meaning and 

utility of the storage coefficient in compactible aquifer 

systems. Within the Los Banos-Kettleman City area, 

both the change in stresses causing compaction of the 

saturated deposits and the change in thickness of the 

deposits can be measured at many sites.

SCOPE OF FIELD AND LABORATORY WORK

Many of the results of the cooperative and federally 

funded investigations are of mutual benefit, as is evident from the following brief description of types of facts 

gathered to assess compaction of saturated deposits due 

to changes in water levels.

FIELD PROGRAM

A vital supporting program for the subsidence investigations has been the periodic surveying of a network 

of bench marks by the Coast and Geodetic Survey to 

determine changes in altitude. Starting in 1955 and 

continuing until 1959, the network was surveyed every 

2 years, and since 1959 the bench marks have been 

surveyed every 3 years.

A method (see section on "Compaction") was developed for the measurement of compaction within 

specified depth intervals. Both unused irrigation wells 

and specially drilled wells were used for this purpose.

The well-numbering system identifies wells according to their location in the township and range grid used 

for subdivision of public land. For example, well 

14/13-11D6 designates the sixth well assigned a

number in the NW% of the NW% of section 11, Township 14 South, Range 13 East. The letters that are used 

to indicate the 40-acre subdivision of the section are as 

follows.

D

E

M

N

C

F

L

P

B

G

K

Q

A

H

J

R

Because all the wells within the study area are south 

and east of the Mount Diablo base and meridian, the 

foregoing abbreviation of the township and range is 

sufficient.

A well canvass was made in the study area west of the 

San Joaquin River and Fresno Slough. The descriptions 

of the 3,600 wells that were canvassed have been tabulated by Ireland (1963).

Periodic water-level measurements have been made 

at the times of the winter or spring recovery highs to 

determine the position of the potentiometric surface of 

the principal confined aquifer system in the study area. 

Water levels were measured each year during the 

1950's and bench-mark surveys during the winters in 

the 1960's.

A problem peculiar to land-subsidence areas is that 

the altitude of the reference point changes with time for 

all water-level, electric log, core hole, and other data. 

Errors in data, such as altitudes of geologic or hydrologic horizons, could be partially corrected by establishing for each data site a history of reference-point 

altitude change. However, this procedure is not practical and would introduce additional problems. One problem would be how to prorate the depth to geologic horizons at different depths in a system in which the unit 

compaction varies with depth. Subsidence corrections 

would also lead to misinterpretation of data. For example, if the depth to the water table at a subsiding site did 

not change over a long time period, a hydrograph of the 

altitude of the water table, if corrected for subsidence 

during the period of record, would show an apparent 

decline in the water table and could be interpreted erroneously as a decrease in storage.

One possible procedure is to make an altitude adjustment for the measuring points of wells at the time of 

each releveling. However, this method results in displacement of the plot of water-level altitude at each 

time of adjustment.

The approach of the Geological Survey has been to use 

the land-surface altitudes established on topographic 

maps made in the 1920's as the reference altitudes for
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E7

all measuring points. This approach introduces a 

gradually increasing error in all maps, sections, and 

hydrographs dependent on altitude that is equal to the 

amount of subsidence since the 1920's. The error is of 

little concern in areas of less than 10 feet of subsidence 

when one considers the general order of accuracy of 

altitude of a rapidly changing potentiometric surface or 

the altitude of the top of the confining clay. The problem 

can be circumvented; for example, indicate the change 

in the position of the water table by using change in 

depth instead of change in altitude.

Observation wells are measured by the Geological 

Survey throughout the study area to obtain information 

about the changes in the water table and the potentiometric levels in the confined aquifer systems above 

and below the principal confining bed. Some of the observation wells are unused irrigation wells, but many 

are wells that have been drilled by the Survey and other 

agencies to obtain a specific type of water-level information. At least one observation well is situated at each 

compaction-recorder site. The wells that are referred to 

in this paper are shown in figure 3.

Another major source of water-level information has 

been the records of the Pacific Gas and Electric Co. 

These records have provided long-term histories of 

water-level declines based on both static and pumping 

measurements. Many of the hydrographs used in this 

paper are based on these records. Measurements usually are made at least once a year. The time of measurement may be anywhere in the seasonal fluctuation 

range but most commonly is during the summer pumping season. The measurements selected for the hydrographs in this paper are those made at the times of 

low-water levels the times of maximum applied stress 

on the aquifer system. Since 1964, the power-company 

measurements have been supplemented by measuring 

selected wells at the time of the summer low-water level 

in late August.

Regional geologic studies also were made of the Los 

Banos-Kettleman City area and the adjacent foothill 

belt to provide an appropriate framework for the studies 

of compaction and land subsidence. The classification 

and correlation of the subsurface geologic and hydrologic units tapped by wells and the mapping of the 

continental deposits exposed in the foothills adjacent to 

the study area are described in detail in a report by 

Miller, Green, and Davis (1971). In addition to establishing the areal extent of the various components of the 

aquifer systems, the regional geologic studies provided 

valuable basic information about the lithology, source, 

and mode of deposition of the deposits.

In order to provide additional information about the 

petrology, and mode and source of deposition of the 

sediments, four core holes were drilled along the axis of

the subsidence trough at the Oro Loma, Mendota, Cantua, and Huron sites by the Inter-Agency Committee. 

These multiple-purpose holes were also used to obtain 

electric logs and caliper logs.

LABORATORY PROGRAM

A laboratory program that was part of the Federally 

financed investigation was conducted at the Geological 

Survey's hydrologic laboratory on cored samples to provide information about the physical, hydrologic, and 

engineering properties of the sediments that are compacting in this and the three other subsidence areas 

shown in figure 1. Some of the test results most applicable to the studies of land subsidence are particle-size 

analyses, specific gravity and unit weight, porosity and 

void ratio, consolidation and rebound, and permeability. The results are reported by Johnson, Moston, and 

Morris (1968).

The core samples also provided abundant samples for 

laboratory petrographic examination. The general petrology of the deposits and the details of the clay 

mineralogy are discussed by Meade (1967). In a major 

contribution, Meade (1968) relates the variations in 

overburden load and petrologic factors to the variations 

in pore volume and fabric of the sediments of several 

subsidence areas in central California.

PURPOSES OF REPORT

This report is part 1 of a series of three reports concerned with land subsidence due to ground-water withdrawal in the Los Banos-Kettleman City area. It describes the subsurface hydrologic environment in 2,000 

square miles of the west-central San Joaquin Valley. 

Within this scope, the report has two specific purposes. 

The first is to describe the extent, thickness, and hydraulic character of the deposits comprising the two 

principal aquifer systems and the confining clay that 

separates them. The second purpose is to assess the 

changes caused by man in the hydrologic environment 

that have been responsible for the increase in applied 

stress, the compaction of the ground-water reservoir, 

and the concurrent subsidence.

The bulk of the information presented in this paper 

concerns events that occurred before April 1966 which 

was the time of completion of a complete leveling of the 

bench-mark network by the Coast and Geodetic Survey. 

Some 1966-68 data are presented and discussed, but 

only to present facts that cannot be demonstrated with 

the earlier data.

The authorship of this report is as follows. Mr. Miller 

prepared most of the section, "Description of the 

Ground-Water Reservoir." Mr. Bull is responsible for 

the rest of the paper. Mr. Miller's detailed and careful 

study of the geologic and hydrologic framework of the 

study area (Miller and others, 1971) has been very
E8 STUDIES OF LAND SUBSIDENCE

helpful in the preparation of all subsequent reports on 

the Los Banos-Kettleman City area.

Two other papers on the Los Banos-Kettleman City 

area were prepared by W. B. Bull as companion reports 

to this paper. Part 2 (Bull, 1974) "Subsidence and Compaction of Deposits") describes the subsidence due to 

artesian-head decline, and compaction of the groundwater reservoir; the paper also discusses the geologic 

factors influencing compaction of the saturated deposits. Part 3 (Bull and Poland, 1974, "Interrelations of 

Water-Level Change, Change in Aquifer-System 

Thickness, and Subsidence") uses the data and interpretation in Parts 1 and 2 as a basis for discussing 

some of the principles of mechanics of aquifer systems.

ACKNOWLEDGMENTS

The cooperation of numerous ranchers, landowners, 

and companies is acknowledged for supplying essential 

information to the subsidence project and for giving 

permission to install and maintain wells and equipment 

for obtaining water-level and compaction information. 

Particular assistance was given by the Pacific Gas and 

Electric Co., Westlands Water District, and Russell Giffen, Inc.

The financial cooperation of the California Department of Water Resources made this study possible, and 

information provided by the U.S. Bureau of Reclamation from core holes and observation wells contributed 

significantly to the essential data.

This work could not have been completed without the 

discussions, interest, and assistance of many people 

who have been associated with the land-subsidence 

studies of the Geological Survey since 1956. We appreciate the helpful discussions and review of the manuscript by the Project Chief, J. F. Poland, and our colleagues G. H. Davis, B. E. Lofgren, S. W. Lohman, and 

F. S. Riley. We enjoyed working together with R. L. 

Ireland and R. G. Pugh on a variety of jobs in the field 

and appreciate their extensive help in the collecting and 

assembling of field data. Particular credit is due Mr. 

Ireland for his meticulous care and thoughtful foresight 

in the installation and operation of the equipment for 

recording compaction and water-level changes during 

the entire period of record.

DEFINITIONS

The geologic and engineering literature contains a 

variety of terms that have been used to describe the 

processes and environmental conditions involved in the 

mechanics of stressed aquifer systems and of land subsidence due to withdrawal of subsurface fluids. The 

usage of certain of these terms in reports by the U.S. 

Geological Survey research staff investigating 

mechanics of aquifer systems and land subsidence is 

defined and explained in a glossary published separately (Poland and others, 1972). Several terms that

have developed as a result of the Survey's investigations are also defined in that glossary.

The aquifer systems that have compacted sufficiently 

to produce significant subsidence in California and 

elsewhere are composed of unconsolidated to semiconsolidated clastic sediments. The definitions given in the 

published glossary are directed toward these types of 

sediments; they do not attempt to span the full range of 

rock types that contain and yield ground water. In 

defining the components of the compacting stresses, the 

contribution of membrane effects due to salinity or electrical gradients has been discounted as relatively 

insignificant in the areas studied.

In this series of research reports, pressures or stresses 

causing compaction are usually expressed in equivalent 

"feet of water head" [1 foot of water =0.433 psi (pounds 

per square inch)].

A committee on redefinition of ground-water terms, 

composed of members of the Geological Survey, recently 

issued a report entitled "Definitions of Selected 

Ground-Water Terms" (Lohman and others, 1972). The 

reader is referred to that report for definitions of many 

ground-water terms.

GEOGRAPHIC SETTING

The area included in this paper includes about 2,000 

square miles of the west side of the San Joaquin Valley 

adjacent to the Diablo Range in central California (figs. 

2, 3). Most of the discussions will concern sites in the 

1,500 square miles west of Fresno Slough, and the San 

Joaquin River between the towns of Los Banos and 

Kettleman City. However, the subsidence bowl extends 

far to the east of the trough of the valley (fig. 4). Between 

the trough of the valley and the Diablo Range to the 

southwest is a belt of coalescing alluvial fans 12-22 

miles wide. The altitude at the base of this bajada 

ranges from 150 to 200 feet, from which the alluvial fans 

rise to altitudes of about 500-900 feet at their apexes. 

The slopes range from about 5 feet per mile near the 

base of the larger fans to about 150 feet per mile on the 

upper slopes of some of the small fans. Local relief generally is less than 5 feet, except where stream channels 

are incised 10-40 feet.

The Diablo Range to the southwest of the study area 

consists of several groups of foothills bordering the San 

Joaquin Valley and the main range, which rises to altitudes of more than 5,000 feet about 10-15 miles from 

the valley. The core of the anticlinal part of the main 

range consists of deformed and slightly metamorphosed 

shale and graywacke of the Franciscan Formation of 

Jurassic to Late Cretaceous age and of ultrabasic rocks. 

The east flank of the range consists mainly of 20,000 

feet of Cretaceous marine mudstone and sandstone. The 

foothill belt is underlain by anticlinally and monocli-
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E9

nally folded Cretaceous marine rocks, by easily eroded 

Tertiary marine rocks, and by Pliocene and Quaternary 

unconsolidated sediments.

LAND SUBSIDENCE

Changes in bench-mark altitudes in the Los BanosKettleman City area during the past five decades have 

been affected by tectonic movements, pumping of petroleum, and compaction due to wetting of 

moisture-deficient alluvial-fan deposits, but mainly 

have been caused by compaction of saturated deposits as 

a result of water-level change.

The compaction due to wetting causes near-surface 

subsidence, which is superimposed on the compaction of 

the saturated deposits. About 130 square miles (fig. 4) 

have subsided; 3-10 feet of near-surface subsidence is 

common, and 10-15 feet of compaction due to wetting 

has occurred locally. Near-surface subsidence results 

chiefly from the compaction of deposits by an overburden load as the clay bond supporting the voids is 

weakened by water percolating through the deposits for 

the first time since burial. The amount of compaction 

due to wetting is dependent mainly on the overburden 

load, natural moisture conditions, and the type and 

amount of clay. Reports about near-surface subsidence 

within the study area include those by Lofgren (1960), 

and Bull (1964,1972). Both the magnitude and extent 

of the subsidence due to artesian-head decline are 

larger than for the near-surface subsidence. Figure 4 

shows the subsidence in the Los Banos-Kettleman City 

area between the time of the first topographic mapping 

in the early 1920's, and the 1966 bench-mark leveling. 

The subsidence pattern is an elongate oval that is 90 

miles long and 24 miles wide. As of 1966, more than 

2,000 square miles had subsided more than 1 foot, and 

the area that had subsided more than 10 feet was 70 

miles long and 7 miles wide. A maximum subsidence of 

about 26 feet had occurred 10 miles southwest of Mendota.

The histories of subsidence rates show that the rate of 

subsidence increased until about the mid-1950's, but 

since then the rate of subsidence has decreased, but not 

so rapidly as the decrease in the rate of artesian-head 

decline. During the 1959-63 period, 480 square miles 

was subsiding more than 0.5 foot per year, and 63 

square miles was subsiding more than 1.0 foot per year.

An example of the change in land-surface altitude 

caused by artesian-head decline is shown in figure 5. 

Subsidence rates in the vicinity of bench mark GWM59 

increased between 1940 and 1955 but since 1955 have 

undergone a continuing decrease in rate. The plot of 

artesian-head decline reveals a parallel history of accelerating and then decelerating rate of head decline. 

Since 1960 the summer low-water levels have shown

little decline, but subsidence has continued at a moderately rapid rate. Much of the subsidence since 1960 is 

interpreted as being the result of delayed compaction 

resulting from continued expulsion of water from 

fine-grained beds of low permeability years after porepressure decline had occurred in the aquifers adjacent 

to the aquicludes and aquitards (Bull and Poland, 

1974).

COMPACTION

Special recorders operating in wells have been 

measuring most of the decrease in thickness of the 

aquifer system that has been responsible for the land 

subsidence. A diagrammatic sketch of one of the compaction recorders is shown in figure 6. At well 

19/16-23P2, the recorder is actually measuring casing 

shortening that results from the compaction of the adjacent deposits. At other sites the anchor weight is set 

below the bottom of the casing, thereby allowing the 

compaction to be measured independently of the casing. 

For the recorder system shown in figure 6, a 300-pound 

anchor was set on the cement plug with a cable that was 

passed over sheaves at land surface, counterweighted, 

and linked to a recorder by a fine wire attached to the 

cable. The Vs-inch, 1 x 19 stranded, reverse-lay, uncoated stainless-steel cable resists corrosion, has low 

stretch and casing-cable friction characteristics, and 

has little tendency to untwist. Friction has been reduced at the land surface by mounting ball-bearing 

sheaves in a teeter bar that can pivot about a fulcrum 

for short distances. The fine wire is passed over the drive 

sheave of a recorder, which records changes in the position of the cable clamp (fig. 6) relative to the concrete 

slab at a 1:1 scale. A 24:1 expanded-scale record is 

obtained by a second recorder (not shown in fig. 6) 

linked to the first by gears. A float-operated water-level 

recorder (not shown in fig. 6) is set on the table below the 

compaction recorders. The tension in the compaction 

cable is uniform only above the uppermost point of contact between the casing and the cable. In wells that have 

casing-cable friction, tension is less below the uppermost friction point than above it during compaction and 

is more during the periods of aquifer-system expansion. 

Thus, casing-cable contact not only introduces friction 

into the recorder system, but it also introduces a 

mechanical lag at those times when the direction of 

movement of the cable, relative to the casing, is reversed. The mechanics of the compaction-recorder systems and the locations of the compaction recorders and 

observation wells operated by the Geological Survey in 

the study area are described in Bull (1974).

The proportion of the subsidence that is being measured has decreased at some compaction-recorder sites. 

For example, at the Cantua site, the 2,000-foot compaction recorder measured 99 percent of the compaction
E10 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00

36°30' -

36°00

EXPLANATION

Boundary of deformed 

rocks

Line of equal subsidence, in feet

Dashed where approximately located. Compiled chiefly as the sum of (1) a comparison of topographic mapping by the 

U.S. Geological Survey done between 

1920 and 28 and in 1955, and (2) leveling of the U.S. Coast and Geodetic Survey in 1955 and 1966. Controlled in part 

by leveling of 1943 and 1959

Boundary of near-surface subsidence areas 

as of 1961 Coalinga 

VALLEY

San Luis Canal section of the California 

Aqueduct

15 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 4. Land subsidence, 1920-28 to 1966.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE Ell

£ 300

.

II

It 

t

400

500

600

Bench mark GWM59

Well 13/12-22N1 

perforated 400 

1223 feet

Well 13/12-22QV 

perforated 602- 

1090 feet

1940 1950 1960

FIGURE 5. Subsidence and artesian-head decline near bench mark GWM59.

causing subsidence between 1959 and 1963 and 88 percent between 1963 and 1966; it measured 79 percent of 

the subsidence that occurred between March 1966 and 

November 1967. The change in the percentage of subsidence measured suggests that pore-pressure decline 

and compaction are occurring at progressively greater 

depths below the anchor weight.

The compaction rates are seasonal, they are most 

rapid during the late winter and the summer when 

water levels are drawn down.

The use of multiple compaction recorders at a site 

permits a determination of the unit compaction occurring at specific depth intervals. The annual unit compaction has varied from zero for the 350-500 foot depth 

interval at the Oro Loma site to 0.00115 foot per foot per 

year in the 503-703 depth interval at the Cantua site.

Casing-failure studies (W. E. Wilson, written commun., April 1968) indicate that little compaction is occurring in the upper 300 feet of deposits; that maximum 

unit compaction is occurring between 100 feet above the 

Corcoran and 400 feet below the Corcoran; and that only 

moderate amounts of unit compaction occur below a 

depth of 400 feet below the Corcoran.

Many geologic factors influence the amounts and 

rates of compaction (see Part 2). The following geologic 

conditions promote large amounts of rapid compaction: 

a confined aquifer system that is undergoing large declines in head; a minimum overburden load that has 

compacted the deposits in the geologic past; many thin 

beds of montmorillonite clay with absorbed sodium interbedded with permeable, highly micaceous sands that 

have a large lateral extent. Meade (1968, p. 28) also 

points out that the presence of diatoms increases the 

compressibility of the deposits.

STRESSES TENDING TO CAUSE COMPACTION

The stress tending to cause compaction of all deposits 

is the grain-to-grain load that is transmitted to a given

- Recorder

Compaction tape

Counterweights

Bench mark\

Cable, 1/8-inch stainless 

steel, 1x19 stranded 

reverse lay

 Well casing 

4 to 13 inches

Anchor weight, 

200 to 300 pounds--^^ H

FIGURE 6. Diagram of compaction-recorder installation.

bed as the result of the sum of all stress-producing 

factors in the overlying stratigraphic section. In the Los 

Banos-Kettleman City area and elsewhere, stress 

changes caused by man's changes of the hydrologic environment are superimposed on the natural stresses 

tending to compact the deposits. The ratio of manmade 

to natural applied stress varies considerably with geographic area and depth, but it can be large. For example, the natural applied stress at the 600-foot depth at 

the Cantua recorder site was increased from about 330 

to about 500 psi as the result of about 400 feet of 

artesian-head decline. About a 52 percent increase in 

applied stress has occurred as a result of man's change 

in the hydrologic environment at the 600-foot depth 

level. However, at the 200-foot depth, no change in 

applied stress has occurred. The 200-foot depth is about 

10 feet below the water table which has not changed 

position appreciably at the site during the past 60 years. 

Water-level changes in both the confined and 

unconfined parts of the aquifer systems have altered the
E12 STUDIES OF LAND SUBSIDENCE

preexisting distribution of stresses. Changes in applied 

stress that result from changes in the hydrologic environment are concurrent with the water-level changes. 

Applied stresses become effective stresses only as 

rapidly as water can be expelled from a bed of a given 

lithology.

A stress that does not tend to cause compaction is a 

neutral or hydrostatic stress. This stress, which is the 

weight of the interstitial water, is transmitted downward through the water between the grains. The hydrostatic stress is considered neutral because, although it 

tends to compress each grain, it does not tend to change 

the grain-to-grain relationships significantly.

The basic theory regarding the stresses produced by 

water-level change within an aquifer system has been 

discussed in detail by Lofgren (1968) and by Poland and 

Davis (1969). The computation of change in applied 

stress in the Los Banos-Kettleman City area studies is 

different with respect to item 4 in the following paragraph than the mode of computation used by Lofgren. 

For a complete discussion of the analysis of stress 

changes resulting from water-level change within the 

study area, the reader is referred to Part 3 (Bull and 

Poland, 1974). The following summary is included here 

in order to provide the reader with a brief background 

regarding the four components of change in applied 

stress and to demonstrate the need for detailed information about changes in water level in subsidence areas.

Changes in water level resulting from pumping of 

ground water and irrigation have changed the applied 

stress tending to compress the deposits in several different ways. Change in total stress applied to a confined 

zone is the algebraic sum of the following stresses:

1. A seepage stress that is equal to the head differential 

caused by change in artesian head within the 

confined zone.

2. A seepage stress that is equal to the head differential 

caused by change in the position of the water table.

3. A stress caused by change in buoyancy of the deposits within the depth interval that is being dewatered, or saturated, as a result of water-table 

change.

4. A stress caused by part of the pore water being 

changed from a condition of neutral stress to applied stress, or vice versa, that occurs within the 

depth interval being affected by water-table 

change.

The magnitudes of the various stress components on the 

confined zone, expressed in feet of water (1 foot of water 

= 0.43 psi), are as follows: an assumed porosity of 0.4, a 

specific gravity of 2.70, and an average moisture content of the dewatered deposits of 0.2 the volume. Seepage stresses resulting from either artesian-head change 

or change in water-table position cause 1 foot of change 

in applied stress per foot of change in head differential.

Buoyant changes cause 0.6 foot of change in applied 

stress per foot of water-table change. Change in the 

stress condition of part of the pore water causes 0.2 foot 

of change in applied stress per foot of water-table 

change. The effects of changes in buoyant support and 

in the stress condition of the pore water tend to cancel 

the effect of change in seepage stress caused by watertable change. The net effect of water-table change on 

the applied stress on the confined zone is an increase of 

0.2 foot of water per foot of water-table rise and a decrease ofO.2 foot of water per foot of water-table decline.

DESCRIPTION OF THE 

GROUND-WATER RESERVOIR

GENERAL FEATURES

The 500 to more than 3,000 feet of poorly to moderately consolidated sediments that form the groundwater reservoir in the Los Banos-Kettleman City area 

was deposited in the San Joaquin Valley geosynclinal 

trough since late Pliocene time. As shown in figure 7, 

these sediments consist primarily of flood-plain, 

alluvial-fan, and lacustrine deposits. Some deeply 

buried deltaic sediments occur in the southern part of 

the area. Most of these deposits are part of the Tulare 

Formation, which is overlain by additional alluvium 

and underlain by Pliocene littoral and estuarine deposits of the San Joaquin and Etchegoin Formations. 

The Pleistocene deposits accumulated rapidly as a result of uplift and erosion in the Diablo Range and uplift 

and glacial scouring in the Sierra Nevada. The rapid 

rate of deposition is one reason for the poorly consolidated nature of most of the deposits.

The subsurface geology of the fresh-water-bearing 

deposits is complex when the deposits are differentiated 

with respect to source, environment of deposition, and 

lithology. The subsurface geology is described by Miller, 

Green, and Davis (1971).

Fortunately, the hydrologic units are not so complex 

as the geologic units. As pointed out by Davis and Poland (1957, p. 421), a general threefold hydrologic subdivision of the continental 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 Member of the Tulare Formation at a 

depth ranging from less than 100 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 pressures and 

chemical qualities; and a lower unit, 400 to more than 

2,000 feet thick that extends down to the main saline 

water body. The two fresh-water-bearing units are referred to as the upper zone and lower zones, and the 

lacustrine clay that separates the two zones is commonly referred to as the Corcoran.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E13

1200' - 

800' - 

400' -

SEA 

LEVEL

400' - 

800' -

1600' - 

2000' -

C 1200' -i

800' -

400' - 

SEA

LEVEL 

400' -

800' - 

1200' - 

1600' - 

2000' - 

2400' -

E 1200' -

800' - 

400' -

SEA

LEVEL 

400' -

800' - 

1200' - 

1600' - 

2000' - 

2400' - 

2800' -

Tumey Hills - EXPLAr

 - V.\ V ~ " ___________ Fresno Slough - Well for which yl

' ': .:> ^< -^

 V-.\^>-, 36° 7.2 9.5 7 - 4 

"' %->V (11) (88) (^7)

>stts __- -- - r rr - =i£ lemperai 

_ ,-<^ ^.'-fo'neof brjcktsh' water -'-'^..^^e^ Number above t

8.6 ZJL TO ^§° ,27 _^___. ^-s = "771~f '.^ '. ' (gallons per n 

^°" 27° ( 2|) w (8^)^ -W*4r. -777^- . :v,'^, ater, ' ' ': .* -' drawdown) tin

6-^s%-': '' ' ' '.''' '-' interval; numb

-I-Xj-'-'^t -"- Chiefly ^""^. . . ' ' e water tern 

'<: ' ' :^?^ -TV -. ^r7r.- ' ' :' ' '" Celsius (F in 

^- ^' : - :.';. ' : \\-J- : .' :'; '. ' ' " Salineweterbody - point of disch 

^^ '"' ' ' The position o

Wells more the 

profile are sho\(

A 

\Mouth ofCantua Creek

 ^ r .

' A ~~~""~ - . ^_ Cantua Creek _ mi. 

 . ; :V | - ___^ i Fresno Slough

 ." ' ''^\ slsT^

'. '. .->. \ 1 Chiefly alluvial r2§J~

':-'.'\\ 10' -- -- - ="==*;:=;:F^t: 

:-..\\ 1^ fan deposits ^-^s:

- . \\ \ 25° __ _ 

: "\\M77) 2.3 / --_.- :-.V\\ \ 25° / .V\\\ 177X U-

 : A \ ~ ~* ' 33 

 ' . .' \\ 30 (92) 

'. .'.'/.XX (86) __ ^ . .

^jol ^--4"" *T-^ J24.2 ^l^B

_ _i '-§*p" Flood-plain deposits (g5) (micaceousjand) _ (72) 

^4- f?!) (74^ <-':T^. rJ^nT5 t"?ftlfl1 .^^-' : V- '.' ' ' ' '-

(86) 5 .' ': : .: : IP ' ' " " "'"

Chiefly f lood-plein x-: : : ' ' 

deposits /' ' '' 

- ^_^^ .^' ' '' '.' Saline water body

Anticline Ridge 

\ ~~~~ | ______ Kings River

\

V \ - -2-3 Alluvial- - ^/Lecust 

\ \ 35° ^i: _-^=: 

\ N (97) 1.3 H 

\ \ ^ fan 28°

\ ^° /BO^ \ \ (79) (82)

\ \ deposits/^ ~~ --^_

JATION

7.2

35° 

L(95)

eld factor and water 

ore is shown 

he line is the yield 

the specific capacity 

linute per foot of 

les 100 divided by 

n feet, of perforated 

*.r below the line is 

perature in degrees 

parentheses) at the 

irge from the well, 

"perforated casing is 

leavy line segment, 

in a mile from the 

m by dashed lines

Confining day 

layer

i

^\ \ \ x w^^

ne sand deposits ^--^^^ Flood-plain deposits 

 ===-=_ i^ = ^S= = ^ ==== = Ff^1

3^ |^- .^-^ 31°

30° (88) - ^ -(87)

86) __^- ' "S.S -4-^- 

__ - 31 ° 32° 

(88) <89) Chiefly deltaic deposits 

Chiefly - flood- plain 

deposits

"^^-'-^i'-Jiii '.'.'.' ' '. '.' f.on?.?'f brack'ish water ' ' ''-' ; '.' ' '. . ' ' ': ' ''}.'.'' "'''""

ri ' ' ~J~^rr ' ^li-^!_' ' ' ' '.'--. . ''

__ __ ^s^-.Tv^ '.'.' ' ' ' Saline water body

 * ^*

E'

-

VERTICAL EXAGGERATION X 13

0123 MILES i i n i r

0123 KILOMETRES 

For location of sections, see figure 3

FIGURE 7. Cross sections showing well-yield factors and depositional environments of the aquifer systems. Lines of sections shown in figure 3. (From Miller and others, 1971, fig. 15.)

The three hydrologic units are shown in figures 8 and report (Miller and others, 1971).

9, and the location of the sections is shown in figure 3. Most of the ground water pumped in the Los Banos

The detailed geologic sections on which these sections -Kettleman City area is withdrawn from the lower

are based have been presented by Miller in another zone. An accurate estimate of the proportion of water
E14 STUDIES OF LAND SUBSIDENCE

800'

SEA LEVEL

1600'

3200'

Fresno Merced 

/County line

Cantua Creek(town) 

xWater table

Fresno Kings 

County line\

8 MILES -.-r^/ °° " ' ' 7^'' \-_\Zone of brackish '

VERTICAL EXAGGERATION X 53

For location of section 

see figure 3

Saline water body

FIGURE 8. Longitudinal section showing general hydrologic units. (Modified from Miller and others, 1971, fig. 13.)

pumped from the upper zone cannot be made with the 

data available because many wells tap both zones and 

because water moves between the zones through well 

casings and gravel envelopes around the casings. However, study of the spacing and number of wells, perforated intervals, and relative aquifer-system productivities suggests that at least 75 percent and possibly 80 

percent of the overall pumpage is from the lower zone.

The general variation in the amount of water pumped 

from the lower zone or its stratigraphic equivalent is 

shown in figure 10. The proportion of lower-zone water 

pumped increases from east to west. The western margin of the 50-75 percent area coincides with the western 

margin of the highly permeable, upper-zone sands derived from the Sierra Nevada (fig. 11). The amounts of 

upper-zone water pumped increase to the east of the 

western margin of these sands because the thickness of 

the Sierran micaceous sands increases towards the east. 

Southeast of Mendota, brackish water unfit for agriculture occurs in the upper zone (figs. 7, 9, 10, 11), and 

virtually all the water pumped within this local area is 

from the lower zone.

The areas of less than 50 percent pumpage from the 

lower zone are large, but much of the agricultural water 

supply for these areas is derived from imported surface

waters. Surface-water imports reduce the amount of 

ground water pumped, thereby reducing the watertable or head decline when compared with areas totally 

dependent on ground water for agriculture.

UPPER ZONE

The upper zone has a water table, and locally the 

water is unconfmed. In general, however, ground water 

in this zone is semiconfined to confined. Under conditions of pumping draft, head differentials of 100-400 

feet have developed between the water table and the 

water levels in wells tapping the base of the upper zone 

immediately above the Corcoran. For example, see 

figure 28. Hence, confinement is known to be substantial in some parts of the area, but in places where the 

deposits are coarse grained and have a large vertical 

permeability, differences in head are not great. In the 

northern and central parts of the study area the upper 

zone consists of many semiconfined aquifers and 

aquitards. In the southeastern part of the area, most of 

the upper zone is as well confined as the lower zone 

because of extensive lake clays that occur at various 

depths. In the southwestern part of the area, lake clays 

(including the Corcoran) are absent, and where the deposits are sufficiently coarse grained, unconfined condi-
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E15

1200' -i

800'

400'

SEA LEVEL

400' -

800' -

1200' -

1600' -

2000'

Tumey Hills

Fresno Slough

SEMICONFINED"

^ -^_ _AQjJI FER S YSTEM OJpper zprjej_ ^__ ^-^^±L-^s==r 

Mft/ater table~N ^ - ^ =^= ^ - ^ ^X^o ran Clay Member

CONFINED

AQUIFER (Lower

SYSTEM

^°/)' Seline water body

Principal confining bed

1200'

400'-

SEA LEVEL

Cantua Creek (town) Fresno Slough

SEMICONFINED AQUIFER

400'- 

800'-

1200'

1600* -

2000' -

2400*

2800*

of brackish water

- __ SYSTEM (Upper zone) __-5= = =*= = = =

- s - 3,- --c _ s: _ 3_ z^sr-^- - -v- -v -s -r^c r£=^s=. = =^= =

CONFINED

AQUIFER (Lower zone) 

SYSTEM

^Corcoran Clay Member 

Principal confining bed

 ' r ^^--^^-r^-T^^-' .' ' 

>' ' : V:'-"

Saline water body

1200' 

BOO* 

400'

SEA LEVEL

400'

8OO'

1200'

1600'

2000' 

2400' 

2800' 

3200'

Anticline 

Ridge

SEMICONFINED TO CONFINED

Potentiomatric surface (lower,zoilsLMaM-l9-fifl 

AQUIFER SYSTEM (Upper zone)

 = = =^- -V -V ' ^ ^Co"nf ining clay beds -

^Corcoran Clay Member 

Principal confining bed

CONFINED 

AQUIFER 

SYSTEM

(Lower zone)

r& 7^4^';Base of fulare Formation

Saline water body

VERTICAL EXAGGERATION X 13 

0123 MILES

I I I I

0123 KILOMETRES

For location of sections, see figure 3 

FIGURE 9. Cross sections showing general hydrologic units. Lines of sections shown in figure 3. (Modified from Miller and others, 1971, fig. 14.)
E16 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37 "00

36°30'

36°00'

EXPLANATION

Boundary of deformed rocks

ESTIMATED AMOUNT OF IRRIGATION 

WATER WITHDRAWN FROM LOWER 

ZONE, IN PERCENT OF TOTAL PUMPAGE

75-100

50-75

25-50 

0-25

Western boundary of irrigated lands as of 

1962

10 15 MILES

10 15 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 10. General variation in the amount of water pumped from the lower zone or its stratigraphic equivalent.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E17

tions prevail for the upper deposits. Considered as a 

unit, the upper zone is termed a semiconfined aquifer 

system in this report.

PHYSICAL CHARACTER

The upper zone, which includes the upper part of the 

Tulare Formation and younger alluvium, ranges from 

about 100 to 900 feet in thickness. The primary upperzone aquifer is a micaceous sand, which was deposited 

over 645 square miles of the Los Banos-Kettleman City 

area (fig. 11) as flood-plain deposits of streams draining 

the Sierra Nevada. The thickness of the micaceous sand 

ranges from a featheredge along its western margin to 

about 580 feet under the present valley trough. In the 

northern half of the area, volcanic glass and pumice 

fragments occur in the micaceous sand in the basal part 

of the aquifer. In the southern part of the area, many of 

the deep irrigation wells tapping the lower zone are also 

perforated opposite lacustrine sands associated with the 

Corcoran Clay Member. Most of these sands are in the 

upper zone and are from 100 to over 200 feet thick. The 

lacustrine sands have a low clay content, are well 

sorted, and are highly permeable.

The alluvial-fan deposits in the upper zone are not 

productive aquifers except in a small area southwest of 

Los Banos, in the extreme northern part of the Los 

Banos-Kettleman City area. The sediments deposited 

by Los Banos Creek consist primarily of gravel; shallow 

wells, 100-250 feet deep, provide sufficient water for 

irrigation. South of the Fresno-Merced County line, the 

alluvial-fan deposits have a low permeability and consist of clayey sand layers with interbedded poorly sorted 

silt and clay.

The alluvial-fan deposits are derived from the Diablo 

Range and are easily recognized in well cuttings or in 

cores by their yellowish to brownish color. They are 

calcareous and gypsiferous and locally contain small 

calcareous concretions, serpentine, glaucophane schist, 

fragments of siliceous shale, chert, and jasper

 lithologies that are typical of Diablo Range source

areas.

PRODUCTIVITY

The most permeable aquifers in the Los Banos

-Kettleman City area are in the upper zone. These 

aquifers, however, are of limited extent. A comparison 

of yield factors1 (Poland, 1959, p. 32), which are approximate measures for the overall permeabilities of the 

water-bearing materials tapped by wells, indicates that 

the gravels forming the Los Banos Creek alluvial-fan

Specific capacity (gallons per minute per foot of drawdown) x 100

1Yield factor = 

Thickness of deposits, in feet, tapped by perforated interval of well casing

TABLE 1. Relation of yield factors to types of upper-zone deposits

Townships Mean Number

represented yield of wells

Area (Township/Range) factor represented

Wells tapping only upper zone alluvial-fan deposits:

Los Banos ________ __________ 10S/10E 95 5

South of Fresno-Merced County line__ 16S/15E; 18S/17E 4 3

Wells tapping only upper zone Sierra micaceous sands:

West of San Joaquin River _______ 10S/12E; 11S/13E; 50 4

12S/14E; 13S/15E 

West of Fresno Slough -_. .-_ _. 15S/15E; 15S/16E; 21 13

16S/16E; 16S/17E;

17S/16E; 17S/17E;

17S/18E; 17S/19E;

18S/18E 

East of Fresno Slough __________ 14S/17E; 15S/17E; 100 15

16S/18E; 16S/19E

deposits are the most permeable. (See table 1.) These 

deposits are two to five times more permeable than the 

Sierra micaceous sands which form the primary upperzone aquifer in the eastern part of the study area. The 

upper zone alluvial-fan deposits south of the Merced 

County line which are derived from the Diablo Range, 

have low permeabilities as indicated by the low productivity of the few wells that tap only these deposits.

A fivefold variation in mean yield factors of the upper 

zone Sierra micaceous sands occurs within the study 

area. A comparison of mean yield factors indicates that 

the Sierra micaceous sands are twice as permeable west 

of the San Joaquin River than west of Fresno Slough. 

Many shallow wells tapping these deposits west of the 

San Joaquin River yield about 1,400 gallons per minute. If the Sierra micaceous sands are present and are 

less than 200 feet thick, most irrigation wells tap both 

the upper and lower water-bearing zones. In the area 

west of the Fresno Slough, where sodium chloride water 

occurs in the upper zone (shown in fig. 11), wells are 

perforated only opposite the lower zone. Mean yield 

factors of wells 3-4 miles east of the Fresno Slough 

indicate that the micaceous sands are five times as 

permeable as the sands west of the slough.

CHEMICAL CHARACTER OF WATER

Ground waters of the upper zone generally contain 

high concentrations of calcium and magnesium sulfate. 

Pronounced changes in the chemical characteristics of 

these waters occur in adjacent areas along the eastern 

and western margins of the area, and gradational 

changes occur with increasing depth (Davis and Poland, 

1957, p. 457-458).

The calcium and magnesium sulfate ground waters 

occurring to a depth of 200-300 feet average about 3,000 

mg/I (milligrams per liter) of dissolved solids and have 

about 35 percent sodium. An abrupt change, however, 

occurs along the border of the area, where the water 

from the west side with high sulfate concentrations
£18 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00' -

X \ \

Los Banos

EXPLANATION

Boundary of deformed rocks

Line of equal thickness of micaceous sand 

derived from the Sierra Nevada; dashed 

where approximately located; interval 100 

feet

Eastern boundary of Corcoran Clay Member 

of the Tulare Formation

Extent of water of high NaCl content in 

micaceous sand overlying the Corcoran 

Clay Member

Kettleman RED 

10 15 KILOMETRES City

36°30' -

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 11. Thickness and extent of the Sierra sand overlying the Corcoran Clay Member of the Tulare Formation. (Modified from Miller and others, 1971, fig.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E19

merges with the calcium and sodium-bicarbonate 

ground water of low dissolved solids from the east side of 

the San Joaquin Valley.

The chemical character of the waters contained in the 

deposits from a depth of 300 feet to the top of the Corcoran can be distinguished from the overlying waters by 

their decrease in total dissolved solids to about 1,500 

mg/1 and an increase in the percent sodium to about 55.

West of the Fresno Slough the water in the micaceous 

sand immediately overlying the Corcoran Clay Member 

(with the exception of the brackish water area shown in 

fig. 11) has a mean total dissolved solids of around 850 

mg/1, and the percent sodium is about 60.

CORCORAN CLAY MEMBER OF THE TULARE FORMATION

A widespread diatomaceous clay stratum in the upper 

part of the Tulare Formation was first described by 

Frink and Kues (1954, p. 2357-2370) and has been 

named the Corcoran Clay Member of the Tulare Formation (Inter-Agency Committee, 1958, p. 120). This 

lacustrine clay extends beneath the entire Los Banos 

-Kettleman City area (fig. 12) except for a narrow zone 

adjacent to the hills in the southwestern part of the area 

where, as is shown in section E-E' (fig. 7), it feathers 

out, presumably along a contour of the ancestral Los 

Gatos Creek fan.

The Corcoran has two lithologies. The upper twothirds of the Corcoran consists of thin-bedded clayey silt 

and silty clay. The lower third of the unit commonly is 

coarser grained, consisting of interbedded sand-siltclay and clayey silt. The greenish-blue color indicates 

that the Corcoran is reduced, except in the extreme 

western part of the study area where it has been uplifted 

and partially oxidized to brown or red.

The Corcoran Clay Member of the Tulare Formation 

is the principal confining layer throughout much of the 

San Joaquin Valley. The vertical permeability of the 

Corcoran which, based on results of consolidation tests 

under a simulated natural overburden load, ranges 

from 4 x 10 ~5 gpd (gallons per day) per square foot (0.002 

feet per year) in the more sandy parts near the top and 

base to as low as 6 x 10 ~ 6 gpd per square foot (0.0003 feet 

per year) in the less permeable middle section (Johnson 

and others, 1968, table 9). By 1960, the difference in 

head in aquifers above and below the Corcoran was as 

much as 200 feet.

The Corcoran was deposited in a fresh-water lake 

that was 10-40 miles wide and more than 200 miles long 

(Davis and others, 1959, p. 77 and pi. 14). Evidence 

presented by Janda (1965) indicates that the lake existed in Pleistocene time about 600,000 years ago. The

longitudinal axis of the lake in which the clay was 

deposited was approximately 5-10 miles west of the 

present topographic axis of the valley. The exact western areal extent of the Corcoran is difficult to determine, because as it thins, it bifurcates and its sand and 

silt content gradually increases until it is not discernible in electric logs from the littoral sands which occur 

along its west edge.

The thickness of the clay varies considerably. The 

maximum known thickness of the Corcoran in the study 

area occurs 5 miles northeast of the mouth of Panoche 

Creek, where an electric log shows the Corcoran to be 

120 feet thick (Miller and others, 1971, fig. 11). Adjacent 

to Monocline Ridge and Ciervo Hills, the Corcoran is 

less than 20 feet thick and is more than 900 feet below 

land surface. In most of the area the Corcoran is 30-60 

feet thick.

The map showing the structure of the Corcoran (fig. 

13) indicates that there has been gentle postdepositional folding and warping of this lacustrine clay bed. 

The shift in the structure contours in the HuronWesthaven area occurs where contours are shown for 

the lower clay stratum in an area where the upper clay 

layer is absent.

LOWER ZONE

The lower zone is effectively confined by the Corcoran 

except in the southwestern part of the Los Banos 

-Kettleman City area where the Corcoran is absent and 

confinement is poor or lacking. The lower zone supplies 

about three-fourths of the ground water for irrigation in 

the Los Banos-Kettleman City area.

If an aquifer is defined as a permeable deposit that 

will yield water to wells, the entire lower zone can be 

considered an aquifer. Permeable sand units can also be 

considered as aquifers separated hydraulically to varying degrees by the finer grained interbeds of silt and 

clay. Silt and clay, especially clay, are much more compressible than sand when compressive stresses are increased owing to artesian-head decline. Therefore, it is 

important in the study of compaction of deposits under 

increased effective stress to differentiate between a 

water-bearing unit that is composed entirely of permeable material such as clean sand and one that contains 

many fine-grained beds of silt and clay. For purposes of 

differentiation in the studies of compaction and subsidence, a water-bearing unit that has hydraulic continuity but that contains many fine-grained beds is 

termed an aquifer system. Under this definition, the 

lower water-bearing zone is a confined aquifer system. 

The beds of silt and clayey silt that impede ground-
E20 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00

EXPLANATION

Boundary of deformed rocks

Line of equal depth to base of Corcoran 

Clay Member of the Tulare Formation; 

dashed where approximately located; interval 100 feet

Boundary of Corcoran Clay Member of the 

Tulare Formation

SANT 

Coalinga

VALLEY

10 15 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 12. Depth to the base of the Corcoran Clay Member of the Tulare Formation.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E21

37°00

EXPLANATION

Boundary of deformed rocks

Structure contour 

Shows altitude of top of Corcoran Clay

Member of the Tulare Formation; dashed 

where approximately located. Contour 

interval 50 feet; above sea level, 100 feet. 

Datum is mean sea level

Approximate boundary of Corcoran Clay 

Member

Approximate boundary of upper clay stratum of Corcoran Clay Member where less 

extensive than lower stratum. Corcoran 

is bifurcated on southwest edge

36°30' -

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 13. Structure of the Corcoran Clay Member of the Tulare Formation, (From Miller and others, 1971, fig. 12.)
E22 STUDIES OF LAND SUBSIDENCE

100

140

180

220

Oro Loma site

12/12-16HJ J

perforated 670-712 feet 12/12-16H6 

.perforated 770-909 feet

- 340

UJ

o Westhaven site

380

420

460

500

540

580

620

20/18-11Q2 

.^perforated 755-805 feet

V 20/18-11Q3 

perforated 1885-1925 feet 20/18-11Q1 

perforated 650-710 feet

15/13-11D2 

perforated 900-960 feet,

15/13-2N2 

perforated 880-1959 feet'

540

580

620

16/15-33J1 

perforated 1013-2792

16/15-34N4 

perforated 1052-1112 feetv x"*

1961 1962 1963 1964

FIGURE 14. Variation in the hydraulic continuity of the lower zone.

1965

water movement may transmit appreciable water between adjacent aquifers they are called aquitards.

Throughout most of the area the lower zone has good 

hydraulic continuity both laterally and vertically. The 

degree of hydraulic continuity is shown at four sites in 

figure 14. Lack of hydraulic continuity in the northern 

part of the area is shown by the marked separation in 

head and difference in water-level trends in wells 

12/12-16H5 and 12/12-16H6 at the Oro Loma site. A 

second confining clay occurs about 300 feet below the 

Corcoran in this part of the area, and at the site of these 

wells it is 38 feet thick. Head differences of 60-75 feet 

occur between the two lower-zone aquifers, and the 

greater amount of seasonal fluctuation shown by the 

record of the deeper well suggests that most of the 

lower-zone wells in the vicinity are perforated mainly

below the lower confining clay. The degree of hydraulic 

separation shown by the records of these two wells extends about as far south as the southern part of township 13 south.

Hydrographs of two lower-zone wells at the Westhaven site in the southern part of the area show a 

marked difference in the degree of hydraulic continuity 

when compared with those at the Oro Loma site. Well 

20/18-11Q2 is perforated from 755 to 805 feet, and well 

20/18-11Q3 is perforated from 1,885 to 1,925 feet; yet 

the records show similar water levels and amounts of 

seasonal fluctuation. The difference in artesian head 

between the two lower-zone wells has not exceeded 25 

feet, although the seasonal fluctuation of head has been 

as much as 80 feet.

The other two sets of hydrographs in figure 14 are
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E23

comparisons of water levels in observation wells perforated in an aquifer a short distance below the base of the 

Corcoran and nonpumping water levels in nearby irrigation wells. The irrigation wells are perforated to 

depths 1,000-1,700 feet deeper than the observation 

wells and are within a third of a mile of the observation 

wells. The small differences in head in each set of hydrographs show that good hydraulic continuity exists 

throughout the lower zone for these sites in the central 

and southern part of the study area. The records also 

indicate that the shallow observation wells have water 

levels that are representative of nearby deep irrigation 

wells.

PHYSICAL AND HYDROLOGIC CHARACTER

In most of the study area, the fresh-water-bearing 

deposits below the Corcoran consist of poorly consolidated alluvial fan, flood-plain, deltaic, and lacustrine 

deposits of the Tulare Formation. In the southern part 

of the area, the basal lacustrine deposits of the Tulare 

are moderately consolidated and contain brackish 

water.

The productivity of the Tulare is generally inadequate for irrigation purposes in a 3- to 7-mile wide belt 

along the margin of the valley between the towns of 

Huron and Cantua Creek. Northwest of the Five 

Points-Coalinga Road, deep wells extend into the moderately consolidated Pliocene marine littoral and estuarine sands and silty clays of the pre-Tulare San 

Joaquin and Etchegoin Formations. To the south, the 

deeper wells tap the upper part of the San Joaquin 

Formation.

The wells tap those parts of the marine section that 

have been largely flushed of their connate water. From 

some wells brackish water of poor quality is pumped 

from the pre-Tulare Pliocene deposits, but when the 

poor quality water is mixed with better quality water 

being drawn through the perforations higher in the 

well, the quality is improved, and the net result is to 

increase the yield of the well to an amount that is 

adequate to irrigate the land in the vicinity. Porepressure decline and compaction occur regardless of the 

quality of the water being removed from unconsolidated 

or partly consolidated deposits.

The areas where water is being pumped from preTulare formations of Pliocene age are shown in figure 

15. Although deposits that are considered to be Pliocene 

in age are tapped in a large area near the foothills of the 

Diablo Range, only the area adjacent to the Big Blue 

Hills and Anticline Ridge is iargely dependent on 

ground-water supplies from the older deposits.

In the northern area where Pliocene deposits are tapped, most of the ground water is pumped from 

flood-plain deposits in the first few hundred feet below

the Corcoran. A few wells are perforated in the upper 

part of the Kreyenhagen Formation of Eocene and 

Oligocene age, and many wells tap the deposits immediately above the Kreyenhagen deposits that have 

been described by Miller, Green, and Davis (1971) as 

Pliocene continental deposits. The electric logs suggest 

considerable variation in lithology and water quality of 

the Pliocene continental deposits. Differences in the 

temperature of the well water being pumped are not 

apparent between wells that in part tap Pliocene continental deposits and those that do not. Since 1960, the 

new wells have been tapping shallower zones.

As much as 2,000 feet of pre-Tulare Pliocene deposits 

is tapped by water wells adjacent to the Big Blue Hills. 

In general, the water being pumped from the pre-Tulare 

Pliocene deposits in this area is distinctly hotter than 

the water being pumped by nearby wells that tap only 

the overlying Tulare Formation. Many of the wells tapping the San Joaquin and Etchegoin Formations have 

water temperatures of more than 38°C (100°F), and 

temperatures as high as 45°C (114°F) have been recorded. Adjacent to the northern part of the Big Blue 

Hills, most of the water being pumped within 5 miles of 

the foothills probably is coming from the pre-Tulare 

Pliocene formations. The Tulare is so clayey that some 

wells are not perforated above a depth of 2,000 feet, and 

one well was perforated to a depth of 3,800 feet. Well 

yields generally are less than in areas where wells tap 

only the Tulare Formation.

The area adjacent to the Big Blue Hills and Anticline 

Ridge has experienced as much as 500 feet of artesianhead decline, but the amounts of subsidence in those 

parts of the area where wells derive most of their water 

from the pre-Tulare Pliocene formations have been 

minor, presumably because of the partly consolidated 

nature of the deposits. Only 1 foot of subsidence has 

occurred in the area of 500 feet of head decline.

The lower zone alluvial-fan deposits are derived from 

the Diablo Range and have low permeabilities. They are 

similar in lithology to the upper-zone fan deposits south 

of the Merced County line. In the southern part of the 

area, as shown on section.E-.E' (fig. 7), most of the lower 

zone tapped by wells consists of alluvial-fan deposits, 

but 20 miles to the northwest (section C-C', fig. 7) fan 

deposits form less than one-eighth of the lower-zone 

aquifer system.

The moderately permeable flood-plain and deltaic deposits which form the major part of the lower zone in 

sections C-C' andE-E' (fig. 7) were derived from the 

granitic rocks of the Sierra Nevada. Consequently, they 

are arkosic in composition and can be recognized in drill 

cuttings or core samples by their mica content. They are 

generally grayish green or blue green.

The lower zone in the area of section B-B' (fig. 7) is
E24 STUDIES OF LAND SUBSIDENCE 

120°30' 120°00'

3 7 "00

EXPLANATION

Boundary of deformed 

rocks

Area of ground-water pumping from preTulare Pliocene deposits based on electric 

logs or depth of well

Coalinga 

VALLEY

Kettleman RFn 

5 10 15 KILOMETRES City

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 15. Areas in which part of ground water is pumped from pre-Tulare deposits of Pliocene age.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE 

TABLE 2. Relation of yield factors to types of lower-zone deposits

E25

Area

Townships

represented

(Township/Range)

Mean 

yield 

factor

Number

of wells

represented

Wells tapping only flood-plain deposits derived from the Diablo Range:

South of Los Banos Creek to vicinity of Fresno-Merced County line ______ 12S/11E; 12S/12E 24 6 

Vicinity of Fresno-Merced County line to Panoche Creek ____________ 12S/11E; 12S/12E; 9 26

13S/12E; 13S/13E;

14S/12E

Wells tapping only flood-plain deposits derived from the Sierra Nevada:

West of Fresno Slough _____________________-______ __________ 14S/14E; 14S/15E; 11 9

15S/14E; 15S/15E; 

17S/16E; 18S/17E

Wells tapping only deltaic deposits derived from the Sierra Nevada:

West of Kings River ____________________________________ _ 20S/19E 9 2

Wells tapping intermixed flood-plain deposits derived from the Diablo Range and the Sierra Nevada:

North of Monocline Ridge ___________ __________________ 13S/13E; 13S/14E; 6 23

14S/13E; 14S/14E; 

15S/13E; 15S/14E

Wells tapping only alluvial-fan deposits derived from the Diablo Range:

Vicinity of Los Gatos Creek ___________________________________ 19S/16E; 19S/18E 3 2

Wells tapping intermixed alluvial-fan deposits derived from the Diablo Range and flood-plain and deltaic deposits derived from the Sierra 

Nevada:

Tulare Lake bed to 12 miles northwest of Cantua Creek ____________ 16S/14E; 16S/15E; 4 72

17S/15E; 17S/16E; 

18S/16E; 18S/17E; 

19S/17E; 19S/18E; 

20S/19E

composed chiefly of flood-plain deposits derived from the 

Diablo Range. These deposits which form the bulk of the 

lower-zone deposits in the northern part of the Los 

Banos-Kettleman City area have low to moderately 

high permeabilities. They are greenish gray to greenish 

black and are characterized by andesitic and basaltic 

detritus, serpentine, chert, and other rock fragments 

derived from the Diablo Range. They are slightly to 

moderately micaceous, in contrast to the generally 

nonmicaceous character of the alluvial-fan deposits derived from the Diablo Range. This characteristic would 

suggest that the flood-plain deposits were derived from 

a different or larger source terrain than the overlying 

nonmicaceous alluvial-fan deposits.

A variety of depositional environments are represented by the deposits in the central part of the study 

area. Flood-plain and alluvial-fan deposits derived from 

the Diablo Range interfinger with flood-plain deposits 

derived from the Sierra Nevada and with lacustrine 

sands and clayey silts.

PRODUCTIVITY

The deposits forming the lower-zone aquifer system 

in the Los Banos -Kettleman City area locally are less 

permeable than the deposits forming the semiconfined 

aquifer system of the upper zone. However, because of 

the greater thickness of the lower-zone deposits and the

general poorer quality of the water in the upper zone 

west of the Sierra sands (fig. 11), at least 75-80 percent 

of the irrigation water pumped in the Los BanosKettleman City area is from the lower zone.

The yield factors of the lower water-bearing zone deposits given in table 2 and the areal distribution shown 

in figure 16 indicate that where wells produce from only 

one type of lower-zone deposit, the flood-plain deposits 

derived from the Diablo Range are slightly less permeable than the flood-plain deposits derived from the 

Sierra Nevada. However, yield factors indicate that 

where wells produce from lower-zone deposits which 

consist of Sierra flood-plain deposits interfingered with 

finer grained Diablo flood-plain deposits, the relative 

permeability is considerably lower. The general area 

where this interfingering occurs is in a north-south 

trending belt 8-9 miles wide which extends 18-25 miles 

north from Monocline Ridge.

In the western part of the Los Banos-Kettleman City 

area, between the towns of Cantua Creek and Westhaven, alluvial-fan deposits occur between the Corcoran and the lower-zone Sierra flood-plain deposits. 

Wells in this area producing from the lower zone and 

with approximately 20-50 percent of their perforated 

intervals opposite alluvial-fan deposits have yield factors ranging from less than 1 to a maximum of 9. The 

average yield factor of lower-zone wells in this area is 4.
E26 STUDIES OF LAND SUBSIDENCE

120°30'

:Los Banos;'-'. . . .' ' .' ' .' . '{ '-.'." ' ' '.S ^ 

i.-^~--- : . . . . :::. . : .: - .{//

Boundary of deformed rocks

Western boundary of Corcoran Clay

Member of the Tulare Formation

Boundary of genetic type

Area of no significant pumping from lower 

water-bearing zone as of 1961

Sierra flood-plain and deltaic deposits 

Diablo flood-plain deposits 

Diablo alluvial-fan deposits

Pumping from deep wells west of confining 

Corcoran Clay Member

Upper number, mean yield factor for wells 

tapping only lower-zone deposits. Lower 

number, number of wells in sample

Kettleman BED 

City

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 16. Yield factors and types of lower-zone deposits.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E27

Only two wells, both located in the Los Gatos Creek area 

north and east of Huron, are known to tap only lowerzone alluvial-fan deposits. The yield factors of both of 

these wells is between 2 and 3. A comparison of yield 

factors suggests that in general the lower-zone 

flood-plain and deltaic deposits are 3-5 times as permeable as the lower-zone alluvial-fan deposits but only 

one-half to one-fifth as permeable as the upper-zone 

flood-plain deposits (Sierra micaceous sands of table 1).

The yield of wells throughout the Los Banos 

-Kettleman City area does not vary much with the 

average permeability of the deposits tapped, because 

the yield needed for irrigation purposes is only from 

1,000-2,000 gallons per minute, and yields within this 

range can be obtained in most of the area. Wells tapping 

the highly permeable upper-zone Sierra sand near 

Fresno Slough may be only 150-200 feet deep and yield 

1,500 gallons per minute. In the western part of the area 

where the upper-zone deposits have low permeabilities 

and the majority of the lower-zone deposits consist of 

alluvial-fan deposits, wells must be 2,500-3,500 feet 

deep to obtain 900-1,200 gallons per minute. Thus, 

where average permeability is low, as indicated by the 

low yield factor, the discharge capacity needed for irrigation can be obtained either by drilling wells to tap 

greater thicknesses of the deposits, or by installing 

pumps to operate with greater drawdowns from static 

level, or both.

The thickness of the fresh-water-bearing deposits of 

the lower zone (fig. 17) has been compiled from two 

maps. One map shows the altitude of the base of the 

Corcoran (Croft, 1969, pi. 4). The other shows the altitude of the base of fresh water determined from examination of several hundred electric logs, using 3,000 

micromhos specific conductance (approximately 

2,000mg/l dissolved solids) as the upper limit of fresh 

water (R. W. Page, 1971). Thus, the thickness map (fig. 

17) represents the difference between the two altitudes.

Comparison of figure 17 with the geologic sections 

showing the base of fresh water (Miller and others, 

1971) indicates that the lower-zone thicknesses in 

figure 17 are, in general, several hundred feet less than 

in Miller's geologic sections. Thus, the base of fresh 

water shown by Page in his appraisal of electric logs for 

water-chemistry purposes is several hundred feet above 

the base shown by Miller in his studies for geologic 

correlation purposes because Page used different 

criteria than Miller.

The thickness of the fresh-water-bearing deposits of 

the lower zone (fig. 17) varies considerably in the northern, central, and southern parts of the study area. In the

northern part of the area, deposits that contain fresh 

water are 200-600 feet thick, and the maximum thickness occurs about halfway between the San Joaquin 

River and the Diablo Range.

The thickness of fresh-water-bearing deposits in the 

central part of the area is highly variable. Near Fresno 

Slough the deposits are only 600 feet thick, but they 

thicken westward abruptly, and opposite the Big Blue 

Hills the thickness exceeds 1,600 feet in an extensive 

area, and locally is 2,200 feet.

In general, the fresh-water-bearing deposits are the 

thickest in the southern part of the area, where thicknesses range from 800 to more than 2,000 feet. The 

thickness increases progressively from Five Points toward Tulare Lake bed.

The thickness of the fresh-water-bearing deposits 

does not define the thickness of deposits being subjected 

to large amounts of pore-pressure decline and concurrent compaction. In parts of the area, sufficient yields 

can be obtained by wells without having to drill to the 

base of the fresh-water-bearing deposits. In other parts 

of the area, sufficient yields can be obtained only by 

pumping part of the water from underlying deposits 

that contain water of poorer quality than 2,000 mg/1.

The maximum thickness of the perforated interval of 

the lower zone, and locally of subjacent deposits containing saline water, provides useful information for 

subsidence-study purposes. Reduction of pore pressure 

may occur several hundred feet below the lowest perforations in deposits that have hydraulic continuity. 

This factor is not taken into account in this study because detailed information about hydraulic continuity 

is not known for the base of the lower zone. Furthermore, the fine-grained lacustrine and deltaic deposits 

near the base of the lower zone are likely to cause poor 

hydraulic continuity in that part of the aquifer system 

in much of the study area. An alternative approach is to 

use the maximum depth of well perforations to a.pproximate the depths to which pore-pressure decline is occurring. Maximum pore-pressure decline may be occurring higher in the aquifer system where the greatest 

abundance of well perforations occurs. However the use 

of the maximum depth of the perforations partly takes 

into account pore-pressure decline that is occurring 

below the base of wells that bottom higher in the aquifer 

system. Maximum depths were not used if only a few 

deeply perforated wells were present in a township or if 

the depths appear to be anomalously deep. The maximum thickness of the lower-zone perforated interval is 

based on the well tabulation compiled by Ireland (1963): 

this table lists the perforated-interval data for wells
E28 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal thickness of the 

fresh-water-bearing deposits of the lower 

zone

Dashed where approximately located; interval 200 feet. Compiled from map showing 

altitude of base ofCorcoran Clay Member 

of Tulare Formation (Croft, 1969, p. 4) 

and map showing altitude of the base of 

fresh water (3,000 micromhos) (R. W. Page, 

1971)

Coalmga 

Boundary of Corcoran Clay Member of the VALLEY

Tulare Formation

15 KILOMETRES

36°30' 

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 17. Thickness of the fresh-water-bearing deposits of the lower zone. (Compiled by 3. F. Poland.)
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E29

drilled before 1962. Since 1960 fewer wells have been 

tapping the brackish waters that occur below the base of 

the lower zone.

The maximum thickness of the perforated interval of 

the lower zone is shown in figure 18. The thickness of 

lower-zone deposits being tapped ranges from less than 

400 feet to more than 2,400 feet. The general pattern is 

one of overall increasing thickness of perforated interval toward the southwest. Thicknesses of more than 

1,800 feet occur in the areas of pumping from the Etchegoin Formation.

Comparison of figures 17 and 18 reveals some interesting differences for the various parts of the study 

area. In the northern part of the area, the perforated 

interval exceeds the thickness of the fresh-waterbearing deposits by 200-400 feet near the San Joaquin 

River. Toward the Diablo Range, however, wells tap 

progressively more of the underlying sediments containing brackish water; as is shown by the greater disparities between the thickness lines of the two maps. A 

maximum disparity of 1,000 feet locally is attained east 

of Panoche Hills.

In the central part of the area, the overall patterns of 

lines in figures 17 and 18 bear little resemblance. The 

wells do not extend to the base of the fresh water in the 

eastern part of the subarea: they do extend as much as 

200 feet below the base of the fresh water in the area 

that is dependent on water yielded from the Pliocene 

marine sands.

In the southern part of the area, the productivity of 

the lower zone is sufficiently high that farmers do not 

need to drill wells to the base of the fresh-water-bearing 

deposits. South of Five Points, comparison of figures 17 

and 18 shows that in nearly all the area the wells do not 

reach the base of fresh water. East of Westhaven, the 

thickness of the lower zone exceeds the thickness of 

perforated interval by as much as 1,000-1,400 feet.

Pore-pressure decline is also occurring below the base 

of the well perforations in the vicinity of Fresno Slough 

and Kings River as a result of the large amounts of 

water being pumped from the deeper aquifers farther 

west. An example of this type of head decline is shown in 

figure 24 at the Yearout site (13/15-35D).

CHEMICAL CHARACTER OF WATER

Lower-zone ground waters are effectively separated 

by the Corcoran Clay Member from upper-zone water 

throughout most of the study area. The chemical 

character of the water has been discussed in some detail 

by Davis and Poland (1957, p. 459-460). Analyses of 

samples taken in August 1951 from wells with perforations restricted to the lower zone and of samples from

older wells in that zone that were not gravel packed 

provide useful information about the chemistry of the 

lower-zone water. It is primarily a sodium sulfate 

water, with noticeably more bicarbonate than in the 

upper-zone waters. The chloride concentration of the 

water is generally 100 mg/1 or less.

The uniform salinity of the lower-zone water at a 

given site can be demonstrated by examination of spontaneous potential electric logs. The mud used when 

drilling a well commonly is mixed with water from a 

nearby irrigation well, thereby causing a minimum of 

contrast between the resistivities of the formation fluids 

and the drilling mud. Under such conditions, the spontaneous potential log will be virtually featureless unless the salinity of the contained waters varies from bed 

to bed. The featureless spontaneous potential logs of the 

study area indicate that lower-zone salinities are very 

uniform or undergo change with depth in a gradual 

manner.

The chemical character of the water in the lower zone 

has been influenced by variations in time and place of 

streamflow from the Coast Ranges, by the initial 

sources of the deposits and their contained waters, by 

the presence or absence of the Corcoran as a control for 

percolation to the lower zone, and by the activities of 

man. The variations in dissolved solids of lower-zone 

water shown in figure 19 probably have been little affected by man. The data for the map were taken from 

values of sums of determined constituents given by 

Davis and Poland (1957, tables 2 and 3). Some of the 

data were from wells that are perforated for short distances immediately above the Corcoran, but sums of 

determined constituents for these wells do not differ 

appreciably from those for nearby wells perforated only 

below the Corcoran.

The map showing the chemical character of the water 

in figure 19 is representative, in general, of the freshwater-bearing section of the lower zone as shown in 

figure 17. The map is biased toward mean or minimum 

sums of determined constituents for two reasons. 

Anomalously high values could be the result of two 

causes: (1) The basal part of the perforations of some 

wells were known to extend below the base of the fresh 

water; and (2) the presence of poorer quality water in 

some wells was thought to have been the result of lack of 

prolonged pumping before sampling in wells that are 

perforated for a short distance above the Corcoran. In 

such wells, when the pump is idle, poorer quality 

upper-zone water may flow down the well and gravel 

pack and replace the lower-zone water immediately 

adjacent to the well.

The concentration of dissolved solids in the lower-
E30 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00'

36°30'

36°00'

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal maximum thickness of the perforated interval of the lower 

zone for wells drilled before 1962

Interval 200 feet.Short dashed where approximately located; long dashed for thickness below estimated stratigraphic equivalent of the Corcoran, where absent

Western boundary of the Corcoran Clay 

Member of the Tulare Formation

10 15 MILES

10 15 KILOMETRES

Kettleman BED 

City_______

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 18. Maximum thickness of the perforated interval of the lower zone.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E31

37°00' -

EXPLANATION

Boundary of deformed 

rocks

Generalized line of sum of determined constituents for water from lower-zone wells

Interval 200 milligrams per liter. Data chiefly 

from table of sum of determined constituents by Davis and Poland, (1957, table 2)

Western boundary of the Corcoran Clay 

Member of the Tulare Formation

Kettleman RFn 

City

36°30' 

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 19. Variation in dissolved solids of the lower-zone water.
E32 STUDIES OF LAND SUBSIDENCE

zone water increases toward the Coast Ranges. Maximum concentrations occur opposite the mouths of 

Panoche, Cantua, and Los Gatos Creeks where more 

than 2,OQO mg/1 of dissolved solids occur in the water. 

The absence of the Corcoran west of Huron may have 

contributed to the high concentration of dissolved solids 

because of possible recharge of the lower zone by 

streamflow (Davis and Poland, 1957, p. 459). A concentration of dissolved solids is not present opposite the 

mouth of Little Panoche Creek, but streamflow from 

this drainage area did not discharge at this point until 

after the deposition of the Corcoran lake clay.

The area of high concentration of dissolved solids 

near the mouth of Cantua Creek is due, in part, to 

pumping of water from marine deposits below the base 

of the fresh-water-bearing deposits. Also, the area of 

high concentration opposite the mouth of Panoche 

Creek conforms with an area in which perforated intervals in the deeper wells extend below the base of the 

fresh water.

Areas of low concentration of dissolved solids occur 

between the mouths of the large streams. The dissolved 

solids are less than 1,000 mg/1 opposite Monocline 

Ridge, the Ciervo Hills, the southeast end of the Big 

Blue Hills, and the Kettleman Hills. These areas have 

received little recharge from streamflow or rainfall 

since the deposition of the Corcoran.

Electric logs and analyses of well waters suggest that 

the water from the Pliocene sands that underlie the 

Tulare Formation has a relatively high dissolved solids 

content. Water temperatures in excess of the normal 

temperature gradient with depth in the Tulare and 

older formations indicate a present lack of circulation of 

the water in this zone. Recharge of stream water from 

the Diablo Range into the Pliocene sands is not expected 

to be rapid because the estuarine deposits have been 

overlapped by the alluvial silts and clays of the Tulare 

Formation.

SALINE WATER BODY

A saline water body occurs beneath all the fresh 

ground-water reservoir in the Los Banos-Kettleman 

City area. Along the east side of the area, northwest 

from about the town of San Joaquin, the saline water 

body occurs at depths of 800-1,500 feet below the land 

surface. (See generalized sections B-B' andC-C", fig. 9.) 

Five miles west of Mendota the chloride content of this 

water has been estimated to be about 7,700 mg/1 (Davis 

and Poland, 1957, p. 462). The position of the top of this 

high chloride water is only approximately known because only a few wells were drilled into the saline 

water-bearing beds. The upper surface of the saline 

water body dips steeply westward. (See fig. 9, section

C-C", beneath Fresno Slough.) Wells drilled along the 

western margin of the valley in 18/15-1 and 2 reach the 

saline water at a depth of 3,150 feet.

The brackish-water body above the base of the Tulare 

Formation in the southeastern part of the study area 

(generalized section E-E', fig. 9) contains fresh-water 

fossils. Its present salinity is thought to be a secondary 

feature such as Pleistocene lake evaporation (Miller 

and others, 1971). Chloride analyses of core samples 

from core hole 19/19-17P show a range of chloride concentration in this zone of 2-60 grains per 1,000 cubic 

centimeters of core sample.2 Porosities in this zone are 

thought to average about 40 percent.

This would indicate an approximate chloride concentration of the water of 320-9,700 mg/1. Core samples 

in the main saline water body below the base of the 

Tulare Formation to a depth of 3,735 feet below land 

surface have chloride concentrations that range from 

2-106 grains per 1,000 cubic centimeters of core sample. 

If a 40 percent porosity is assumed for these samples, 

the chloride content of this water ranges from about 

320-17,000 mg/1.

NATURAL FLOW SYSTEM

Natural flow conditions in the ground-water reservoir in the central part of the San Joaquin Valley were 

greatly different before agricultural development of the 

area. Consideration of the entire hydrologic system, 

from the Diablo Range to the Sierra Nevada, provides 

useful information about the natural flow system and 

the changes of the general flow pattern that have been 

made by man. Early measurements made by the 

Geological Survey in 1906 (Mendenhall and others, 

1916) form the basis of appraisal of the original conditions.

The extent of the lower-zone confinement and the 

change in flow conditions for the northern half of the Los 

Banos-Kettleman City area and the area to the east are 

shown in figure 20. The great extent of the Corcoran is 

demonstrated in figure 20A. The only sources of potential recharge to the lower zone, under natural conditions, were along the eastern and western boundaries of 

the confining clay. The amounts of water percolating 

into stratigraphically lower deposits in the Diablo 

Range probably have always been small in the northern 

half of the study area. In the southern part of the study 

area, the boundary of the Corcoran is east of the mountain front, and the potential for recharge from the Diablo Range is much greater.

"Shell Oil Co., 1929, unpublished report. Results of core drilling on the Boston Land Co. 

property.
37°00'

CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120 0 30' 120°00'

E33

EXPLANATION

Boundary of deformed 

rocks

Eastern and western limits and 

area of flowing wells, 1906 

(from Mendenhall and others, 

1916)

Eastern boundary of Corcoran 

Clay Member of the Tulare 

Formation

2000'-

B Area of 2000' -i lower-zone confinement 

B {B' B"

Line of section B-B', geology 1000' 

from Miller,Green, and Davis 

(197 l).B'-B".geology from H.T. 

Mitten (U.S.Geological Survey, JE* L 

written commun. May, 1968)

General direction of 1000' 

ground-water flow

B"

10 MILES

2000'

Potentiometric surface, 

lower zone, 1966

VERTICAL EXAGGERATION X 20

0 5 10 KILOMETRES C

FIGURE 20. Change in the natural-flow conditions in the central San Joaquin Valley .A, Extent of lower-zone confinement. B, Flow conditions in 1900. C, Flow conditions in 1966.
E34 STUDIES OF LAND SUBSIDENCE

The largest recharge area for the deposits below the 

Corcoran is the 10- to 20-mile-wide belt of the San 

Joaquin Valley west of the Sierra Nevada. Major 

streams such as the San Joaquin River have supplied 

large amounts of water to the lower zone. Recharge 

directly from rainfall before the advent of irrigation 

probably was insignificant.

Flow conditions in about 1900 are shown in figure 

2QB. Waters of markedly different chemical quality 

from the two source terrains moved under the Corcoran 

and migrated to the trough of the valley. General circulation and upward movement through the Corcoran 

occurred at very slow rates because of the exceedingly 

low permeability and large thickness of the lacustrine 

confining clay. As a result, the lower-zone potentiometric surface was more than 20 feet above land surface in 

the valley trough area. The slope of the potentiometric 

surface toward the trough of the valley was only 3-4 feet 

per mile.

The large-scale agricultural development of the west 

side of the valley resulted in the change in flow shown in 

figure 20C. The potentiometric surface, instead of being 

above the land surface, was below sea level in most of 

the area west of Fresno Slough in 1966. Near the Diablo 

Range, lower-zone water levels were below the Corcoran, and water-table conditions existed. The slope of the 

potentiometric surface has been reversed to a major 

degree. Under the initial flow conditions, the potentiometric surface sloped to the east in all the area west 

of Fresno Slough. By 1966, a belt that was only a few 

miles wide adjacent to the Diablo Range was still an 

area of eastern gradient for lower-zone water movement.

Upper-zone conditions were not changed as much as 

the lower-zone conditions in the northern part of the 

study area because of the limited pumping of these 

waters. Recharge to the ground-water reservoir from 

the surface was occurring in contrast to the times before agricultural development as a result of irrigation 

water percolating below the root zone. Upper-zone 

changes have been much greater in the central and 

southern parts of the area where the semiconfined and 

confined aquifer systems have been pumped heavily.

CHANGES IN THE HYDROLOGIC 

ENVIRONMENT CAUSED BY MAN

Man has greatly disrupted the natural flow system. 

Water-level changes have occurred in the different 

parts of the ground-water reservoir the water table, 

the semiconfined aquifer system, and the confined

aquifer system. Significant hydrologic changes are responsible for the increased applied stress that has 

caused land subsidence.

HISTORY OF GROUND-WATER DEVELOPMENT

The early settlers used the Los Banos-Kettleman 

City area for the grazing of cattle, sheep, and horses. 

The first canal diversions of surface water in the 1870's, 

and the first artesian wells put down in the 1880's were 

primarily for watering of livestock and for irrigation of 

land for pasture. The land was not irrigated and farmed 

on a large scale until the First World War.

Although some wells were drilled for stock and 

domestic water supply as early as 1870 (Mendenhall 

and others, 1916, table 45), the first known artesian 

well in the Los Banos-Kettleman City area was drilled 

in 1886. At the time of the first Geological Survey well 

canvass in the San Joaquin Valley in 1905-6,14 flowing 

artesian wells were reported in the area. In 1905, a well 

2 miles west of Tranquillity was described as having a 

head sufficient to raise a column of water at least 22 feet 

above land surface. In 1914, artesian flows of more than 

1,000 gallons per minute were measured from wells in 

the trough of the valley. In 1919, the water level in the 

San Joaquin City well was 19 feet above the land surface. These facts suggest that artesian-head decline was 

minor in the valley trough between 1905 and 1919.

The use of ground water for irrigation expanded 

rapidly in the early 1920's, initiating a rapid decline in 

artesian pressures. The last report of a flowing well in 

the Los Banos-Kettleman City area was in the winter of 

1925-26. By this time 170 wells had tapped the confined 

aquifer system. In sec. 28, T. 19 S., R. 19 E., where there 

had been a flowing well in 1905, the static level was at a 

depth of 50 feet in 1926, indicating a mean head decline 

of about 3 feet per year.

The first areas to use ground water for diversified 

agriculture were near Oro Loma, Mendota, Westhaven, 

and along Fresno Slough. The general areas of early 

ground-water development are shown in figure 21. In 

1915, the area to the west of Oro Loma was subdivided 

into small tracts which were irrigated with water from 

12 wells.

In 1917, the Boston Land Co. began irrigation of 

10,000 acres near Westhaven in the southern part of the 

area, and by 1924, 54 irrigation wells had been drilled 

on the property. Information about these wells is available in an unpublished report made by H. L. Haehl and 

Hyde Forbes for the Boston Land Co. in 1926.

In 1926, more than 170 wells had tapped the lower-
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E35

37°00' -

Cantua CreelK EXPLANATION

///////////,

Boundary of deformed 

rocks

Generalized areas of early ground-water 

development, from recorded distribution 

of irrigation wells from various sources

Coalinga 

VALLEY

Western and eastern limits of flowing artesian wells in 1906, (from Mendenhall and 

others, 1916, pi. 1)

Kettleman BED 

City

36°30' 

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 21. Areas of early ground-water development.
E36 STUDIES OF LAND SUBSIDENCE

TABLE 3. Estimated ground-water pumpage, 1935-66, Los Banos -Kettleman City area

[Pumpage in thousands of acre-feet; for agricultural year beginning April 1 and ending March 31; data chiefly from Pacific Gas and Electric Co. Northern district is area from FresnoMerced county line to north line of T. 16 S.; Southern district is area from north line of T. 16 S. to Kettleman City. East boundary is San Joaquin River, Fresno Slough, and 

Kings River]

Year

1935-36 __

1936-37 _____

1937-38 __ _

1938-39 ___ _

1939-40 __

1940-41 ___

1941-42 __ _

1942-43

1943_44 _____

1944_45

1945-46 _____

1946-47

1947-48 ___

1948-49 __ _

1949-50 __ _

1950-51 _____

Northern 

district

_______ 115

. ____ 130

_____ _ 140

_____ _ 150

__ ____ 145

_ _ __ 140

__ ____ 135

_ _ 150

_______ 165

___ __ 175

___ ___ 180

___ _ 200

_______ 240

_ _____ 235

_______ 255

_ _ __ 305

Southern 

district

20

30

75

110

130

130

145

170

175

175

190

255

355

410

590

695

Total

135

160

215

260

275

270

280

320

340

350

370

455

595

645

845

1,000

Year

1951-52 _ __

1952-53 _____

1953-54 _____

1954-55

1955-56

1956-57 _____

1957-58

1958-59 _ _

1959-60 __

1960-61 ____

1961-62 _____

1962-63 ____

1963-64

1964-65 _____

1965-66 __

Northern 

district

__ _ __ 245

340

_ __ - 350

_______ 315

___ _ 405

430

.__ _ _ 385

__ _ - 405

_ _ ___ 375

370

_ _ _ 345

375

360

- 330

_ __ 310

Southern 

district

805

935

840

750

725

775

775

700

765

720

685

730

685

780

675

Total

1,050

1,275

1,190

1,065

1,130

1,205

1,160

1,105

1,140

1,090

1,030

1,105

1,045

1,110

985

zone waters in the Los Banos-Kettleman City area. By 

1937, about 250 wells were pumping from the lower 

zone, and by 1942 the number had increased to at least 

350. In 1960, there were about 1,100 active irrigation 

wells, most of which were pumping from the lower zone.

Irrigation with ground water expanded rapidly during the early 1920's, but a low level of commodity prices 

in the late 1920's and early 1930's discouraged further 

agricultural expansion. After 1936, a renewed expansion occurred, and pumpage increased rapidly until 

World War II.

The increase in the irrigated area since about 1940 is 

shown in figure 22. The growth of the ground-water 

service areas expanded most rapidly between about 

1940 and 1950. Most of this expansion was associated 

with the high prices paid for crops after World War II. 

By 1955, most of the available land had been placed 

under cultivation. Since 1955, the irrigated area has 

edged closer to the foothills of the Diablo Range, particularly in T. 14 S., R. 12 E., and T. 16 S., R. 14 E.

TRENDS IN TOTAL GROUND-WATER PUMPAGE

The total amount of ground water pumped in the 

study area increased until the early 1950's. Early in the 

development of the area, the Boston Land Co. pumped 

an average of 12,500 acre-feet of water per year between 

1917 and 1926 (Haehl and Forbes, 1926, unpub. rept.). 

In 1924, the total annual pumping draft from the area 

was about 35,000 acre-feet (Davis and Poland, 1957, p. 

431).

The ground-water pumpage in the Los Banos 

-Kettleman City area (excluding the small area north 

of the Merced County line) is shown in table 3 and figure

23 for the period 1935-65. Pumpage for a northern and 

southern district is shown, in addition to the total 

pumpage, in order to illustrate the rapid growth of 

pumpage in the southern district from 1945 to 1953. 

Pumpage in the area north of the Fresno-Merced 

County line was not included because the available 

figures for electric-power consumption included power 

used for many surface-water booster plants.

The data for years 1935-36 through 1961-62 were 

compiled largely by E. J. Griffith, Pacific Gas and Electric Co., Fresno, and were made available through the 

cooperation of the San Joaquin Power Division, Pacific 

Gas and Electric Co. The ground-water withdrawals 

were computed chiefly from the total power consumption per customer per year; and this amount was divided 

by an average figure for kilowatt hours per acre-foot for 

each customer as determined from pump efficiency tests 

for that customer. Pumpage from 1962-63 through 

1965-66 has been compiled from a report by Ogilbee and 

Rose (1969).

Before 1940, most of the ground water was pumped in 

the northern district, but the rapid expansion of agriculture in the southern district after 1945 caused the 

pumpage in that district to surpass pumpage in the 

northern district, and, since 1948, pumpage in the 

southern district has been about double that of the 

northern district (table 3).

The total pumping rate increased until 1952-53 when 

1,275,000 acre-feet of water was pumped. Since then the 

total pumpage has declined gradually to about 

1,000,000 acre-feet in 1965-66. The end of the period of 

accelerated pumping coincided roughly with a sharply 

reduced rate of agricultural expansion. Although some
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E37

37 "00

EXPLANATION

Boundary of deformed 

rocks

Areas receiving surface water as of 1940. 

[rrigation supply wholly surface water or 

supplemented by ground water

Areas irrigated with ground water as of 

1940. Data chiefly from aerial photographs 1937, 1940, and 1942

Growth of ground-water service area, 1940- 

50, from aerial photographs 195U

Coahnga

VALLEY

Growth of ground-water service area, 1950- 

55, from aerial photographs 1954-55

Kettleman BED 

10 15 KILOMETRES City

36°30' 

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 22. Increase in irrigated land.
E38 STUDIES OF LAND SUBSIDENCE

1400

/v-v-XKettleman 

X ^ City

1935-36 1945-46 1955-56 

AGRICULTURAL YEAR, APRIL 1 toMARCH 31

FIGURE 23. Estimated ground-water pumpage, 1935-66 (area north of Merced County line excluded).

1965-66

new land has been irrigated for the first time since 1952, 

the amount of new land is small compared to the overall 

acreage being irrigated.

The fluctuations in total pumpage since 1952 are 

largely the result of weather, crop practices, and

changes in irrigation procedures. Long hot summers 

and larger proportions of acreage planted to crops such 

as alfalfa tend to increase the amounts of water 

pumped. The trend from furrow to sprinkler irrigation 

has reduced the amount of water needed to grow a given
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E39

crop and has required fewer wells because water can be 

readily transported several miles in pipelines.

The tripling of the overall pumpage since 1945 has 

resulted in a large overdraft, declining water levels in 

the zones from which water is being withdrawn, and 

large amounts of subsidence as water is expelled from 

unconsolidated sediments to furnish about one-third of 

the water pumped.

CHANGES IN GROUND-WATER LEVELS

Pumping of ground water and irrigation has changed 

the water table as well as the water levels in the 

semiconfined aquifer system above the Corcoran Clay 

Member and in the confined lower zone. Water-level 

change varies greatly for the different depth zones of the 

ground-water reservoir and in the different parts of the 

area.

The low permeability of the upper-zone deposits, and 

in some places the inferior quality of the upper-zone 

water, makes the upper zone generally undesirable as a 

source of irrigation water. However, in a belt paralleling the trough of the valley from Tranquillity to Stratford, permeable upper zone sands derived from the 

Sierra Nevada yield good quality water. Many of the 

wells in this belt are completed only in the upper zone, 

and they yield ample supplies of irrigation water. Elsewhere in the area many lower-zone wells are perforated 

opposite sands for a short distance above the 

Corcoran a situation that is most common in the 

southern part of the area.

Water-level trends in three Bureau of Reclamation 

piezometers east of Mendota at the Yearout site are 

shown in figure 24 to illustrate water-level trends in the 

main hydrologic units in the study area. The winter 

high and the summer low water levels are shown for the 

period 1951-66. Well 13/15-35D1 reflects the water 

level of the water table and the upper part of the 

semiconfined zone. Well 35D2 reflects the water levels 

in a confined zone above the Corcoran. Well 35D3 

reflects lower-zone water-level changes.

Most of the irrigation wells in the vicinity of the 

Yearout site are perforated only in the upper zone, but a 

few are perforated in both the upper and lower zones. 

The result is a 40-foot seasonal fluctuation in the piezometer tapping the upper-zone confined aquifer. The 

large seasonal fluctuation and the degree of separation 

between the water levels at well points 100 and 300 feet 

deep suggest that confinement is good. Water levels in 

the confined part of the zone did not decline during the 

early part of the period of record but have declined 8 feet 

since 1958.

The water level in well 35D1 remained about the 

same until 1960, but since then it has declined steadily 

with small seasonal fluctuations. The water-level trend

13/15-35D1, well point at 100 feet

13/15-35D2,well 

point at 300 feet

13/15-35D3, well point at 

(lower zone)

160

FIGURE 24. Hydrographs of upper- and lower-zone piezometers at the Yearout site. Data 

from the U.S. Bureau of Reclamation.

may be representative, but the seasonal fluctuations in 

well 35D1 are much smaller than in irrigation well 

34A1 (325 ft west of 35D1 and perforated at depths of 

100-276 ft). Apparently, well 35D1 has limited hydraulic continuity with the adjacent aquifer.

The water levels in the lower-zone well, 35D3, have 

shown the steadiest and largest decline despite the fact 

that few wells in the area are perforated in the lower 

zone. The lack of nearby pumping from the lower zone 

accounts for the small amounts of seasonal fluctuation 

of water level. The high winter levels in 1956 and 1958 

were coincident with two of the wettest winters since 

1870. The 60-foot head decline in 14 years most likely is 

related to intensive lower-zone pumping farther west. 

This intensive pumping has produced a steep gradient 

on the east side of the Los Banos-Kettleman City area 

which has induced recharge from the east side of the 

San Joaquin Valley. Hydrographs of wells such as 

35D3, from east of Mendota to Stratford, have histories 

of head decline resulting from the increase in gradient. 

In most of the project area, the seasonal fluctuation has 

been larger in the lower than in the upper zone, and 

water levels have declined more.

THE WATER TABLE

The surface of the unconfined water the water 

table in the Los Banos-Kettleman City area is 

difficult to define. Very few wells tap only the upper 

10-50 feet of the saturated deposits. The lensing, 

heterogeneous character of the alluvium results in 

water levels that are not truly indicative of the water 

table in those wells that tap more than 50-100 feet of 

saturated alluvium. For example, a 200-foot well may 

have a gradually rising water level during a 10-year 

period suggestive of a rising water table that is receiving irrigation water that percolates below the root zone. 

A nearby 100-foot well may have a more rapidly rising 

water level, thereby suggesting that it is more indicative of water-table conditions than the 200-foot well.
E40 STUDIES OF LAND SUBSIDENCE

The minor differences in permeability of adjacent 

water-yielding beds are such that differences in head 

can exist between shallow wells during times of heavy 

pumping. Many of these shallow wells recover to the 

level of the water table during times of little pumping.

Both semiconfined and perched conditions occur in 

various degrees. Apparent depths to the water table 

that are too deep are the result of semiconfinement of 

part of the beds penetrated by a well. Apparent depths 

that are too shallow result when the well is tapping a 

water body that is perched on a lense of fine-grained 

alluvium. Perched conditions occur where a 

fine-grained lense allows only part of the water to percolate through it, has unsaturated deposits below it, and 

saturated deposits above it.

In order to be able to analyze the change in effective 

stress that causes the subsidence, it is necessary to have 

knowledge of the changes in the position of the water 

table as well as the change in conditions in the 

semiconfined and confined aquifer systems. A rising or 

falling water table not only can cause expansion or 

compaction of the unconfined deposits, but also affects 

the effective stress on the deposits in the confined zone.

The approximate position of the water table was determined by Davis, Green, Olmsted, and Brown (1959, 

p. 147, 148, pi. 16) on the basis of 1951 measurements 

and was supplemented by earlier measurements. The 

approximate position was determined partly by measurements in wells tapping unconfined and 

semiconfined zones and was supplemented by estimates 

of the top of the zone of saturation based on electric logs. 

The depth to water was less than 10 feet in a large area 

along the trough of the valley from Tranquillity to Los 

Banos. In general, the depth to water increased from 

east to west, and near the foothills of the Diablo Range 

the depth to water was more than 300 feet. These authors concluded that the position of the water table had 

remained approximately constant, declining slightly in 

some areas and rising some in others (p. 147). A comparison of the altitude of the water table in 1951 (Davis and 

others, 1959, pi. 15) with the altitude of the water table 

in 1906 as plotted by Mendenhall (Mendenhall and 

others, 1916, pi. 1) suggests less than 20 feet of change 

in the position of the water table in the 46-year period. 

The water table declined as much as 20 feet in the 

southern part and rose as much as 20 feet in the northern part of the Los Banos-Kettleman City area.

The Bureau of Reclamation has been obtaining more 

recent information regarding the water table, as part of 

projects to bring large amounts of surface water into the 

area in the Delta-Mendota Canal and the San Luis

Canal. The raising of the water table to near the land 

surface will require that drainage systems be built in 

order to continue growing crops. The Bureau of Reclamation has drilled or augered more than 100 shallow 

wells to obtain information about water-levels in the 

unconfined zone. As a result of these studies, post-1961 

water-table information is available for most of the area 

downslope from the San Luis Canal.

The depth to shallow ground water in 1965 is shown 

in figure 25. Water levels in most of these wells approximate the water table, but for many wells it is not 

possible to determine the presence of perched or 

semiconfined conditions that might affect the water 

level to a minor degree. Most of the data northeast of the 

San Luis Canal were obtained from the Bureau of Reclamation. Electric logs of water wells drilled in the 

mid-1960's were used to determine the depth to the 

water table in most of the area west of the canal.

The general pattern of the depth to water is much the 

same as in 1951, with depths of more than 200 feet to 

water suggested by the map in the western part of the 

area. West of Huron, the depth to the water table exceeded 500 feet in 1965. The area of depths to water 

greater than 400 feet at the mouth of Los Gatos Creek 

coincides with an area of permeable coarse-grained deposits laid down on the ancestral alluvial fan of Los 

Gatos Creek. Little confinement is present in this area, 

and the great depth to the water table is the result of 

water-table declines caused by pumping of wells perforated at depths of more than 1,000 feet. Davis and Poland (1957, p. 429-430) note that the low water temperatures and high sulfate content of the water suggests 

that recharge from Los Gatos Creek is able to reach the 

deposits tapped by wells. A similar situation probably 

exists at the mouth of Cantua Creek.

Water levels were shallow in the eastern half of the 

area, the depth to water north of Five Points being less 

than 20 feet, and south of Five Points less than 50 feet. 

The area in which the depth to water was less than 10 

feet was larger than in 1951.

The change in the depth to shallow water between 

1951 and 1965 can be obtained in a general way by 

comparing the 1951 and 1965 maps, as has been done in 

figure 26. Considerable variation in the trends of shallow water levels are apparent in the different parts of 

the area. In the northern part of the area, water levels 

have risen from less than 25 feet to more than 100 feet. 

A large area in which the water table has risen more 

than 50 feet extends from the town of Cantua Creek to 

15 miles west of Mendota. In 1951 the water table in this 

area was generally at a depth of about 100-150 feet.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E41

37°00'

36°30'

36 "00

/ Af

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal depth to shallow 

ground water (approximately the water 

table), in feet, 1965

Interval variable. From electric-log data, 

and an unpublished U.S. Bureau of Reclamation report entitled "Ground-Water 

conditions and potential pumping resources above the Corcoran Clay. An 

addendum to the ground-water geology 

and resources definite plan appendix 1963, 

1965"

Western boundary of the Corcoran Clay 

Member of the Tulare Formation

Stratford

San Luis Canal- California Aqueduct TULARE

10 15 MILES

10 15 KILOMETRES City

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 25. Depth to shallow ground water, 1965.
E42 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00' 

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal change of depth 

to the water table, 1951-65

Interval 25 and 50 feet. 1951 depth to 

water from plate 16 (Davis and others, 

1959). 1965 depth to water is from 

electric log data and from an unpublished 

U.S. Bureau of Reclamation report entitled "Ground-water conditions and potential pumping resources above the 

Corcoran Clay. An addendum to the 

ground water geology and resources definite plan appendix 1963, 1965"

Coalinga 

VALLEY

Western boundary of the Corcoran Clay 

Member of the Tulare Formation

15 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 26. Change in depth to the water table, 1951-65.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E43

Outflow of water accumulating in the upper zone occurs 

as (1) movement of water toward Fresno Slough and the 

San Joaquin River, (2) westward movement toward 

areas of lower ground-water table that are present because of lesser amounts of water being received from 

irrigation or because the water table has been lowered 

by pumping; and (3) downward flow through the Corcoran in gravel packs around well casings and through 

broken well casings.

Water-level rises have been much less along the 

trough of the valley where many wells are perforated in 

the upper zone. The water table has risen less than 30 

feet in most of this area.

In the southern part of the area, the depth to shallow 

water has increased southwest of Westhaven and has 

decreased northeast of Westhaven. The areas in which 

the depth to water was less than 40 feet in 1951 had a 

shallower water table in 1965, but the rise has not been 

large because the water table was close to the land 

surface in 1951.

Water-table decline occurred in the area west of the 

Corcoran. The effects of water-table decline west of the 

Corcoran have resulted in water-table declines for as 

much as 5 miles east of the western boundary of the 

aquiclude and may have influenced the rates of watertable rise for even greater distances to the east. The 

area of 250 to more than 350 feet of water-table decline 

at the mouth of Los Gatos Creek coincides with the area 

of maximum depth to water shown in figure 25.

The overall pattern of water-table decline in the 

southern part of the area and of water-table rise in the 

northern part was the same as for the 1906-51 period.

Three hydrographs of water-table wells are shown in 

figure 27. Each of these water levels is believed to be 

representative of water-table conditions although part 

of the perforations may be opposite beds in which the 

water is semiconfined. Wells 14/13-11D3 and 

16/15-34N5 are at the Mendota and Cantua recorder 

sites. Well 12/13-32A2 shows the steady rising trend 

that is characteristic of the water table in most of the 

northern part of the area. Well 14/13-1 IDS had a rising 

water level until 1964; since then the water table has 

declined. Well 16/15-34N5 has had a fairly constant or 

slightly rising water table a situation that apparently 

has existed at the Cantua site since at least 1952 (fig. 

27) and possibly since 1906 (Mendenhall and others, 

1916, plate 1) when the depth to water in shallow wells 

in the vicinity was about 165 feet.

THE UPPER-ZONE SEMICONFINED TO 

CONFINED AQUIFER SYSTEM

Roughly 25 percent of the water pumped in the Los

DEPTH TOWATER BELOW LAND SURFACE, FEET IN 

NJ -»-» 

§

N) 00£> 

0 OC

1 1 1 1 

12/13-32A2, 

161 feet deep

 __^x 

ol I I I

I I I I

 ~~ ~~ ""

ml I I I

i i i i

14/13-11D3. 

perforated 

180-240 feet

16/15-34N5, 

perforated 

240-300 feet *^

ol I I I

i

'X X

in |

FIGURE 27. Hydrographs of wells perforated in the unconfined zone.

Banos-Kettleman City area is withdrawn from the 

upper zone. The areal distribution of water withdrawal 

is not uniform, as is shown by figure 10. In some areas, 

water is pumped entirely from below the Corcoran, and 

in other areas water is pumped entirely from above the 

Corcoran. In most of the area, and particularly south of 

Five Points, water is pumped from both the lower and 

upper zones. Most of the lower-zone wells that have 

perforations in the upper zone are perforated immediately above the Corcoran. In general, there is an 

improvement in water quality and an increase in permeability of the deposits with depth in the upper zone, 

and in parts of the area the water obtained from immediately above the Corcoran is as usable for irrigation 

as the lower-zone waters.

In most of the area, a large downward head differential has developed across the Corcoran confining clay as 

a result of lower-zone pumping. Downward head differentials of 100-200 feet may be common in much of the 

northern part of the area. Water levels in wells tapping 

the lower zone and the base of the upper zone can be 

compared at two locations. Hydrographs for wells 

15/14-15E3 (fig. 28), tapping the upper zone, and 

15/14-14J1 (fig. 44), tapping the lower zone, suggest a 

downward head differential of about 120 feet in 1965. 

Farther east at the Tranquillity site, in 1967 the water 

level in a well perforated a short distance below the 

Corcoran was 120 feet deeper than a well tapping the 

base of the upper zone.

However, in the southern part of the area, head declines in the upper zone have been large where upperzone water has been pumped intensively for irrigation. 

Observation wells tap both the upper and lower zones at 

the Westhaven site (figs. 3 and 14). The well tapping the 

sands (well 20/18-11Q1) immediately above the Corco-
E44 STUDIES OF LAND SUBSIDENCE

ran has a deeper water level than the lower-zone wells 

(fig. 14). The record for well 11Q1 shows about the same 

seasonal fluctuation as for the lower-zone wells. This 

situation may represent pumping from a confined lense 

of sand of limited extent that is not connected with 

permeable beds leading to recharge areas. Upward 

gradients across the Corcoran may be fairly common in 

the southern part of the study area. At the Lemoore site, 

downward gradients of as much as 40 feet are present in 

the winter, but small upward gradients are present in 

the summer.

The degree of confinement southwest of the edge of 

the Corcoran is highly variable. The head differential, 

as of 1943, between the water table and water levels in 

deep irrigation wells suggests only moderate lowerzone confinement in the area west of Huron (Bull, 1974). 

Head differentials in this subarea ranged from less than 

50 feet to more than 100 feet.

Hydrographs of three upper-zone Bureau of Reclamation piezometers are shown in figure 28. The three records are markedly different. The hydrographs illustrate 

the differences of confinement and separation of water 

bodies that occur in the upper zone as a result of 

heterogeneous lensing deposits derived from different 

sources. The summer low- and winter high-water levels 

have been used for the hydrographs.

Well 15E1 shows little seasonal fluctuation and 

shows a steady rise in water level. Although this well 

taps both unconfined and semiconfined water, the record represents chiefly semiconfined conditions. The 

water table at the location has risen twice as much 

during the same period.

Well 15E2 has a record of consistent seasonal 

fluctuations of 10-20 feet. The overall trend has been 

up, but the water-level rise has not been as much as in 

well 15E1. Deposits within the depth interval tapped by 

well 15E2 probably have a moderately good degree of 

confinement, but the amount of seasonal fluctuation is 

low because few nearby wells are perforated in this 

interval.

Well 15E3 has a record of erratic seasonal 

fluctuations that exceed 80 feet in some years. The 

fluctuations indicate that water levels in this confined 

depth interval are influenced by irrigation wells in the 

vicinity that are pumping in part from the basal upper 

zone. An overall decline of water levels has occurred for 

this zone, which is immediately above the Corcoran.

The hydrographs in figure 28 show why it is impossible to make water-level maps, or water-level change 

maps, for most of the upper zone, in an area that is as 

large as the Los Banos-Kettleman City area. Even if 

abundant water-level data were available for the many 

different units within the upper zone, consistent results 

could not be obtained for more than a few miles because

120

160

15/14-15E1,

well point at

230 feet

15/14-15E2,

well point at

385 feet

15/14-15E3,

well point at

575 feet

200

240

280

320

FIGURE 28. Hydrographs of upper-zone piezometers at 15/14-15E. Data from the U.S. 

Bureau of Reclamation.

of the many semiconfining beds of low permeability.

Hydrographs of two unused irrigation wells perforated in the upper zone are shown in figure 29. The rising 

trend in the water levels of well 13/14-17N2 is a result 

of recharge from irrigation water, which in this area is 

obtained largely from surface-water sources. The shallow water level in 1959 appears to represent mainly 

water-table conditions. Later in the same year, however, the water level rose rapidly to a depth of only 8 

feet, probably as a result of a casing break that permitted unconfined water to dominate the water level. The 

abrupt rise in water-level indicates that the water 

tapped by this well was semiconfined although the well 

is only 196 feet deep.

Well 15/16-20R1 was initially drilled to pump from 

both the upper and lower zones. Casing failures termiO ui 40

-I HI 

HI LL

cc -

gs

Q. Z

HI <

Q _1

80

40

80

120

15/16-20R1

FIGURE 29. Hydrographs of wells perforated in the upper zone.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E45

160

200

Q z.

< 240

§ 

O 

_i 

Ul 

OQ

DC 

UJ 

h- 280

O

I

320

I 1

17/17-21N2, perforated 403- 

139 7 feet

21/18-28M2, perforated 

464-1221 feet

I f 19501 III19551

FIGURE 30. Hydrographs of wells perforated in both the upper and lower zone

I I 11965

nated the use of this well for irrigation purposes and 

apparently sealed off the lower-zone waters. Another 

well, 1 mile away, that is representative of the lower 

zone has a water level more than 100 feet deeper than 

that of well 20R1.

The winter high- and the summer low-water levels for 

well 20R1 have been obtained from a recorder that has 

been operating continuously since 1952. The consistent 

seasonal fluctuation of about 30 feet probably is representative of the upper zone, which is heavily pumped 

in the vicinity. The depth interval at which water moves 

in and out of the well casing is not known, but the large 

seasonal fluctuation indicates that the zone has good 

confinement. In 1956 and 1958, the summer low-water 

levels were abnormally high. These summers followed 

exceptionally wet winters. In these 2 years, a surplus of 

irrigation water from the Kings River was available for 

use in the vicinity, and apparently little ground water 

was pumped. The overall trend of the water level has 

been down declining 10-13 feet in 12 years.

Water levels in wells that tap both the upper and 

lower zones are shown in figure 30. The large seasonal 

fluctuation in well 17/17-21N2 is characteristic of irrigation wells southwest of Five Points. A declining 

trend of water levels is characteristic of the lower zone 

in this part of the area (fig. 45B), but the record obtained 

from well 21N2 is too short to show a well-defined 

water-level decline. The availability of the unused well 

probably was in part due to the fact that it was no longer 

usable for irrigation purposes. Casing breaks that shut 

off production from the deeper aquifers are common in 

the area; therefore, the record for well 21N2 probably is

representative of a much higher depth interval than 

indicated by the full perforated interval. As a result of 

the record obtained from this and other unused wells 

and the consistently high water levels noted in most 

unused irrigation wells during well rounds, it has been 

concluded that most unused wells are of dubious value 

for obtaining representative water-level records in a 

subsidence area.

The record for well 21/1&-28M2 was obtained from 

the California Department of Water Resources. This 

well is adjacent to Kettleman Hills and near the west 

edge of the Corcoran. Water levels in this area did not 

decline until the early 1950's when agricultural development of the area near the Kettleman Hills expanded rapidly and numerous wells were drilled. A 

steady overall decline of about 6 feet per year has occurred between 1955 and 1963, and hydrographs of 

other wells in the vicinity (fig. 47) show that the decline 

was continued at about the same rate through 1965.

In general, not many mixed-zone wells were monitored because of the difficulty of determining the relative effects of the heads in the upper and lower zones. 

The differences in head and permeability of the various 

water-yielding beds make it difficult to use perforated 

interval in more than a general way to determine the 

effect of upper- or lower-zone head on the composite 

water levels or on the amounts of seasonal fluctuation.

THE LOWER-ZONE AQUIFER SYSTEM

The Corcoran Clay Member of the Tulare Formation 

provides excellent confinement for artesian pressures in 

nearly all of the Los Banos-Kettleman City area (see
E46 STUDIES OF LAND SUBSIDENCE

fig. 12). The thick sequence of alluvial deposits below 

the Corcoran furnishes roughly three-quarters of the 

irrigation water pumped in the area. Overdraft has 

resulted in large declines in head in the lower zone, and 

it is here in the lower zone that three-fourths of the 

compaction that causes subsidence occurs. Fortunately, 

a large amount of water-level data is available for the 

lower zone, and a measurement of a single well is likely 

to be representative of the potentiometric head in the 

vicinity because the hydraulic continuity within the 

lower zone is good in most of the area (fig. 14).

CHANGES IN THE POTENTIOMETRIC SURFACE

The potentiometric surface was nearly flat prior to 

the pumping of ground water. On the basis of measurements made in 1906, Mendenhall, Dole, and Stabler 

(1916) estimated that the potentiometric surface sloped 

2-5 feet per mile to the east and had a northward component of slope along the trough of the valley of about 

ll/2 feet per mile.

By the time that Haehl and Forbes made their study 

for the Boston Land Co. in 1926, the potentiometric 

surface had been lowered, particularly in areas irrigated with lower-zone water. Generalized contours of 

the potentiometric surface in the southern part of the 

area as of 1926 are shown in figure 31. The three major 

depressions of the potentiometric surface coincide with 

the areas of early agricultural development (fig. 21). 

Similar pumping depressions probably existed in the 

areas of early development west of Mendota: these are 

indicated by scattered measurements made in about 

1929. Unfortunately, the density of the control points is 

insufficient to permit contouring of the potentiometric 

surface north of the area studied by Haehl and Forbes.

With the expansion of agriculture, measurements 

were made available through the pump-efficiency tests 

made by the Pacific Gas and Electric Co. The static and 

10-minute recovery levels made by this company in 

1943 are numerous enough to permit preparation of a 

map of the lower-zone potentiometric surface (fig. 32).

The 1943 map shows that the trough of the potentiometric surface in the southern part of the area had 

moved west of the 1926 position and that a pronounced 

trough in the potentiometric surface extended from 

Tulare Lake bed to the Merced-Fresno County line. Part 

of the potentiometric surface southwest of Firebaugh 

had been depressed to below sea level. Pumping overdraft within the area had established a recharge gradient of 13-35 feet per mile along the east side of the 

area.

A widespread survey of the area was made by the U.S. 

Coast and Geodetic Survey in 1943. Thus, the 1943 

vertical control and water-level control provide a base 

for comparison with more recent years.

By 1960 the gradient had steepened to 18-44 feet per 

mile, and the trough of the pumping depression had 

moved even further west (fig. 33). The westward migration of the trough of the pumping depression shown in 

figures 31-33, 35, and 36 is in the same direction as the 

increase in irrigated area shown in figure 22. By 1960 

the potentiometric surface had been depressed below 

sea level in virtually all the area, and much of the area 

along the trough of deepest water levels was more than 

250 feet below sea level.

Northwest of Mendota the potentiometric surface was 

not at its historic low in 1960 because initiation of 

surface-water deliveries by the Delta-Mendota Canal in 

1954 had decreased the amount of ground water 

pumped, thereby causing water levels to rise locally. 

The minimum altitude of the potentiometric surface in 

the area northwest of Mendota is based on historic 

low-water levels measured prior to 1960 mainly in the 

middle 1950's.

The time of year in which the water levels are measured has a distinct influence on the altitude and 

configuration of the potentiometric surface. The lowerzone seasonal fluctuation within the study area ranges 

from less than 10 feet to more than 150 feet, therefore it 

is desirable to make water-level measurements in the 

area either at the winter high-recovery level or at the 

summer low-recovery level caused by intensive pumping. Numerous and well-spaced static measurements 

are much easier to obtain in December when most of the 

wells are shut down a factor that contributes to an 

accurate map. Static measurements are not easy to obtain in August when most of the wells are pumping, but 

measurements made in August are more meaningful 

because they are made at the times of maximum applied 

stress and maximum compaction rates. Instead of 

summer static measurements, static levels (actually 

10-minute recovery levels) made by the Pacific Gas and 

Electric Co. as part of pump-efficiency tests were used. 

By using selected measurements made in those months 

of the year in which there is intensive pumping (early 

spring and the summer), the minimum altitude of the 

potentiometric surface shown in figure 33 was obtained. 

The 1960 measurements were supplemented in part by 

measurements made in the summer of 1959, and in 

areas where no Pacific Gas and Electric Co. measurements were made, spring measurements made by the 

U.S. Geological Survey were used. Most of the spring
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E47

37°00' -

EXPLANATION

Generalized potentiometric contour 

Shows altitude of potentiometric surface of 

lower water-bearing zone. Contour interval 

25 feet. Datum is mean sea level. Measurements from unpublished report by Haehl 

and Forbes, 1926

PLEIASANT

Coalinga

VALLEY

Kettleman BED

15 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 31. Water-level contours for the lower zone or its stratigraphic equivalent, 1926.
E48 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00'-

EXPLANAT1ON

Boundary of deformed 

rocks

Generalized potentiometric contour 

Shows altitude of potentiometric surface of 

lower water-bearing zone. Dashed where 

approximately located. Contour interval 

25 feet. Datum is mean sea level. Chief 

source of water-level measurements used 

for control was the Pacific Gas and 

Electric Co.

Western boundary of the Corcoran Clay 

Member of the Tulare Formation

Kettleman BED 

10 15 KILOMETRES City

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 32. Water-level contours for the lower water-bearing zone, 1943.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E49

120°30' 120°00'

37°00

36°30'

.Los Banos

25-

:%>

Dos 

Palos

\

 m

\

Fresno . River

1 Madera

S^

^

*Firebaugh ** % '

^\

'<r& % ^\\\

 250,

EXPLANATION

Boundary of deformed 

rocks

\

**r

^

\(

--150-

Generalized potentiometric contour 

Shows altitude of potentiometric surface of the 

lower zone. Dashed line indicates approximate 

position in areas of poor minimum water-level 

control. Contour interval 25 feet. Datum is 

mean sea level. Chief sources and dates of 

water-level measurements used for control: 

Pacific Gas and Electric Co., 1959-60, but 

mainly summer 1960 (recovery about 10 minutes after pump off); and U.S. Geological Survey, May I960, and in part May 1959

Areas in which contoors are drawn on 

minimum water levels that occurred between 

1950 and 1958

Water levels in this area rose for several years 

prior to 1960 because water from the DeltaMendota Canal has in general replaced 

ground water for irrigation

Western and eastern boundaries of the Corcoran Clay Member of the Tulare Formation

Water-level control points west of the Corcoran 

are from measurements in wells that are perforated in the same stratigraphic unit as the 

lower-zone wells in areas of the Corcoran

F_______ F'

Line along which the slope of the potentiometric 

surface was computed from maps representative of the period 1926-65. See figures 37 

and 38

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-W\ 

V 5*

l<*'**K 

o

\v

Westhaven,

'A.

PLBASANT

^m

(l^N-NT^ xW" 1 lim \*\

^Coalinga 

VALLEY

,Y^X

%*\ x\1f x

XT

v? /'///

///

xx

Slrat- 'ord

.TULARE

r/ ' ***

10 15 MILES

.^

*+.

/

.-50-

10 15 KILOMETRES '<*

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

LKettleman 

City

LAK

BED

S

FIGURE 33. Minimum altitude of the potentiometric surface of the lower zone as of 1960.
E50 STUDIES OF LAND SUBSIDENCE

measurements were not made at times of maximum 

pumping, and those parts of the map are dashed.

The 1943 map is also based on measurements made 

by the Pacific Gas and Electric Co. The measurements 

were made at various times of the year, but mainly 

during times of maximum pumping. Thus, the 1943 

map is more representative of the summer lows than of 

the winter highs.

Although the decline had been large as of 1960, 

sufficient pressure remained in the lower zone to cause 

water levels in wells to rise above the base of the Corcoran in most of the area. The artesian head of the lower 

zone as of May 1960 a time of seasonally high water 

levels is shown in figure 34. Artesian head of 300-500 

feet above the base of the Corcoran still existed in most 

of the study area. The amount of head present decreased 

to the southwest. In the southern part of the area, 

200-400 feet of head was still present at the western 

boundary of the Corcoran. In the central part of the 

area, the lower-zone head was less than 100 feet near 

the mouth of Cantua Creek. The lower-zone water 

levels were more than 200 feet below the base of the 

Corcoran adjacent to the Diablo Range in the northern 

part of the area where the Corcoran has been strongly 

folded (fig. 13). Water-table conditions exist where the 

lower-zone water levels have declined below the base of 

the Corcoran if deeper confining beds are not present.

The decline of lower-zone water levels below the base 

of the Corcoran does not greatly change the rate of 

increase of stress being applied to the lower zone, however, the processes of stress increase are changed markedly. During water-level declines under confined conditions, increase in applied stress equal to 1 foot of water 

will occur for each foot of additional decline in artesian 

head. The process involved is one of increased seepage 

stress equal to the magnitude of the head differential. 

After the lower-zone water levels have declined below 

the Corcoran, further decline in head does not cause 

further increase in seepage stress. Instead the applied 

stresses are increased as a result of two other types of 

processes. Under the assumptions specified in the section "Stresses Tending to Cause Compaction," removal 

of buoyant support of the grains in the aquifers during 

the course of dewatering will cause an increase in applied stress equal to 0.6 foot of water for each foot of 

additional water-level decline. Added to this stress increase is 0.2 foot of water that results from part of the 

intergranular water changing from a neutral to an applied stress condition the amount being equal to the 

water of specific retention.

The overall effect of lower-zone water levels dropping

below the Corcoran and then continuing to decline is a 

decrease in the rate of stress application of about 0.2 foot 

per foot of additional water-level decline. The amount of 

increase in applied stress under such conditions has 

decreased from 1.0-0.8 foot of water per additional foot 

of lower-zone water-level decline.

The 1962 map (fig. 35) is representative of the winter 

high in the potentiometric surface, and all the measurements were made in about a week. In most of the 

area, the December 1962 potentiometric surface is 

higher than in the summer of 1960.

The lowest part of the potentiometric surface was 

northeast of the Big Blue Hills where the surface was 

more than 325 feet below sea level. The gradient along 

the east side of the area was more uniform and had a 

more gentle slope than in the summers of 1943 and 

1960. In December 1962, the gradient ranged from 22 to 

33 feet per mile. The trough of the potentiometric surface was farther west than in earlier years, and it was 

narrower than the troughs in the summers of 1943 and 

1960.

The water-level measurements of December 1962 and 

December 1965 were made 2-4 months before the 

bench-mark network was releveled by the Coast and 

Geodetic Survey. The potentiometric surface just before 

the 1966 releveling of the bench-mark network, is 

shown in figure 36. Comparison of the potentiometric 

surfaces at the time of the winter highs of 1962 and 1965 

shows that the configuration and altitude of the potentiometric surface were virtually the same in 1965 as in 

1962. All the maps for the previous years (most of which 

are not included in this paper) show a progressive decline of the potentiometric surface (figs. 39, 40), and a 

westward migration of the trough of maximum depth to 

the potentiometric surface. By 1965, winter water 

levels were slightly higher in part of the area than in 

1962.

The overall similarity of the 1962 and 1965 maps 

suggests that a rough balance had been established 

between total pumpage, the amount of water derived 

from compaction, and the amount of subsurface recharge to the lower zone as a result of change in the 

gradient of the potentiometric surface along the northeast side of the study area.

The hydraulic gradient along the east side of the 

study area has steepened as a result of increased pumping of ground water to the west. Changes in the slope of 

the potentiometric surface along two section lines have 

been derived from maps of the potentiometric surface 

and are shown in figures 37 and 38. Line G-G', 4.3 miles 

long, extends southwest from Five Points. Line F-F',
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E51

37-00' -

s ^Cantua Creek

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal distance between 

the base of the Corcoran Clay Member of 

the Tulare Formation and water level in 

wells tapping the lower zone, in feet

Interval 100 feet. Areas of positive numbers 

indicate where artesian pressure causes the 

water level to rise above the base of the 

Corcoran, in wells. Negative numbers indicate where the water level is below the 

Corcoran and unconfined conditions exist. 

Based on maps showing the depth to the 

base of the Corcoran (figure 12) and the 

depth of the water level as of May 1960

Western boundary of the Corcoran Clay 

Member of the Tulare Formation

15 KILOMETRES

36°30' -

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 34. Artesian head of the lower zone as of May 1960.
E52 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00' 

EXPLANATION

Boundary of deformed 

rocks

Generalized potentiometric contour 

Shows altitude of potentiometric surface of 

lower water-bearing zone. Contour interval 

50 feet, except the 25 - foot line. Datum 

is mean sea level. Measurements, by U.S. 

Geological Survey, represent approximate 

high level for the 1962-63 winter season

PLEIASANT

Coalinga 

VALLEY

Kettleman RED 

15 KILOMETRES City

36°30' 

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 35. Water-level contours for the lower-water-bearing zone, December 1962.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E53

37°00' 

y//////////,

Boundary of deformed 

rocks

 -/ &u 

Generalized potentiometric contour 

Shows altitude of potentiometric surface of 

lower zone; dashed where approximately 

located; contour interval 50 feet. Datum is 

mean sea level. Measurements represent 

approximate high level for the 1965-66 

winter season

36°30' -

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 36. Generalized water-level contours for the lower zone, December 1965.
E54 STUDIES OF LAND SUBSIDENCE

Line of measurement 

along G-G'

1960

FIGURE 37. Change in slope of the potentiometric surface of the lower zone southwest of Five Points, 1906-66. Line of section shown in figure 33.

7.7 miles long, extends to the southwest from a point 

midway between Firebaugh and Mendota, but distances of 4.0 and 5.6 miles had to be used for some 

periods. The location of the section lines are shown in 

figure 33. The head differential for each period along 

both lines has been corrected for the estimated 

post-1906 subsidence.

Mendenhall, Dole, and Stabler (1916) estimated that 

the slope of the lower-zone potentiometric surface in 

1906 was 2-5 feet per mile to the east. A value of 4 feet 

per mile to the east has been used in both figures.

Both graphs indicate that the amount of underflow

Line of measurement 

along F-F

1960

FIGURE 38. Change in slope of the potentiometric surface of the lower zone southwest of Firebaugh, 1906-66. Line of section shown in figure 33.

from the east side of the San Joaquin Valley has increased substantially since about 1916. Unfortunately, 

as of 1968, the hydraulic conductivities of the lowerzone deposits are not known so the amount of change in 

underflow cannot be computed.

Along the span of section lines F-F' and G-G', the 

westward steepening of the potentiometric surface appears to have ceased in the early 1960's most likely 

because a general equilibrium between underflow, 

water of compaction, and withdrawal may have been 

approached. The rate of steepening of the potentiometric gradient decreased about a decade after the increase 

in total pumpage stopped (fig. 23). Part of the post-1960 

change can be attributed to the fact that the 1962 and 

1965 slopes were taken from maps of the winter high 

potentiometric level. The surface has a steeper slope in 

the summer than in the winter.

Profiles indicating the changes in the configuration of 

the potentiometric surface in the northern and southern 

parts of the area are shown in figures 39 and 40. All the 

data, except the 1943 data, are for times of seasonal 

recovery highs. The May recovery high is almost the 

same as the December recovery high, and for some years 

in the southern part of the area, May water levels are 

higher than December water levels.

The altitude of the potentiometric surface for the line 

of section between Tumey Hills and Mendota, measured 

six times between 1943 and December 1965, is shown in 

figure 39. A progressive deepening of the potentiometric 

surface is shown by the profiles. In 1943 most of the 

potentiometric surface was above sea level, but by 1966 

the potentiometric level was as deep as 270 feet below 

sea level. The 1943 profile is symmetrical, but the 

1953-65 profiles have varying degrees of asymmetry. 

The location of the troughs of the profiles have varied, 

but the trend has been an overall westward migration of 

the trough of the deepest water levels. The greater separation of the lines of profile in the western part of the 

line of section shows that greater head declines occurred 

between the various periods of measurement in the 

western part than in the eastern part of the line of 

section.

The altitude of the potentiometric surface for the line 

of section between Anticline Ridge and Fresno Slough, 

measured six times between 1943 and December 1965, 

is shown in figure 40. In contrast to the previous set of 

potentiometric levels shown in figure 39, the potentiometric levels have not deepened uniformly here. 

Most of the head decline occurred between 1943 and 

1953. Since 1953 the overall trend has been toward a 

slow decline in artesian head, but the depth to water 

varies greatly for the individual years. All the profiles 

are asymmetrical and have steeper slopes in the western parts of the line of section than in the eastern. As in
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E55

F'

100'

SEA LEVEL

100'

200'

300'

6 MILES

6 KILOMETRES

VERTICAL EXAGGERATION X 211

FIGURE 39. Change in the altitude of the lower-zone potentiometric surface, 1943-66, Tumey Hills to Mendota. Line of section F-F' shown in figure 3.

figure 39, the trough of deepest water levels has migrated to the west, and the largest amounts of post-1943 

head decline have been in the western part of the line of 

section.

The change in the potentiometric surface between 

1943 and 1960 is shown in figure 41. The maximum 

head decline shown is northeast of the Big Blue Hills 

where the potentiometric surface had dropped more 

than 400 feet in the 17-year period an average of about 

25 feet per year. Areas of lesser head decline, such as 

along the road southwest of Five Points near Anticline 

Ridge, are largely the result of a low density of wells 

where less water has been pumped than in adjacent 

areas of more abundant wells.

In general, the decline in head was only 50-150 feet in 

the eastern and northern parts of the area, but more 

than 300 feet of head decline was common in areas close 

to the Diablo Range.

The amounts of head decline are in part a function of

distance from the recharge area. The eastern and 

northern parts of the area are closest to the area of 

major recharge the east side of the San Joaquin Valley. Very little recharge is derived from the Diablo 

Range, particularly lower-zone recharge. The areas 

near the Diablo Range have had the most severe head 

declines because they are farthest from the Sierra recharge water and because they are adjacent to a mountain front that approximates an impermeable boundary. Much of the recharge water from the east is intercepted by wells before it reaches areas near the Diablo 

Range.

In the southern part of the area, the maximum head 

decline is nearer Huron than the Diablo Range. The 

lower zone in the area between Huron and the Diablo 

Range is receiving undetermined amounts of recharge 

from intermittent flows of Los Gatos Creek. The Corcoran is poorly defined or absent in most of this area, 

thereby permitting recharge of the lower zone. The
E56 STUDIES OF LAND SUBSIDENCE

150' r

100' -

SEA LEVEL

0246 KILOMETRES 

VERTICAL EXAGGERATION X 211

100'

150'

200' -

250'

FIGURE 40. Change in the altitude of the lower-zone potentiometric surface, 1943-66, Anticline Ridge to Fresno Slough. Line of section G-G' shown in figure 3.

1951-65 change in depth to water-table map (fig. 26) 

shows that the area southwest of Huron has had the 

maximum decline in the water table in the study area. 

This indicates that water in beds that are stratigraphically equivalent to beds in the upper zone east of Huron 

is moving down to partly recharge water withdrawn by 

the deep wells.

Another reason for the lesser amounts of head decline 

in the area west of Huron, as compared to the areas 

adjacent to the Diablo Range farther north in the study 

area, is the lack of an impermeable boundary. In this 

area, the impermeable boundary is actually the southwest side of Pleasant Valley because ground water can 

move from Pleasant Valley to the San Joaquin Valley 

through the gaps in the foothill belt.

In the area northeast of the Big Blue Hills and southwest of the town of Cantua Creek, the head declines in

excess of 300 feet are due, in part, to the aquifers penetrated by the irrigation wells. The wells in this subarea 

are perforated in the Tulare Formation below the Corcoran and in the marine sands of the Etchegoin Formation. Although fresh water has largely replaced the salt 

water in the marine sands, very little recharge reaches 

the sands compared to the amount of recharge to the 

Tulare Formation. The lack of significant recharge to 

the Etchegoin sands probably is the main reason why 

this part of the study area has undergone the maximum 

decline in head between 1943 and 1960.

The change in altitude of the lower-zone potentiometric surface between December 1962 and December 1965 

is shown in figure 42. In marked contrast to large head 

declines that occurred between 1943 and 1960, the recent 3-year period has been one of rise, as well as decline, in the potentiometric level. The extremes within
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE

120°30' 120°00'

E57

37°00

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal water-level change 

for the lower zone

Interval 50 feet. Chief sources of water-level 

measurements used for control: Pacific 

Gas and Electric Co. and U.S. Geological 

Survey

Areas in which the lines for the 1960 map 

are drawn on minimum water levels that 

occurred between 1950 and 1958

Water levels in this area rose for several years 

prior to 1960 because water from DeltaMendota Canal has in general replaced 

ground water for irrigation

Western and eastern boundaries of the 

Corcoran Clay Member of the Tulare 

Formation

Coalinga 

VALLEY

15 KILOMETRES

36°30' -

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 41. Decline in the altitude of the potentiometric surface of the lower zone, 1943-60.
E58 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00'

36°30'

36°00'

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal water-level change 

for the lower zone

Interval 25 feet. Based on measurements 

made by U.S. Geological Survey and California Department of Water Resources

Areas of more than 25 feet of head rise

Western boundary of the Corcoran Clay 

Member of the Tulare Formation

10 15 MILES

10 15 KILOMETRES

Kettleman BED 

City_______

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 42. Change in altitude of the lower-zone potentiometric surface between December 1962 and December 1965.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E59

the study area are 50 feet of head rise west of Firebaugh, 

and 75 feet of head decline southwest of Huron. Locally, 

in areas such as southwest of Huron, and adjacent to the 

Big Blue Hills, lower-zone head decline was continuing 

at rates similar to those in the early 1950's the period 

of maximum rates of head decline for much of the area. 

Between 1962 and 1965 pronounced head decline was 

occurring in only about 25 percent of the area. Areas of 

head rise of more than 25 feet totaled about 5 percent of 

the study area; the remaining 70 percent had little 

change in potentiometric level or underwent minor 

amounts of head rise. The areas of maximum head decline were farthest from the area of major recharge east 

of Fresno Slough. In the rest of the area, a rough balance 

between pumpage and sources of ground water appeared to have been achieved, as was noted in the discussion of the change in potentiometric slope.

SEASONAL FLUCTUATION OF THE POTENTIOMETRIC LEVEL

The trend in seasonal changes in the lower-zone artesian head is roughly the same throughout most of the 

Los Banos-Kettleman City area. After the summer, 

pumpage decreases during the fall as many crops are 

harvested. Some irrigation continues for the planting of 

winter grains. The winter recovery high occurs most 

commonly during the last part of December. Pumping 

during the first months of the year for preirrigation of 

summer crops causes the head to decline by the middle 

of March to almost the same level as the summer low. 

Little pumping occurs while the summer crops germinate, and by early May water levels in much of the area 

have recovered almost to the December high levels. 

Summer is the time of maximum pumping, and the 

lowest water levels usually occur during August. Thus, 

the typical seasonal trend of the lower-zone water levels 

has been to have two major fluctuations each year low 

levels in March and August separated by periods of 

pronounced recovery that peak in May and December.

The pattern of seasonal head decline between December 1965 and August 1966 is shown in figure 43. In 

general, the trough of maximum seasonal fluctuation, 

about halfway between the topographic trough of the 

valley and the Diablo Range, is largely controlled by the 

density of well spacing. This is particularly true in the 

northern half of the study area.

In the southern half of the area, the gross lithologic 

properties of the lower zone are important in 

influencing the extremely large amounts of seasonal 

fluctuation. A lithofacies map (Part 2, fig. 68), based on 

the mean resistivity of the lower-zone deposits corrected

to 100°F and 1,000 mg/1 NaCl salinity, shows a remarkable similarity of pattern with the seasonal fluctuation 

map of figure 43. The arc of seasonal fluctuation in 

excess of 80 feet corresponds with an arc of minimum 

resistivity of the lower-zone deposits. Thus, the large 

seasonal fluctuations appear to be the result of the presence of thick fine-grained deposits of low permeability. 

In order to get sufficient yields, many pumps have to be 

operated with drawdowns of 50-100 feet. Northwest of 

Tu_lare Lake bed, farmers prefer to operate the pumps in 

this fashion instead of drilling wells 2,500-3,000 feet 

deep to tap the deeper fresh-water-bearing deposits 

(figs. 12, 17).

In the small area southwest of Mendota, seasonal 

fluctuation in excess of 80 feet is also influenced partly 

by lithology. This area is part of the area of intertonguing fine-grained facies of the Sierra and Diablo 

flood-plain deposits. It is also the area of lowest wellyield factors in the northern part of the study area (fig. 

16).

The seasonal fluctuation map indicates the variation 

in applied stress during a given year. In those areas of 

10-20 feet of seasonal fluctuation, the maps of the 

potentiometric surface made at the times of minimum 

applied stress, such as December 1962 and December 

1965, are useful in determining the relation between 

change in applied stress and compaction. However, in 

much of the area, seasonal head declines of 60-150 feet 

result in substantially greater stresses being applied to 

the lower-zone deposits during times of maximum 

pumping than during times of minimum pumping. For 

this reason, the critical maps and hydrographs used in 

this series of papers for studies of the interrelations of 

hydrologic and geologic factors are based on changes 

between summer water levels.

The variation in seasonal fluctuation from east to 

west across the central part of the area is shown by the 

records of lower-zone observation wells 15/16-34E1, 

15/14-14J1, and 16/14-16N1 in figure 44. Well 34E1 

shows a fairly consistent seasonal fluctuation of 10-15 

feet, particularly since 1959. Few, if any, wells pump 

from the lower zone in the vicinity. The seasonal 

fluctuation and the overall decline in artesian head at 

this site are chiefly the result of intensive lower-zone 

pumping farther west. Well 14Jl is in an area which has 

moderately high density of wells and where nearly all 

the irrigation water is pumped from the lower zone. The 

40-70 feet of seasonal fluctuation is typical of other 

lower-zone wells in the vicinity that are deeper than 

well 14J1. Well 16N1 is only a mile east of the Diablo 

Range. The 40-50 feet of seasonal fluctuation is less
£60

37=00' 

36°30' -

STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal water-level change 

for the lower water-bearing zone

Interval is 20 feet, except for the 10-foot 

line. Chief sources of water-level measurements used for control: U.S. Geological 

Survey and Pacific Gas and Electric Co.

Western boundary of the Corcoran Clay 

Member of the Tulare Formation Coalinga 

VALLEY

Kettleman BED 

City

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 43. Seasonal decline in the altitude of the potentiometric surface of the lower zone, December 1965 to August 1966.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E61

120

140

160

180

200

220

300

320

340

360

380

400

420

720

740

760

780

800

15/16-34E1

15/14-14J1, 1010 feet deep

16/14-16N1, 2027 feet deep

FIGURE 44. Variation in seasonal fluctuation of water levels in lower-zone wells in 

the central part of the Los Banos-Kettleman City area.

than for well 14J1, despite the fact that well 16N1 is 

farther from areas of potential recharge. The smaller 

fluctuation at well 16N1 most likely is due to a lower 

density of wells in the vicinity. There were no irrigation 

wells west or southwest of well 16N1 during the period 

of record.

HISTORY OF HEAD DECLINE

In an area as complex as the Los Banos-Kettleman 

City area, the history of head decline is highly variable. 

Factors influencing the patterns of lower-zone head decline, as shown by hydrographs, include the rate of 

agricultural development, changes in the types of crops 

grown, recharge, hydraulic conductivity of the aquifer 

materials, and the amount of imported surface water 

available.

The trends of head decline within the area are separated into long-term and short-term records; the longterm hydrographs show trends from as early as the 

1920's, and the short-term hydrographs show trends 

from the late 1940's through 1965. Nearly all the data 

are from the Pacific Gas and Electric Co. Pumping 

levels were used because they are much more abundant 

than static levels. The drawdown between static and 

pumping levels remains essentially the same for a given 

well over a period of years. This is because the well yield 

must be sufficient to supply the crop requirements of the

fields being irrigated. If the yield declines because of 

head decline, a larger pump is installed, and the 

amounts of yield and drawdown for the well remain 

about the same as previously. Only those measurements made during times of widespread pumping were 

used. Winter high measurements were not used because 

not enough of them were available to show overall 

water-level trends within ranges of seasonal fluctuation 

as was done in figure 44. The use of occasional winter 

measurements would distort the overall trend in water 

levels. The use of summer and spring low pumping 

measurements wherever possible permits a smoother 

portrayal of the trends. Summer measurements also 

permit the trends to be based on the times of the year in 

which the potentiometric surfaces are at their lowest 

levels, maximum stresses are being applied to the 

aquifer system, and compaction rates are highest.

The five long-term hydrographs shown in figure 45 

represent different trends, from the northern part of the 

area in figure 45A, to the southern part of the area in 

figure 45C. Additional long-term hydrographs have 

been paired with subsidence graphs in Part 3.

The 1932-66 lower-zone head decline near the 

Merced County line is shown in figure 45A (wells 

12/12-34N1 and PI). The pre-1932 head decline in this 

area is estimated to be about 150 feet. A period of rapid 

decline ended in the late 1930's. Between 1937 and 1951 

the head declined only 25 feet. The rate of head decline 

increased between 1951 and 1954. Since delivery of 

Delta-Mendota Canal water in 1954, the head has continued to decline, but at a decreasing rate. In contrast to 

the gradual decline in summer water levels since 1960, 

the winter levels have risen about 0-25 feet in the 

vicinity (fig. 42).

The other hydrographs shown in figure 45A are for 

wells about 8 miles southwest of Mendota. Well 

14/14-30E 1 was one of the first wells to be drilled in this 

part of the township, but several miles to the northeast 

pumpage of lower-zone water had occurred prior to 

1924. After World War II many additional wells were 

drilled to the southwest, as agricultural development 

expanded rapidly. Well 30E2 was drilled to replace well 

30E1. The rate of head decline was rapid before 1946, 

but it has been even more rapid since then. The 1937-63 

head decline is almost 300 feet.

The hydrograph in figure 45B shows more than 200 

feet of head decline in the 1937-56 period for the area 

southeast of the town of Cantua Creek. The rate of 

artesian-head decline increased fairly steadily between 

1937 and 1952, and during the period 1946-52, the head 

declined an average of about 23 feet per year. Since 1952
E62 STUDIES OF LAND SUBSIDENCE

180

260

340

420

O 500

580

12/12-34N1, perforated 

320-1152 feet

12/12-34 PI, perforated 

551-1057 feet

14/14-30E2, 1234 

feet deep

100

180

260

340

420

500

19/18-3N1, perforated 

1010-1900 feet

1920 1930 1940 1950 1960

FIGURE 45. Long-term hydrographs of lower-zone wells. A, Northern part of area. B, Central part of area. C, Southern part of area.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E63

the potentiometric level has declined at a slower rate, as 

shown in figure 45B, and in the hydrograph for well 

17/16-18Q2 (fig. 47).

The composite hydrograph of three wells southwest of 

Five Points in 18/17-17 is shown in the bottom of figure 

45C. Although water levels in these wells are, in general, representative of the lower zone, a small portion of 

the perforated intervals may be in the basal part of the 

upper zone. The 1923 pumping level suggests that the 

potentiometric surface was only 10-30 feet below its 

estimated 1906 position. The record indicates that the 

head has declined 400 feet at a fairly constant rate over 

a 40-year period about 10 feet per year.

The composite hydrograph of the three wells north of 

Westhaven in 19/18 (fig. 45C) shows a different pattern 

than that for the wells southwest of Five Points. North 

of Westhaven, it is apparent that water levels declined 

only moderately between 1918 and the end of World 

War II. After World War II the rapid development of 

nearby areas to the west and southwest caused the rate 

of head decline to accelerate. Since 1957, the trend in 

head decline has flattened. The measurements for the 

1920's are from the unpublished Haehl and Forbes report. When pumping levels were only 100 feet below 

land surface, the potentiometric surface probably was 

about the same as in 1906. A similar long-term hydrograph for wells a few miles farther south has been 

paired with a bench-mark graph and is shown in Part 3.

Long-term records are not available for the area of 

heavy pumping from the marine sands of the Etchegoin 

Formation. An 8-year record for a well tapping the 

Etchegoin Formation adjacent to the Big Blue Hills is 

shown in figure 46. The nonpumping water levels in this 

well ranged between 800 and 940 feet below land surface. By the middle 1960's, wells adjacent to the Big 

Blue Hills were pumping from depths of more than 

1,000 feet (see Part 3). Monthly measurements made 

between May 1960 and February 1961 outline a seasonal head recovery of 60 feet. Between December 1965 

and August 1966, the seasonal head decline was 45 feet. 

The overall trend of water levels during the 1960's for 

this well has been a large and steady decline. From 

August 1960 to August 1967, the water level declined 

64 feet an average of 7 feet per year.

More than 600 feet of artesian-head decline has occurred at the site of well 18/15-5E1. The altitude of the 

land surface at the well is 529 feet, therefore the August 

1967 static water level was at an altitude of 402 feet. 

The trough of the San Joaquin Valley opposite the well 

site has an altitude of 180 feet. The potentiometric surface was at least 20 feet above the land surface in 1906. 

Mendenhall, Dole, and Stabler (1916) reported that the 

gradient of the potentiometric surface west of the valley

800

O UJ

H 

< 

H 

w

OIH 340

UJ

920

960

Well 18S/15E-5E1

depth, 2103 feet

Water levels

o Winter high

A Summer low

1959 1960 1961 1962 T963 1964 1965 1966 1967 1968

FIGURE 46. Hydrograph of irrigation well tapping the Etchegoin and San Joaquin 

Formations.

trough was only 2-5 feet per mile. Assuming an initial 

gradient of 4 feet per mile to the east, the potentiometric 

surface was 80 feet higher (an altitude of +280 feet) at 

the well site than at the valley trough in 1906. Thus, in 

declining from about +280 feet to -400 feet, the potentiometric surface declined about 680 feet; if one assumed that no gradient was present in the potentiometric surface in 1906, 600 feet of head decline occurred.

The short-term trends of lower-zone pumping levels 

are shown in the 13 hydrographs in figure 47. These 

hydrographs have been placed on the map in order to 

facilitate comparison of the various trends and locations 

of the wells. Four of the wells 15/14-9E1,20/17-33N1, 

20/18-24D1, and 21/18-35N1 have had steadily declining water levels since 1951 or before. The continuing agricultural expansion to the southwest of wells 

9E1 and 33N1 probably has influenced the trends in 

artesian head at these two sites. Well 35N1 is situated 

where little recharge can reach the well. No recharge is 

derived from the Kettleman Hills to the south and west, 

and the thick sequence of lake clays beneath Tulare 

Lake bed prevent recharge from the east. Recharge that 

might move towards the well from the north would be 

largely intercepted by other wells.

The other nine hydrographs all show a decreasing 

trend in the rate of artesian-head decline.

Well 12/11-13D2 is in an area that has had a reversal 

of pumping levels since 1958. The abrupt reduction in 

the rate of artesian-head decline between 1953 and 

1959 is associated with the delivery of surface water in 

the vicinity of the well. Since 1953 ground water 

pumped from well 13D2 has been used to supplement 

the surface-water supply. In 1959 a large area to the 

south of the well started receiving surface water (Bull 

and Poland, 1974). The effect of surface-water imports 

both in 1954 and in 1959 is clearly shown in the hydrograph of well 13D2.

The other eight hydrographs that show a decreasing 

rate of artesian-head decline suggest a trend toward
E64 STUDIES OF LAND SUBSIDENCE 

120°30' 120eOO'

37 eOO

Boundary of deformed 

rocks

YEARS 

Hydrograph of selected well

.15/14-9E1 

Location of selected well

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 47. Trends of lower-zone pumping levels.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E65

equilibrium between pumpage and the various sources 

of water within the lower-zone aquifer system in most of 

the Los Banos-Kettleman City area. If the amount and 

distribution of pumpage within the area remained uniform, eventually the decline in water levels would establish a steep gradient that would permit sufficient 

recharge to the lower zone from the east side of the San 

Joaquin Valley to eliminate overdraft within the study 

area. Water levels would remain at low levels and 

would have large seasonal fluctuations in the areas of 

large lower-zone pumping, and the steep gradient of the 

potentiometric surface would be maintained around the 

borders of the study area.

Table 3 and figure 23 show that the amount of total 

pumpage within the area has not increased since 1952. 

The maps of the potentiometric surface between 1926 

and 1965 (figs. 31-33, 35, 36) show a progressive steepening of the potentiometric surface along the east side of 

the study area. Thus, the above figures and figure 47 all 

support the conclusion that a strong tendency toward 

reduction of overdraft within the lower-zone aquifer 

system has been occurring.

SUMMARY AND CONCLUSIONS

The 500-3,500 feet of unconsolidated to poorly consolidated deposits that form the ground-water reservoir 

in the Los Banos-Kettleman City area consist of 

flood-plain, alluvial-fan, lacustrine, deltaic continental, 

and littoral and estuarine marine deposits. The sediments were derived from both the Diablo Range and the 

Sierra Nevada. The stratigraphy of such diverse genetic 

units is complex, but a simple three-part hydrologic 

classification can be made of the deposits penetrated by 

wells.

The upper zone extends from the land surface to the 

top of the principal confining clay. The upper zone, 

100-900 feet thick, has a degree of confinement that 

ranges from unconfined in thick bedded sands to excellent confinement between extensive lacustrine clay 

beds. Much of the zone consists of lensing deposits in 

which the water is semiconfined. The primary aquifer 

consists of micaceous arkosic sands derived from the 

Sierra Nevada. The Sierra sands are almost 600 feet 

thick under the present valley trough but pinch out 

toward the west at distances of 5-15 miles from the 

eastern margin of the Diablo Range. Diablo alluvial-fan 

deposits make up most of the upper zone. Few wells tap 

the poor quality water in these deposits of low permeability. The upper-zone water, a calcium-magnesium sulfate water, commonly contains 3,000-4,000 mg/1 total 

dissolved solids. Water quality improves with depth,

and near the basal part of the zone, the total dissolved 

solids are about 1,500 mg/1. Most of the pumpage of 

upper-zone water is in the southeastern part of the 

study area and along Fresno Slough, south of the town 

of San Joaquin.

A widespread diatomaceous clay stratum, deposited 

in a fresh-water Pleistocene lake 600,000 years ago, is 

the second hydrologic unit. The Corcoran Clay Member 

of the Tulare Formation extends beneath the entire 

study area, except for an area adjacent to the foothills in 

the southwestern part. The Corcoran is the principal 

confining layer throughout much of the San Joaquin 

Valley, and locally it separates waters of greatly differing quality and head.

The Corcoran provides effective confinement for the 

third hydrologic unit the lower zone. The lower zone, 

which supplies about three-fourths of the ground water 

in the study area, ranges from less than 500 to more 

than 2,000 feet thick. Although the zone contains many 

lensing aquitards, the overall hydraulic continuity between the basal and upper parts of the zone is good, 

except in the northern third of the area where a widespread clay layer acts as an effective separator within 

the lower zone.

The lower zone consists chiefly of the alluvial-fan, 

flood-plain, and lacustrine deposits of the Tulare Formation. In the southern part of the area, deltaic deposits 

are tapped also. Along the western margin of the valley, 

between the towns of Huron and Cantua Creek, wells 

are drilled still deeper to tap estuarine and littoral 

deposits of the San Joaquin and Etchegoin Formations. 

The alluvial-fan deposits, derived from the Diablo 

Range, consist of materials of low to moderate permeability. Individual beds within the Diablo flood-plain deposits give this unit a moderate to high overall permeability. Well-yield factors indicate that the flood-plain 

deposits are 3-5 times as permeable as the alluvial-fan 

deposits. The Sierra flood-plain deposits have the highest permeabilities because the sand beds are thicker, 

and they make up a greater porportion of a given section 

than do the Diablo flood-plain deposits.

The thickness of the fresh-water-bearing deposits and 

the perforated interval of the lower zone both range 

from 400 to more than 2,000 feet, but rarely are they the 

same in a given part of the area. In some areas, 

sufficient yields can be obtained without drilling to the 

"base of the fresh water. Only 1,000-1,200 feet of the 

more than 2,000 feet of lower-zone fresh-water-bearing 

' deposits are tapped northwest of Tulare Lake bed. Adjacent to the Big Blue Hills, sufficient quantities of water 

cannot be obtained from the continental deposits, and
E66 STUDIES OF LAND SUBSIDENCE

3,000-foot wells obtain part of their water from 

brackish-water-bearing marine deposits to depths of as 

much as 200 feet below the base of the fresh water.

The total dissolved solids in the lower-zone water in 

most of the area west of the valley trough ranges from 

800-1,500 mg/1, but locally they are more than 2,000 

mg/1. The water is primarily a sodium-sulfate water 

with more bicarbonate than the upper-zone water.

The chemical character of the water indicates that 

water derived from the Diablo Range has flushed the 

connate waters out of the marine and Sierra sands. 

Maximum concentrations of dissolved solids occur opposite the mouths of Panoche and Los Gatos Creeks and 

in the area of maximum dependency of pumpage from 

the marine sands. Areas of low concentrations of dissolved solids occur between the mouths of the large 

streams.

Before the agricultural development of the central 

part of the San Joaquin Valley, the lower-zone potentiometric surface sloped gently towards the valley 

trough from both the Diablo Range and the Sierra 

Nevada. Because of the low permeability of the Corcoran, upward movement of lower zone water probably 

was very slow; and as a result, the potentiometric surface was more than 20 feet above the land surface in the 

valley-trough area.

Large-scale agricultural development has lowered 

the potentiometric surface on the west side of the valley 

to as much as 400 feet below sea level. Water-table 

conditions now exist below the Corcoran near the Diablo Range. The slope of the potentiometric surface has 

been reversed. By 1966, a belt only a few miles wide 

adjacent to the Diablo Range was still an area of eastern 

gradient for lower-zone water movement. Farther east, 

areas in which the potentiometric surface originally 

sloped eastward, locally had a westward gradient of as 

much as 40 feet per mile by 1960.

Disruption of the natural flow system by man has 

resulted from the pumping of more than 1,000,000 

acre-feet of irrigation water per year since 1950. In 

1924, the total estimated pumpage was only 35,000 

acre-feet. By 1945, pumpage was 370,000 acre-feet and 

by 1953, 1,200,000 acre-feet. Total pumpage has not 

increased since 1953. The increase in pumpage has 

closely paralleled the agricultural growth in the area 

from a few wells to irrigate pasture to a modern complex 

of large-scale diversified farming that occupies nearly 

all the area.

Changes in the upper-zone water levels have not been 

pronounced in the northern and central parts of the 

area, but in the.southeastern part of the area, where 

large amounts of upper-zone water is pumped, both the 

water table and the water levels in the confined aquifer 

system have declined. Locally the water table has declined more than 300 feet, and elsewhere the artesian 

head at the base of the upper zone has declined more 

than 300 feet. North of Five Points, the water table has 

risen from less than 25 feet to more than 100 feet, and 

much of the area may be threatened with insufficient 

drainage for crops. In the northern area, water levels 

representative of the semiconfined zone have risen in 

some areas and have declined in others, depending on 

local variations in the amount of water pumped in the 

upper zone.

The changes in the hydrologic environment have 

been the greatest in the lower zone. Flowing wells once 

were common along the trough of the valley. In other 

areas where the potentiometric surface initially was 

less than 100 feet below the land surface, static levels 

were at depths of about 500 feet by the 1960's. Overall 

head declines of 300 to more than 400 feet are common 

in much of the area, and an estimated 600 feet of head 

decline has occurred next to the Big Blue Hills.

The lower-zone aquifer system has responded to the 

changes imposed by man by developing a steep gradient 

in the potentiometric surface around the trough of maximum pumping. In 1906, the potentiometric surface 

sloped 2-5 feet per mile to the east; by 1926, 6 feet per 

mile to the west; by 1943,14 feet per mile; and by 1960, 

30 feet per mile to the west. As the gradient became 

steeper and total pumpage stopped increasing, recharge 

from the east side of the San Joaquin Valley increased 

sufficiently to roughly balance the large overdraft from 

the lower zone. As a result, the rate of head decline has 

become progressively less since 1955 throughout most 

of the area. The records of many wells for the 1960-66 

period show a seasonal fluctuation of 60-120 feet but 

less than 5 feet of year-to-year head decline.

Most of the compaction has occurred in the lower zone 

as a direct result of the head decline that has occurred 

within it. Water-table changes also have affected the 

amounts of lower-zone compaction but only to a minor 

extent. Lower-zone applied stresses and compaction 

have been increased in areas of water-table rise and 

have been decreased in areas of water-table decline.

Decline of the lower-zone water levels below the base 

of the Corcoran decreases the change in applied stress 

from 1.0-0.8 foot of water per additional foot of waterlevel decline. The processes of applied-stress increase 

are changed from that of seepage stress equal to head 

differentials, to those of loss of buoyancy and transfer of 

part of the contained water from a neutral to an 

applied-stress condition as the deposits are dewatered.

REFERENCES CITED

American Geological Institute, 1972, Glossary of geology: Washington, D.C., Am. Geol. Inst. 805 p.
CHANGES IN THE HYDROLOGIC ENVIRONMENT CONDUCIVE TO SUBSIDENCE E67

Bull, W. B., 1964, Alluvial fans and near-surface subsidence in western Fresno County, California: U.S. Geol. Survey Prof. Paper 

437-A, 71 p.

 1972, Prehistoric near-surface subsidence cracks in western 

Fresno County, California: U.S. Geol. Survey Prof. Paper 437-C, 

85 p. 

-1974, Land subsidence due to ground-water withdrawal in the

Los Banos-Kettleman City area, California Part 2, Subsidence 

and compaction of deposits: U.S. Geol. Survey Prof. Paper 437-F 

(in press).

Bull, W. B., and Poland, J. F., 1974, Land subsidence due to groundwater withdrawal in the Los Banos-Kettleman City area, 

California Part 3, Interrelations of water-level change, change 

in aquifer-system thickness, and subsidence: U.S. Geol. Survey 

Prof. Paper 437-G (in press).

Croft, M. G., 1972, Subsurface geology of the late Tertiary and 

Quaternary water-bearing deposits of the southern part of the 

San Joaquin Valley, California: U.S. Geol. Survey Water-Supply 

Paper 1999-H, 29 p.

Davis, G. H., Green, J. H., Olmsted, F. H., and Brown, D. W., 1959, 

Ground-water conditions and storage capacity in the San Joaquin 

Valley, California: U.S. Geol. Survey Water-Supply Paper 1469, 

287 p.

Davis, G. H., and Poland, J. F., 1957, Ground-water conditions in the 

Mendota-Huron area, Fresno and Kings Counties, California: 

U.S. Geol. Survey Water-Supply Paper 1360-G, p. 409-588.

Frink, J. W., and Kues, H. A., 1954, Corcoran Clay A Pleistocene 

lacustrine deposit in San Joaquin Valley, Calif.: Am. Assoc. Petroleum Geologists Bull., v. 38, no. 11, p. 2357-2371.

Inter-Agency Committee on Land Subsidence in the San Joaquin 

Valley, 1955, Proposed program for investigating land subsidence in the San Joaquin Valley, California: Sacramento, Calif., 

Inter-Agency Committee on Land Subsidence in the San Joaquin 

Valley, Calif., open-file report, 60 p.

 1958, Progress report on land-subsidence investigations in the 

San Joaquin Valley, California, through 1957: Sacramento, 

Calif., Inter-Agency Committee on Land Subsidence in the San 

Joaquin Valley, Calif., open-file report, 160 p.

Ireland, R. L., 1963, Description of wells in the Los Banos-Kettleman 

City area, Merced, Fresno, and Kings Counties, California: U.S. 

Geol. Survey open-file report, 519 p.

Janda, R. J., 1965, Quaternary alluvium near Friant, Calif., in 

Guidebook for Field Conference I, Northern Great Basin and 

California Internat. Assoc. Quaternary Research, 7th Cong., 

U.S.A., 1965: Lincoln, Nebr., Nebraska Acad. Sci., p. 128-133. 

'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. Geol Survey Prof. Paper 497-A, 

71 p.

Lofgren, B. E., 1960, Near-surface land subsidence in western San 

Joaquin Valley, California: Jour. Geophys. Research, v. 65, no. 3, 

p. 1053-1062.

 1968, Analysis of stresses causing land subsidence, in Geological Survey research 1968: U.S. Geol. Survey Prof. Paper 600-B, p. 

B219-B225. 

-1969, Land subsidence due to the application of water, in

Varnes, D. J., and Kiersch, George, eds., Reviews in Engineering 

Geology, Volume II: Boulder, Colo., Geol. Soc. America, p. 

271-303.

Lohman, S. W., and others, 1972, Definitions of selected ground-water 

terms, Revisions and conceptual refinements: U.S. Geol. Survey 

Water-Supply Paper 1988, 21 p.

Meade, R. H., 1967, Petrology of sediments underlying areas of land 

subsidence in central California: U.S. Geol. Survey Prof. Paper 

497-C, 83 p.

 1968, Compaction of sediments underlying areas of land 

subsidence in central California: U.S. Geol. Survey Prof. Paper 

497-D, 39 p.

Mendenhall, W. C., Dole, R. R., and Stabler, Herman, 1916, Ground 

water in the San Joaquin Valley, Calif.: U.S. Geol. Survey 

Water-Supply Paper 398, 310 p.

Miller, R. E., Green, J. H., and Davis, G. H., 1971, Geology of the 

compacting deposits in the Los Banos-Kettleman City subsidence 

area, California: U.S. Geol. Survey Prof. Paper 497-E, 46 p.

Ogilbee, William, and Rose, M. A., 1969, Ground-water pumpage on 

the west side of the San Joaquin Valley, Calif., 1962-66: U.S. 

Geol. Survey basic-data compilation, 7 p.

Page, R. W., 1971, Base of fresh ground water (approximately 3,000 

micromhos) San Joaquin Valley, California: U.S. Geol. Survey 

open-file report, 13 p.

Poland, J. F., 1959, Hydrology of the Long Beach-Santa Ana area, 

California, with special reference to the water-tightness of the 

Newport-Inglewood structural zone: U.S. Geol. Survey WaterSupply Paper 1471, 257 p.

Poland, J. F., and Davis, G. H., 1969, Land subsidence due to withdrawal of fluids, in Varnes, D. J., and Kiersch, George, eds., 

Reviews in Engineering Geology, Volume II: Boulder, Colo., Geol. 

Soc. America, p. 187-269.

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. Geol. Survey 

Water-Supply Paper 2025, 9 p.

Terzaghi, Karl, and Peck, R. B., 1948, Soil mechanics in engineering 

practice: New York, John Wiley and Sons, Inc., 566 p.

INDEX

[Italic page numbers indicate major references]

A, B Page 

Acknowledgments ________________________ ES

Alluvial fans ________________________________ 8

Alluvial-fan deposits____________ 12, 17, 23, 25, 27, 65

derived from the Diablo Range __ 17,23,25.65 

permeability _____________________ 17, 65

Anticline Ridge________________________________ 23

Aquifer system, confined ________________ 6,19,66

wells ______________________ 34

definition ________________________________ 19

lower zone ___________ ____ 22, 23, 65, 66 

measuring equipment______________________ 9

permeable ________________________ 17

primary ______________________________ 65

semiconfined _______________________ 14

upper zone, micaceous sand ____________ 17

water levels, changes ____________ 39,65,66

Aquifer systems ___________________ 2, 6, 7, 8

definition of terms ___________________ 8

Aquitards _________________________ 22

semiconfined ____________________________ 14

Artesian head, lower zone __________________ 22. 50

decline______________ 9, 23, 39, 61, 63, 66 

Cantua __________________________ 11

upper zone _____________________________ 66

Bench-mark surveys ____________________ 6, 7, 50

Bench marks, changes in altitudes________________ 9

Big Blue Hills________________ 23, 27, 32, 50, 63, 66

Boston Land Co __________________ 34, 36

California Aqueduct ____________________ 2

California Department of Water Resources____ 6, 8, 45

Cantua Creek __________________ 32, 40, 50 

Cantua, core hole site______________________ 7

Cantua recorder site, annual unit compaction____ 11 

natural applied stress______________________ 11

water table__________________________ 43

Casing-failure studies__-_-__________________ 11

Ciervo Hills __________ ____________ 32

Compaction ___________________________ 6, 9

definition of terms --_-_________________ 8

delayed ______________________________ 9

due to wetting _________________________ 9

measurement_________________________ 6

rapid, geologic factors________________ 11

saturated deposits -___________________ 9

stress factors _____________________ 11

buoyant support __________________ 50

Compaction recorders ________________________ 9

mechanics of systems ________________________ 9

multiple ________________________ 11

sites ______________________________ 9

Conclusions ________________________________ 65

Corcoran Clay Member, Tulare

Formation __ 12, 17, 19, 34, 43, 45, 50, 65 

Tulare Formation, altitude of base__________ 27

areal extent _________________ ________ 32

diatomaceous clay ________________ 19, 65

flow system ___________________ 34

lacustrine sands _ ________________ 17

lithology ________ ____________ 19 

principal confining layer_________ 19, 65

stratigraphy __________________________ 19

thickness__________________ 12, 19 

unit compaction ____________________ 11

vertical permeability ________________ 19

water-table decline ___________________ 43

Corcoran lake____________________ E19. 65 

Corcoran lake clay ______________________ 32

structure. ___________________________ 19

thickness _________________________ 19

vertical permeability __________________ 19

Core holes _____________________________ 7

Core samples, saline water body ____ -_____---_ 32

D, E 

Definitions ____________________________ 8

Delta-Mendota Canal _________________ 40, 46, 61

Deltaic deposits ____________________ 12.23,25,27

derived from the Sierra Nevada ________ 23, 25

Diablo Range ________ 8, 9, 12, 17, 23, 25. 32, 36, 65

alluvial-fan deposits ______________ 17, 25. 65

flood-plain deposits ________________ 25, 59, 65

head decline _________________________ 55

lithology _____________________________ 8,9

recharge ________________________________ 32

water __________________________ 66 

Diatomaceous clay ____________________ 19, 65

Dissolved solids, concentrations________ 29, 32, 66

Los Gates Creek __._____________ 32.66 

lower zone _________________ 29,32,66 

Panoche Creek _________________ 32, 66 

upper zone ___________________ 17,19.65

variations ______________________ 19, 29

Estuarme deposits, Pliocene_________________ 12

Etchegoin Formation ________ 12,23,56.63,65

Five Points________ ________________ 40 

Flood-plain deposits__________ 12, 17, 23, 25. 27

derived from the Diablo Range _________ 25, 65

derived from the Sierra Nevada __ 17, 23, 25. 65 

lithology ____________________ 25

micaceous ________________________ 17, 25

permeability _____________________ 25, 65

Flow system, lower zone, initial ____________ 34

natural__.__________________ 32, 66 

man's disruption _____________._ 34,66

Fossils, fresh-water ________________________ 32

Franciscan Formation__________________ 8

Fresh-water-bearing deposits ___ __ 12.13,27,59 

altitude of base.___________ __________ 27

geologic sections ____________________________ 13

hydrologic units.-________________ 12, 13

lacustrine clay _______________ ________ 13

lower unit____________ _____ 12,13,23

lower zone _______________________ 13, 29

thickness ___________________ 27.29.65

subsurface geology ______________ ___ 12

Tulare Formation, Corcoran Clay

Member _ _____________ 12,13

upper unit ________ _______ _____ __ 12,13

upper zone __________________ _____ 13

G 

Geologic studies, regional __________________ 7

Gravel, Los Banos Creek ________________ __ 17

Ground water, agricultural use ___________ 2,34

calcium concentrations_ ___________ 17,19,65

definitions of terms _______________ 8

depth _____________________________ 40

development, history _________ ____._ 34

dissolved solids, variation ___________ 19, 65

irrigation________________________ 34, 36

magnesium sulfate concentrations ________ 17,65

pumpage ______________ 14, 36, 38, 39, 46

Page 

Ground water Continued

sodium bicarbonate concentrations _________ E19

upper zone ______________ _______ ______ 14

withdrawals, computation_____________ 36

Ground-water levels, changes _________________ 39

Ground-water reservoir, description __________ 12

general features ________________ _________ 12

lower zone ______________________ 13,14,79

hydrologic character __________________ 23

physical character ________________ 23

productivity __--____-_________________ 25

pumpage________________ __.._.____ 14

water, chemical character _______________ 29

natural flow system________-__-________ 32

saline water body_______________________ 32

sediments, lithology ____ _____________ 12

thickness _________________________ 12

Tulare Formation, Corcoran Clay Member ____ 19

upper zone _______ _____ ____________ 14

physical character _________ ________ 17

productivity _____________________ 14,17

sands ____________________________ 14

water, chemical character ______________ 17

water-level changes____ ______ ______ _ 34

H

Head, decline __ 34, 39, 43, 54, 55, 56, 59, 61, 63, 66 

decline, Big Blue Hills _____________ ____ 66

history_______________________ __ 61

near the Merced County line _ __________ 61

north of Westhaven. ___ _____________ 63

southeast of Cantua Creek _________ 61

southwest of Five Points __________ _ 63

southwest of Mendota______________ _ 61

west of Huron_________________ _ _ 55,56

differential ___ _____ ____ _____ 14, 43, 44, 54

Huron, core hole site _________ ________ ___ 7

Hydraulic continuity ______________________ 23

Hydraulic gradient, lower zone _________ _ __ 50

Hydrologic environment, changes

caused by man _____ ___________ 34

changes caused by man, ground-water

development, history _____ ________ 34

ground-water levels, changes ______ ____ 39

ground-water pumpage, total, trends__ ___ 36

lower zone ____________________ _______ 45

head decline, history ___ __ ______ 61

potentiometric level, seasonal 

fluctuation ______________ _ ___ 5.9

potentiometric surface changes _____ 46 

upper zone, confined ___ ____________ 43

semiconfined __ _______ ____ _ 43

water table__ ____________ __ ___ 39

Hydrologic system, San Joaquin Valley ______ ___ 32

Hydrologic units____ _______ ___________ _ 12,13,65

I, K

Inter-Agency Committee on Land Subsidence______ 2

cooperative program __ _ _______ ____ 6

Federal program ___________ ______ _ 6

field program___________________ _ 6

laboratory program _______ __ ____ ____ 7

Introduction ___________ ________ __ _ /

Ireland, R. L., cited ____ ____ ____ _ __ _______ 27

Irrigated land-- __ _ ________ ______ 36,38

Kettleman Hills_________ ___ __ ___ 32,63

Kings River, irrigation water _______________ 45

E69
E70 INDEX

Page

Laboratory program ____________________ E7

Lacustrine clay________________________ 19

Lacustrine deposits ______________________ 12, 17, 23

Lacustrine sands ________________________ 17

Land subsidence ____________________________ 9

Lemoore site ___________________________ 44

Little Panoche Creek __________________ 32 

Littoral deposits, Pliocene ________________ 12

Los Banos Creek, gravel _________________ 17

sediments ____________________________ 17

Los Banos-Kettleman City study area __________ 2

alluvial-fan deposits _____ 12, 17, 23, 25, 27, 46 

aquifer systems___________________________ 7

boundary _____________________________ 2

compaction ______________ 6, 9, 11, 46, 66

cultural features _____________________ 2

deltaic deposits_______________ 12, 23, 25, 27

flood-plain deposits _______ 12, 17, 23, 25, 27

flow system, natural ________________ 32

fresh-water-bearing deposits________ ___ 27

thickness __________________ 27, 29

ground water.___________________ 13

pumpage ______________ 36,38,39

ground-water reservoir __________________ 12

head declines ____________________ 55, 59, 61

head differential _______________ 43,44 

hydrologic environment____________________ 7, 66

hydrologic units ______________ 12, 13, 65 

irrigation water___________________ 46, 66

lacustrine clay ___________________ 19

lacustrine deposits ____________ 12, 17, 23

lower zone __________ 13, 19, 25, 29, 65, 66

artesian head _________________ 50

seasonal changes _____________ 59

compaction _________________ 46, 66 

confinement, extent _____________ 32

perforated intervals_________ ____________ 29

recharge gradient ________________ 46, 66

stress, applied ______________ 50, 66

wells .______________ 36,61,63,66

micaceous sand____________________________ 17

potentiometric surface ________ 34, 46, 54, 65

principal confining layer ____________ 12, 19, 65

pumpage _________________ 65, 66 

recharge ______________________ 55, 59

regional geologic studies _______ _____ 7 

saline water body__________________________ 32

sediments __________________________ 12, 14

lithology ____________________ 12, 17, 65

stress, applied, variation ____________________ 59

subsidence __________________________ 2, 6, 7. 9

area ___________________________ 9

topography__________________ _____ 2

upper zone, micaceous sand ________________ 17

permeable aquifers _____________ 17

pumpage _______________ 43, 65, 66 

recharge __________________________ 34

water quality_____________________ 65

water, irrigation _________________ 25, 66

water table _________________ 39,56,66

well yields _________________ 27,59,65

Los Gatos Creek ____________ 32,40,43,55,66

alluvial fan, ancestral _______________ 19, 40

dissolved solids ____________________ 32, 66

recharge ______________________ 40, 55

Lower zone ________________________ 19, 65, 66

alluvial-fan deposits ___________ 23, 27, 46

aquifer system ______________________ 45

confined ___________________________ 19

artesian head ________________________ 22, 50

chloride concentration _______ _____ 29

compaction _________________ 19,46,66 

confinement, degree._______________________ 44

extent ________________________ 32

deltaic deposits ______________________ 23,25,27

dissolved solids, concentrations _____ 29, 32, 66 

variations ________________________ 29

flood-plain deposits ______________________ 23, 25

Lower zone Continued

flow system, initial ___________________ E34, 66

fresh-water-bearing deposits, thickness ____ 27, 29

ground water _____________ 13,23,29,65 

irrigation ______________________ 19

head declines _________ 39, 46, 59, 61, 63, 66

hydrographs ______________________ 61, 63

head differentials _____________ 22, 50, 54 

hydraulic continuity__________________ 22, 65

hydraulic gradient ______________________ 50

irrigation water ________________ 46, 59

lithology ______________________ 23,65 

perforated interval, thickness ______ 27, 29

permeability ______________________ 25, 65

pore-pressure decline _________________ 29

potentiometric level, seasonal fluctuation___ 59 

potentiometric surface ___ 34, 46, 54, 56, 63, 66 

productivity _____________________ 25, 29

pumpage __________________________ 14, 59, 63

pumping depressions ____________________ 46

recharge ____________ 32, 34, 55, 59, 63, 65, 66

area _______________________________ 34

gradient __________________ 46, 66 

stress, applied ____________________ 50, 66

seepage ________________________ 50

surface water, imports ________________ 63

thickness _____________________ 29, 65 

water, chemical character _______________ 29

salinity ___________________________ 29

sodium sulfate ___________________ 29

temperatures_________________________ 32

water levels _________________ 39, 45, 46 

decline. ____________________________ 50

seasonal fluctuation ____________ 59, 66

water table ___________________ 50, 66 

yield factors ________________ 25, 27, 65

M, O

Meade, R. H., cited ___________________ 7 

Mendota ________________________________ 34

core hole site ________________________ 7

Mendota recorder site, water table.__________ 43

Miller, R. E., cited ____________________ 13 

Monocline Ridge _____________________ 32 

Oro Loma _________________________________ 34

core hole site__________________________ 7

Oro Loma recorder site ______________________ 22

annual unit compaction ____________ 11

Pacific Gas and Electric Co_____ 7, 8, 36, 46, 50, 61 

Panoche Creek, dissolved solids ____________ 32, 66

Perched water ____________________________ 40

Pleasant Valley ______________________ 56 

Potentiometric surface ________________ 46, 50, 63

altitudes _________________________ 54, 56

between Anticline Ridge and Fresno Slough 54, 55 

between Tumey Hills and Mendota _______ 54

lower zone changes ____ ___ 34, 46, 54, 56, 66

northeast of Big Blue Hills _ _ ___ _ __ _ 55

profiles _______--___________________ 54

slope __________________ 46, 50, 54, 66 

Purposes of report ______________________ 7

R, S

Recharge, Diablo Range ______________ 32, 55 

Kettleman Hills ___________________ 63

Los Gatos Creek _______________ 40,55 

lower zone_________ 32, 34, 55, 59, 63, 65, 66 

San Joaquin River __________________ 34

San Joaquin Valley _ ___________ 55,65,66 

References cited ______________________ 66

Russell Giffen, Inc ___________________ 8

Saline water body ___________________ 32

San Joaquin Formation ________________ 12, 23, 65

San Joaquin River __________________-___ 34

San Joaquin Valley_____-_-________________ 2

geographic setting ______________________ 8

geosynclinal trough___-----____--_- _______ 12

hydrologic system ___ ___ ____ _ 32

San Joaquin Valley Continued

recharge area_______________ E34, 55

subsidence ______________ _ 2, 6, 7

underflow ____ _______________ 54

San Luis Canal ___________________ 2,40 

Sands, arkosic, micaceous ______ 14, 17, 23, 27, 65

micaceous, upper zone ________ 14, 17, 23, 27

upper zone, dissolved solids ______________ 19

permeability ____________ _______ 17

Santa Clara Valley ___________________ 6 

Sediments, buoyancy change _____________ 12

Semiconfined aquifers.___________________ 14

Semiconfined water ____________________ 40,44

Shallow water, depth ____________________ 43

Sierra Nevada ___________________ 12,65 

arkosic sands, micaceous ______ 14, 17, 23, 27, 65

deltaic deposits ______________________ 23, 25

flood-plain deposits _______ 17,23,25,59,65 

sands __________________ 14,39,65,66

Stress, applied _____________________________ 2, 12

applied, computation ____________________ 12

confined zone, water-table change ____ 12, 50

increase at Cantua ___________ ___ 11

variation _______ ___ _ _ ___ ____ _ 59

aquifer system, water-level change, basic theory 12 

confined zone, magnitudes of components ____ 12 

effective _______________________ 12

hydrostatic ____________________________ 12

seepage-_________________________ 12, 50

Study area boundaries ___ _ 2 

Subsidence _____________________ ____ 9

altitude, changes ______________-------_____ 6

corrections _______________ ____ 6

area adjacent to Big Blue Hills ______________ 23

central California-______________________ 7

effects on canals __________________________ 2

Los Banos-Kettleman City area ________ 2, 6

measurement, change in percentage __________ 11

near-surface _______________________ 9

rates___________________________ 9

reference point changes __________________ 6

San Joaquin Valley ___________________ 2,6

Summary ________________ __ ___ __ 65

Surface water, deliveries by the Delta-Mendota Canal 46 

imports______________________ 14, 63

Thickness, Corcoran lake clay __________________ 19

lacustrine sands ___________-___ _______ 17

micaceous sands ___-_________ ________ 17

Tranquillity site ____________________________ 43

Tulare Formation________.__ 12, 17, 23, 32, 65

Corcoran Clay Member ________________ 12,19

areal extent _______________-_-----____ 32

flow system ________________________ 34

lacustrine sands ______ __ ______ 17

lithology _____________ ____ 19 

principal confining layer ___ __ 12, 19, 65 

stratigraphy _________ ___ ___ -___ 19

thickness___________________ 12, 19 

unit compaction ______________________ 11

vertical permeability _________________ 19

water-table decline __________________ 43

productivity __________________________ 23

upper zone ____________________________ 17

Tulare Lake bed ______________-___ 59,63

Twenhofel, W. S., cited _________________ 3

U

U.S. Bureau of Reclamation __________ 8, 40, 44 

U.S. Coast and Geodetic Survey _________ 6, 7, 46 

U.S. Geological Survey _____ _ 6, 8 

Upper zone ______________________ ___ 14, 65

alluvial-fan deposits _ 17 

aquifer, primary __ _________ ________ 65

arkosic sands, micaceous ______ 14, 17, 23, 27, 65

head, decline ____ 43 

differentials ___________ ______ 14

irrigation wells__ ______ ______________ 44

lacustrine sands______________________ 17, 65
INDEX E71

Upper zone Continued

micaceous sands _____ __ E14, 17, 23, 27, 65 

permeability ________________________ 39

piezometers ______________________ 44

productivity _________________________ 17

pumpage _________________ 43, 65 

recharge ___________________________ 34

seasonal fluctuation __________________ 44, 45

semiconfined aquifer system___________ 43

thickness __________________________ 65

water, chemical character __________ 17, 65

calcium _________________ 17, 19, 65 

magnesium sulfate ________________ 17, 65

water table ____________ ______ _ 14, 66 

yield factors __________________________ 17

W, Y

Water, agricultural_____________ 14, 34, 36, 38 

brackish________________ 14, 23, 29, 65 

calcium-magnesium sulfate ___ ________ 65

chloride concentrations ____________________ 32

connate______________________ 23, 66 

Diablo Range____________________ 66 

dissolved solids _____________ 19, 29, 32, 65, 66

fresh __________________________ 27, 29, 65, 66

irrigation _______________ 25,39,45,66 

perched ____________________________________ 40

Pliocene sands ________________________ 32

productivity, lower zone____________ 14

saline ______________________ 29,32 

sodium chloride ______________________ 17

sodium sulfate ______________________ 29,66

surface imports ___________________ 14, 63

temperatures ________________________ 23, 32

Page

Water levels, changes _______________ E39, 50 

confined zone______________________________ 39

lower zone _____________ 39,45,50,61,63 

measurements _____________________ 7

periodic measurements __________________ 6, 46

seasonal fluctuation __________________ 39, 59

semiconfined zone ___________________ 39

upper zone__________________ 43, 44, 45, 66

Water-level recorder __________________ 9

Water table_________________________ 39, 66

altitude _______________________ 40 

decline _______________ 40, 43, 44, 56, 66 

lower zone _______________________ 50,66

rise_________ ____________ 40,43,66 

upper zone ___________________ 14, 66

Wells, alluvium ______________________ 39

artesian __________________________ 34

head decline______________ 23, 34, 61 

Big Blue Hills ______________________ 63,65

brackish water ________________ 29,66 

Cantua recorder site ___________________ 43

descriptions by Ireland ____________-___ 6 

Etchegoin Formation _________ 23, 29, 56, 63 

flowing ___________________-__ 34, 66

freshwater ____________________ 56,65,66

base _____ __________________ 29 

irrigation ________ 7,17,23,27,34,36,39,44,56

Kreyenhagen Formation ______________ 23

Los Gates Creek area ______________________ 27

lower zone ___________________ 22,34,36

head differentials________________ 22

hydrographs ___________________ 22

water levels, declines _______________ 39

yield factors _______________ 25,27 

Mendota recorder site________________ 43

mixed zone_________________________ 45

Wells Continued

near the Merced County line _______________ E61

north of Westhaven_____-_-________________ 63

northwest of Tulare Lake bed ________ 59,65

numbering system ____________________ 6

observation _________________ 7, 59

location ____________________________ 9

perforated ________________ 22,27,29,39,40,43

permeability ______________________ 17, 65

Pliocene deposits ________________________ 23

saline water _______________________ 32

San Joaquin Formation _____________ 23

San Joaquin Valley______________________ 63

seasonal fluctuations ____________________ 44, 66

shallow ______________________ 40

sodium chloride water ____________ 17

southwest of Five Points ____________________ 63

southwest of Los Banos _______________ 17

southwest of Mendota ___ _ __ _____ _ 59, 61

Tranquillity site ______________________ 43

Tulare Formation _____________ 23,32,56 

unused____________________________ 45

upper zone, yield factors ____________________ 27

water levels ______________ 39,40,45,50 

water table_ _________________________ 43

water temperature ______________________ 23,32

west of Fresno Slough________________________ 17

west of the San Joaquin River______________ 17

Westhaven site__ ________________________ 43

yields _____________________________ 27,65

Westhaven ______________________________ 34,43,63

Westhaven site_____________________________ 43

Westlands Water District _______________ 8 

Yearout site, wells, irrigation ______________ 39

Yield factors ___________________ 17,25,65

U.S.GOVERNMENT PRINTING OFFICE:1975-0-689-905/10