Land Subsidence due to 

Ground-Water Withdrawal 

Tulare-Wasco Area 

California

GEOLOGICAL SURVEY PROFESSIONAL PAPER 437-B

Prepared in cooperation with the 

California Department of Water Resources
Land Subsidence due to 

Ground-Water Withdrawal 

Tulare-Wasco Area 

California

By B. E. LOFGREN and R. L. KLAUSING

STUDIES OF LAND SUBSIDENCE

GEOLOGICAL SURVEY PROFESSIONAL PAPER 437-B

Prepared in cooperation with the 

California Department of Water Resources

A study of land subsidence caused by water-level 

changes in complex aquifer systems, including 

analysis of stresses and appraisal of 

parameters for estimating subsidence

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price $1.25 (paper cover)
CONTENTS

Glossary _ _________________________________

Abstract. ___________________________________

Introduction. _______________________________

Statement of problem. ___________________

Location and general features of the area. __ 

Scope of investigation and purpose of reportPrevious investigations. _ _________________

Well-numbering system. _ _______________

Collection of data and field program. ______

Acknowledgments--... . __________________

Geologic setting. _______________________________

Physiography. _________________________________

Tulare Lake_________.______________________

Geologic units__ ________________________________

Continental deposits from the Sierra Nevada. __

Corcoran Clay Member of the Tulare Formation. _____________________________

Upper Pliocene and Pliocene (?) marine strata __

Santa Margarita Formation as used by Diepenbrock (1933) _________________ _ _________

Tertiary sedimentary deposits, undifferentiatedSierra Nevada basement complex. ____________

Clay-mineral assemblage in cored sediments________

Surface water_ _____________________________________

Natural streams. _______________________________

Canals. _______________________________________

Surface-water supply. ___________________________

Ground water. _____________________________________

General features ________________________________

History of development. ________________________

Hydrologic units. ______________________________

Semiconfined aquifer system. ________________

Confined aquifer system. ____________________

Santa Margarita Formation as used by 

Diepenbrock (1933). ______________________

Aquifer tests. __________________________________

Ground-water pumpage __ _ _ ____________________

History of water-level trends. ____________________

General decline, 1905-51___ _ _________________

Partial recovery, 1951-59_ ___________________

Water levels in 1959________________________

Water table, semiconfined aquifer system. _ _

Piezometric surface, semiconfined aquifer

system. _____________________________

Water level of the confined aquifer system.

Water level in the Santa Margarita Formation as used by Diepenbrock (1933)_____

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Ground water Continued

History of water-level trends Continued

Summary of water-level trends.______________ B45

Semiconfined aquifer system.____________ 46

Confined aquifer system.________________ 48

Subsidence of the land surface..______________________ 49

Leveling data available___-_------___--_-__-_____ 50

Problems related to accurate leveling in subsidence

areas__ ______-_____-_____-----_-____--__--_-- 50

Magnitude and areal extent of subsidence ______ 52

Subsidence profiles..____---_-___--_-________ 53

Subsidence maps_____-_-_-_------_--------- 56

Volume of subsidence.______________________ 61

Possible causes of land subsidence.______________ 62

Analysis of hydraulic stresses causing compaction_______ 64

Unconfined (water-table) conditions.______________ 65

Confined (artesian) conditions.___________________ 65

Compaction of the water-yielding deposits.____________ 69

Compaction-recorder installations._______________ 69

Compaction of deposits near Pixley_______________ 70

Measured compaction.______________________ 70

Computed compaction_____________________ 79

Time lag of compaction____________________ 83

Correlation of subsidence, compaction, and 

water-level change-____-__-__-_-____--____ 85

Compaction in the vicinity of Richgrove___________ 86

Measured compaction at 24/26-36A2__ _ _ _ _ _ _ 87

Measured compaction at 25/26-1A2 and 1J3___ 88 

Laboratory consolidation tests._____-___-__- 88

Measured compaction at 24/26-34Fl__________ 89

Relation of subsidence to water-level change.__________ 91

Parameters for estimating subsidence under assumed hydrologic change_________-__-________-------_---- 92

Examples of application of parameters at four sites-- 94 

At the Pixley core hole, 23/25-16N1___ _ 94 

At Alpaugh, 23/23-33Al_____-____-----._____ 95

At well 25/23-29A1, 11 miles southwest of

Alpaugh._______----------___---_--_-_-__ 95

Five miles northeast of Delano_______________ 95

Methods of decreasing or stopping subsidence._________ 96

Seasonal changes in water levels __________________ 96

Long-term water-level changes__________--_-_-__ 97

Conclusions as to methods of decreasing or stopping 

subsidence.__________--_------____----__---__ 97

Summary and conclusions.___________________________ 97

References cited-_____-_-_----______-_____----___-__ 100

Index________________________-_---___-----------_ 103
IV CONTENTS

ILLUSTRATIONS

Page 

FIGURE 1. Map showing principal areas in California where ground-water withdrawal has caused land subsidence.____ B2

2. Map showing principal geomorphic features of southern San Joaquin Valley and area of this report.______ 3

3. Chart showing well-numbering system_____________________________-___-________-___-__-----_------ 6

4. Geologic section A-A" through the Pixley core hole_______________________________________________ 10

5. Geologic section B-B' through the Richgrove core hole---------------------------------------------- 11

6. Map showing location of geologic and hydrologic sections.__-_____-_____-----___-------_-----------_- 12

7. Chart of composite logs of core hole 23/25-16N1 near Pixley-----_----------_------------------------ 13

8. Chart of composite logs of core hole 24/26-36A2 at Richgrove-____________--______-__--__-------_---- 14

9. Geologic section C-C' through the Richgrove core hole.___________________-______-__---___----_----- 15

10. Geologic section D-D' through Alpaugh-_________-_..____-_---__-_-------.---------_---------------- 16

11. Map showing the structure and extent of the Corcoran Clay Member of the Tulare Formation, and location

of core holes________________________________________________________________________________ 17

12. Graph showing the discharge of Tule River, 1902-64______-___-_-______________________ ___ 20

13. Map showing surface-water diversions during 1960 and boundaries of incorporated districts receiving water

from the Friant-Kern Canal_____________________________________-..___-_-___--__---..-------- 21

14. Graph showing surface-water supply, 1930-64, exclusive of canal imports from the Kern and Kaweah Rivers- 22

15. Map showing land irrigated in 1920-21__--------_---_--_-----_---------_---------- ________ 24

16. Map showing land irrigated in 1958_---_------_----_---------------------------------------------- 25

17. Generalized east-west hydrologic section_________-______-------------_----------------------------- 26

18. Hydrologic sections A'-A" and B-B' showing perforated intervals and water levels in wells____________ 27

19. Map showing areas in which wells tap confined aquifer systems and locations where aquifer tests have been

made_____-____________.______________--__._______-______-__----------_------------------ 29

20. Map showing power districts and rate of power consumption by township __________________________ 31

21. Graph showing estimated use of ground water and surface water for irrigation, 1950-62_________-___-_-__ 33

22. Altitude of the water table and area of flowing wells in 1905__________________________-___-----_-_-_- 35

23. Generalized water-level contours as of December 1920 (Kern County) and November 1921 (Tulare County). 36

24. Hydrographs showing long-term trends of average water levels, 1921-61, in eight ground-water subareas

wholly or partly within the Tulare-Wasco area._____-________________-____-__--_-___-------_--- 37

25-30. Maps showing:

25. Change in water level in the semiconfined aquifer system, 1920-21 to 1948______-________---__- 38

26. Change in the water level in the semiconfined aquifer system, 1948-54, in the eastern part of the

Tulare-Wasco area._____________________________-___________________-_--..____-------_- 40

27. Change in the water level in the semiconfined aquifer system, 1954-59, in the eastern part of the

Tulare-Wasco area______________________________-___-_-_____-______-----_____---_-_..-_ 41

28. Altitude of the water table in the semiconfined aquifer system, February 1959-_______________ 42

29. Piezometric surface of the semiconfined aquifer system, February 1959_______________________ 43

30. Piezometric surfaces of the confined aquifer systems, February 1959-_________---__-___------__ 44

31. Hydrograph of well 25/27-18A1 tapping the confined Santa Margarita Formation as used by

Diepenbrock (1933), 3 miles south of Richgrove_______________________________________________ 45

32. Map showing location of wells and bench marks for which graphs are included in this report._____________ 46

33-35. Hydrographs of 

33. Six wells tapping the semiconfined aquifer system and graphs of subsidence of selected nearby

bench marks________________________________________________________________________ 47

34. Piezometers tapping the semiconfined and the confined aquifer systems at and south of Alpaugh,

and graphs of subsidence of nearby bench marks_________________________________________ 48

35. Two wells tapping the confined aquifer system west of Delano and graphs of subsidence of nearby

bench marks_________________________________________________________________________ 49

36. Map showing lines of equal subsidence in the Delano area, 1902-40-_______--___-___-_______--------_- 49

37. Map showing network of leveling by the U.S. Coast and Geodetic Survey____________________________ 51

38. Graph showing subsidence of bench marks near center of maximum subsidence, 1901-2 to 1964__________ 52

39-42. Land-subsidence profiles 

39. W-W, 1901-2 to 1964_______________________________________________________________ 54

40. X-X', 1942-43 to 1964__________________________________________________________________ 54

41. Y-Y', 1948-62__________________________________________________________________________ 55

42. Z-Z', 1935-64__________________________________________________________________________ 56

43-47. Maps showing land subsidence:

43. 1926-54________________________________________________________________________________ 57

44. 1948-54, and location of subsidence profiles_______________________________________________ 58

45. 1954-57, and districts receiving irrigation water fron the Friant-Kern Canal in 1956._____-__--__ 59

46. 1957-59________________________________________________________________________________ 60

47. 1959-62._______________________________________________________________________________ 61
CONTENTS V

Page 

FIGURE 48. Graph showing cumulative volume of subsidence, 1926-62___---------------------------------------- B62

49. Graph showing rate of subsidence, 1926-62_______________________________________________________ 62

50. Map showing land subsidence, 1926-62___________-______________----_-_------------------__------- 63

51. Graph showing the relation of magnitude to area of subsidence, 1926-62-______________________________ 64

52. Effective-stress diagrams for a confined aquifer system overlain by an unconfined aquifer_________________ 66

53. Diagram of compaction-recorder installation_________________________-____---___---------_-_----___ 69

54. Graphs showing land subsidence, compaction, water-level fluctuations, and change in effective stress in the

subsidence center 3 miles south of Pixley._________________________________________________________ 71

55. Graph of record of four compaction recorders and subsidence of a nearby bench mark, 3 miles south of

Pixley, 1960-64.___________________________________________________________.-_-__-____-_-.___ 72

56. Diagram showing annual rate of compaction of deposits in four depth zones, 3 miles south of Pixley, 1960-64. _ 73 

57-59. Graphs showing 

57. Relation of seasonal unit compaction to stress change during the compaction period in two depth

zones of the confined aquifer system near Pixley, 1960-64___________________________________ 75

58. Correlation of compaction and water-level fluctuations near Pixley.___________________________ 76

59. Observed rebound and compaction near Pixley.____-__--__--____---_______-----_-..____---___ 77

60. Chart of lithologic subdivision of the Pixley core hole, 23/25-16N1, for application of consolidation test data. 81 

61-68. Graphs showing:

61. Trend of water levels in the semiconfined and confined aquifer systems at the Pixley core hole,

23/25-16N1, and observed subsidence of nearby bench marks________-_-__------____----_-__ 82

62. One-dimensional consolidation data for core sample 23L-229, Pixley core hole__________________ 83

63. Estimated time required for compaction of deposits to 760-foot depth at Pixley following an increase

in effective stress______________________________________________________________________ 84

64. Computed ultimate compaction, measured compaction, and observed subsidence at the Pixley core

hole, 1902-64.._____________________________-________.-__----_-_-_-_-_-_-_________ 85

65. Relation of subsidence to water-level decline at Richgrove, 1905-64__________________________ 86

66. Correlation of water-level fluctuations in an 892-foot well with subsidence of four bench marks near

Richgrove, 1959-64_____________________________________________________ 87

67. Correlation of subsidence and compaction with water-level fluctuations, 2y% miles west of Richgrove,

1957-64_._________________________________________________________________________-. 89

68. Correlation of water-level fluctuations in wells northeast of Delano with subsidence of nearby bench

marks. ______________________________________________________________________________ 90

69. Map showing subsidence to head-decline rations for that part of the Tulare-Wasco area where data on longterm water-level change and subsidence were available___-____-___----------__--------__-------- 93

TABLES

Page 

TABLE 1. Core holes in the Tulare-Wasco area_____________________________________________________________- B6

2. Geologic units of the Tulare-Wasco area_____________________________________________________-_____ 9

3. Surface-water deliveries from the Friant-Kern Canal to irrigation districts in the Tulare-Wasco area,

1949-64._______________________________________________________________________________ 20

4. Aquifer-test results._____________________________________________________________________________ 30

5. Yield characteristics of irrigation wells in the Tulare-Wasco area, by townships.________________________ 32

6. Estimated ground-water pumpage in the Tulare-Wasco area, 1950-62._______________________-_----_ 33

7. Dates of leveling control by the U.S. Coast and Geodetic Survey in the Tulare-Wasco area, 1931-64. _____ 52

8. Water-level and compaction recorders in the Tulare-Wasco area.___________________________________ 70

9. Compaction rate of unconsolidated deposits in the Pixley area in four depth zones during 5 years of record 73

10. Compaction and rebound characteristics of the confined aquifer system near Pixley_____________________ 78

11. Results of consolidation tests on samples from the Pixley core hole, 23/25-16N1________________________ 79

12. Depths to water in the confined and semiconfined aquifer systems and seepage stresses used in computing

compaction at the Pixley core hole, 1905-64__________________________________________________ 79

13. Effective stress, void ratio, and computed compaction for each of the lithologic zones at the Pisley core hole,

1905-64________________________________________________.__________________________________ 80

14. Description of consolidation test data for samples from the Richgrove core hole________________________ 89

15. Relationship between subsidence and head decline at nine locations._________________________________ 92
GLOSSARY

In the studies of water-bearing deposits that compact sufficiently in response to change in effective stress (caused by changes 

in water levels) to produce significant land subsidence, certain 

terms have been used in the literature to cover a broad span of 

physical conditions and rock units are denned and explained as 

used for purposes of these studies. In addition, several terms 

utilized by soil-mechanics engineers and a few terms introduced 

as a result of the subsidence investigations are denned here for 

readers who have diverse backgrounds.

The compactible deposits or sediments that have undergone 

sufficient compaction to produce significant subsidence in 

California or elsewhere are clastic sediments. The definitions 

given in this glossary are directed toward this type of sediment; 

they do not attempt to span the full range of rock types that 

contain and yield ground water.

In this report, the stresses causing compaction are expressed 

in equivalent "feet of water" (1 ft of water=0.433 psi). Thus, 

the unit weight of water, yw, equals 1 foot of water. In this 

glossary, dimensions are listed first in the usual convention, and 

second in parentheses, with stresses expressed in "feet of water." 

Aquiclude. An areally extensive body of saturated but relatively impermeable material that functions as an upper or 

lower boundary to an aquifer system and does not yield 

appreciable quantities of water to wells or to adjacent 

aquifers.

Aquifer. A body of saturated relatively permeable material 

that conducts significant ground-water flow and is capable 

of yielding water to wells in economic quantities. 

Aquifer system. A heterogeneous body of intercalated permeable 

and poorly permeable material that functions regionally as 

a water-yielding hydraulic unit; it comprises two or more 

interconnected aquifers separated by laterally discontinuous 

aquitards that locally impede ground-water movement but 

do not greatly affect the overall hydraulic continuity of the 

system.

Aquitard. A saturated, but poorly permeable, interbed within 

an aquifer system that impedes ground-water movement 

and does not yield freely to wells, but which may transmit 

appreciable water to or from adjacent aquifers and, where 

sufficiently thick, may function as an important groundwater storage unit.

Coefficient of volume compressibility. The compression of a 

clay (aquitard), per unit of original thickness, per unit 

increase of pressure. Symbol mv (Terzaghi and Peck, 1948 

p. 64).

Dimensions: L2 /F 

(L)

Compaction. "Decrease in volume of sediments, as a result of 

compressive stress, usually resulting from continued deposition above them" (American Geological Institute, 1957, 

p. 58). In this report, compaction is defined as the decrease in 

thickness of sediments as a result of increase in vertical 

compressive stress and is synonomous with "one-dimensional 

consolidation" as used by engineers. The term "compaction" 

is applied both to the process and to the measured change in 

thickness.

In thick fine-grained beds, compaction is a delayed process 

involving the slow escape of pore water and the gradual 

transfer of stress from neutral to effective. Until sufficient 

time has passed for ultimate compaction to occur, measured 

values of compaction are transient.

VI

Consolidation. In soil mechanics, consolidation is the adjustment of a saturated soil in response to increased load, involving the squeezing of water from the pores and the decrease 

in void ratio (American Society of Civil Engineers, 1962, 

p. 85). In this report, the geologic term "compaction" is used 

in preference to consolidation, except in reporting and discussing results of laboratory consolidation tests made in 

accordance with soil-mechanics techniques.

Effective pressure or stress. Stress that is transmitted through 

the grain-to-grain contacts of a deposit and that thus affects 

its porosity, or void ratio, and other physical properties is 

called effective stress. Effective stress is the average grainto-grain load per unit area borne by the granular skeleton of 

the sediments. Above the water table, the effective stress at 

any given depth is equal to the weight per unit area of the 

overlying sediments and their contained moisture. Below the 

water table, the effective stress is the weight (per unit area) 

of sediments and moisture above the water table, plus the 

submerged weight of overlying sediments below the water 

table, plus or minus the seepage stress (hydrodynamic drag) 

produced by downward or upward components, respectively, 

of water movement through the sediments.

The total stress, p, normal to any horizontal plane of 

reference in a saturated deposit can be resolved into two 

components: a neutral stress, um , and an effective stress, p'. 

Therefore, p=p'-\-ua (Terzaghi and Peck, 1948, p. 52.)

In a complex aquifier system containing compressible 

aquitards, a given decline of head in the aquifers results in 

an immediate increase in effective stress in the aquifers. 

Within the aquitards, however, the transfer from neutral to 

effective stress occurs only as rapidly as drainage from the 

aquitard takes place. Months or years may be required to 

reach equilibrium that is, for the applied stress to become 

fully effective within the aquitard.

Dimensions: F/L2 

[L(feet of water)]

Geostatic load. The total load of sediments and water above 

some plane of reference. It is the sum of (1) the unit weight 

of sediments and moisture above the water table multiplied by their thickness and (2) the unit weight of saturated 

sediments (solids plus water) below the water table multiplied by their thickness.

Neutral pressure. Pressure produced by the head of water. 

Hydrostatic pressure does not have a measurable influence 

on the void ratio or on any other mechanical property of 

the deposits and is called a neutral pressure. The neutral 

pressure is equal to the hydraulic head multiplied by the 

unit weight of water (Terzaghi and Peck, 1948, p. 52), or

where

WM,=neutral pressure, 

7,,,=unit weight of water, and 

AM,=hydraulic head.

Neutral pressures are transmitted to the base of the deposit

through the pore water.

Dimensions: F/L2 

(L)
GLOSSARY VII

Seepage stress. When water flows through a porous medium, 

energy is transferred from the water to the medium by 

viscous friction. This energy is equal to the loss of hydraulic 

head. The force corresponding to this energy transfer is 

called the seepage force. (See Harr, 1962, p. 23.)

The total seepage force, F, at the base of an aquiclude 

across which a hydraulic head differential, H, exists, can be 

expressed as

F=H-yw-A

where yw equals the unit weight of water and A equals the 

cross sectional area. The total seepage force per unit area, 

J, referred to in this report as the seepage stress, is

F

Dimensions: F/L2

If jw is expressed in feet of water, then

J=H

(L)

This seepage stress is algebraically additive with gravitational stresses and is transmitted downward through the 

granular structure of the aquifer system below the 

aquiclude.

Specific compaction. The ratio between compaction during a 

specified period of time and the responsible increase in 

applied stress.

Dimensions: JJ/F 

(L/L)

Specific rebound. The ratio between rebound and the decrease 

in applied stress.

Dimensions: L3/F 

(L/L)

Specific unit compaction. The ratio between unit compaction 

(compaction per unit thickness) and the increase in applied 

stress, which is equal to the increase in effective stress in the 

coarse-grained beds of the aquifer system. For a given decline of head in the aquifers of a complex aquifer system 

containing compressible aquitards, ultimate specific unit 

compaction is attained when pore pressures in the aquitards 

have reached hydraulic equilibrium with pore pressures in 

the aquifers; at that time specific unit compaction equals 

gross compressibility of the system.

Dimensions L2/F 

(L/L2)

Specific unit rebound. The ratio between the unit rebound 

(rebound per unit thickness) and the decrease in applied 

stress, which is equal to the decrease in effective stress in the 

coarse-grained beds of the aquifer system.

Dimensions: L2/F 

(L/L2)

Subsidence to head-decline ratio. The ratio between land 

subsidence and the hydraulic head decline in the coarsegrained beds of the compacting aquifer system.

Dimensions: L/L

Unit compaction. The amount of compaction per unit thickness 

of the compacting deposits. Usually computed as the measured compaction in a given depth interval during a specified 

period of time divided by the thickness of the interval.

Dimensions: L/L

Unit compaction to head-decline ratio. The ratio between the 

amount of compaction per unit thickness of the compacting 

deposits and the head decline in the coarse-grained beds of 

the compacting aquifer system.

Dimensions: L/L2=L-1

STUDIES OF LAND SUBSIDENCE

LAND SUBSIDENCE DUE TO GROUND-WATER WITHDRAWAL 

TULARE-WASCO AREA, CALIFORNIA

By B. E. LOFGREN and K. L. KLATJSING a

ABSTRACT

Intensive pumping of ground water has caused more than 

800 square miles of Irrigable land to subside in the TulareWasco area, which is in the southeastern part of the San Joaquin Valley, Calif. Locally, ground-water levels declined as 

much as 200 feet between 1905 and 1964, and the maximum 

subsidence was about 12 feet by 1964. Subsidence was due to the 

compaction of the water-yielding deposits as the intergranular 

effective stresses increased.

The compacting deposits include a thick sequence of unconsolidated Quaternary continental deposits from the Sierra 

Nevada and, in the eastern part of the area, semiconsolidated 

and consolidated upper Pliocene and Pliocene(?) marine strata. 

Within the continental sequence, a thin lacustrine clay underlying the western half of the area separates a confined aquifer 

system for an overlying semiconfined aquifer system.

The magnitude and rate of subsidence are directly related to 

(1) the change in effective stress within the various compacting 

beds that results from water-level changes and (2) the thickness and compressibility of the compacting deposits. The compressibility of the deposits can be approximated either by testing selected cored samples in the laboratory or by measuring 

in the field the compaction that results from a given change 

in effective stress in a subsiding area.

The annual rate of subsidence varies greatly in direct response 

to seasonal pumping. This rate varied from an average of about 

136,000 acre-feet per year from 1948 to 1954, to 45,000 acrefeet per year from 1957 to 1959, and to 173,000 acre-feet per 

year from 1959 to 1962. During the 13 years from 1950 to 1962, 

the volume of subsidence (1.40X10* acre-ft) was roughly 10 

percent of the total ground-water pumpage (13.5X10" acre-ft).

Subsidence to head-decline ratios range from about 

0.5X10"2 foot of subsidence per foot of head decline in outlying 

areas io more than 5.0X1Q-2 foot of subsidence per foot of head 

decline where subsidence has been the most intense. This ratio, 

established during periods of continuing subsidence and waterlevel decline, is the best means now available of estimating 

future subsidence.

Subsidence at a given location will continue as long as declining water levels continue to cause increased effective

X A11 sections were written by B. B. Lofgren except for those on 

"Geology" and "Ground water," which were co-authored.

stresses. Subsidence will stop as soon as excess pore pressures 

in the aquitards are dissipated. In the southeastern part of the 

Tulare-Wasco area, subsidence was arrested in the late fifties, 

when water levels recovered as much as 130 feet in response to 

reduced pumping and increased recharge resulting from importation of water through the Friant-Kern Canal. Additional 

subsidence caused by lowering of water levels can be kept at a 

minimum by reducing withdrawal or by wider dispersal of withdrawal wells. Slight rebound of the land surface has been 

observed in areas of large water-level recovery.

INTRODUCTION

STATEMENT OF PROBLEM

Land subsidence in the San Joaquin Valley, Calif., 

has been an increasing problem for the past two decades. Most of this subsidence has been attributed to intensive pumping of ground water and to the resultant 

water-level decline. Ground-water pumpage for irrigation in this valley amounts to about one-fourth of all 

ground water pumped for irrigation in the continental 

United States. This intensive withdrawal has developed 

extensive areas of overdraft, where water-level declines 

are 100 feet to more than 400 feet in some areas. As a 

consequence, at least 3,500 square miles in the central 

and southern parts of the valley has subsided more than 

a foot. This subsidence is most severe in three major 

areas (fig. 1) : the Los Banos-Kettleman City area on 

the central west side, the Tulare-Wasco area on the 

southeast, and the Arvin-Maricopa area at the south 

end of the valley. As of 1962, maximum subsidence was 

23 feet in the Los Banos-Kettleman City area and at 

least 6 feet in the Arvin-Maricopa area. In the TulareWasco area, as of 1962, 800 square miles had undergone 

more than 1 foot of subsidence, and as much as 12 feet 

of subsidence had occurred locally since the first detailed topographic maps were prepared in 1926.

Bl
B2 STUDIES OF LAND SUBSIDENCE

Eurek;

FIGURE 1. Principal areas in California where ground-water withdrawal has caused land subsidence. Outline of Central Valley 

dashed; areas of major subsidence shaded black; areas of lesser 

subsidence hatched.

Although land subsidence has been occurring in the 

Tulare-Wasco area for more than 40 years and has been 

recognized by engineers since the late thirties, the 

causes, the rate and magnitude, and the areal extent of 

the subsidence have not been clearly understood. Settlement has occurred over such a broad area and so 

gradually that it has gone unnoticed to most residents. 

The detrimental and costly effects of subsidence, however, have been of serious concern to design and construction engineers, irrigation districts, and landowners 

for more than 20 years.

When this investigation was initiated in 1957, the 

need for an interpretive study of the causes and effects 

of the land subsidence was readily apparent. Groundwater levels in areas of concentrated pumping had declined more than 200 feet, and the land had subsided 

more than 10 feet. Already the Friant-Kern Canal, constructed by the U.S. Bureau of Reclamation in the early 

1950's on a gentle gradient of less than 0.5 foot per 

mile, had suffered differential settlement of as much as 

2 feet. Water-distribution systems and drainage and 

flood-control structures were becoming less effective 

owing to subsidence. Water-well casings were breaking 

under the compressive stresses imposed by subsidence, 

and altitudes on topographic maps were out of date 

before the maps were published. The costly effects of 

subsidence were of concern to many people and agencies.

LOCATION AND GENERAL FEATURES OF THE AREA

The Tulare-Wasco area is in the southeastern part of 

the San Joaquin Valley, Calif., north of Bakersfield 

(fig. 2). It includes roughly 1,500 square miles of intensively farmed land on the gently westward-sloping 

alluvial plain between the lofty Sierra Nevada on the 

east and the valley trough on the west.

Designated by cities near its north and south limits, 

the project area is bounded on the north by the north 

line of T. 20 S., on the south by the center line of T. 27 

S., on the west by a line roughly through the center of 

R. 22 E. (Dairy Avenue), and on the east by the 119°00' 

west longitude line. (See fig. 6.) The area-is traversed 

by U.S. Highway 99, by a network of secondary roads, 

and by main lines of two major railroads. The cities of 

Tulare and Delano, with respective 1960 populations of 

13,284 and 11,913, are the principal centers of commerce 

and, with Porterville (7,991), Wasco (6,841), and a 

dozen smaller communities, serve the social and commercial needs of the dominantly agricultural economy.

The climate of the Tulare-Wasco area is characterized by hot, dry summers and mild winters. Precipitation occurs principally as rain between December and 

March and averages about 9 inches a year. Occasional 

violent thunderstorms over local areas of the foothills 

contribute the only summer rainfall. Summer midday 

temperatures frequently exceed 100° F, and day and 

night temperatures may differ by more than 40 degrees.

Water for irrigation in the Tulare-Wasco area is 

obtained both from surface-water sources and from 

wells. Irrigation diversions from the Tule, Kaweah, 

and Kern Rivers and from the Friant-Kern Canal since 

1950 constitute the principal surface-water supply (fig. 

13). Three secondary streams, Deer Creek, White River, 

and Poso Creek, also are significant sources of irrigation water. Ground water has been used for irrigation 

in this part of the valley since about 1885, largely to 

supplement surface-water supplies. Ground-water withdrawal increased greatly from the 1920's to 1950 and 

far exceeded the natural and artificial replenishment 

to the ground-water reservoir until the large import of 

surface water through the Friant-Kern Canal, beginning in 1950, decreased demand from wells and supplied 

a new source of replenishment to the ground-water 

body.

SCOPE OF INVESTIGATION AND PURPOSE OF REPORT

In December 1954, after several preliminary planning conferences, an Inter-Agency Committee on Land 

Subsidence in the San Joaquin Valley was formed by 

concerned Federal and State agencies to plan and coordinate subsidence investigations. As one result of the
36°30'

LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

120°00' 119-30' 119°00'

B3

36 "00

35°30' 

35°00

KINGS CO KHTULARE_CO 

KERN CO f\\ KERN CQ

EXPLANATION

Coast Ranges River flood plains 

and channels

Maricopa :'.; : ^V-v':'-;:':V.'-.vX-.' ';

Dissected uplands Overflow lands and 

lake bottoms

FIGURE 2. Principal geomorphic features of southern San Joaquin Valley and area of this report. Modified from Davis and others,

1959, pi. 1.)
B4 STUDIES OF LAND SUBSIDENCE

interagency planning, an intensive investigation of 

land subsidence in the San Joaquin Valley was begun 

by the U.S. Geological Survey in 1956, in financial cooperation with the California Department of Water 

Kesources. The objectives of the cooperative investigation are:

1. To obtain vertical control on the land surface adequate to define the extent, rate, and magnitude 

of subsidence. The vertical control program is a 

companion project of the U.S. Coast and Geodetic 

Survey, which that agency has carried on since 

1960 in financial cooperation with the California 

Department of Water Resources.

2. To determine causes of the subsidence, the relative 

magnitude attributable to the different causes, 

and the depth range within which compaction is 

occurring.

3. To furnish criteria for estimating the rates and 

amounts of subsidence that might occur under assumed hydrologic change; to determine whether 

any part of the subsidence is reversible and, if so, 

to what extent; and to suggest methods for decreasing or stopping subsidence.

Because the subsidence in the San Joaquin Valley is 

concentrated in three nearly independent areas, the cooperative studies by the Geological Survey were divided into three project areas spanning the areas of 

major subsidence. These are the Los Banos-Kettleman 

City, Tulare-Wasco, and Arvin-Maricopa areas of figure 

1. The Tulare-Wasco area of this report is the central 

of these three project areas. Cooperative subsidence 

studies in the other two areas are continuing and interpretive reports are in preparation. The objectives 

just listed are common to the investigations in all three 

areas.

The purpose of this report is to describe the geologic 

framework and the aquifer systems of the ground-water 

reservoir; to present the history of ground-water withdrawal and its effects on water levels in the several 

aquifer systems; to describe the land subsidence; to 

report on the field measurements of compaction; to 

show the relation of land subsidence and the compaction of the sediments to water-level decline and recovery; to furnish criteria for estimating subsidence that 

might occur under assumed hydrologic change; to furnish evidence on whether any part of the subsidence is 

reversible; and to suggest methods for decreasing or 

stopping the subsidence.

Concurrently with the cooperative subsidence studies, 

the Geological Survey is carrying on a closely allied 

Federal research project on the Mechanics of Aquifer

Systems, which is directed toward determining the principles controlling the compaction or expansion of 

aquifer systems resulting from change in grain-to-grain 

load caused by change in internal fluid pressure. This 

Federal project has been utilizing areas of rapid land 

subsidence, including those in the San Joaquin Valley, 

as field laboratories for the study of compaction of 

sediments in response to decrease in fluid pressure. The 

two projects, Federal and cooperative, have benefited 

mutually from the closely allied studies.

Four reports prepared as a part of the Federal project on Mechanics of Aquifer Systems are pertinent to 

land-subsidence studies in the Tulare-Wasco area. The 

first report (Johnson, Moston, and Morris, 1968) describes the results of laboratory tests on cores from eight 

core holes in subsiding areas in central California, including two drilled in the Tulare-Wasco area. For these 

two core holes, the laboratory studies included tests of 

physical and hydrologic properties for 157 samples by 

the Denver Hydrologic Laboratory of the Geological 

Survey and consolidation and rebound tests for 22 cores 

by the Earth Laboratory of the U.S. Bureau of Reclamation. Results of the tests have been utilized in this 

report, in particular for the computation of compaction 

by means of Terzaghi's soil-mechanics theory (Terzaghi 

and Peck, 1948).

The second Federal report (Meade, 1964) is a review 

of the pertinent literature on the factors influencing 

the water content and clay-particle fabric of clayey 

sediments under increasing overburden pressures.

The third Federal report (Meade, 1967) describes the 

petrology of the cored sediments with special reference 

to particle-size distribution and clay-mineral assemblages (determined by X-ray diffraction methods). 

The characters of the clay-mineral assemblage in sediments is one of the factors that determines the amount 

of compaction that occurs in response to an increase in 

effective stress. Meade's findings with respect to claymineral assemblages in cored sediments in the TulareWasco area are summarized briefly at the end of the 

geologic section of this report.

The fourth Federal report (Meade, 1968) is a study, 

partly statistical, of the factors that influence the pore 

volume and the compaction of the water-bearing sediments in the subsiding areas of central California. For 

the Tulare-Wasco area, Meade examined the effect of 

particle size on void ratio of alluvial-fan samples. Also, 

for fine-grained sediments from the Richgrove core 

hole, he examined the relations of void ratio to depth of 

burial, type of deposit, and overburden load and the 

relations of montmorillonite particle orientation to 

depth of burial and type of deposit.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B5

The investigation in the Tulare-Wasco area, which 

was started in August 1957, was made under the general 

direction of J. F. Poland, research geologist in charge 

of subsidence studies. B. E. Lofgren, the project chief, 

was assisted by R. L. Klausing intermittently from 

September 1957 to September 1962. Klausing made a 

field canvass of wells and collected well records in the 

northern part of the area and contributed substantially 

to the interpretive work and to the sections of the report 

on geology and ground water. R. L. Ireland assisted in 

the installation of compaction and water-level recorders 

and has had primary responsibility for their maintenance and for the plotting and filing of records.

Although the principal investigation of subsidence in 

the Tulare-Wasco area is completed, the operation of 

field installations for measuring compaction and waterlevel change will probably be continued to obtain more 

specfic information on compaction and subsidence in 

certain critical areas. These are areas where field data 

collected to date have not adequately resolved the problem of the depth distribution of compaction and also 

areas where sensitive compaction recorders are supplying information critical to a better understanding of 

the response of sediments to changes in effective stress 

as defined by water-level change. Periodic releveling of 

the Tulare-Wasco area at about 5-year intervals should 

be continued as long as water levels continue to decline 

and land subsidence remains a problem. Subsidence 

maps for these intervals will define the extent of the subsidence and will serve as a basis for interpreting the 

continuing compaction-recorder data.

PREVIOUS INVESTIGATIONS

During the 1880's, W. H. Hall 2 made hydrologic 

studies in the San Joaquin Valley and described early 

ground-water conditions in the Tulare-Wasco area, 

Grunsky (1898) reported on the early irrigation methods in the area between Bakersfield and Visalia. Between 1905 and 1910, field studies were made by the 

Geological Survey (Mendenhall and others, 1916) on 

the ground-water resources of the San Joaquin Valley 

describing occurrence and use of ground water before 

extensive exploitation began.

Hydrologic data utilized in this study are contained 

in several reports by the State of California, including 

the following: California Department of Engineering 

(1921), California Department of Public Works (1922, 

1929), and California Water Resources Board (1951).

2 Unpublished reports, field notes, and hydrologic maps of the San 

Joaquin Valley, Calif., on file in the archives of the California Department of Water Resources.

Additional hydrologic data have been reported in 

studies by Harding (1927, 1949).

Several investigations of ground-water conditions 

and occurrence in the southern part of the San Joaquin 

Valley, made by the Geological Survey since 1950 in 

cooperation with the California Department of Water 

Resources, have furnished basic data pertinent to this 

investigation. An extensive study of ground-water conditions and storage capacity in the San Joaquin Valley 

(Davis and others, 1959) included the Tulare-Wasco 

area and thus furnished background information. A detailed study by the Geological Survey (Hilton and 

others, 1963) of ground-water conditions in the Terra 

Bella-Lost Hills area, which includes the southern twothirds of the Tulare-Wasco area, resulted in the collection and assembling of much of the basic well data used 

in this present study. A detailed investigation of the 

ground-water conditions in the Hanford-Visalia area, 

which includes the northern third of the Tulare-Wasco 

area, is currently in progress (M. G. Croft, oral conimun., 1965). Data on wells within the Tulare-Wasco 

area, derived from the investigations of Hilton and 

Croft, have been assembled in two open-file reports (Hilton and others, 1960; Gordon and Croft, 1964).

Ingerson (1941) published the first report describing 

land subsidence in the Tulare-Wasco area. Poland and 

Davis (1956) outlined three areas of active subsidence 

in the San Joaquin Valley and prepared a 1948-54 subsidence map for the Tulare-Wasco area. This study was 

followed by a progress report through 1957 (InterAgency Committee, 1958) of subsidence investigations 

by a committee representing several Federal and State 

agencies. The background data from all these earlier 

studies have been freely drawn on for this present 

report.

WELL-NUMBERING SYSTEM

The well-numbering system used in California by 

the Geological Survey and the State of California 

shows the locations of wells according to the rectangular system for the subdivision of public land. For example, in the number 23/25-16N1, the part of the number preceding the slash indicates the township (T. 23 

S.), the part between the slash and the hyphen shows 

the range (R. 25 E.), the number between the hyphen 

and the letter indicates the section (sec. 16), and the 

letter following the section number indicates the 40-acre 

subdivision of the section as shown in figure 3. Within 

each 40-acre tract, wells are numbered serially, as indicated by the final digit of the well number. Thus, well 

23/25-16N1 is the first well to be listed in the SW% 

SWi/4 sec. 16, T. 23 S., R. 25 E. Wells other than water
B6 STUDIES OF LAND SUBSIDENCE

wells and exploration test holes are indicated by location 

numbers without the final digit. For example, an oil 

test hole in the SW^NW^ sec. 33, T. 21 S., R. 25 E., 2 

miles east of Pixley is designated as 21/25-33E. The 

entire Tulare-Wasco area lies south and east of the 

Mount Diablo base line and meridian; therefore, the 

foregoing abbreviation of the township and range is 

sufficient.

D

E

M

N

C

F

L

P

B

G

K

Q

A

H

J

R

FIGDRE 3. Well-numbering 

system.

COLLECTION OF DATA AND FIELD PROGRAM

When this investigation was begun, a large volume 

of basic data drillers' logs, electric logs, core-hole 

logs, and water-level measurements collected in earlier and concurrent studies by the Geological Survey was 

available to the authors. Most of these records had been 

obtained initially from the California Department of 

Water Resources, the U.S. Bureau of Reclamation, and 

the irrigation districts. A detailed field canvass of about 

2,000 wells was made during the early part of the investigation, and this canvass included the assembling 

of additional electric and drillers' logs and water-level 

records. Also, several months were spent reviewing the 

general geology of the area and preparing the geologic 

sections used in this report. After review of these data, 

the principal hydrologic units of the area were defined, 

and a selection was made of representative observation 

wells tapping the various aquifers.

As part of this investigation, two core holes were 

drilled in areas of maximum subsidence: one (23/25- 

16N1) near Pixley, 760 feet deep and cored to 752 feet; 

the other (24/26-36A2) at Richgrove, 2,200 feet deep 

and cored to 2,180 feet. Results of tests of selected core 

samples from these two sites have been reported by 

Johnson, Moston, and Morris (1968) as part of the 

Mechanics of Aquifer Systems studies. Also, paleontologic studies made by Lohman (Klausing and Lohman, 

1964) of fossils from cores of the Richgrove hole have 

assisted in the dating of the deposits in this part of the 

valley.

Eleven compaction recorders and six water-level recorders were installed between September 1957 and

June 1959 to furnish specific data on compaction and 

on the relation of compaction of the water-bearing deposits to changes in ground-water level in areas of 

rapid subsidence. During the investigation, installation 

and maintenance of these recorders have represented a 

substantial part of the field program. Interpretive results from these installations have been the basis for 

many of the conclusions made in this report. Table 8 

gives the location and length of records available for 

each of the recorders maintained during this investigation.

Unpublished data from 19 core holes drilled by the 

Bureau of Reclamation in 1950-52 have been used extensively in this study. These records include electric 

and descriptive logs of the core holes, together with 

particle-size analyses and permeability test data. Table 

1 gives information on the core holes that have been 

drilled in the Tulare-Wasco area, and their locations 

are shown in figure 11.

TABLE 1. Core holes in the Tulare-Wasco area 

[Location of core holes shown in figure 11]

Core hole Year 

drilled

Depth Drilled 

(ft) by

Cored interval (ft)

20/23-8D-. _ ...

20/25-14F. ______

20/26-24K1.. .

21/24-31D1 

35Ml_.._.

21/26-1Q1- 

6F1. __ ..

35J2 .

22/26-6F1.......

23/23-33 Al. _.

23/24-16R1 

23/25-9Q2 ... .

16N1... ...

23/26-8R1 .

24/25-2H1 .

24/26-36A2 -

25/23-29 Al 

25/24-15H1. 

25/25-22D1 ...

25/26-16P1- -

27/23-1R1. ...

... 1952

... 1951

... 1951

... 1950

... 1950

... 1951

... 1951

... 1951

... 1951

... 1951

... 1951

... 1951

... 1958

... 1951

... 1952

.. 1959

 1952

 1952

... 1952

 1952

.. 1952

730

1,000

1,070

1,180

1,490

700

900

700

700

1,200

1,400

770

760

90

1,188

2,200

800

600

1,291

1,170

1,160

USER

USER

USER

USER

USER

USER

USER

USER

USER

USER

USER

USER

USGS

USER

USER

USGS

USER

USER

USER

USER

USER

12 to 700.

10 per 100.

Continuous.

10 per 100; continuous

340-430.

1,200 to 1,330.

10 per 100 below 290.

10 per 100.

100 to 700.

10 per 100.

0 to 800.

10 per 50 from 0-400;

10 per 100 below 400.

10 per 50.

10 per 40 to 250; continuous 250-752.

10 per 50.

Do.

50-1,900; 10 per 40

below 1,900.

About 75 percent.

10 per 50.

Do.

0-500; 10 per 100

below 500.

0-800; 10 per 100

below 800.

ACKNOWLEDGMENTS

The cooperation of numerous landowners and irrigation districts in supplying information vital to this investigation is acknowledged. Special credit is expressed 

to the Pixley Irrigation District for purchasing the test 

site for the Pixley core hole and to Vincent B. Zaninovich and Sons for permission to drill the Richgrove 

core hole in their headquarters area. Particular assistance has been rendered by the Pacific Gas and Electric 

Co., the Southern California Edison Co., the Southern 

Pacific Co., and the Delano-Earlimart and Rag Gulch 

Irrigation Districts. To the various well drillers, oil
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B7

companies, and service companies, appreciation is extended for supplying drillers' logs and electric logs 

used in this study. Also, the cooperation and assistance 

of local, State, and Federal agencies in furnishing data 

throughout the investigation are gratefully acknowledged. The U. S. Bureau of Keclamation and the California Department of Water Resources have been 

particularly helpful throughout the investigation.

The U.S. Coast and Geodetic Survey provided the 

leveling data used in preparing almost all the subsidence 

maps and graphs in this report and has been most 

cooperative in extending level lines to compactionrecorder sites. In 1964, the Coast and Geodetic Survey 

made an unscheduled circuit through the area of most 

rapid subsidence. Since 1960, the vertical control program of the Coast and Geodetic Survey has been carried 

on in financial cooperation with the California Department of Water Kesources.

GEOLOGY 

GEOLOGIC SETTING

The San Joaquin Valley represents roughly the southern two-thirds of the Central Valley of California, extending from the combined delta of the San Joaquin 

and Sacramento Elvers on the north to the Tehachapi 

Mountains on the south, a distance of 250 miles. The 

relatively flat floor of the San Joaquin Valley overlies 

thousands of feet of alluvial, lacustrine, and marine deposits that have accumulated in the valley as the trough 

has been lowered and the adjacent mountains have been 

elevated.

The San Joaquin Valley is a structural trough, whose 

main axis trends northwest-southeast to the west of the 

valley's drainage axis. The valley is bordered on the 

east by the granitic complex of the Sierra Nevada and 

on the west by the folded and faulted sedimentary, 

volcanic, and metamorphic rocks of the Coast Kanges. 

The highly deformed sedimentary deposits and granitic rocks of the Tehachapi and San Emigdio Mountains 

form the south boundary of the valley. On the north the 

San Joaquin Valley is open to the Sacramento Valley, 

a northward extension of the same structural system.

Throughout Late Cretaceous and much of Tertiary 

time the San Joaquin Valley was the site of marine deposition, and thousands of feet of shallow-water marine 

sediments were deposited in this geosyncline. Presently, 

overlying these marine sedimentary deposits are continental deposits of late Tertiary and Quaternary age. 

In aggregate, these marine and continental deposit? 

form an immense wedge which thickens from east to 

west, and from north to south, and attains a thickness

in excess of 22,000 feet at the axis of the structural 

trough at Elk Hills (deLaveaga, 1952, p. 100). In the 

extreme south end of the valley, the maximum thick: 

ness of the sediments of Tertiary and Quaternary age is 

about 28,000 feet (deLaveaga, 1952, p. 103). The deposits of continental origin, whose thickness exceeds 

15,000 feet at the south end of the valley, occur as successive layers of interfingering lacustrine, deltaic, floodplain, and fan deposits. These continental deposits have 

been tilted to the west and downwarped, and their base 

is now several hundred to many thousand feet below sea 

level. This very slow downwarping of the valley trough 

is probably continuing, but at a rate too small to be 

significant in this study.

The present form of the San Joaquin Valley is chiefly 

a result of tectonic movement during late Tertiary and 

Quaternary time. Structural deformation during 

Quaternary time has occurred principally along the 

south and west borders of the valley, where marine and 

continental rocks are tightly folded and faulted and 

where elevated stream terraces and deformed strata 

give ample evidences of recent tectonic activity. Deformation along the east side of the valley has consisted 

primarily of uplift and westward tilting of the Sierra 

Nevada block (which extends westward beneath much 

of the valley) and the resultant westward tilting of the 

overlying sediments. For a more extensive discussion 

of the general geology and ground-water conditions in 

the San Joaquin Valley, reference is made to earlier 

studies by Davis and coworkers (1959 and 1964).

PHYSIOGRAPHY

The Tulare-Wasco area is in the southeastern part of 

the San Joaquin Valley and is bordered on the east by 

the foothills and mountain block of the Sierra Nevada. 

Figure 2 delineates the principal geomorphic features of 

the southern third of the San Joaquin Valley and of the 

Tulare-Wasco area.

Except for the dissected uplands in its southeastern 

part, the Tulare-Wasco area is a gently westwardsloping plain ranging in altitude from 500 to 600 feet 

on its east margin to 200 feet on the dry bed of Tulare 

Lake. In large part, this plain represents a surface of 

aggradation immediately underlain by deposits of Recent age laid down by the westward-flowing streams. In 

the northeast corner of the area, deeply weathered 

granitic and metamorphic rocks of the Sierra Nevada 

rise abruptly above the valley surface. Also, inliers of 

old crystalline rocks project through the alluvium and 

form rocky hills above the valley plain near the mountain front. These inliers reveal the process of gradual 

burial of the rugged mountain block.
B8 STUDIES OF LAND SUBSIDENCE

South of the Tule River, the dissected foothill belt of 

Tertiary and Quaternary marine and continental rocks 

separates the crystalline complex of the Sierra Nevada 

from the alluvial deposits of the valley plain. This dissected belt is in marked contrast to the alluvial plain 

with respect to physiography and underlying sediments 

as well as agricultural use and farming practices. Thus, 

a sharp line of demarcation separates the highly productive vineyards, citrus groves, and cultivated fields on 

the valley plain from the low-yield dry farms and 

parched ranges of the largely undeveloped foothills.

As shown in figure 2, the Tulare-Wasco area includes 

the following five geomorphic units as classified by 

Davis, Green, Olmsted, and Brown (1959, pi. 1): (1) 

overflow lands and lake bottoms in the west-central part 

of the area, representing the historically inundated lake 

bottom of Tulare Lake, (2) alluvial plains and fans of 

low relief that occupy three-quarters of the area, (3) 

flood-plain and channel deposits that occur as narrow 

strips along three streams extending onto the alluvial 

plain from the east, (4) dissected uplands (foothills) in 

the southeast corner of the area and in the ridge of older 

sediments in the southwest corner, and (5) bedrock outcrops of the Sierra Nevada near Porterville and 

Lindsay.

TULARE LAKE

Tulare Lake bed, which has been the site of lacustrine 

deposition during most of Quaternary time, has been 

largely dry since 1919. Today Tulare Lake receives water 

during high-water periods from the Kaweah and Tule 

Rivers and possibly, during exceptional floods, from the 

Kings and Kern Rivers, Deer Creek, and several small 

intermittent streams. Its natural boundary has been 

greatly altered by construction of levees and other reclamation work. The altitude of the lowest point of the 

lakebed, 10 miles west of the study area, is now about 

180 feet above mean sea level.

According to Mendenhall, Dole, and Stabler (1916, p. 

281), Tulare Lake filled and overflowed northward to 

the San Joaquin River three times during the period 

between 1848, the beginning of record, and 1906; these 

spills occurred in 1861-63,1867-68, and 1878 (Harding, 

1949, p. 30), when the water level rose to 220 feet above 

sea level. Since 1906, the maximum observed altitude 

of the lake surface occurred in late June 1941 at 

196,8 feet above sea level (maximum depth of water 

about 17 ft). At this high stage, the shore of the transient lake was just west of the study area. The Tulare 

Lake bed has remained dry since August 1958. Today 

most of the lake bottom area is diked, drained, and intensively farmed. Most of the former inflow from the 

Kings River has been regulated since December 1952 

by the Pine Flat Dam.

GEOLOGIC UNITS

The deposits penetrated by wells in the Tulare-Wasco 

area and also the underlying sediments and bedrock 

are divided, for purposes of this report, into five geologic 

units. In descending order of occurrence, these are: (1) 

a thick sequence of unconsolidated continental deposits 

derived from the Sierra Nevada that constitutes the 

principal ground-water reservoir in the area, (2) semiconsolidated and consolidated upper Pliocene and Pliocene(?) marine strata, tapped by water wells in the 

eastern part of the area, (3) the Santa Margarita Formation as used by Diepenbrock (1933), a thin marine 

sand that is tapped by water wells in the vicinity of 

Richgrove, (4) an undifferentiated sequence of lower 

Tertiary sands and silts, and (5) the crystalline basement complex. The age and general character of these 

geologic units are summarized in table 2 and are 

discussed in greater detail in succeeding pages.

CONTINENTAL DEPOSITS FROM THE SIEBBA NEVADA

The gently sloping land surface of the Tulare-Wasco 

area is underlain everywhere by unconsolidated continental deposits derived from the Sierra Nevada; these 

deposits range in thickness from 0 feet to at least 3,000 

feet. They consist chiefly of alluvial, lacustrine, and 

flood-plain deposits which form a westward-thickening 

wedge of Sierran detritus (figs. 4, 5). As shown in 

figure 5 and on east-west geologic sections A-A" and 

B-B' (figs. 4, 5; for location see fig. 6), this sequence 

of poorly bedded and generally poorly sorted sediments 

ranges in thickness from 0 to about 800 feet along the 

east boundary of the area and thickens abruptly to the 

west. The maximum thickness of about 3,200 feet was 

measured north of Alpaugh (geologic section D-D', fig. 

10). As shown in table 2, these continental deposits 

range in age from late Pliocene to the present, and are, 

in general, correlative with the Tulare Formation and 

younger deposits to the west, with the upper part of the 

Kern River Series of Diepenbrock (1933) to the south, 

and with the continental deposits, undifferentiated, and 

younger deposits of Hilton, McClelland, Klausing, and 

Kunkel (1963) in the Terra Bella-Lost Hills area. For 

the purposes of this investigation, these deposits are 

called continental deposits from the Sierra Nevada.

Three major facies are recognized in the continental 

deposits (figs. 4, 5): oxidized alluvial deposits, reduced 

flood-plain and lacustrine deposits, and lacustrine clays.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA 

TABLE 2. Geologic units of the Tulare-Wasco area

B9

Geologic age

Quaternary

Tertiary

Recent to 

Pliocene

Pliocene

Miocene

Miocene 

and Eocene

Pre-Tertiary

Depositional 

environment

Continental (alluvial fan,flood plain, and lacustrine)

Marine

Geologic unit

Continental deposits from the 

Sierra Nevada

Upper Pliocene and 

Pliocene(?) marine strata

Santa Margarita Formation 

as used by Diepenbrock 

(1933)

Tertiary sedimentary deposits, 

undifferentiated

Sierra Nevada basement 

complex

Thickness » 

(ft)

0-3,200

630-2,500±

150-525

200-1,500+

General character

Interbedded gravel, sand, silt, and 

clay. Principal water-producing 

zone.

Siltstone, clayey, diatomaceous, with 

numerous thin interbeds of quartzose sand. Limited ground-water production.

Sand, fine to coarse, arkosic, some 

gravel. Local water-producing zone.

Semiconsolidated to consolidated sand, 

silt, and clay.

Granite, gneiss, and schist.

Generally equivalent geologic units 

as described by others

Upper part of Kern River Group of 

Park and Weddle (1959); upper part 

of Kern River Series of Diepenbrock 

(1933); Tulare Formation and overlying deposits (Woodring and others, 

1940); Tertiary and Quaternary(?) 

deposits, undifferentiated, and overlying strata of Hilton, McClelland, 

Klausing, and Kunkel (1963).

Lower part of Kern River Group of 

Park and Weddle (1959); lower part 

of Kern River Series of Diepenbrock 

(1933); part of San Joaquin Formation (Woodring and others, 1940).

Round Mountain Silt of Diepenbrock 

(1933); Olcese Sand of Diepenbrock 

(1933); Freeman-Jewett Silt of 

Weaver and others (1944); Vedder 

Sand of Wilhelm and Saunders 

(1927) ; Walker Formation of Wilhelm 

and Saunders (1927).

1 Thickness from geologic sections.

These facies represent distinct depositional environments and are differentiated by their color and texture 

and by the state of preservation of plant remains as revealed in well cores or samples. In general, the oxidized 

alluvial deposits are thickest in the eastern part of the 

area and interfinger with and overlie the reduced deposits ; also, they are characterized by their yellow, red, 

and brown color and by highly weathered, crumbling 

feldspar grains. The reduced lacustrine and flood-plain 

deposits, on the other hand, are recognized by their drab 

green, blue, and dark-gray color, well-preserved plant 

remains, and an ever-present dissemination of iron 

sulfide.

Although several distinct tongues of lacustrine clay 

extend eastward and southward from the Tulare Lake 

bed area where a nearly continuous sequence of lake 

clays has accumulated, only the one most significant clay 

layer has been delineated in the geologic sections. This 

extensive diatomaceous clay, which is in the upper part 

of the Tulare Formation, has been designated the Corcoran Clay Member of the Tulare Formation (InterAgency Committee, 1958, p. 119-120). Except for the 

Corcoran Clay Member which represents nearly valleywide lake deposition in part of Pleistocene time, all 

the continental deposits in the Tulare-Wasco area are 

believed to be derived from a Sierran source.

Within the Sierran continental sequence in the eastern 

part of the area (figs. 4, 5), 200-250 feet of slightly 

weathered permeable alluvial deposits is underlain by 

300-700 feet of highly weathered less permeable alluvium. Data from several core holes indicate that for the 

most part the upper deposits are relatively fresh, sandy, 

and noncalcareous, whereas the lower weathered deposits are decomposed, much finer grained, and highly 

calcareous. The sharp break separating these two sequences, which probably represents 'both <a lapse of time 

and a transition in weathering regime, is clearly shown 

on many electric logs. It is especially well displayed at 

a depth of about 255 feet in the electric log of core hole 

24/26-36A2 near the east end of geologic section B-B' 

(fig. 5).

In core hole 23/25-16N1 (fig. 7), about 3 miles south 

of Pixley, the entire thickness of unconsolidated deposits penetrated was of continental origin. (Also see fig. 

4.) All deposits, except the 16-foot thickness of the 

Corcoran Clay Member (280-296-foot depth interval, 

fig. 7) and a very thin clay layer at the 730-foot depth, 

are oxidized alluvial-fan deposits. In general, the deposits in this core hole consist of thin heterogeneous 

beds of yellowish-brown sand, silt, and sandy clay. The 

sand fraction predominates and consists largely of fine 

to coarse subangular grains of quartz and feldspar.

About 8 miles west of core hole 23/25-16N1, the oxidized fluvial deposits intertongue with poorly sorted, 

reduced flood-plain and lacustrine sediments (geologic 

section A-A", fig. 4). Beneath Tulare Lake bed in the 

vicinity of Alpaugh (figs. 6, 10), well-sorted reduced 

lacustrine strata of clay, silt, and sand constitute the 

principal sediments in about the lower half of the continental deposits and indicate more or less continuous

332-133 O 69 2
BIO STUDIES OF LAND SUBSIDENCE

^Oxidized alluvial-fan deposits

Sligitly

iWeathere

Oxidized alluvial-fanf 

deposits

Reduced flood-plain

Base

lacustrine(?)

water ^.vV

riNt^v °/// 

/

^,1.^ -Q EXPLANATION

^ ____________

*«<

Xs" '

UPPER

PL\OC*

Boundary of geologic unit

Boundary of stratigraphic 

horizon

Lithologic contact

Boundary of Sierra 

Nevada basement 

complex

Base of fresh water 

2 4 6 MILES

^r

VERTICAL EXAGGERATION X 26

deposits

r

SIERRA NEVADA 

BASEMENT 

COMPLEX

FIGURE 4. Geologic section A-A" through the Pixley core bole. See figure 6 for well locations.

lake deposition through this interval. In general, evidence from electric logs of oil-test holes indicates that 

the water in these deposits is too saline for ordinary 

uses.

At Richgrove, core hole 24/26-36A2 (fig. 8) penetrated 744 feet of continental deposits overlying a thick 

sequence of marine siltstone. Oxidized alliivial-f an deposits, consisting predominantly of yellowish-brown 

poorly sorted sands, compose the upper 620 feet of the 

continental section (fig. 5). Underlying the oxidized 

zone is 124 feet of greenish-gray reduced flood-plain 

deposits. As shown in north-south geologic section C-C' 

through this core hole (fig. 9), the threefold sequence of 

upper slightly weathered oxidized alluvium, intermediate highly weathered calcareous oxidized alluvium, and 

lower reduced flood-plain deposits persists within the

continental section along the east side of the TulareWasco area.

As shown by north-south geologic section D-D' (fig. 

10), the sequence of interbedded continental deposits 

attains a maximum thickness of about 3,200 feet north 

of Alpaugh. A thick tongue of oxidized alluvial deposits beneath the Corcoran Clay Member extends 

northward about 10 miles from the south end of section 

D-D'. This tongue is inferred to represent deposition 

on an ancestral Kern River fan.

Most of the ground water pumped in the TulareWasco area comes from the unconsolidated continental 

deposits (figs. 4, 5, 9, 10). These deposits, for the most 

part, are moderately permeable, and the yields of most 

wells tapping this geologic unit range from 400 to 1,500 

gpm (gallons per minute).
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA Bll

E

gg^^^ .& o%?

Reduced flood-plain and lacustr

FIGURE 5. Geologic section B-B' through the Richgrove core hole. See figure 6 for location of wells and figure 4 for explanation.

CORCORAN CLAY MEMBER OF THE TULARE FORMATION

A well-sorted bed of diatomaceous lake clay occurs 

within the continental deposits in the western part of 

the Tulare-Wasco area. This clay bed was first identified and described by Frink and Kues (1954) and 

later was mapped in more detail by Davis, Green, Olmstead, and Brown (1959, p. 76-81, pi. 14), who showed 

that it extended beneath at least 5,000 square miles of 

the San Joaquin Valley. It has been designated the Corcoran Clay Member of the Tulare Formation (InterAgency Committee, 1958, p. 119-120). The Corcoran 

serves not only as the one distinctive geologic marker in 

the continental deposits but also as the principal confining bed beneath about half the San Joaquin Valley.

The Corcoran Clay Member underlies about half of 

the Tulare-Wasco area (fig. 11), mostly west of U.S.

Highway 99. The boundary of the Corcoran is 2-3 miles 

east of U.S. Highway 99 from Tulare to Earlimart; 

there it swings to the southwest crossing the south 

boundary of the study area west of Wasco. Near the 

outer margin, the lake clays give way to well-sorted 

sand and silt which in turn grade into, and interfinger 

with, poorly sorted reduced flood-plain and oxidized alluvial deposits.

The thickness of the Corcoran ranges from 0 feet at 

its east boundary to about 110 feet at Alpaugh (fig. 

10). Within most of its extent, core logs and electric 

logs indicate it to be a well-defined and distinct silty 

clay or clayey silt, bounded above and below by coarser, 

more permeable deposits. At some places, however, the 

upper or lower contact is indefinite and subject to more 

than one interpretation. North of Alpaugh, for ex-
B12 STUDIES OF LAND SUBSIDENCE

R 22 E 119°3Q' R 23 E R 25 E 15 R 27 E 119 = 00' R 28 E

EXPLANATION

Unconsolidated sedimentary deposits of late Tertiary and 

Quaternary age

Consolidated sedimentary rocks

Sierra Nevada basement 

complex

0 31L2

Well and number for which electric log is shown on geologic

Eastern edge of Tulare Lake bed

7 V

 / 

34R1 I TULARE CO

FIGURE 6. Location of geologic and hydrologic sections shown in figures 4, 5, &, and 10.

ample, the Corcoran as defined in figure 10 is immediately overlain by clay as much as 90 feet thick. (See 

electric logs for wells 22/23-33A5, 22D, and 9B, 

fig. 10.) Although this overlying clay is not considered 

a part of the Corcoran in this report, it does add substantially to the overall thickness of the principal confining stratum where present. To the east, between Pixley and Wasco, a clay tongue beneath the Corcoran as 

here delimited extends beyond the east boundary shown 

in figure 11. In the Pixley core hole, the lower tongue 

is a yellowish-brown silty clay containing thin sand interbeds 330-360 feet below the land surface (fig. 7). 

M. G. Croft (oral commun., 1966) considers this tongue 

to represent an earlier phase of deposition near the 

shore of Corcoran lake. Hydraulic data from a series of 

piezometers installed near the Pixley core hole (23/25- 

16N1) indicate that this lower tongue is the principal 

confining bed locally. Throughout most of the western 

half of the Tulare-Wasco area, however, the Corcoran 

tlay Member as mapped in figures 4, 5,10, and 11 is the 

principal confining bed in the continental deposits.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B13

SPONTANEOUS 

POTENTIAL 

(millivolts)

- 4°< + <

j

ij

1

]

?

\

\

\

RESISTIVITY 

16-in. normal 

(ohms m 2 /m)

) 20 40

t^

;-s~

-f>

>^~

fl

* ==

GRAPHIC 

LOG

Continental deposits the SierraNevad from 

>-£:.:£" .

 -^.

 rrl-vL-

::lii-:::i:

^ :'-:'-:'-

tt- tt

_ ---- -

;iil jiji

Zr- Hj

Si-iii

.

SIBi

DEPTH 

(feet)

30-80

80-115

115-138

138-258

258-280

280-296

296-330

330-360

360-420

420-520

520-560

560-620

620-660

660-680

680-710

710-752

GENERALIZED LITHOLOGIC DESCRIPTION 

(from core descriptions and electric log)

Silt, sandy, loose to plastic, micaceous, yellowish-brown.

Sand, silty, loose to plastic, fine to coarse, yellowish-brown.

Silt, sandy, loose to plastic, gravelly, calcareous, micaceous, yellowish-brown.

Sand, silty, loose to plastic, fine to coarse, micaceous, yellowish-brown.

Sand, silty, clayey, fine, some coarse, calcareous near bottom, micaceous, yellowish-brown.

Clay, plastic, silty, micaceous, pale brown to bluish-gray, diatoms 1.

Sand, silty, loose to plastic, fine to coarse, micaceous, pale olive to yellowish-brown.

Clay, sandy, silty, plastic, micaceous, calcareous streaks, yellowish-brown; thin sand interbeds.

Sand, silty, fine to coarse, gravelly, micaceous, yellowish-brown; thin clay interbeds.

Sand, silty, clayey, fine to coarse, some gravel, calcareous streaks, micaceous, yellowishbrown; clay, silt interbeds.

Clay, sandy, silty, plastic, gravelly, calcareous streaks, carbonaceous material, micaceous, 

yellowish-brown; thin sand interbeds.

Sand, silty, loose to friable, fine to corase, gravelly, some biotite, yellowish-brown; clay 

interbeds.

Silt, sandy, loose to plastic, some carbonaceous material, calcareous nodules, micaceous, 

yellowish-brown; thin sand and clay interbeds.

Sand, silty, clayey, loose, fine to coarse, carbonaceous material, brown to olive.

Clay, plastic, massive, calcareous nodules, micaceous, yellowish-brown.

Sand, loose, friable, massive, fine to coarse, micaceous.

i Corcoran Clay Member of the Tulare Formation

FIGURE 7. Composite logs of core hole 23/25-16N1 near Pixley.

The structural contours drawn on the base of the Corcoran Clay Member (fig. 11) show its configuration 

and altitude. The base of the Corcoran ranges in altitude from slightly above sea level at its east edge to 

more than 600 feet below sea level northwest of 

Alpaugh. The well-defined trough trending northwest 

from the vicinity of Delano (fig. 11) represents either 

the configuration of the surface of the pre-Corcoran 

lake bottom or a downwarping of the lake deposit since 

Corcoran time. The sharpness of the trough suggests 

that the second interpretation is the more likely one.

UPPER PLIOCENE AND PLIOCENE( ?) MARINE STRATA

Underlying the unconsolidated continental deposits 

throughout the Tulare-Wasco area is a thick section of 

marine strata, chiefly siltstone, of late Pliocene and 

Pliocene(?) age (figs. 4, 5,9,10). In the Eichgrove core 

hole, this siltstone, which is diatomaceous in part, is 

differentiated from the overlying continental deposits 

by a marked change in lithology. This lithologic transition was recognized in the electric log of core hole 

24/26-36A2 (fig. 8) and was correlated with other electric logs through much of the area. On the basis of fossils recognized in a number of oil-test holes, the top of 

the upper Pliocene strata is tentatively correlated with 

the upper Mya zone described by Woodring, Stewart, 

and Kichards (1940, p. 28). (Also see fig. 5.)

At Kichgrove (fig. 8), the marine strata extend in 

depth from 744 to 1,900 feet. Partially cemented clayey 

siltstone (logged from core inspection as clay stone, but 

particle-size analyses indicate mostly silt sizes) dominates the interval, but thin sand beds occur at several 

intervals. K. E. Lohman examined a marine diatom assemblage in the depth interval between 1,141 and 1,641 

feet (Klausing and Lohman, 1964), assigned a late 

Pliocene age to this interval, and concluded that it may 

be the equivalent of the late Pliocene San Joaquin Formation of the Kettleman Hills area. The lithologic 

similarity of the siltstone through the full thickness 

from 744 to 1,900 feet suggests that the entire marine 

section from 744 to 1,641 feet should be assigned to the 

upper Pliocene; the marine siltstone from 1,641 to 1,900 

feet has been tentatively assigned to the Pliocene(?) 

(Klausing and Lohman, 1964).
B14 STUDIES OF LAND SUBSIDENCE

SPONTANEOUS RESISTIVITY

(millivolts) (ohms m2/m) 

- 40.1 + k. 0 20 40

GRAPHIC 

LOG

DEPTH 

(feet)

GENERALIZED LITHOLOGIC DESCRIPTION 

(from core descriptions and electric logs)

200

400

600

800

1000

1400

1600

1800

2000

0-230 Sand, clean to silty, yellowish-brown; silt and sandy silt interbeds; several gravelly layers.

23D-41 9 Sand, silty and clayey, fine to coarse, yellowish-brown; calcareous toward bottom, carbo 

naceous material

Al2-429 Sand, clean to silty. medium,loose, dark-yellowish-brown__________________ 

429-535 Silt, sandy, fine to coarse, moderate-yellowish-brown; some gravel, calcareous zones.

535-620 Sand, silty and clayey, fine to coarse, yellowish-brown to olive-gray 

O >='i'W: 620-637 Clay and silt, sandy, firm to lithified, brownish-to olive-gray._____________________

637-744 Sand, silty, greenish-to bluish-gray; thin interbeds of silt, clay, and claystone; some cemen 

tation.

744-779 Claystone 1 , siltstone, and silty sand, calcareous streaks, dark-bluish- to greenish-gray 

779-841 Claystone and clay, silty, with sandy layers, greenish-gray.

Claystone, silty to sandy, dark-greenish-to bluish-gray; thin interbeds of clay, silt, and 

841-1176 loose sand, plant remains; rhyolitic ash zone at 1058 ft.

___ 1176-1206 Sand, silty, clayey^fine to medium, dark-greenish- to bluish-gray.

8 ."'""""_

Claystone, silty, sandy, dark-greenish-to bluish-gray; thin interbeds of silt, sand, and fine 

1206-1369 gravel, diatomaceous, plant remains. 

_ ._ - ..

1369-1384 Sand, silty, clayey, fine to medium, bluish-gray_____________________________

1384-1500 Claystone and sand interbedded, firm to loose, dark-bluish-to greenish-gray; 10-ft sand 

layer at base, diatomaceous.

Claystone, silty, sand, bluish-togreenish-gray; interbeds of silt, sand, and fine gravel, more 

1500-1745 sand toward bottom, carbonaceous material, mollusk shells, crab remains, diatomaceous

above 1641 ft. 

15 r-L=-r>

til j;~£=.~

II

0- 5 [: £: : 1745-1818 Sand, silty, clayey, bluish-gray; claystone interbeds. mollusk shells and fish remains

1818-1900 Claystone, sandy, silty, bluish-gray; sand interbeds, mollusk shells, fish scales and teeth

carbonaceous material W ' -.--.-.- ________ __

° ^ .........

rt .Z'l.I.t*

Sand, slightly clayey, some gravel, fine to coarse, greenish-gray; carbonaceous material 

<5 d :: : : :: ~~ shell fragments 

o

I °

(/>

J The many beds in the depth interval 744- 

examination of cores are shown by pi

 1900 feet described as claystone from field 

irticle -size analyses to be chiefly siltstone

FIGUBH 8. Composite logs of core hole 24/26-36A2 at Rlchgrove. Modified from Klausing and Lohman, 1964.
2000' -

FIGURE 9. Geologic section 0-0' through the Richgrove core hole. See Sgure 6 for location of wells and figure 4 for exp
B16 STUDIES OF LAND SUBSIDENCE

y%? &7 <x &/ .<$/ &'

FIGURE 10. Gteologlc section D-D' through Alpaugh. See figure 6 for location of wells and figure 4 for explanation.

As shown in geologic section A-A" (fig. 4), the marine strata were not penetrated by the Pixley core hole, 

23/25-16N1, or by other wells on the western half of 

the section. The upper Myd zone, and thus the top of 

the marine strata, has been identified, however, in other 

deep oil-test holes in the vicinity (fig. 5), and the dashed 

formational contact of figure 4 is projected into the 

section from, wells not shown.

The thin sandstone beds in this Pliocene marine siltstone sequence are tapped by a few wells, but the overall 

transmissibility of the siltstone unit is very low; thus

it contributes little ground water to wells. Beneath 

about two-thirds of the Tulare-Wasco area, the sands 

still contain saline water that is unusable for ordinary 

purposes. Therefore, this unit is not important as a 

source of fresh water, nor is it an appreciable factor 

in the problem of land subsidence in most of the area.

SANTA MABGABITA FORMATION AS USED BY 

DIEPENBROCK (1933)

On the basis of electric-log correlations north from 

the Mount Poso oil field, the marine sand immediately
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

R 22 E 119°30'R 23 E R. 24 E. R 25 E 15' R. 26 E. R 27 E U9°00'

BIT

j____ -. _____

' ' " Terra Bella

 /-___ I 

______>_

Famoso

EXPLANATION

 400 

Structure contour

Drawn on base of Corcoran Clay 

Member; dashed where approximate. Datum is mean sea level. 

Contour interval, lOOfeet

Approximate boundary of Corcoran 

Clay Member

Control point for structure contour

9 8R1

Core hole and number of U.S. 

Bureau of Reclamation

@36A2

Core hole and number of 

U.S. Geological Survey

FIGURE 11. Structure and extent of the Corcoran Clay Member of the Tulare Formation, and location of core holes.

below the siltstone sequence is correlated with the Miocene Santa Margarita Formation as used by Diepenbrock (1933). He noted (1933, p. 13) that the name, as 

he used it, is of local significance and therefore that this 

unit may not be correlative with the type Santa Margarita Formation as defined in the vicinity of Santa 

Margarita.

Along the east side of the Tulare-Wasco area, Diepenbrock's Santa Margarita occurs as a well-defined

subsurface unit. It ranges in thickness from about 150 

feet (geologic section A-A", fig. 4) to as much as 520 

feet (geologic section C-C', fig. 9). Basinward the 

formation is represented by organic shale facies that 

may be as much as 6,000 feet thick (Hoots and others, 

1954, p. 122). About 300 feet of the Santa Margarita 

was penetrated by the Eichgrove core hole, 24/26-36A5* 

(figs. 5, 8). Core samples show the formation to consist 

of greenish-gray to bluish-gray loose to well-indurated
B18 STUDIES OF LAND SUBSIDENCE

clayey very fine to coarse arkosic sand and thin streaks 

of fine gravel.

About 20 water wells tap the Santa Margarita in 

the vicinity of Biohgrove. Most of these wells are also 

perforated in overlying aquifers and do not give specific 

information on the water-yielding characteristics of the 

Santa Margarita. Six deep irrigation wells perforated 

exclusively in the Santa Margarita, however, yield up 

to 1,950 gpm; they indicate that this unit is highly 

permeable. The Santa Margarita also serves as an important ground-water aquifer in a limited area near 

Bichgrove.

TERTIARY SEDIMENTARY DEPOSITS, 

UNDIFFERENTIATED

Beneath the sands of Diepenbrock's (1933) Santa 

Margarita Formation along the east edge of the valley 

is a sequence of semiconsolidated to consolidated sand, 

silt, and clay of Miocene or greater age which is here 

termed Tertiary sedimentary deposits undifferentiated. 

This sequence crops out in the foothills south of White 

Biver and is shown in figure 6 as consolidated sedimentary rocks of Tertiary age. Although oil in several 

nearby oil fields is derived from sediments of this unit, 

no water wells in the Tulare-Wasco area are known 

to tap these deposits. For the most part, water in these 

deposits is highly saline and unusable for most 

purposes.

Park and Weddle (1959, pi. 2) have subdivided this 

sequence of Tertiary deposits overlying the basement 

complex into the Bound Mountain Silt, Olcese Sand, 

Freeman-Jewett Silt, Pyramid Hill Sand, Vedder Sand, 

and Walker Formation. All except the Walker Formation are of marine origin. Of these, Hilton, McClelland, 

Klausing, and Kunkel (1963, table 3) consider only 

the Olcese Sand and the Pyramid Hill and Vedder 

Sands as potential sources of ground water. Potable 

water from these sands would be limited to a, narrow 

belt east of Bichgrove (fig. 5).

As observed in geologic sections A-A" (fig. 4) and 

B-B' (fig. 5) the undifferentiated Tertiary sedimentary 

deposits dip steeply valleyward and range in thickness 

from about 200 feet to more than 2,000 feet. These deposits crop out near Poso Creek and in this area have 

been described by Albright, Hluza, and Sullivan (1957, 

p. 13) and Diepenbrock (1933, p. 14-16). For a more 

detailed description of the deposits beneath the Santa 

Margarita, reference is made to Hilton, McClelland, 

Klausing, and Kunkel (1963).

SIERRA NEVADA BASEMENT COMPLEX

Bocks of the Sierra Nevada basement complex crop 

out along part of the east margin of the Tulare-Wasco

area (fig. 6) and extend westward beneath the area. 

The dominant rock types are igneous rocks ranging in 

composition from granite to gabbro and metamorphic 

rocks consisting of quartzite, schist, gneiss, and crystalline limestone. That the basement complex is found in 

wells at increasing depths in a westward direction indicates that the westward-tilted Sierran mountain block 

dips beneath the younger sedimentary deposits in this 

part of the valley (figs. 4, 5).

In general, the structural contours on top of the 

basement complex (Smith, 1964) roughly parallel the 

surface contours but do so with an apparent westward 

dip of 400-800 feet per mile. This dip generally 

steepens toward the west and also toward the south and 

thus suggests that tectonic warping in the valley trough 

accompanied the tectonic uplift of the mountain block. 

The depth of the basement complex below the land surface increases from 0 feet east of Porterville to 7,200 feet 

at Pixley and about 11,000 feet at Corcoran. For the 

purposes of this investigation, the Sierran basement 

rocks are considered both non-water bearing and noncompactible under changes in load.

CLAY-MINERAL ASSEMBLAGE IN CORED SEDIMENTS

As summarized by Meade (1964, p. 20), the removal 

of water and the compaction of clayey sediments under 

increased effective stress are complex functions of particle size, clay minerals and associated ions, interstitialelectrolyte concentration, acidity, temperature, and the 

arrangement of particles at the onset of compaction. Of 

these, particle size is perhaps the most significant factor.

The response of water-saturated clayey sediments to 

compacting stresses is directly related to forces associated with clay-mineral surfaces. Because of the large 

surface areas of clay minerals, these forces are more effective than are the gravitational forces associated with 

the particle mass. Surface effects are especially significant in the very fine grained montmorillonitic clay minerals, which have a specific surface (surface area per 

unit mass) 10-100 times as great as other clay minerals 

(Meade, 1964, p. 6). The finer grained clayey sediments 

are more porous under a given load and more compressible under a given change in load than the coarser silty 

sediments (Meade, 1964, fig. 3). Also, clays rich in montmorillonite are more porous and more compressible 

under a given load or change in load than clays that 

consist mainly of the other clay minerals (Meade, 1964, 

fig. 4).

From detailed study of core samples from the Pixley 

and Bichgrove core holes (figs. 7, 8), Meade (1967, p. 

116) found that the principal clay mineral of the sediments tapped by water wells in the Tulare-Wasco area 

is montmorillonite. Subsidiary minerals include illite, a 

kaolinite-type mineral, and vermiculite, with lesser
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B19

amounts of chlorite and a low-grade' illite-montmorillonite mixture. The average clay-mineral composition of 

these sediments is approximately as follows (Meade, 

1967, p. 117):

Montmorillonite_

Kaolinite-type mineral- ___________

Vermiculite. _____________________

Chlorite_ ________________________

Mixed-layer illite-montmorillonite_ _

Nonmarine 

sediments 

(nearest 5 

percent)

60

20

10

10

0

Trace

Marine 

siltstones 

(nearest 5 

percent)

80 

5 

5 

0 

5 

Trace

The total clay-mineral content of the sediments from 

the Pixley and Richgrove core holes is estimated 

(Meade, 1967, p. 120) to be as follows:

Total day 

minerals 

(percent)

Nonmarine sediments._____-_-_-__

Marine siltstones and sands ________

Santa Margarita Formation as used 

by Diepenbrock (1933)__________

15

25

<2

Total montmorillonite and vermicvMte

(percent)

10

20

<2

SURFACE WATER

NATURAL STREAMS

Four natural streams enter the Tulare-Wasco area 

from the Sierra Nevada on the east (fig 2). Tule River, 

the only major stream, has long been an important 

source of irrigation supply. The other streams Deer 

Creek, White River, and Poso Creek flow only intermittently and in most years supply only small quantities 

of water to the valley.

The Tule River is the only natural stream for which 

long-term discharge records are available. Figure 12 

shows the discharge of Tule River for the period of record 1902-64. During this period the locations of gaging 

stations along Tule River were moved several times, and 

the recorded discharge measurements are not entirely 

comparable throughout the period. The inconsistencies, 

however, are relatively small. The annual discharge 

of the river is here reported for the water year October 1 

through September 30. Inasmuch as changes in groundwater level, subsidence of surface bench marks, and 

computations of land subsidence and compaction are 

considered primarily on a calendar-year basis in subsequent chapters, stream discharge also is reported by 

calendar year hereafter. As shown in figure 12, the 

yearly discharge fluctuates widely from a high of about 

340,000 acre-feet in 1906 (excluding South Fork runoff) 

to less than 20,000 acre-feet in 1931 and 1961 (South 

Fork runoff included). Since the completion of Success Reservoir on the Tule River (partial regulation began in 1961), the discharge has been regulated.

Streamflow measurements of Deer Creek, White 

River, and Poso Creek were made by the Bureau of 

Reclamation for a number of years between 1952 and 

1960. In those years the annual discharge of Tule River 

represented between 65 and 75 percent of the combined 

flow of the four streams entering the Tulare-Wasco 

area. The flows of Deer Creek, White River, and Poso 

Creek composed the remaining 25-35 percent of the 

natural surface inflow. In this report the combined 

flow of these three intermittent streams has been estimated as three-sevenths of the annual discharge of 

Tule River. This quantity was the basis for the estimate 

of combined discharge of Deer Creek, White River, and 

Poso Creek shown in figure 14.

CANALS

In addition to discharge from the natural streams, 

canal diversions from the Kern and Kaweah Rivers and, 

since 1950, from the Friant-Kern Canal have been an 

important source of irrigation supply. Water is imported from the Kern River via the Lerdo and Galloway Canals of the Kern County Land Company. Prior 

to deliveries from the Friant-Kern Canal, surface water 

generally was not available after June of each year, so 

during the late summer and autumn months ground 

water was usually the only source of supply.

The Friant-Kern Canal was constructed by the 

Bureau of Reclamation as part of the Central Valley 

Project. Diverting water from Millerton Lake (storage 

capacity 520,500 acre-ft) on the San Joaquin River, the 

Friant-Kent Canal has provided a major part of the 

irrigation water used in the Tulare-Wasco area since 

1950. Water from the Friant-Kern Canal has supplemented surface supplies from the natural streams and 

has greatly reduced the ground-water pumpage within 

the canal service area.

The first 70 miles of the Friant-Kern Canal was in 

operation by July 1949. Deliveries of water were fiifet 

made to the Tulare and the Lindsay-Strathmore Irrigation Districts (fig. 13) in the fall of that year. By 

1950, construction had progressed, so that deliveries 

were being made as far south as White River and the 

Delano-Earlimart Irrigation District. During 1951, 

water deliveries extended into Kern County,-and construction was virtually completed in 1952. Contracted 

surface-water deliveries were made throughout the area 

as rapidly as distribution systems in the individual districts could be provided. The actual water deliveries to 

the various irrigation districts from the Friant-Kern 

Canal through 1964, as reported by the Bureau of Reclamation, are given in table 3. The locations of the districts 

are shown in figure 13.
B20 STUDIES OF LAND SUBSIDENCE

400

200

100

n

Tule River near 

Porterville (excludes 

South Fork)

Tule River near

South Fork near Porterville

EXPLANATION

_

-

-

-i

^

V

&

%

I

I

I

I

Porterville

South Fork near Success

South Fork

Main stem, excluding South Fork

p| At Worth Bridge 

pa below Success

11 Dam

I

rn

%.

I

I

I

I

I

&

I

I

%

W

^

22

I

I

&

I

I

!

I

1

I

1

%

^&

I

I

1

I

^

w 

%

%

<&& ^

Below Succes 

Dam; total 

discharge

s

Regulation by 

Success Dam\

^

I

11

I

I

3x

1m

1

11

i

88

II 

11 

II

1 

88

II 

I

83m

i

¥:S

1

i

1

i!i

1 

1

II

II

11

1 

1

88 

1

I 

II

88

II

1

83

p

111

pi m,

IT

8x 8s 

III

fcX; Xvl ;:;X;

II II ii

? 8S 38 38 ilii

FIGURE 12. Discharge of Tule River, 1902-64. For water year October 1 through September 30. Data from U.S. Geological Survey WaterSupply Papers 1315-A and 1735, and annual summaries since 1960.

TABLE 3. Surface-water deliveries from the Friant-Kern Canal to irrigation districts in the Tulare-Wasco area, 1949-64 

[In thousands of acre-feet per calendar year; data from U.S. Bur. Reclamation]

District > 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963

Total (rounded)......._...._...... 31 163 304 412 573 627 724 868 788 800 724 441 374 1,096 1,042

1964

Cloer .............................

Pixley... ......................

Porterville __ , ....... ._ . .

Saucelito .........................

Shatter- Wasco __________

Tea Pot Dome . .... .........

Tulare ______________ .

<; A.

................... 1.7

........... 4.3 2.2

................... 76.1

........ ........... 7.4

.._ . 8.0

............. __ .. 1.9

-.... 26.5 60.0

33.6

ft ft

11.0

Q4 9

5.3

23.5

22.3

5.0

100.1

64.8

9O f\

7.0

153.0

8.2

29.6

40 4

4.7

75.0

TO A

44 ft

13.2

196.5

8.0

2 A

9O ^

79 9

5.4

129.0

Oft f\

48 0

17.0

170.0

d. Q

5

n

29.6

QA Q

7.3

151.5

1 QK *7

52.4

17 9

211.6

4.7

0.3

9O i

105.9

7.6

159.0

0.4 .

172.3

47.5

15.6

971 A

6.6

6.4

33.7

124.0

7.1

182.9

162.0

An Q

IRQ

245.7

5.0

9 Q

33.4

2.1

m n

o n

150.1

3.0 .

0.2

150.4

44 5

17.1

226.6

23.2

5.8

6.0

30.8

32.9

101.3

6.1

152.0

0.1 .

151.3

41.5

24 0

m »

20.3 .

7.2

4.2 .

26.7

42.5

101.6

o n

101.3

1.2 .

109.8

34.1

20.1

OA Q

9.1

20.1

45.9

94.7

0.4

9.6

31.4

87 1

97 A.

21.5

io n

10.2

<; A.

16.2

36.2

76.6

3.6

8.6

32.3

0.1

169.5

53.3

18.5

326.6

48.5

21.1

6.3

48.4

46.9

130.3

3.6

11.3

211.4

0.2 .

162.3

45.0

12.7

307.7

51.8

19.6

8.9

46.7

45.3

124.5

3.2

9.6

204.0

127.7

40.6

19.1

124.7

6.0

18.9

1.0

28.9

54.9

114.6

4.4

14.5

82.2

638

i For district location and complete name, see fig. 13.

Several of the districts listed in table 3 extend beyond the boundaries of the Tulare-Wasco area. The 

amount of water shown in table 3 that is used outside 

the area, however, is small in proportion to the total 

deliveries. The tabulated deliveries of table 3 are thus 

used herein as an approximation of the total FriantKern deliveries within the Tulare-Wasco area.

SURFACE-WATER SUPPLY

Figure 13 shows schematically the quantities of surface water that were diverted for irrigation and groundwater recharge from the various sources in the TulareWasco area during 1960; it also shows the boundaries 

and names of the incorporated districts that received 

and distributed this water. Several of the quantities
LAND SUBSIDENCE, TTILARE-WASCO AREA, CALIFORNIA B21

35°45' 

EXPLANATION

DISTRICTS 1

Alpaugh I. D. 

Cloer C. S. D. 

Delano-Earlimart I. D. 

Lindmore I. D. 

Lindsay-Strathmore I. D. 

Lower Tule River I. D. 

Pixley I. D. 

Porterville I. D. 

Rag Gulch I. D. 

Saucelito I. D. 

Shafter-Wasco I. D. 

South San Joaquin M. U. D. 

Tea Pot Dome W. D. 

Terra Bella I. D. 

Tulare I. D.

1 I. D. = Irrigation District 

C. S. D. = Community Services District 

M. U. D. = Municipal Utility District 

W. D.=Water District

2 Galloway Canal from the Kern 

River

95

Diversion, in thousand 

acre-feet

6 MILES

FIGURE 13. Surface-water diversions during 1960, in thousands of acre-feet, and boundaries of incorporated districts receiving

water from the Friant-Kern Canal.

given in figure 13 are not identical to quantities in 

table 3 because, at some places, diversions to several districts have been lumped to simplify the diagram.

The approximate amounts of surface water distributed for irrigation and ground-water recharge in the 

Tulare-Wasco area from 1930 through 1964 are shown 

in figure 14. Canal imports from the Kern and Kaweah 

Rivers are not included. Neither is the measured'discharge (inflow) of Tule River corrected for outflow to 

Tulare Lake. Prior to closure of Success Dam on the 

Tule River in 1962, part of the discharge of Tule River

flowed out of the Tulare-Wasco area to Tulare Lake 

bed in years when Tule River discharge exceeded about 

130,000 acre-feet (California Department of Public 

Works, 1922, p. 40). In years of high stream discharge, 

however, canal imports from the Kaweah and Kern 

Rivers to the Tulare-Wasco area probably compensated 

for much of the outflow of Tule River discharge to 

Tulare Lake. Furthermore, Tule River discharge has 

appreciably exceeded 130,000 acre-feet only in 2 years 

since 1950 (fig. 14).
B22

1400

STUDIES OF LAND SUBSIDENCE

1200

1000

800

- 600

400

200

EXPLANATION

Measured diversions from 

Friant-Kern Canal

Estimated discharge of Deer 

Creek, White River, and Poso 

Creek

Measured discharge of Tule River

FIGURE 14. .Surface-water supply, 1930-64, exclusive of canal Imports from the Kern and Kaweah Rivers (calendar year).

The most striking feature of figure 14 is the effect of 

deliveries of Friant-Kern Canal water on total surfacewater supply. From 1950 through 1964, the annual 

deliveries from the Friant-Kern Canal ranged from 51 o

percent (1952) to more than 96 percent (1959) and 

averaged roughly 80 percent of the surface-water inflow 

to the area. This influx of a dependable, economical irrigation supply has had a marked effect on groundwater pumpage in the area and indirectly on the magnitude and rate of subsidence that has occurred.

Most of the water diverted from the Friant-Kern 

Canal is delivered for direct irrigation during the 

growing season. Some of the water, however, especially 

during the early years of construction and during years 

of plentiful runoff, has been deliberately spread as 

ground-water recharge, but few of the irrigation districts have made measurements of the amount of water 

diverted for this purpose. The Delano-Earlimart Irrigation District, which since 1955 has received from 15 

to 25 percent of the Friant-Kern water delivered in the
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B23

area (table 3), diverted the following amounts of canal 

water into spreading areas for ground-water recharge 

from 1950 through 1964:

Year Acre-feel Year Acre-feet

1950. _ ._-

1951_-_._-

1952______

1953_-___-

1954 _____

1955___-_-

1956 __ ___

1957_-__-_

1,580

6,280

11,430

7,690

5,200

10

1,860

1,920

1958----.-

1959_.____

1960_-_--_

1961-.----

1962.-----

1963----.-

1964.. _.._

4,030

0

0

0

0

5,623

0

GROUND WATER

GENERAL FEATURES

The unconsolidated continental deposits that form 

the westward-thickening wedge of Sierran detritus 

constitute the principal source of ground water in the 

Tulare-Wasco area (figs. 4, 5, 9, 10). These deposits 

comprise the extensive sand and gravel aquifers and the 

less extensive fine-grained aquitards of the groundwater reservoir. In the eastern part of the area, the 

thin sands within the poorly permeable marine siltstones 

and the underlying permeable sand of the Santa Margarita Formation of Diepenbrock (1933) also supply 

water to wells.

Kecharge to the ground-water reservoir is primarily 

from precipitation that falls on the tributary watershed 

east of the Tulare-Wasco area and that enters the 

ground-water reservoir as deep percolation from the 

Sierran streams or from the stream diversions and as 

underflow from the foothill recharge areas. Thus, runoff from Tule River, and to a lesser extent, from Poso 

Creek, Deer Creek, and White River plays a dominant 

role in the recharge of the ground-water reservoir. Imports from canals, largely from the Friant-Kern Canal 

since 1949, also serve as a major source of groundwater recharge. Very little recharge results from precipitation falling within the Tulare-Wasco area proper. 

Of the 9 inches of precipitation that falls within the 

Tulare-Wasco area in an average year, less than V-/2 

inches is "effective" in supplying agricultural requirements (computed by method of Blaney and Griddle, 

1950), and probably only a trivial amount percolates 

down to the water table.

In general, ground water moves westward across the 

Tulare-Wasco area in much the same direction as the 

Sierran streams that laid down the sediment now composing the aquifers. In this westward circulation, 

ground water moves from recharge areas of little 

confinement through regions of increasing confinement, 

and in the western part of the area it passes either over

or under the lip of the principal confining clay the 

Corcoran Clay Member of the Tulare Formation. Under 

each of these conditions unconfined, semioonfined, and 

confined ground water moves in the direction of maximum hydraulic gradient; that is, from recharge areas 

of high water level to pumping areas of depressed 

water level. The direction of movement at any particular 

time and place can be determined from detailed maps 

showing the altitude of the water table or of the piezometric surface in confined aquifer systems.

Prior to intensive development, discharge from the 

ground-water reservoir was by upward percolation 

from the confined and semi-confined aquifer systems to 

surface drains or evapotranspiration and by subsurface 

outflow toward the valley trough. For many years, however, little ground water has discharged naturally, as 

water levels in all the aquifer systems have been depressed far below the land surface. In spite of the very 

large surface-water imports from the Friant-Kern and 

other canals since 1950, pumpage still exceeds replenishment in some years. Pumpage, therefore, represents the 

principal discharge from the ground-water reservoir 

under present conditions, but subsurface outflow to the 

west still occurs in both the semiconfined and the confined aquifer systems.

HISTORY OF DEVELOPMENT

From 1849 to 1870, land in the Tulare-Wasco area 

was used chiefly for grazing cattle (Small, 1926, p. 310). 

Hay and other forage crops necessary for the production of livestock were obtained by dry farming until 

about 1855, at which time the practice of irrigating 

pasture and cropland with water diverted from streams 

was initiated.

Following the construction of the Southern Pacific 

Railroad in 1871-73, a rapid surge in land development 

occurred. With this new means of transporting farm 

products to market, there was a transition from the 

raising of cattle to the growing of cereal grains. By the 

late 1870's and early 1880's much of the arable land was 

utilized for growing wheat. Beginning about 1885 there 

was another transition, from the growing of predominantly grain crops to diversified farming. This change 

was due largely to the increasing population and to the 

increased use of surface and ground water for irrigation. By 1886, the total irrigated area was about 40,000 

acres.3 Most of this area was irrigated with water 

diverted from the Kaweah and Tule Rivers. Smaller 

acreages were irrigated along Deer Creek and White 

River. In the southern part of the area about 8,000

3 W. H. Hall, 1886. Unpublished topographic and hydrologic maps 

of the San Joaquin Valley, Calif., on file in the archives of the California Department of Water Resources.
B24 STUDIES OF LAND SUBSIDENCE

acres was irrigated with water imported by canals from 

the Kern River.

The drilling of a flowing well near Tipton in 1875 

by the Southern Pacific Co. stimulated interest in the 

development of ground water for irrigation purposes. 

In 1881, a well drilled to a depth of 330 feet on a ranch 

4 miles west of Tulare flowed at a rate of about 30 

gallons per minutes (Small, 1926, p. 300). Subsequently, 

many flowing artesian wells were drilled west of the 

Southern Pacific Railroad. Hall 4 reported 93 flowing 

wells in the area in 1886. Many of these flowing wells 

were unregulated, and much of the flow was wasted. 

The use of ground water for irrigation rapidly expanded beyond the area of surface-water diversion and 

outside the area of artesian flow. In 1891, several wells 

were drilled near Lindsay to provide irrigation water 

for citrus crops. At the time the wells were drilled', 

water levels were reported to be about 20 feet below 

land surface (Menefee and Dodge, 1913, p. 88). The 

introduction of electrically powered pumping plants 

about 1900 accelerated the drilling of irrigation wells. 

By 1905, the number of irrigation wells in the area had 

increased to about 300 (Mendenhall and others, 1916, 

p. 252-295).

By 1920-21, an estimated 183,000 acres, 20 percent of 

the Tulare-Wasco area, was irrigated (fig. 15). Most of 

this acreage was in the northern part of the area, where 

surface streams supplied the bulk of the irrigation demands and ground water was used as a supplemental 

supply during periods of low streamflow. In the southern and western parts of the area, where surface supplies 

were inadequate or absent, irrigation depended entirely 

on ground water. Data are not available to differentiate 

in figure 15 the areas irrigated solely by ground water. 

The early exploitation of ground water caused artesian water levels to fall rapidly, and by the late 1920's 

most of the flowing wells had ceased to flow. The period 

1921 to 1939 was a time of accelerated increase in 

ground-water pumpage. By 1939, water levels had declined 125 feet between Delano and Kichgrove (Ingerson, 1941, p. 34-35). Land development and the use of 

ground water continued to increase from 1939 to 1945. 

Immediately following World War II, extensive 

undeveloped areas were brought into production. The 

accelerated use of ground water caused another surge of 

water-level decline, especially in areas of intensive 

pumpage and restricted recharge. During the 4-year 

period from 1945 to 1949, water levels declined as much 

as 25 feet near Lindsay, 30 feet near Pixley, and about 

80 feet in the Delano-Richgrove area.

4 Unpublished reports, field notes, and hydrologic maps of the San 

Joaquin Valley, Oalif., on file in the archives of the California Department of Water Resources.

119°30 119"00'

FIGURE 15. Land irrigated in 1920-21 (shaded). Data from California Department of Engineering (1921) and, California Department of Public Works (1922).

Prior to 1949, irrigation in the Tulare-Wasco area 

depended almost wholly on local supplies. With the 

importation of surface water from the San Joaquin 

Kiver via the Friant-Kern Canal beginning in 1949, 

however, additional acreage was cultivated. Also, 

much of the ground-water pumping was supplanted 

by surface diversions from the Friant-Kern Canal. In 

the area served by the Friant-Kern Canal agricultural expansion continued until about 1958, when 

roughly half of the Tulare-Wasco area (456,500 acres, 

based on unpublished crop survey by the California 

Department of Water Resources, 1958) was under irrigation (fig. 16). As of 1958, most of the unirrigated 

area was either along the eastern foothills, where irrigation water is presently unavailable from either 

surface or underground sources, or in a crescentic area 

delineated roughly by the historic shorelines of Tuare Lake, where ground-water quality and soil conditions are marginal. Information is riot available to 

discriminate in figure 16 ithe areas irrigated solely or 

Dartly by ground water.

During the period from 1949 to 1959, surface-water 

mports from the Friant-Kern Canal had a marked
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B25

FIGURE 16. Land irrigated in 1958 (shaded). Dashed contours show 

th« eastern, extent of .Tulare Lake 220 feet above sea level in 

1862, 1868, and 1878 and 200 'feet above sea level in 1880. Data 

from unpublished crop survey of California Department of Water 

Resources (1958).

effect on ground-water trends within the service area. 

Water levels rose as much as 150 feet near Lindsay 

and as much as 40-170 feet in the Delano-Richgrove 

area. At only a few places within the general service 

area, particularly between Pixley and Earlimart, did 

water levels continue to decline. Deficient stream runoff in 1959, 1960, and 1961 (fig. 14) caused a renewed 

surge of ground-water pumping throughout most of 

the area. Many irrigation pumps that had been idle 

for 6-8 years were operated, and water levels temporarily resumed a downward trend.

HYDROLOOIC UNITS

Ground water is generally thought of as occurring 

under either unconfined (water table) or confined (artesian) conditions. In the Tulare-Wasco area, however, 

ground water occurs almost wholly under semiconfined 

or confined conditions. As shown diagrammatically in 

figure 17, fresh ground water occurs in (1) a semiconfined aquifer system that underlies the entire area, and 

that extends down to the top of the Corcoran Clay Member in the western part of the area and to the top of the

marine strata or to the base of the fresh-water body in 

the eastern part; (2) a confined aquifer system beneath 

the confining Corcoran Clay Member in the western 

part of the area that extends down to the base of the 

fresh-water body; and (3) a deep confined aquifer 

tapped only in the Kichgrove area, the Santa Margarita 

Formation as used by Diepenbrock (1933).

SEMICONFINED AQUIFER SYSTEM

The semiconfined aquifer system underlies all the Tulare-Wasco area except where the impermeable Sierran 

basement complex rises above the water table along the 

northeast border. In the western part of the area, the 

semiconfined water body in this aquifer system occupies all but the uppermost part of the deposits extending from the land surface to the top of the Corcoran 

Clay Member. The thickness of these deposits ranges 

from about 200 feet at Delano and Pixley to 700 feet 

northwest of Alpaugh. In 1905, the top of the semiconfined water body overlying the Corcoran was 5-20 feet 

below the land surface. East of the boundary of the 

Corcoran Clay Member, the deposits containing the 

semiconfined water body extend from the land surface 

down to the top of the marine siltstones of Pliocene age 

or to the base of the fresh-water body. In most of this 

eastern area, the thickness of the deposits containing the 

semiconfined water body ranges from a few hundred to 

1,400 feet. The depth to the water table in 1905 was 

generally less than 100 feet but ranged from 10 to 20 

feet at the east boundary of the Corcoran Clay Member 

to 150 feet or more locally at the east edge of the TulareWasco area. (See 1905 water-table profile, fig. 17.)

In the eastern part of the area, the semiconfined 

aquifer system can be separated into two units: (1) a 

shallow, highly permeable zone that underlies much of 

the area and (2) a deep zone that is hydraulically continuous with the shallow zone but in which confinement 

increases with depth. The contact between these zones 

is readily recognized on many of the electric logs and 

is shown as the contact between the upper slightly 

weathered alluvium and the lower highly weathered 

alluvium in figures 4, 5, and 9.

The shallow zone in the semiconfined aquifer system 

occupies the uppermost part of the uncohsolidated continental deposits and ranges in thickness from about 

100 to as much as 300 feet. The most permeable deposits 

in this zone are along the White River, Deer Creek, and 

the Tule River. During the early years of agricultural 

development, water for irrigation was pumped almost 

exclusively from this zone. As water levels declined, 

deeper wells were drilled and many of the shallow wells 

were abandoned or restricted to domestic and stock use.

332-JL33 O 69-
B26 STUDIES OF LAND SUBSIDENCE

w 800'-i

Piezometric level, confined aquifer system (1905)

 witer_t.able,_19q5_.

 -..Water tab,

"'-- .'.?:. 1951 *S ,\?&

FIGURE 17. Generalized east-west hydrologic section. Alinement same as for figure 4.

At the present time irrigation wells pump from the shallow zone only along Tule River in the vicinity of 

Porterville.

The water-table map for 1905 (fig. 22) and the 1905 

profile (fig. 17) depict the top of the zone of saturation 

as determined from measurements of depth to water in 

wells that were almost all less than 300 feet deep; thus 

they represent the water table in this shallow zone. By 

1951, however, the water table had been drawn down to 

depths below 200-300 feet in most of the eastern part 

of the area (see 1951 water-table profile, fig. 17) and 

hence was below the base of this shallow zone.

The deep zone in the semiconfined aquifer system extends eastward from the east margin of the Corcoran 

Clay Member and is hydraulically continuous with the 

confined aquifer system beneath the Corcoran. Wells 

tapping the deep zone range in depth from about 400 to 

more than 1,000 feet. Although data are insufficient to 

determine the actual pumpage from the deep semiconfined zone, probably half the ground water pumped for 

irrigation in the entire area comes from this sequence 

of deep continental deposits in the semiconfined aquifer 

system.

In general, the deeper sand and gravel aquifers show 

the effects of confinement more than the shallower ones. 

The degree of confinement also increases from east to 

west as more and more silt and clay beds interfinger 

from the west. Before intensive development, water 

levels in these various discontinuous beds rose to about 

the same common level, and contour maps could be 

drawn to represent the composite water surface of this 

semiconfined aquifer system. Intensive pumping from 

these beds, however, especially since 1930, has developed 

differences in head between the various strata of the 

system. These variations are greatest during the summer months of heaviest pumping, but also persist to a 

lesser degree through the months of winter recovery.

The perforated interval and variation of water level 

in water wells of different depths along two east-west 

lines in the Tulare-Wasco area are shown in hydrologic 

sections A'-A" and B-B' (fig. 18). (For location see 

fig. 6.) As shown, in the eastern half of the area beyond 

the boundary of the Corcoran Clay Member, most of the 

wells tap only the semiconfined aquifer system in the 

continental deposits, and only a few wells extend down 

into the poorly permeable upper Pliocene marine strata
SK 353 i s nil 1 liiiJLLi-

EXPLANATION 

«, Well number (asterisk denotes 

g more than 1 mile projection 

*i into section)

Land surface

0123 MILES

I I I I

SEA LEVEL 

VERTICAL EXAGGERATION X 13

FIGURE 18. Hydrologic sections A'-A" and S-B' showing perforated intervals and water levels in wells. Alinement of sections shown 
B28 STUDIES OF LAND SUBSIDENCE

or into the underlying Santa Margarita. Most of the 

wells tapping the semiconfined aquifer system are perforated continuously from near the water table to the 

well bottom, and thus the water level in the well is a 

composite of the head in the various aquifers tapped. 

In this eastern part of the area, water levels in nearby 

wells of unequal depth perforated entirely in the continental sands and gravels differ by as much as 40 feet 

(fig. 18), the deeper wells having the lower water level. 

Water levels in the deep wells extending downward into 

the poorly permeable marine strata usually are much 

lower than those of nearby shallower wells. This head 

difference indicates that during periods of no pumping, 

ground water moves downward from the semiconfined 

continental deposits into the underlying marine strata 

through wells perforated in both. These consolidated 

marine strata do not have direct contact with stream recharge and, when drawn down by heavy pumping, may 

receive most of their recharge by downward movement 

from the overlying semiconfined beds through well 

casings.

Because of the wide variation in head in wells of unequal depth in the semiconfined aquifer system east of 

the Corcoran boundary, water level contour maps for the 

semiconfined system are difficult to draw. In general, 

however, in the eastern part of the Tulare-Wasco area, 

water levels in wells less than 400 feet deep are considered to represent the top of the semiconfined water body, 

that is, the water table at the top of the zone of saturation. On the other hand, water levels in wells more than 

500 feet deep but not extending into the marine deposits 

beneath are considered to represent a semiconfined 

piezometric surface that in recent years has stood 

roughly 20-50 feet below the water table.

In the western half of the area overlying the Cbrcoran 

Clay Member confining layer, few wells are perforated 

solely within the semiconfined aquifer system (fig. 18). 

These shallow wells are mostly old and of small yield. 

Most of the larger irrigation wells drilled in recent years 

extend through the Corcoran and register water levels 

that are a composite of the semiconfined and confined 

pressures.

CONFINED AQUIFER SYSTEM

Figure 19 shows the areas in which deep wells tap 

confined aquifer systems. The principal confined aquifer 

system is beneath the Corcoran Clay Member. It underlies about 40 percent of the Tulare-Wasco area and extends from the base of the Corcoran down to the base 

of the fresh-water body (fig. 18). This aquifer system 

consists of the interfingering lenses and layers of continental gravel and sand, silt, and clay of Tertiary and

Quaternary age and merges eastward into the deeper 

beds of the semiconfined aquifer system. Eecharge to 

this confined aquifer system is almost entirely by subsurface movement under the lip of the Corcoran from 

the semiconfined aquifer system to the east.

The confined aquifer system is effectively separated 

from the overlying semiconfined system by the relatively 

impermeable Corcoran Clay Member of the Tulare Formation and other related clays. As shown in hydrologic 

sections A'-A" and B-B' (fig. 18) and geologic section D-D' (fig. 10), the depth below the land surface 

of the Cbrcoran Clay Member ranges from 200 to 700 

feet. Throughout most of the confined aquifer, wells 

show rapid interference effects of nearby pumping, low 

storage coefficients, and other characteristic features of 

an artesian system. At the margin of the Corcoran, 

however, hydraulic continuity between the shallow and 

deeper aquifers increases, and the aquifer system displays the characteristics of semiconfinement.

The depths of wells tapping the sub-Corcoran confined aquifer system range from about 400 to 2,000 feet, 

depending partly on the depth to the top of the confined 

aquifer system (fig. 11) and depth to the base of fresh 

water (fig. 10). East of E. 23 E., most of the wells are 

less than 800 feet deep. In E. 22 and 23 E. in Tulare 

County, however, about half the wells are on the order 

of 1,200 feet deep, and a few are in excess of 1,500 feet 

deep. Beneath the Corcoran Clay Member, the top of 

the saline water body ranges from 900 to more than 2,000 

feet below the land surface. As far as is known, no 

water is being pumped from this deep confined body of 

saline water.

Hydrographs of piezometer wells constructed by the 

Bureau of Eeclamation in 1952 (23/23-33A1 and 

25/23-29A1, fig. 34) show that near and south of 

Alpaugh substantial hydraulic separation exists between the upper 350 feet of the confined system and 

the deposits beneath. This hydraulic separation may be 

fairly widespread; it was small in 1952 but subsequently 

increased until in 1964 it was as much as 50 feet (spring 

high) and 100 feet (summer low). This much head differential within the confined system suggests the possibility of more than one confining layer.

SANTA MARGARITA FORMATION AS USED BY 

DIEPENBROCK (1933)

During the 1950's, wells drilled to depths of 1,800- 

2,400 feet in the vicinity of Eichgrove first tapped 

artesian water-bearing sands of the Santa Margarita 

Formation as used by Diepenbrock (1933); they proved 

to be a valuable source of ground-water supply. By 

1957, about 20 large irrigation wells were taking water
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B29

EXPLANATION

Area in which wells tap the confined aquifer system below the 

Corcoran Clay Member- of the 

Tulare Formation

Area in which wells tap the 

Santa Margarita Formation as 

used by Dipenbrock (1933)

Location of aquifer test

TULAEE CO

:;:;KEEN co

' t IFIGURE 19. Areas in which wells tap confined aquifer systems and locations where aquifer tests

have been made.

from the Santa Margarita. Most of these wells are perforated in overlying strata as well as in the Santa Margarita ; only six are perforated exclusively in the Santa 

Margarita.

As shown in hydrologic sections A'-A" and B-B* 

(fig. 18), the westward dip of the Santa Margarita increases westward from 100 to 250 feet per mile and is 

much steeper than the land-surface slope; therefore, 

only in a narrow belt in the eastern part of the area 

can water be pumped economically from the Santa 

Margarita. Figure 19 shows the area in which large irrigation wells tap the productive water-bearing sands 

of the Santa Margarita. The Santa Margarita is overlain by the poorly permeable consolidated upper Pliocene and Pliocene(?) marine siltstone sequence which

prevents recharge from above. Because the Santa Margarita does not crop out, recharge to this deep aquifer is 

probably rather limited. The artesian head in this 

aquifer was about 100 feet above the water table in 1956 

but had been drawn down 110 feet by 1961.

Because the Santa Margarita was deposited in a 

marine environment, it contained saline water initially. 

In most of the area where this aquifer is shallow enough 

to be of economic interest as a source of water supply, 

the saline water has since been flushed out of tlie formation by natural ground-water circulation (fig. 18). To 

the west, it still contains saline water. Where tapped by 

deep irrigation wells in the Richgrove area, this aquifer 

yields water that is used extensively to irrigate grapes, 

citrus fruits, and field crops.
B30 STUDIES OP LAND SUBSIDENCE

AQUIFER TESTS

Controlled pumping tests have proved to be an effective tool in determining the hydraulic characteristics of 

an aquifer system. In the usual test, the discharge rate 

of a pumped well is held constant and measurements are 

made of the drawdown, which varies with time. The 

resulting data are analyzed graphically, as outlined by 

Ferris, Knowles, Brown, and Stallman (1962, p. 91), 

and the values of T (transmissibility) and B (storage 

coefficient) (Ferris and others, 1962, p. 72-74) of the 

aquifer are computed.

Aquifer tests have been made at six sites in the TulareWasco area to determine the aquifer constants, T and $, 

of the water-bearing deposits. The results of these tests 

are given in table 4 (written communication, E. J. 

McClelland, December 1965). The location of the 

pumped wells at these test locations is shown in figure 

19. Four of the tests were made in the semiconfined 

aquifer system, and two tests, at wells 17Q2 and 17R2, 

were made in the confined system beneath the Corcoran 

Clay Member. A seventh test, at well 24/22-28 A2, half a 

mile west of the area boundary, also tested the sub-Corcoran confined aquifer system in an area where it contains thick clayey aquitards. Because of the heterogeneity of the deposits tested and the type of test data 

obtained, the values of T and S derived from the tests 

are considered to be only rough approximations of the 

actual formational constants.

These aquifer tests indicate a wide range in transmissibility and in general suggest that the transmissibility of the deposits in the semiconfined aquifer system 

is two to three times as great per 100 feet of deposits 

tapped as that of the sub-Corcoran confined system. The 

tests for wells 26/24-4H1, 26/25-26N1, and 27/25-3J2,

tapping the semiconfined system, were too short, however, for a rigorous interpretation of the data. The 

coefficient of storage estimated from the tests was on 

the order of 10-5 for the confined aquifer system and 

10"3-10~4 for the semiconfined system. The tests for 

the semiconfined system were far too short to develop 

reliable storage coefficients; nevertheless, their very low 

value supports the conclusion that at the depths tested 

the semiconfined system approaches truly confined conditions (Ferris and others, 1962, p. 76).

GROUND-WATER PUMPAGE

Pumping of ground water has been the primary cause 

of the major changes in water level in the Tulare-Wasco 

area, and therefore the magnitude of and variation in 

rate of withdrawals is of basic interest in the study of 

land subsidence. At least 95 percent of the pumpage is 

for irrigation use. Estimates of the amount of ground 

water pumped for irrigation have been made for 

the years 1950-62 from records of electrical power 

consumed. In these computations, the pumpage was 

approximated on the basis of the electrical energy sold 

on the agricultural power schedule in the various power 

districts and the average energy required to pump 1 acrefoot of water. Although a small amount of the power 

sold on the agricultural power schedule was used for 

purposes other than pumping ground water, a small 

amount of water was pumped by gas engines or by 

electricity sold on another power schedule. Data were 

not available to make estimates of pumpage prior to 

1950.

Cities and towns in the Tulare-Wasco area obtain 

their water supply almost exclusively from wells. Their 

total use, however, is less than 5 percent of the ground 

water pumped for irrigation, and therefore estimates

TABLE 4. Aquifer-test results

Pumped well Date Test by Depth interval Transmissibility ' Coefficient Aquifer system tested Length 

tested (ft) (gpd per ft) of storage > of test

Tulare-Wasco area: 

23/25-17Q2 .......

17R2... ........

24/25-36J1............

26/24-4H1 a..... ......

26/25-26N1... .....

27/25-3J2 ..........

Just west of area: 

24/22-28A2.. .........

...... 2-15-61

...... 3-13-63

...... 2-19-61

...... 3-26-58

...... 3-12-58

and 

. 3-18-58.

Q-91 KC

...... 4-4-60

USGS....... ......

USGS...... .......

USGS.............

KCL <-...........

KCL and USQS..

KCL and USGS..

USGS.............

2300-

280- 

437-1, 

148- 

340-

260-

575-

600?

603 

398 

502 

800

816 

947

15,000

14,000- 18,000 

8,000 ..

150,000-300,000 

60, 000- 70, 000

25, 000- 80, 000 

20,000

10 "5 Confined, subCorcoran. 

5X10-5 ..... do -.. .

.. SftTnifinnfined

10 "3 

10 -3-10 "<

10" * 

10'*

.....do.................

.....do... ..............

.....do.................

Confined, subCorcoran.

144 hr.

48 hr. 

144 hr. 

165 rain. 

135 min. 

105 min.

120 min. 

24 hr.

i Tentative values, subject to revision.

a Perforated interval unknown. Believed to be perforated entirely 

below the Corcoran Clay Member of the Tulare Formation.

n Observation well.

* Kern County Land Company.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B31

of ground water used for municipal and domestic purposes were not made for this study.

Two-thirds of the Tula/re-Wasoo area receives electrical power from the Southern California Edison Co. 

and comprises all or part of four power districts of its 

San Joaquin Valley Division (fig. 20). The remaining 

third of the area receives power from the Pacific Gas 

and Electric Co. and comprises parts of two large power 

districts (the Kern and Corcoran districts) of its San 

Joaquin Division. Because the water-level trends and 

the type of power data available for computing pumpage 

in the two power-company service areas differed, the

methods used for estimating pumpage in the two areas 

were different.

In much of the area supplied with power by the Southern California Edison Co., the downward trend of water 

levels that had persisted through the 1930's and 1940's 

was generally reversed in the 1950's with the completion 

of the Friant-Kern Canal. Although the amount of surface water so imported has varied from year to year 

(fig. 14), the general effect has been to decrease the demand on wells in the service area and to supply a new 

source of replenishment to the ground-water reservoir. 

As a result, water levels rose appreciably in much of the

R 22 E 119°30'R 23 E R 24 E. R 25 E 15'

36

369\\ D e I a n o 

..District

10 MILES

i i i i

FIGURE 20. Power districts and rate of power consumption (kwhr per *acre-ft, from table 5)

township.
B32 STUDIES OF LAND SUBSIDENCE

service area from 1951 to 1958; then in years of deficient surface-water supply 1959 through 1961 

water levels remained about constant or declined.

Power records made available by the Southern California Edison Co. included (1) total agricultural power 

consumed in each of its four pertinent power districts 

for agricultural power years (April 1-March 31) 1956- 

57, 1959-60, and 1960-61; (2) total agricultural power 

consumed each year for 1950-62 in its entire San Joaquin 

Valley Division; and (3) data of several hundred pumpefficiency tests summarized for the pertinent townships 

in table 5 and in figure 20. During the 3 years for which 

complete records are available, the agricultural power 

used in the four pertinent power districts was about 80 

percent of the agricultural power consumed in the entire

San Joaquin Valley Division of the Southern California 

Edison Co. The percentage by power districts was 

Tulare, 23; Lindsay, 8; Porterville, 11; and Delano, 38. 

It was assumed that the proportionate distribution of 

power within the four districts for the 3 years of available data was constant for the remainder of the period 

1950-62.

The kilowatthours per acre-foot factor given by township in table 5 and shown in figure 20, is considered to 

represent an average factor for the years 1950-53. To obtain appropriate factors for the years 1954-62, the 1950- 

53 factor was modified by deriving an average yearly 

water-level change in each power district from the 

average water-level graphs for the appropriate groundwater subareas of figure 24. For each foot of rise or

TABLE 5. Yield characteristics of irrigation wells in the Tulare-Wasco area, by townships

[From table 3, Davis, Lofgren, and Mack (1964); data presented as averages for most recent test on each well, 1950-54. Pump test data from Pacific Gas

and Electric Co. and Southern California Edison Co.]

Townships 

(Mount Diablo base line and 

meridian)

T. 20 S., R. 22E_______

T. 20 S., R. 23E._.___.

T. 20 S., R. 24E.___.__

T. 20 S., R. 25E_....__

T. 20 S., R. 26E____.._

T. 20 S., R. 27 E_______

T. 21 S., R. 22 E...___.

T. 21 S., R. 23E___.___

T. 21 S., R. 24E_.____.

T. 21 S., R. 25 E_______

T. 21 S., R. 26 E.___.._

T. 21 S., R. 27 E_______

T. 22 S., R. 22 E_______

T. 22 S., R. 23 E_______

T. 22 S., R. 24E__.___.

T. 22 S., R. 25E______-

T. 22 S., R. 26 E_______

T. 22 S., R. 27E_______

T. 23 S., R. 23E.______

T. 23 S., R. 24 E _ ____

T. 23 S., R. 25E___.___

T. 23 S., R. 26 E._._.._

T. 23 S., R. 27E_.__.__

T. 24 S., R. 22 E_._____

T. 24 S., R. 23E.___._.

T. 24 S., R. 24E__._.__

T. 24 S., R. 25 E_______

T. 24 S., R. 26E___.___

T. 24 S., R. 27E.______

T. 25 S., R. 22 E _ ____

T. 25 S., R. 23E_______

T. 25 S., R. 24E_______

T. 25 S., R. 25 E_______

T. 25 S., R. 26 E..__.__

T. 25 S., R. 27 E_______

T. 26 S., R. 22E___._.

T. 26 S., R. 23 E___..._

T. 26 S., R. 24 E_._____

T. 26 S., R. 25 E_._____

T. 26 S., R. 26E.___.__

T. 26 S., R. 27 E_______

T. 27 S., R. 22 E_______

T. 27 S., R. 23E_______

T. 27 S., R. 24E_______

T. 27 S., R. 25 E_______

T. 27 S., R. 26E.._____

Number of Static level Pumping Drawdown Discharge Specific Kilowatt- Plant 

tests (ft.) level (ft.) (ft.) (gpm) capacity hours per efficiency 

(discharge) (gpm per ft) acre-foot

16 

186 

223 

160 

344 

111 

25 

58 

96 

145 

220 

232 

14 

56 

109 

153 

190 

61 

9 

40 

158 

76 

21 

4 

10 

8 

147 

94 

21 

7 

58 

50 

140 

125 

12 

10 

37 

68 

102 

83 

1 _..

16 

73 

198

84 

48

74 

95 

81 

69 

192 

219 

78 

110 

86 

109 

94 

95 

92 

107 

128 

152 

144 

107 

113 

114 

144 

195 

230 

116 

146 

87 

191 

332 

363 

116 

125 

117 

189 

332 

383 

112 

115 

138 

217 

303

133 

143 

146 

168 

273

110 

107 

95 

86 

211 

254 

111 

124 

108 

131 

110 

121 

158 

144 

145 

172 

161 

131 

166 

143 __-

174 

222 

278 

140 

175 

133 

228 

358 

379 

153 

149 

140 

218 

363 

437 

145 

131 

160 

240 

323 

308.2 _..

161 

161 

160 

182 

295

33 

13 

13 

18 

23 

35 

33 

24 

22 

24 

19 

27 

31 

31 

21 

20 

15 

30 

50

27 

26 

29 

24 

18 

43 

38 

39 

36 

37 

24 

25 

31 

37 

54 

28 

16 

22 

19 

21

26 

16 

14 

14 

23

1,078 

578 

492 

625 

221 

103 

682 

1,139 

728 

676 

575 

297 

1,036 

1,080 

672 

545 

558 

288 

868 

871 

514 

773 

319 

498 

707 

595 

571 

693 

428 

994 

665 

864 

640 

618 

683 

1,334 

921 

936 

623 

780 

804 __.

1,012 

1,264 

681 

1,060 

1,092

38 

52 

45 

42 

14 

6 

23 

58 

50 

35 

43 

20 

41 

48 

38 

41 

43 

26 

23 

37 

27 

41 

13 

21 

50 

33 

19 

26 

20 

37 

42 

56 

24 

25 

13 

39 

65 

58 

59 

47

61 

92 

65 

102 

56

193 

221 

217 

183 

477 

617 

232 

253 

215 

263 

238 

303 

294 

282 

289 

374 

328 

326 

321 

249 

369 

442.5 

636 

351 

326 

256 

483 

739 

840 

317 

300 

283 

453 

707 

853 

282 

261 

304 

458 

600 

535.7 

317 

302 

326 

349 

531

61 

53 

50 

50 

48 

45 

47 

57 

52 

53 

51 

46 

56 

60 

54 

51 

54 

47 

55 

58 

51 

56 

48 

42 

55 

61 

51 

53 

50 

52 

59 

54 

54 

54 

53 

55 

56 

58 

56 

58 

59.5 

49 

60 

55 

56 

60
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B33

decline in average water level in the individual power 

districts, 2 kwhr per acre-ft were subtracted or added, 

respectively, from the base 1950-53 factor.

After deriving the annual electric power use and kilowatthour per acre-foot factors by these procedures, the 

agricultural pumpage for the part of the San Joaquin 

Valley Division within the Tulare-Wasco area and the 

northern strip of the Tulare and Lindsay power districts outside the area was estimated for each of the 

years from 1950 through 1962. The pumpage in the part 

of the Tulare-Wasco area west of the Tulare power district was then assumed to equal the pumpage in the 

northern strip of the Tulare and Lindsay power districts outside of the project area (fig. 20) in each of 

these years, as these two areas are approximately equal. 

Thus, the total pumpage estimated by this means represented that in all of the Southern California Edison 

Co. service area in the Tulare-Wasco area plus that in 

the northern part of the Pacific Gas and Electric Co. 

service area.

In the southwestern part of the Tulare-Wasco area, 

including the parts of the Corcoran and Kern Districts 

of the Pacific Gas and Electric Co. lying west and south 

of the Southern California Edison Co. Delano district 

(fig. 20), the water-level trend has been generally downward during the fifties and early sixties. Much of this 

area is supplied solely by ground water, and considerable new land has been brought under cultivation. 

Water levels in wells declined fairly consistently during 

the period from 1950 through 1962.

Eecords available from the Pacific Gas and Electric 

Co. included (1) the total agricultural power used 

yearly in its two power districts for the years 1950-62, 

(2) the amount of power used in the pertinent meter 

route areas within the two districts for the agricultural 

power years 1956-5Y, 195Y-58, and 1958-59, and (3) 

the average rate of power consumption, in kilowatthours 

per acre-foot, for each pertinent township in their service area for the agricultural power years 1950 through 

195Y and for the entire Kern district for the period 

1950-62. The proportion of power used in this southwestern area to power used in the entire Kern power 

district was known for the 3 years from 1956-5Y to 

1958-59 and was assumed to be constant during the full 

period 1950-62. The trend of the average kilowatthours 

per acre-foot for the southwestern area was known for 

1950-5Y and was extended through 1962 on the basis 

of the trend in the entire Kern power district. The values 

of agricultural power and the kilowatthours per acrefeet so obtained were used to compute the ground-water 

pumpage in this southwestern area west and south of 

the Southern California Edison Co. Delano power district for the years 1950-62. Table 6 gives the estimated

Year

1950

1951

1952

1953

1954

1QKK

1957... ______

Pumpage 

(acre-ft)

1,050,000

__ 1,110,000

870,000

960,000

960,000

940,000

860,000

970,000

Pumpage 

Year (acre-ft)

1958 __ ----- 710,000

1959----_-__--- 1,260,000

1960 ___._-____ 1,370,000

1961_ ____-__. 1,430,000

1962 ________ 980,000

Total ___- 18,470,000

annual ground-water pumpage for the overall TulareWasco area for the period 1950-62. Details of the pumpage calculation are available in the project files of the 

Geological Survey.

TABLE 6. Estimated ground-water pumpage in the Tulare-Wasco

area, 1950-62 

[For agricultural power year April 1 to March 81]

Figure 21 shows the estimated amount of ground 

water used for irrigation in the Tulare-Wasco area 

(table 6) and also the amount of surface water available 

for irrigation from natural streams and the FriantKern Canal (fig 14), for the 13 years I960 through 1962. 

The gradual increase in use of combined ground-water 

and surface-water supply during the period is readily 

apparent. Ground-water pumpage ranged from 39 percent (1958) to Y9 percent (1961) of the total irrigation 

water used, averaging about 64 percent of annual total

1950

FIGURE 21. Estimated use of ground water and surface water 

for irrigation, 1950-62.
B34 STUDIES OF LAND SUBSIDENCE

supply. There was an irregular but general decrease of 

ground-water use from 1950 through 1958, followed by 

a sharp increase in the years of deficient surface supply, 

1959-61.

HISTORY OF WATER-LEVEL TRENDS

As discussed later, a decline of the water level generally increases the effective stress on the deposits. In 

the compactible deposits of the Tulare-Wasco area, the 

increase in effective stress developed by the historic 

water-level declines has been sufficient to cause several 

feet of land subsidence in about half the area and as 

much as 12 feet near Delano (fig. 50). Therefore, to appraise the relation of subsidence to water-level decline, 

it is important to document the history of water-level 

change as specifically as possible. This appraisal is complicated, however, by the distribution and nature of the 

aquifer systems, the composite nature of the water-level 

measurements1 obtained from many of the observation 

wells, and the fact that periodic measurements were 

made in very few wells prior to the late forties.

In the western part of the area, a substantial number 

of the irrigation wells have been drilled into the subCorcoran aquifer system. Eelatively few of these are 

known to be perforated only in this confined system, 

and no periodic measurements are available for such 

wells prior to 1948. Although the Bureau of Reclamation began a continuing program of water-level measurements in the late forties, periodic measurements 

have been obtained in very few wells perforated only in 

the sub-Corcoran aquifer system. At several places, 

however, the Bureau of Reclamation has installed piezometers that register the head in one or more intervals 

below the Corcoran Clay Member and has recorded 

these measurements periodically.

In the eastern part of the area beyond the limits of 

the Corcoran Clay Member, the degree of hydraulic 

confinement in the semiconfined aquifer system increases with depth. Intensive pumping has lowered the 

head in some aquifers much more than in others. Well 

casings usually are perforated throughout the saturated section penetrated. Water levels in deep wells, 

therefore, are composite levels influenced to some degree by the head in each aquifer tapped and thus do 

not define the head in the deeper aquifers. No wells 

tap only the deeper aquifers, so the change in head with 

depth has not been recorded directly. This is a severe 

limitation in the calculation of changes in effective 

stress that are directly related to subsidence.

Several maps showing the altitude of or the change 

in water levels in wells are included in this report. The 

maps that show the altitude of the water surface for 

the semiconfined aquifer system for 1905 (fig. 22) and

for 1920-21 (fig. 23) were based primarily on water 

levels in relatively shallow wells (less than 500 feet 

deep) and are considered to depict a level that approximately represents the water table at the top of the semiconfined water body. Since 1948, however, the distribution of measurements in shallow wells has been 

insufficient to furnish adequate control on the water 

table. Therefore, the maps showing water-level change 

in the semiconfined system from 1920-21 to 1948 (fig. 

25), from 1948 to 1954 (fig. 26), and from 1954 to 1959 

(fig. 27) have been constructed from measurements in 

wells of various depths, some as deep as 1,000 feet. Accordingly, these change maps are only gross approximations of the changes in water level that have occurred in the semiconfined system. Only in February 

1959 were sufficient measurements made in shallow wells 

(less than 400 feet deep) to construct a map (fig. 28) 

that is a fair approximation of the water table at the 

top of the semiconfined water body. This map, therefore, is directly comparable to the water-table maps of 

1905 and 1920-21.

Hydrographs have been included in the report to 

illustrate the water-level trend in various parts of the 

area. These are of two types: (1) hydrographs showing 

long-term average levels for eight ground-water subareas (fig. 24) and (2) hydrographs that show the 

fluctuations of the water level for particular depth intervals at specific locations (figs. 31, 33, 34, and 35). 

Many of these hydrographs are paired with benchmark graphs which are considered later in relating subsidence to water-level decline.

GENERAL DECLINE, 19O5-51

Before extensive ground-water development, wells 

tapping the principal confined aquifer system flowed 

throughout almost all the area underlain by the Corcoran Clay Member. During a, well canvass of the area 

in 1905-6, Mendenhall, Dole, and Stabler (1916) located 

about 200 flowing wells, mostly with small discharges. 

Artesian heads for these wells were not measured in 

1905-6; thus, a map showing the piezometric surface 

for the sub-Corcoran confined aquifer system for this 

early date cannot be drawn. Figure 22 shows the area of 

flowing wells and the altitude of the water table in the 

 eastern part of the semiconfined aquifer system as of 

1905. The east boundary of the area of flowing wells 

was approximately along the 280-foot topographic contour from Tulare to Delano and generally was about 

2 miles west of the east boundary of the Corcoran confining layer. Although Mendenhall did not attempt to 

extend water-table contours on the semiconfined system westward into the area of flowing wells, measurements of depth to water in shallow wells reported by
119°30'

LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

15' 119°00'

B35

36°00'

35°45'

EXPLANATION

Eastern boundary of area of 

flowing wells

Approximate boundary of 

the Corcoran Clay Member 

of the Tulare Formation

Water-table contour

Shows altitude of water table; 

dashed where uncertain. Contour interval 20 feet. Datum, 

is mean sea level

PIGDHE 22. Altitude of the water table and area of flowing wells In 1905. Modified from Mendenhall, Dole, and Stabler (1916, pi. 1).

him show that the depth to water in the semiconfined 

aquifer system overlying the Corcoran Clay Member 

ranged from 5 to 15 feet below the land surface at that 

time.

Increased ground-water development between 1905 

and 1921 caused decline of water levels. Figure 23 shows 

the altitude of water levels in the semiconfined aquifer 

system in 1920-21. Water levels in this system had been 

drawn down from 10 to 80 feet since 1905. In the northwest quadrant of the area, the Tule and Kaweah Rivers 

still furnished most of the irrigation demands. Waterlevel declines were greatest in an intense cone of pumping drawdown at Lindsay. With the exception of the 

Lindsay pumping cone, ground waiter moved generally 

westward across the area toward the Tulare Lake bed 

at gradients of about 15 feet per mile on the east to 

about 3 feet per mile on the west. The marked groundwater mound along the distributaries of the Tule River 

west of Porterville shows the influence of stream recharge (fig. 23).

In the sub-Corcoran confined aquifer system, artesian 

wells continued to flow only in a small area northwest
B36

119°30'

STUDIES OF LAND SUBSIDENCE

15' 119°00'

36 "00'

35°45'

EXPLANATION

-32OWater-table contour

Shows altitude of water table; 

dashed where uncertain. Contour 

interval 10 feet. Datum is mean 

sea level

 25O 

Piezometric contour

Shows altitude ofpiezometric surface 

of confined aquifer system. Contour interval 10 feet. Datum is 

mean sea level

Boundary of area of flowing 

wells

0 

I__I

10 MILES

FIGURE 23. Generalized water-level contours as of December 1920 (Kern County) and November 1921 (Tulare County). Data 

from California Department of Engineering (1921, map 2) and California Department of Public Works (1922, map 2).

of Wasco (fig. 23). Southwest of Tulare, the piezometric surface of the confined aquifer system had been 

drawn down to 5-10 feet above the water table by 1921. 

Ground-water levels throughout the Tulare-Wasco 

area declined from 1921 through 1935, owing to prolonged subnormal stream runoff (fig. 12) and accelerated 

pumping. As shown in the hydrographs of figure 24, the 

long-term trends of average ground-water levels in 

eight subareas wholly or partly in the Tulare-Wasco 

area (California Department of Water Resources, 1964, 

pis. 10, 11) indicate a general decline of 2-4 feet per

year through 1935 for all parts of the area represented. 

West of these subareas, ground-water pumpage was 

considerably less intensive, and water-level declines 

were less than those shown in figure 24.

From 1936 to 1943, average water levels rose 20-30 

feet in areas served by diversions from the Kaweah and 

Tule Rivers (see hydrographs of subareas 10, 11, 13; 

fig. 24) in response to increased surface-water supply 

(fig. 14). Recovery was less and of shorter duration in 

the Lindsay-Exeter area of intensive ground-water 

pumping (subarea 12). Water levels in these northern
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B37

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B38 STUDIES OF LAND SUBSIDENCE

subareas resumed their downward trend from 1944 to 

1951, during a period of deficient stream runoff and increased ground-water pumpage following World War 

II. In the central and south-central parts of the TulareWasco area (hydrographs of subareas 14,16, 17; fig. 24), 

where surface supplies were limited and more large 

wells were being drilled, average water levels continued 

to decline throughout the 30-year period from 1921 

through 1951.

Figure 25 shows the change in ground-water levels 

in the semiconfined aquifer system from 1920-21 to

119-30'

36°00'

35°45'

1948. This map is based on the comparison of a waterlevel contour map for February 1948 (not included in 

this report) with the water-table contours shown in figure 23. The water level had declined more than 40 feet 

throughout more than half the Tulare-Wasco area, and 

in most of the southeastern quadrant, declines ranged 

from 60 to 220 feet during the 28-year period. In the 

vicinity of Richgrove, where little recharge occurs, an 

especially sharp pumping cone had developed around a 

cluster of highly productive deep wells. Water-level 

decline was small in the western part of the area, but

119-00'

EXPLANATION

--1-20-

Line of equal water-level change

Dashed where uncertain. Rise (+) 

or decline ( ), interval 20 feet

0

I__L

10 MILES

FIGURE 25. Change in water level in the semiconfined aquifer system, 1920-21 to 1948. Change based on water-level contour 

maps for 1920-21 (see fig. 23) and 1948. The 1920-21 measurements were made during November and December, and the 

1948 measurements were made mostly in February.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B39

measurements in 1948 were not adequate to provide 

control for extending lines of equal change through 

that area.

PARTIAL RECOVERY, 1951-59

The importation of water to the Tulare-Wasco area 

through the Friant-Kern Canal, which began in 1949 

(fig. 14), had a marked effect on the ground-water 

regimen within and adjacent to the canal service areas. 

The newly imported water replaced much of the 

ground-water pumpage in these areas and also supplied a new source of replenishment to the groundwater reservoir by downward percolation of irrigation 

water applied in excess of consumptive-use requirements of the crops. As a result, by 1951, when the canal 

import had grown to 304 thousand acre-feet (table 3), 

the water levels beneath and adjacent to the canal service areas began to respond to the decrease in draft and 

increase in replenishment. The effect of the new imports 

on the water levels is strikingly illustrated by the rapid 

recovery of average water levels in ground-water subareas 12, 13, and 16 of figure 24. Average water levels 

in the other five subareas also showed a general cessation 

of the downward trend of prior years. This marked 

change in water level trend had a significant effect on 

the rate of land subsidence, as is discussed later in this 

report.

In general, by 1951, water levels in deep wells had 

been drawn down considerably below the levels of shallower wells. During the 1951-59 recovery period, water 

levels in both deep and shallow wells rose abruptly; 

however, in most parts of the area, the water levels in 

deeper wells rose more than those in shallow wells. In 

1959, therefore, the difference in water level between 

shallow and deep wells at any location was generally 

less than at any time since the forties.

The effect of the Friant-Kern imports on water levels 

in the semiconfined aquifer system is shown by two 

water-level change maps. Figure 26 shows the change 

from 1948 to 1954, and figure 27 the change from 1954 

to 1959. These two periods were selected to evaluate the 

change in the water level, primarily because of the availability of vertical-control data. A network of bench 

marks was established in the Tulare-Wasco area in 

1948 and was releveled in 1954 to define the magnitude 

of subsidence in the 6-year period; it was also releveled 

in 1958-59, at about the time of the greatest recovery 

of the water levels. Although maps showing change in 

the piezometric surface of the deeper part of the semiconfined aquifer system and of the piezometric surface 

of the sub-Corcoran aquifer system would be more directly related to the subsidence of the land surface, data

were not available for constructing water-level change 

maps for those piezometric surfaces.

The change in the position of the water level from 

1948 to 1954 in most of the Friant-Kern Canal service 

area south of Porterville is illustrated areally in figure 

26. Water-level recovery occurred in two areas: southwest of Porterville, where it exceeded 20 feet, and northeast of Delano, where it was as much as 40 feet. Water 

levels continued to decline in a narrow belt 4-6 miles 

east of the Friant-Kern Canal, in the southern part of 

the area that had not yet received a large quantity of 

canal water, and in a small area east of Earlimart. More 

than 60 feet of decline occurred in a pumping depression southwest of Richgrove.

From 1954 to 1959, the water level in the semiconfined aquifer system rose in most of the east-central 

part of the Tulare-Wasco area in response to increased 

surface-water imports from the Friant-Kern Canal 

(fig. 27). In the 5-year period 1954-58, inclusive, the 

average yearly delivery of Friant-Kern Canal water to 

the area was 760 thousand acre-feet (table 3). The 

water-level rise was greatest east and southeast of Delano, where it ranged from 40 to 100 feet, and west of 

Porterville, where it exceeded 20 feet. Maximum recovery was about 4 miles northeast of Delano, where water 

levels had risen 100 feet since 1954 and as much as 130 

feet since 1948. Water-level decline continued south 

of Porterville and in the southwestern part of the area 

where canal water was not available. The maximum decline of water level during this period occurred in a 

local cone of pumping drawdown south of Terra Bella.

From 1950 through 1958, more than 5 million acrefeet of Friant-Kern Canal water was supplied to irrigation districts in the Tulare-Wasco area (table 3) to 

bring about the water-level recovery shown in figures 

26 and 27. This rise in water levels had a marked effect 

in decreasing the rate of land subsidence.

WATER LEVELS IN 1959

Water-level measurements were made by the Geological Survey in about 800 selected observation wells 

in February 1959 to determine the position of the water 

level in deep and shallow wells in the semiconfined 

aquifer system and the piezometric levels of the confined aquifer systems, also to assist in defining the 

changes that had occurred in more than 60 years of 

ground-water exploitation. On the basis of these data 

and some additional measurements by the Bureau of 

Reclamation, three ground-water contour maps have 

been prepared. One (based on measurements in wells 

less than 400 ft deep) depicts the water table in the 

semiconfined aquifer system; the second (based on
B40

119°30'

STUDIES OF LAND SUBSIDENCE

15' 119°00'

36°00

35°45

EXPLANATION

Line of equal water-level change

Dashed where uncertain. Rise (+) 

or decline ( ), interval 20 feet

Observation well used for control

10 MILES

FIGURE 26. Change In the water level in the semioonfined aquifer system, 1948-54, in the eastern part of the Tulare-Wasco

area. Change based on February measurements in 1948 and 1954.

measurements in wells more than 500 ft deep) shows 

the piezometric surface in the deeper, more confined, 

beds of the semiconfined aquifer system; the third defines the piezometric surfaces of the sub-Corcoran and 

the Santa Margarita confined water bodies.

WATER TABLE, SEMICONFINED AQUIFER SYSTEM

Figure 28 shows the altitude of the water table in 

the semiconfined aquifer system as of February 1959. 

Only water levels in wells less than 400 feet deep were 

used in the preparation of this map, and where nearby

wells had different water levels, only the shallowest 

were used. Therefore, the map shows, in effect, the configuration of the water table at the top of the zone of 

saturation. The water table contours of 1959 are highly 

irregular, instead of being relatively smooth and denoting a gentle westward-sloping water table as in 

1905 (fig. 22) and 1920-21 (fig. 23).

Within much of the eastern part of the area, the 

water table in February 1959 was the highest it had 

been since the middle to late forties (fig. 24). This high 

level was the result of increasing deliveries from the
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

119-30' 15' 119-00'

B41

36°00

35"45

EXPLANATION

Line of equal water-level change

Dashed where uncertain. Rise (+) 

or decline ( ); interval 20 feet

Observation well used for 

control

10 MILES

FIGURE) 27. Change In the water level in the semiconfined aquifer system, 1954-59, in the eastern part of the Tulare-Wasco

area. Change based on February measurements in 1954 and 1959.

Friant-Kern Canal, decreasing pumping demand in 

the fifties (figs. 14, 21), and better than average local 

surface-water diversions in 1958 (fig. 14).

The most prominent replenishment features shown 

in figure 28 are the recharge mounds along the Tule 

Biver. to a lesser extent along Deer Creek, and in the 

vicinity of Delano along the southern service area of 

the Friant-Kern Canal. At Lindsay, the water table 

had recovered to roughly the same level it was at in 

1921 (fig. 23); however, the cone of maximum draw332-133 O -69 1

down had shifted about 6 miles to the south west where 

the water table was about 75 feet lower than in 1921.

The water table was lowest in the pumping trough 

extending west from Pixley and Alpaugh and in a 

small area west of Wasco. In these areas, the water 

table had declined from a few feet below the land surface (alt 200-260 ft above sea level) in 1905 to an 

altitude of about 120 feet in 1959. South of Kichgrove, 

pumping from an area of minimal recharge had created a pumping trough along the Kichgrove-Famoso 

highway.
B42 STUDIES OF LAND SUBSIDENCE

119°00'

36°00'

35° 45'

EXPLANATION

Water-table contour

Shows altitude of water table. 

Dashed where uncertain; contour 

interval 20 feet. Datum is mean 

sea level

Observation well used for 

control; less than 400 feet 

deep

10 MILES

FIOUBB 28. Altitude of the water table In the semiconfined aquifer system, February 1959.

PIEZOMETEIC SURFACE, SEMICONFINED AQUIFER SYSTEM

Figure 29 shows the configuration of the water surface in February 1959 for deep wells tapping the semiconfined aquifer system. Only the water levels in wells 

deeper than 500 feet and not tapping the Santa Margarita water body (fig. 18) were used in the preparation of 

this map. Therefore, this map shows only the piezometric surface in the deeper, more confined, aquifers of 

the semiconfined system. Compaction of this lower part 

of the semiconfined system is believed to have caused 

most of the land subsidence east of U.S. Highway 99.

As shown in figure 29, the contours for this piezometric surface have been terminated at the east edge of 

the Corcoran confining layer where the deeper sands 

and gravels of the semiconfined system merge with the 

confined aquifer system below the Corcoran Clay Member (figs. 4, 5). Also, contours have been omitted in the 

northern part of the map where insufficient water-level 

control was available for deep wells. Few of the wells 

drilled in the Lindsay-Tulare area are deeper than 500 

feet, and most of these sure perforated throughout the 

saturated section. Of the water levels measured in that
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

119°30' 15' 119"00'

B43

36°00'

35°45'

EXPLANATION

Piezometric contour

Shows altitude of piezo metric turface;dashed where uncertain. Contour intervals 20 and 50 feet. Do.tum 

is mean sea level

Approximate boundary of the 

confining Corcoran Clay 

Member of the Tulare Formation

Observation well used for control; more than 500 feet deep

FIGURE 29. Piezometric surface of the semiconflned aquifer system, February 1959.

area in the spring of 1959, none was considered representative for the lower part of the semiconfined system. 

In February 1959, the water table (fig. 28) was higher 

than the piezometric surface of the deeper zones of the 

semiconfined aquifer system (fig. 29) in most of the area 

where major imports of surface water had been received from the Friant-Kem Canal. This difference 

was particularly evident in the central area between 

Delano, Richgrove, Terra Bella, and a point 5 miles 

northeast of Tipton. In a broad area east of Delano, 

and also in a small area southeast of Pixley, the water 

level in shallow wells was as much as 60 feet above the

level of deeper wells. In the southern part of the area 

where much less canal water had been received (table 

3; fig. 13), notably northeast and northwest of Famoso, 

the water table was generally 10-40 feet below the piezometric surface. Between and to the west of Terra Bella 

and Porterville, the water level in shallow wells stood 

10-60 feet below the level of the deeper wells.

WATER LEVEL OF THE CONFINED AOTIFER SYSTEM

Few wells in the western part of the Tulare-Wasco 

area tap only the confined aquifer system below the 

Corcoran Clay Member (Eg. 18). Many of the deeper
B44 STUDIES OF LAND SUBSIDENCE

wells are perforated both above and below this confining layer, and their water leA7 els are a composite of 

the upper semiconfined and lower confined pressures. 

Only 14 of the observation wells measured during the 

spring of 1959 were considered representative of the 

sub-Corcoran confined system. The measurements obtained from these wells were the basis of figure 30 

which shows the February 1959 piezometric surface for 

this confined aquifer system. Dashed contours have been 

extended east to the boundary of the Oorcoran Clay 

Member to join the piezometric contours for water

levels in the deep wells in the semiconfined aquifer system (fig. 29) because the two water bodies are continuous. Owing to the wide range of perforated intervals 

in wells whose water levels were used to construct figure 29, however, the dashed contours of figure 32 immediately west of the Corcoran boundary represent 

only a rough approximation of the piezometric surface 

in the confined aquifer system.

Because of the scarcity of observation wells, the contours defining the sub-Corcoran piezometric surface are 

generalized. These piezometric contours, considered to119°30' 119°00'

36°00'

35°45'

EXPLANATION

Piezometric contour

Shows altitude of piezometric surface; 

dashed where inferred. Contour 

interval, 10 feet. Datum is mean 

sea level

Approximate boundary of the 

confining Corcoran Clay 

Member of the Tulare Formation

O

Observation well

Taps the sub-Corcoran confined

aquifer system,

Observation well

Taps the Santa Margarita Formation

as used by Diepenbrock (1933)

10 MILES

FIGURE 30. Piezometric surfaces of the confined aquifer systems, February 1959. Dashed contours near boundary of the Corcoran 

Clay Member are extensions of the piezometric surface in the semiconfined aquifer system (fig. 29).
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B45

gether with the piezometric contours in the semiconfined aquifer system to the east (fig. 29), indicate however, that ground-water movement beneath the edge 

of the confining clay converged toward the west-central 

part of the area. The artesian head at Alpaugh had 

been drawn down more than 130 feet since 1905 by heavy 

pumping.

An upward gradient through the Corcoran confining 

layer prevailed until about 1920, but subsequent depression of the piezometric head in the underlying confined system reversed the direction of this gradient. As 

of spring 1959, the piezometric head in the confined 

aquifer system was as much as 60 feet below the overlying semiconfined water surface. Because of the very 

low permeability of the clay confining layer, however, 

the amount of recharge that moves downward through 

the clay under this downward hydraulic gradient is 

small. Recharge to the confined aquifer system is thus 

derived almost exclusively from the deep semiconfined 

aquifers that project under the confining clay and to an 

unknown extent through irrigation wells and gravel 

envelopes from the overlying semiconfined aquifer 

system.

WATER LEVEL IN THE SANTA MARGARITA FORMATION AS USED 

BY DIEFENBROCK (1933)

Eighteen large irrigation wells in the vicinity of Richgrove, drilled to depths greater than 1,800 feet, are perforated in the productive Santa Margarita Formation 

as used by Diepenbrock (1933). Only six of these wells 

tap exclusively this deep artesian aquifer; however, a 

half dozen others include in their perforated interval 

only the lower part of the overlying poorly permeable 

marine siltstone as shown in hydrologic section B-B' 

(fig. 18) and thus have water levels believed to be representative of the Santa Margarita. Figure 30 shows 

the configuration of the piezometric surface of the confined water in the Santa Margarita in February 1959; 

the plotting was controlled by the water levels of the 

12 wells that are not perforated in the semiconfined 

aquifer system.

Ground water has been pumped from the confined 

Santa Margarita water body since the early 1950?s. This 

withdrawal has had a marked effect on water levels in 

wells tapping this formation. As indicated by the hydrograph of well 25/27-18A1 (fig. 31). The head in the 

Santa Margarita declined as much as 156 feet from 

August 1956 to October 1964, at an average rate of 

about 20 feet per year.

As of spring 1959, the water level in wells tapping 

the Santa Margarita (fig. 30) generally stood within 

50 feet of the same altitude as the water level of the

deep aquifers of the semiconfined aquifer system (fig. 

29), but ranged from 20 feet higher to 90 feet lower. 

Piezometric contours are highly contorted, and probably 

are influenced by pumping cones around individual 

wells as well as by the regional drawdown that has 

developed since this aquifer was first tapped in 1954. 

Contours indicate a local westward piezometric gradient 

in the Santa Margarita of about 25 feet per mile.

SUMMARY OF WATER-LEVEL TRENDS

Hydrographs of 15 observation wells or piezometers 

are included to indicate long-term water-level trends 

at various locations in each of the aquifer systems. Also 

included are graphs showing subsidence of bench marks 

near many of these observation wells; they will be considered later in the discussion "Relation of subsidence 

to water-level change." Locations of all wells and bench 

marks for which graphs are included in this report are 

shown in figure 32.

Because effective stresses are generally greatest and 

subsidence usually most rapid during periods of maximum water-level decline, changes in seasonal low water

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1955 1960 1964

FIGURE 31. Hydrograph of well 25/27-18Al tapping the confined 

Santa Margarita Formation as used by Diepenbrock (1933), 3 

miles south of Richgrove. See figure 32 for location of well.
B46 STUDIES OF LAND SUBSIDENCE

R 22 E 119°30'R 23 E R 25 E 15' R 27 E 119-00'

~ \ ' i ~~ ' IT ~~~'t , xey _ 1 I /*"" p_ S ______ TVrra Rella^ r

EXPLANATION

Basement complex

Edge of foothills

Approximate boundary of the 

Corcoran Clay Member of 

the Tulare Formation

Observation well and number 

for which hydrograph is included in this report

Bench mark and number for which 

subsidence graph is included 

in this report

FIGURE S2. Location of wells and bench marks for which graphs are included In this report.

levels are more significant in relation to compaction, and 

subsidence than are changes in seasonal high levels. 

The discussion of water-level trends that follows relates 

to seasonal low levels where possible.

SEMICONFINED AQUIFER SYSTEM

The long-term hydrographs of six wells tapping the 

semiconfmed aquifer system in the eastern part of the 

area are shown in figure 33. Well 20/26-22C2, drilled to 

a depth of 247 feet in the northeastern part of the area 

(fig. 32), shows the water-level trend from 1925 to 1964, 

4 miles southwest of Lindsay. Few irrigation wells in 

this part of the area are more than 600 feet deep, and

water levels are relatively shallow. As shown by the 

hydrograph of well 20/26-22C2, the water level was 

declining when the record began in 1925, and it declined 

an additional 135 feet from 1925 to 1951, owing to heavy 

pumping. From 1951 to 1959, the water level rose about 

80 feet in response to surface water imports from the 

Friant-Kern Canal. Following a 2-year decline, it rose 

again in 1964 to about the same level as in 1936.

Shallow water levels in the semiconfmed aquifer system overlying the outer fringe of the Corcoran Clay 

Member in the Tipton-Pixley area followed much the 

same pattern. As shown by hydrographs of wells 

22/25-6J and 22/25-7H1 (fig. 33), 2 miles south of
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B47

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FIOUEE 33. Hydrographs of six wells tapping the semieonflned aquifer 

system and graphs of subsidence of selected nearby bench marks. 

See figure 32 for location of wells and bench marks.

Tipton, the water level declined about 75 feet from 192Y 

to 1952, then rose sharply in response to surface-water 

imports, and in 1958 stood at about the same height as 

in 192Y.

In the east-central part of the area, intensive pumping has caused water levels to decline almost continuously since records began. Observation well 23/27-28 Jl, 

900 feet deep and about 8 miles northeast of Eichgrove, 

is considerably east of the Friant-Kern service area. 

The water level in this well (fig. 33) showed a uniform 

decline of about 85 feet from 1925 to 1953, then an 

accelerated decline of 160 feet through 1964. Of special

significance was the marked increase in the range of 

seasonal fluctuations, from 4 feet in 1925-26, to about 

20 feet in the early fifties, to TO feet in 1964. This change 

suggests a marked increase in the rate of seasonal 

pumping which closely parallels the trend of waterlevel decline. No evidence of water-level recovery during the fifties was observed in any of the wells of this 

area.

Observation well 24/26-30R1, drilled to a depth of 

1,239 feet in an intensely developed area 4 miles northeast of Delano, is typical of irrigation wells in this 

vicinity. Because it is perforated throughout most of 

its depth, this well registers a composite water level of 

various depth zones. The water level in this well declined about 1YO feet from 1925 to 1951, but rose sharply 

about the same amount during the period of surfacewater import, 1951-64. Seasonal fluctuations due to 

pumping were much less after 1951 than during the 

forties when ground-water pumpage supplied most of 

the irrigation requirements.

Hydrographs of wells 24/2Y-1YL1 and 26/25-19P1 

(fig. 33), located 3 miles northeast of Eichgrove and 

4 miles north of Wasco, respectively, each show an uninterrupted downward water-level trend throughout the 

period of record. Like well 23/2Y-28J1, well 24/2Y-1YL1 

is located in an interfan area of little natural recharge 

east of the service area of the Friant-Kern Canal. 

Similarly, much of the area around well 26/25-19P1, 

is outside of organized irrigation districts that have 

received surface water deliveries from the Friant-Kern 

Canal. Though the region has received canal imports 

from the Kern Eiver for many years, pumpage has 

exceeded recharge, and water levels in most of the irrigation wells have declined without interruption. The 

spring high water level in well 26/25-19P1 declined 

about 85 feet during the period of available record, 

1945-61.

In the western part of the area, water levels in the 

semiconfined aquifer system overlying the Corcoran 

Clay Member generally declined throughout the period 

of record, 1952-64. As shown by the hydrograph of 

piezometer 1, well 23/23-33A1 (fig. 34), completed by 

the Bureau of Eeclamation in 1952 to register waterlevel changes in the 350-550-foot depth zone of the semiconfined aquifer at Alpaugh, the shallow water level 

declined about 25 feet from 1952 to 1964. During this 

13-year period, the seasonal fluctuation and the longterm downward trend remained relatively constant. 

Eleven miles to the south-southwest, the hydrograph of 

piezometer 3, well 25/23-29A1 (fig. 34), completed by 

the Bureau of Eeclamation in 1952 in the 0-280-foot 

depth zone, shows a general decline of about 1Y feet dur-
B48 STUDIES OF LAND SUBSIDENCE

No. 1. Zone 350-550 feet. Semiconfmed

No. 2. Zone 570-920 feet. Confined

No. 3. Zone 940-1200 feet. Confined

FIGURE 34. Hydrographs of piezometers tapping the semiconflned 

and confined aquifer systems at and south of Alpaugh, and graphs 

of subsidence of nearby bench marks. See figure 32 for location of 

wells and bench marks.

ing the 13 years of record. The range of seasonal fluctuations decreased from 40 feet in 1952 to about 17 feet in 

1964.

CONFINED AQUIFER SYSTEM

In 1905, wells tapping the confined aquifer system 

flowed throughout most of the area underlain by the 

Corcoran Clay Member (fig. 22). Field notes of 1906 

(in files of the U.S. Geological Survey, Sacramento, 

Calif.) reported an artesian head 20 feet above land surface in a well in T. 23 S., R. 23 E., sec. 33, which tapped 

sands 1,200-1,400 feet deep. From 1906 to 1952, when 

Bureau of Reclamation piezometers were installed, little information is available to indicate the trend of water 

levels in the sub-Corcoran aquifer system. The 1906 field 

notes and the hydrograph for piezometer 3 (fig. 34) indicate, however, that the artesian head in the deeper 

part of the confined system in well 23/23-33 at Alpaugh 

declined about 114 feet from 1906 to 1953.

The hydrographs of the two deepest piezometers in 

well 23/23-33Al (fig. 34), which were completed by the

Bureau of Reclamation in 1952, to register head at two 

different depth intervals, indicate change in piezometric 

head in the confined aquifer system at Alpaugh. The 

hydrograph for piezometer 2, registering water-level 

changes in the 570-920-foot depth zone, shows a continuing seasonal fluctuation of about 20 feet per year and 

an overall downward trend of about 40 feet during the 

10 years of available record. A suggested flattening of 

the hydrograph from 1955 to spring 1959, however, and 

a marked increase in rate of decline from 1959 to 1961, 

are in contrast to the nearly uniform decline of water 

level in the overlying semiconfined zone (piezometer 1, 

fig. 34). The water level in the deeper confined zone 

(piezometer 3, 940-1,200-foot depth zone), on the other 

hand, fluctuated from 45 to 60 feet each year and declined erratically during the 1952-59 period of available 

record. Through this period, the downward hydraulic 

gradient through the confining layer (zone 1 to zone 2) 

and also within the confined aquifer system (zone 2 to 

zone 3) increased with time. It is noteworthy that at all 

times during the period shown, a greater downward 

head differential existed within the confined aquifer 

system than across the confining clay.

At the piezometer site 11 miles south-southwest of 

Alpaugh, hydrographs of two piezometers in Bureau of 

Reclamation well 25/23-29Al (fig. 34) indicate the 

changes in water level in two depth zones in the confined 

aquifer system. As at Alpaugh, two different water levels 

are registered in the confined system at this location, 

with a definite and increasing gradient between the two. 

Piezometer 1, measuring the 300-630-foot depth zone, 

showed a continuing seasonal fluctuation of 35-50 feet 

per year and a general downward trend of seasonal lows 

of about 3 feet per year. The water level in piezometer 

2, measuring the 650-800-foot depth zone fluctuated 

through a range of 70-80 feet per year and declined 

about 9 feet per year from 1952 to 1964. Here also, the 

downward head differential within the confined system 

(piezometers 1, 2) was much greater than that across 

the confining layer (piezometers 3,1). The seasonal and 

long-term patterns of all three hydrographs are similar, 

varying mostly in the amount of seasonal fluctuation 

and long-term decline.

Hydrographs of two other wells tapping the confined 

aquifer system northwest and southwest of Delano are 

shown in figure 35. Well 24/24-9Q1, 1,200 feet deep 

and 9 miles northwest of Delano, reportedly flowed 

when first drilled (date unknown). Although intermediate records are not available, the spring-high-water 

level in this well had fallen to 70 feet in 1951 and continued to decline to 110 feet below land surface by the 

spring of 1961, the last year of available record. Seasonal 

fluctuations during the 12 years of record varied from 10
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B49

50 

70 

90

no

40 

60 

80 

100 

120 

140 

160 

180

 fl

V-.

I /

^

Well 

owec

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repo 

at o

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V

rtedl 

ne ti

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-v-\

b_e_n

y v

\

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\

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irfc

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V

r 

 ^

^n

k/

-42

\ \ , \ /

V

J4S

V

,,

V

x .

V

 -^

V

* .

\ 1

Well 24/24-9Q1 V 

(Depth 1,200 feet)

a^

^ \

V

\

V

~~~~,

»\

[V

*- ,

\

i-754

^

*^>.

\/

Well 26/24-3H1 

(Depth 600 feet)

\ ^

\/

Ca

\

I

sing 

Iged

K

0 

1.0 

2.0 

3.0

4.0 

0

1.0 

2.0 

3.0 

4.0

CT» CTI CT» CTl

FIGURE 35. Hydrographs of two wells tapping the confined aquifer 

system west of Delano and graphs of subsidence of nearby bench 

marks. See figure 32 for location of wells and bench marks.

to 30 feet. Well 26/24-3H1, drilled to a depth of 600 

feet 9 miles southwest of Delano, showed a similar 

downward trend from 1947 to 1961 (fig. 35). Although 

a lack of data makes the hydrograph of this well appear 

more erratic than probably was the actual case, the 

trend of the annual spring highs declined about 6 feet 

per year.

As indicated "by the hydrographs of figure 34, multiple water levels and large head differentials occur 

within the confined aquifer system near Alpaugh. A 

consistent downward head differential that is greater 

than the differential across the principal confining layer 

has existed since 1952 within the confined aquifer system. Confined water levels throughout the area have 

shown a consistent long-term downward trend, with 

no suggestion of cessation or recovery as was typical 

of the semiconfined aquifer system in the eastern part 

of the area during the fifties. No effects of recharge 

from surface-water deliveries from the Friant-Kern 

Canal are observed in any of the hydrographs of the 

confined aquifer system.

SUBSIDENCE OF THE LAND SURFACE

Land subsidence was first recognized in the TulareWasco area in 1935, when consulting engineer I. H. 

Althouse of Porterville completed a survey which indicated considerable settlement of bench marks in the 

central part of the area (Ingerson, 1941, p. 40). Certain 

levels that he ran indicated definite subsidence when 

compared with altitudes given on topographic maps of 

the Geological Survey surveyed in 1926. The following 

was reported in the local Porterville newspaper 

(July 20, 1939) :

Two miles north of Delano the valley floor has sunk five feet 

below the elevation established in 1927 * * *. At Barlimart 

the subsidence amounts to about two feet * * *. That the sinking of the earth's surface is probably due to the removal of 

great amounts of underground water, allowing deep strata to 

be compressed under the weight of the overlying soil is supported by the fact that the point where the subsidence is the 

deepest is approximately where the greatest amount of water 

has been pumped from below and further by the fact that west 

of Delano where there has been very little pumping, no depressing of the surface is shown.

This evidence of subsidence caused considerable concern, and in 1940, a detailed survey was made of the 

subsiding area by the California, Division of Water Resources. Level circuits were run from stable bench 

marks in the eastern foothills throughout the subsidence area, and ties were made to more than 100 bench 

marks of the Geological Survey and the Coast and Geodetic Survey. New altitudes were established at roughly 

500 section corners, and these were compared with 

corresponding altitudes on Geological Survey topographic maps (surveyed in 1925-27, but based largely on 

1902 leveling control along U.S. Highway 99). Using 

these data, Ingerson (1941, fig. 7) prepared the first 

map delineating subsidence in the Tulare-Wasco area 

(fig. 36). The map showed that an area extending about 

20 miles along the Southern Pacific Railroad from Pixley to McFarland and totaling more than 200 square

119°30'R 23 E R 24 E R 25 E

EXPLANATION

Line of equal subsidence

Interval 0.5-foot

FIGURE 36. Lines of equal subsidence in the Delano area, 

1902-40 (from Ingerson, 1941, fig. 7).
B50 STUDIES OF LAND SUBSIDENCE

miles subsided more than 1 foot from 1902 to 1940. 

Ingerson also presented a series of depth-to-water and 

subsidence profiles along the Southern Pacific Eailroad. 

He attributed the subsidence primarily to water-level 

decline, which had ranged from 25 to 125 feet in the 

subsiding area from 1921 to 1939 (Ingerson, 1941, 

fig. 4).

LEVELING DATA AVAILABLE

The first precise leveling in the Tulare-Wasco area 

was done by the Geological Survey in 1901-2. Bench 

marks were established along the main line of the 

Southern Pacific Railroad as part of a line of levels run 

from the tidal bench mark at Benicia to Mojave, Calif. 

Altitudes for this early survey were published in Geological Survey Bulletin 342 and later in Bulletin 766 

(U.S. Geological Survey, 1908, 1925). Only eight of 

these early bench marks were recovered during the 1931 

resurvey of this line by the Coast and Geodetic Survey. 

Altitudes for these eight bench marks, published in 

Geological Survey Bulletins 342 and 766, were recently 

revised but not published by the Topographic Division 

of the Geological Survey. Unpublished readjusted altitudes, based on a recomputation of the 1901-2 levels 

in areas now known to be subsiding were furnished by 

the Topographic Division (written commun., Nov. 

1961) and were used in preparing figure 39. The Topographic Division also established bench marks along 

several survey lines in conjunction with their 1926 mapping program.

In 1931, a line of first-order levels was run by the 

Coast and Geodetic Survey along the Southern Pacific 

Eailroad adjacent to Highway 99. Subsequently, firstand second-order levels were run along various lines in 

the Tulare-Wasco area in 1935,1940,1943, and 1947. In 

1948, with the realization of the importance of adequate 

leveling control in this area of land subsidence, the 

Coast and Geodetic Survey, in consultation with the 

Geological Survey and other interested agencies, laid 

out a detailed network of level lines throughout the 

subsidence area, and a schedule of periodic releveling 

was set up.

Figure 37 shows the network of level lines for which 

comparative leveling by the Coast and Geodetic Survey 

in 1948 and in subsequent resurveys is available. Lines 

from this network extend beyond the limits of the map 

and tie on the north, west, and south with an extensive 

network of level lines in the San Joaquin Valley. As 

shown, first-order lines extend to stable bench marks 

in bedrock east of Porterville and at Woody. Bench 

marks along these lines furnish control for areal topographic mapping by the Geological Survey, for engineering surveys by public and private agencies, and for

the computation of the rate and extent of land 

subsidence.

PROBLEMS RELATED TO ACCURATE LEVELING IN 

SUBSIDENCE AREAS

Standard methods of leveling and adjusting errors 

of closure in a leveling circuit are inadequate in an area 

of active land subsidence. Concepts of assigning absolute altitude to bench marks and of distributing the 

error of closure proportionately along the length of the 

circuit usually cannot be applied. Altitudes assigned to 

bench marks apply strictly only to the date that the 

survey was made and then are only as accurate as is 

the altitude of the reference bench mark. During periods of rapid subsidence, bench marks in centers of 

the most active areas may subside as much as 0.004 foot 

per day. From the time a leveling party quits work at 

a particular bench mark on a Friday evening until the 

following Monday morning, more than 0.01 foot of subsidence could have occurred, and thus, maintaining an 

accuracy of even 0.01 foot requires that several special 

procedures be followed. Because of the unstable conditions, absolute altitudes reported for bench marks in 

centers of most rapid subsidence should be considered 

accurate to no more than a tenth of a foot. Eelative 

altitudes between adjacent bench marks, however, are 

usually much more accurate.

The Tulare-Wasco area falls within four 30-minute 

quadrangles, as designated by the Coast and Geodetic 

Survey (fig. 37). Two additional quadrangles include 

the level lines that tie to bedrock bench marks on the 

east. Within these quadrangles, the Coast and Geodetic 

Survey has assigned the individual line numbers (fig. 

37), which are used in identifying the individual bench 

marks. Table 7 gives the years and months in which 

leveling has been done by the Coast and Geodetic Survey for each of these level lines. In the tabulation, quadrangles and level lines are numbered in accordance with 

Coast and Geodetic Survey published designations (fig. 

37). In addition to the leveling summarized in table 7, 

leveling control used in the subsidence investigation of 

the Tulare-Wasco area includes the 1902 leveling of 

bench marks along line 101 by the Geological Survey 

and the 1940 leveling of the California Division of 

Water Resources used by Ingerson (1941) in preparing 

his figure 7 (reproduced here as figure 36). The amount 

of subsidence between successive levelings is readily 

computed as the difference between the respective altitudes shown. Chronologic tabulations of adjusted altitudes of bench marks throughout the Tulare-Wasco 

area, prepared by the Coast and Geodetic Survey, have 

served as the basis for preparing the subsidence maps, 

profiles, and graphs in this report and have proved 

invaluable in this investigation.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

R 22 E 119°30' R 23 E R 24 E R 25 E 15' R 26 E R 27 E.ngoQQ/ R 28 E

Unconsolidated sedimentary deposits of late Tertiary and 

Quaternary age

Sierra Nevada basement complex

U.S. Coast and Geodetic Survey 

d

»J- . U.O. V^UiJOL dllU VJCVUCLll; OUIVC

!' "V_ quadrangle boundary an 

J ''\ number

I '. S'7 L.

'<&*?*

FIGURE 37. Network of leveling by the U.S. Coast and Geodetic Survey. The level-line numbers in each quadrangle are those published

by the Coast and Geodetic Survey.

In order to maintain leveling accuracy in subsidence

areas, the following precautions should be considered:

1. Insofar as possible, leveling should be completed

during the season of least rapid subsidence. In the

Tulare-Wasco area, the rate of subsidence is most

rapid during the seasonal water-level decline and

is at a minimum during the winter months of

December through February, when water levels are

high.

2. In areas of major land subsidence, bench marks must 

be considered as continually changing in altitude. Level circuits should be tied to bench marks 

outside the centers of most rapid subsidence. If

leveling of a line is interrupted for more than a 

few days, the survey should be rerun from a reference bench mark in a relatively stable area before 

continuing the circuit. Also, errors in circuit 

closure should be assigned where subsidence is most 

rapid.

3. The network should tie at several places, if possible, 

to bench marks on stable bedrock outside the subsidence area. The part of the leveling network 

within the subsidence area should be considered as 

"floating" until a tie to a stable bench mark can 

be made; then the error of closure should be distributed back into the circuit.
B52 STUDIES OF LAND SUBSIDENCE

TABLE 7. Dates of leveling control by the U.S. Coast and Geodetic Svrvey in the Tulare-Wasco area, 1981-64

Quadrangle

351191.............

351194..............

361183 .. 

361192..............

361193..... . ........

Line

101

102

103

104

105

106

107

10?

109

110

111

112

113

114

115

116

101

102

103

107

102

101

102

107

108

109

110

102

112

1931 1933 1935 1940 1942 1943 1947 1948 1953-54 1957 1958-59 1962 1964

Feb . Sept.-Oct __ .. Mar... May.. Feb. Nov. 53.. ___ Jan.... __ Feb. 59.. _____ Feb.-Mar _ Feb.

 ________________ Mar _ Dec. 53-Jan. 54. Feb _____ Mar. 59 ______ Feb.-Mar _

 _____________ May.. Jan. 54.. . _ Feb. __ Mar. 59. _____ Mar ____

__ .. ._ _ . ______-_ _ ........... May.. Feb. 54... . _ .. Feb... __ .. Mar. 59. . ____ Mar. . ....

... .. ___ .. _____ Mar Dec. 53 _ . __ Feb. ____ Feb.-Mar. 59 ___ Jan.-Mar _ Feb.

 . ... Mar.. . . __ __ Apr _ Apr... Nov. 53... __ Mar _ ...... Feb. 59 ____ ; _ Feb _____ Feb.

 Mar. . .... May.. Apr... Nov. 53-Mar. 54. . Jan....... Feb. 59 ______ Jan. -Feb _ Feb.

...... ___ . __ ... ___ . ________ . ___ .. Apr _ Nov. 53-Mar. 54.. Feb. ____ Mar. 59. _____ Feb.......

.. _____ ___ Dec _____ June.. Apr _ Mar. 54 ______ Feb ____ Feb. 59 ______ Feb ____ Feb.

_ ___ . ______________ Apr _ Mar. 54 ______ Feb.-Mar _ Mar. 59 ______ Feb ...... ...

.. .... ... __ ... _____________ Apr... Mar. 54... ____ Feb.-Mar _ Mar. 59 ______ Feb ... ...

.. Jan... _____ Mar.. ____ Feb _ Nov. 53-Jan. 54. Feb.-Mar _ Feb. 59 ______ Mar .........

... . .. ................ _ ................................. Nov. 53.. _ ...... Feb.. Mar. 59.. ___ ..... __ . ......

. -. .. ..................................... _ ............. Mar. 54... ... Feb. ____ Mar. 59... _____ .... __ . _

 Feb ... Dec . June... . Feb. 54 __ ..... Mar... ___ Mar. 59 ______ Feb ____ Feb.

 .. ___ Dec ______________ Mar. 54.. ____ June.. ___ Mar. 59. __ __ _ ..

 .... Feb. . . Dec. . .. May.. Jan.-Feb. 54...... Feb.-Mar _ Jan.-Feb. 59... _ Mar ____

 .. . .. May.. Jan. 54 ___ Feb ____ Mar. 59 ______ Mar ____

 Dec Feb.-Mar. 54 _ .. Mar.-Apr _ Nov.-Dec. 58 __ Mar ____

_ ---. .. Jan.... _____ . ____ .... ___ Apr ____ ... Feb. 54.. _____ Mar.... __ Nov. 58-Mar. 59.. Mar.. .

-_- . __ . ___ Apr.......... Nov. 53-Mar. 54... Mar... .. Feb.-Mar. 59.... Feb. Feb.

Jan........... Feb... Aug _______ Feb _ June.. Mar _ Feb.-Mar. 54..... Feb.-Apr _ Feb. 59 ______ Feb.-Mar ...

................ Feb... Aug. .................. Apr Mar. 54..... Mar.-May_.(g£- ffaVw"" "" }Feb ..... - Feb.

... .. Feb.- Aug....... ................................ Feb. 54...... .................... Feb. 59...... .. Feb.-Mar...

.... _ .___. _ -..... ..... Apr... Mar. 54.. .. Feb.. ....... Mar. 59..... ...... Feb..... .

... -....- . . --.-...... _ .. Jan.......-,- May.. Feb. 54 - ....... Feb. -.... Feb. 59 ........ Mar..... ....

..... ........ Feb---.----...-.-.....-- Apr... ........ Feb. 54 -..... Mar. -... Mar. 59....... __ Feb ----- Feb.

_ ..... ____ Feb _ . _____ Dec _ ________ June.. Feb. 54, ____ .. Mar. __ Dec. 58.. . Mar

------...--- ..--- --..---. Jan........... May.. Feb. 54.... ........ Feb... ...... Feb. 59 Mar.....

Fortunately, most of the leveling by the Coast and 

Geodetic Survey in the Tulare-Wasco area has been done 

during the winter months when water levels in wells are 

high and the rate of subsidence is minimal. When the 

level network was established in 1948, many of the problems involved in the leveling of subsiding areas were 

clearly recognized. Later, bench marks were established 

on bedrock outcrops east of Porterville and at Woody, 

east of Delano, and these were used as stable reference 

ties for each subsequent resurvey. Adjustments that have 

been made in closing leveling traverses have taken areas 

of subsidence into account, and floating sections of the 

network have been tied to the stable bench marks.

Land subsidence also poses serious problems in maintaining topographic-map control as bench marks continue to subside. Eight of the thirty 7%-minute topographic quadrangle maps of the Geological Survey that 

cover the Tulare-Wasco area had been remapped as of 

1954 to correct for the land subsidence since the original surveys. By 1959, however, as much as 2% feet of 

additional subsidence had occurred locally in the remapped area, and by 1962, some of the topographic contours 

were as much as 5 feet in error. For two-thirds of the 

Tulare-Wasco area, the latest topographic mapping was 

done in 1926, and much of this apparently was tied to 

1901-02 benchmark control.

MAGNITUDE AND AREAL EXTENT OF SUBSIDENCE

The magnitude, extent, and rate of subsidence in the 

Tulare-Wasco area, as denned primarily by the results 

of releveling of bench marks but in part by the topographic mapping, are shown by a series of graphs, profiles, and maps (figs. 38-51) in this section. These 

illustrate the great variation in subsidence, both areally 

and in time, during the period of leveling control.

Plots of subsidence at bench marks of longest record 

near the two centers of maximum subsidence in the 

Tulare-Wasco area illustrate the magnitude and the 

variation in rate of subsidence at those places from 

1901-2 to 1964 (fig. 38). The locations of these bench 

marks and their relation to the centers of maximum 

subsidence are shown in figure 50. They also are included in the series of subsidence profiles along U.S. 

Highway 99 (fig. 38). Bench mark 302.847 is 4 miles

\

Bench mark 302.847 \

^Bench mark 274.875

* -A-A

4 miles north of Delano

EXPLANATION

Leveling by U.S. Geological 

Survey

Leveling by U.S. Coast and 

Geodetic Survey

\

S

Bench marks 

about 2 miles 

iouth of Pixley

LxBench mark M829

\ k 

\ \

FIGURE 38. Subsidence of bench marks near centers of maximum subsidence, 19O1-2 to 1964. Location of bench marks shown in 

figure 50.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B53

north of Delano; bench marks 274.875 and M829 are 

about 2 miles south of Pixley and 0.5 mile apart.

The rate of subsidence of the bench marks at both 

sites increased almost continuously from 1931 to 1954, 

although the pattern of increase differed at the two 

sites, presumably owing to differing rates of water-level 

decline. After 1954, however, the rate of subsidence at 

the bench mark north of Delano decreased greatly in 

response to a rise in water levels attributable to the increased water supply and ground-water recharge from 

Friant-Kern Canal imports. In contrast, bench mark 

M829, south of Pixley, continued to subside at approximately the same rate as before 1954, because it is in an 

area relying almost wholly on ground water for irrigation. The bench mark north of Delano subsided only 

about 0.7 foot from 1954 to 1964, whereas bench mark 

M829 south of Pixley subsided 5.3 feet, or about seven 

times as much. Graphs showing the subsidence of a 

number of bench marks in other parts of the subsidence 

area are shown in figures 33-35.

SUBSIDENCE PROFILES

The available leveling data along line 101 (fig. 37) 

were used to prepare the subsidence profiles of figure 

39, which show the magnitude and extent of subsidence 

from Tulare to Famoso between successive levelings 

since 1901-2. Each profile is based on the altitude of the 

individual bench marks for the date indicated. The 1931 

altitude of each bench mark, as determined by the first 

leveling of the Coast and Geodetic Survey, is used as 

the reference datum. Eight of the Geological Survey 

bench marks from Tulare to south of Earlimart surveyed in 1902 were recovered in 1931. The subsidence at 

these bench marks between 1901-2 and 1931 is shown by 

a dashed line above the 1931 datum. Profiles between 

Pixley and Delano show the subsidence between successive levelings from 1931 to 1964. North of Pixley and 

south of Delano, the latest releveling was in 1962.

As shown in figure 39, the entire reach from Tulare 

on the north to Famoso on the south has been affected 

by subsidence since 1931. Prior to 1948, the most rapid 

subsidence was between Earlimart and Delano, in the 

vicinity of bench mark 302.847 (fig. 38); the location 

of most rapid subsidence since 1948 has been about 8 

miles northward. Between Pixley and Earlimart, the 

continued decline of water levels in the confined aquifer 

system due to heavy pumping caused a nearly constant 

rate of subsidence from 1948 to 1964 (bench mark M829, 

fig. 38). As of spring 1964, 12.1 feet of subsidence had 

occurred at bench mark P88, in the center of maximum 

subsidence between Pixley and Earlimart. Through 

much of the area, the subsidence rate slowed markedly 

between the 1953-54 leveling and the 1957 leveling, and

in the southern half of the section, between Earlimart 

and Famoso, subsidence stopped from 1957 to 1959 (fig. 

46). This cessation was in direct response to large 

water-level recoveries brought about by the importation 

of surface water through the Friant-Kern Canal, beginning in 1950. From 1959 through 1962, which were years 

of deficient surface supply and increased pumping, 

water levels in deep wells again began to decline, and 

subsidence resumed along the entire reach from Tulare 

to Famoso; maximum rates between Tulare and Tipton 

and between Pixley and Earlimart were about 0.7 foot 

per year.

Figure 40 shows the magnitude of subsidence between successive levelings along line X-X', eastward 

through Pixley (fig. 44), for the period 1942-43 to 

1964 (to 1962, west of Pixley). This line of profiles extends from bench mark M662,6 miles south of Corcoran, 

eastward to bench mark N288 at Terra Bella. As shown 

in figure 44, the line is offset 3 miles to the south at 

Pixley. Because earlier leveling data were not available, the 1942-43 bench-mark altitudes were used as the 

straightline base for this section. The amount of subsidence since 1942-43 along this line is least near Terra 

Bella and greatest east of Pixley. The substantial decrease in the rate of subsidence between 1954 and 1959 

(5-year period) compared to the rate between 1948 and 

1954 (6-year period) reflects the effect of decreased 

pumping and increased recharge from surface-water 

imports. The accelerated subsidence in 1959-62 was the 

result of increased pumping and water-level decline 

during 3 years of deficient surface supply. In the confined aquifer system west of Pixley, the decline was a 

continuation of the earlier trend. In the semiconfined 

system east of Pixley, the decline was primarily in the 

piezometric surface of the deeper more confined zones; 

in some of the canal service area, the water table of the 

semiconfined system actually rose from 1959 to 1962. 

(For an example, see figure 68, middle graph, hydrograph for 25/26-6H1.)

The amount of subsidence along the Tulare-Kern 

County line between successive levelings from 1948 to 

1962 is shown in figure 41. From bench mark B758 to 

a point east of Richgrove, the line is offset about 1 

mile north of the county line. In general, less subsidence 

has occurred since 1948 in this part of the area than 

farther north (line X-X', fig. 40). The longest history 

of subsidence along this line is at bench mark U88, adjacent to U.S. Highway 99, where 4.36 feet of subsidence occurred from 1931 to 1948. Of particular 

interest is the belt of decreased subsidence in the vicinity 

of the Friant-Kern Canal. Water deliveries from the 

canal began in this area in 1951 and apparently had a 

direct effect on reducing the rate of subsidence.
FEET IN SUBSIDENCE, 

FEET IN SUBSIDENCE, 

saianis QNVT aojKcaaisans 
 1931

FIGURE 41. Land-subsidence profiles Y Y', 1948-62. For location see figure 44.
B56 STUDIES OF LAND SUBSIDENCE

Subsidence profiles along line Z-Z' for the period 

1935-64 are shown in figure 42. The southwest half of 

line Z-Z' was not surveyed in 1962 and 1964; therefore, 

profiles for these years could not be plotted for this part 

of the line. As shown, nearly 5 feet of subsidence has 

occurred since 1935 in two centers, one at Richgrove and 

the other about 4 miles southwest of Richgrove. The rate 

of subsidence in these areas was much greater from 1948 

to 1953 than during subsequent periods. The subsidence 

depression at Richgrove coincides in general with the 

area of maximum decline of water level from 1920-21 

to 1948 (fig. 25).

SUBSIDENCE MAPS

Two sets of topographic maps of the Tulare-Wasco 

area have been published by the U.S. Geological Survey: 

(1) T^-minute quadrangle maps (scale 1: 31,680), prepared from a 1925-26 survey but referenced in part to 

bench-mark altitudes of the 1901-2 survey and (2) T1^- 

minute quadrangle maps (scale 1:24,000), eight of 

which were resurveyed in 1953 and 1954 by using as primary vertical control the Coast and Geodetic Survey's 

1953-54 bench-mark altitudes. These eight quadrangles 

include most of the area of major subsidence. Within 

the extent of the eight remapped quadrangles, the landsurface contours on the two sets of quadrangles were 

compared in order to obtain a rough approximation of

the magnitude and areal extent of the land subsidence 

that had occurred as of 1054. Outside the area of the 

eight remapped quadrangles, subsidence was approximated by comparing the contours on the 1925-26 maps 

with the altitude of bench marks established by the 

1953-54 releveling of the Coast and Geodetic Survey. 

The subsidence map so obtained (fig. 43) shows the 

approximate extent and magnitude of land subsidence 

in the Tulare-Wasco area between 1926 and 1954. 

Although a small amount of subsidence may have 

occurred prior to 1926, the magnitude is indeterminate; 

however, it is known to be negligible compared to subsidence since 1926. Therefore, 1926 is considered to be 

the beginning date of appreciable subsidence in the 

Tulare-Wasco area.

As shown in figure 43, subsidence as of 1954 amounted 

to 12 feet in the principal subsidence depression north 

of Delano and to more than 6 feet between Pixley and 

Earlimart. Also, the configuration of the lines of equal 

subsidence is not far different from the configuration of 

the lines on Ingerson's map showing subsidence as of 

1940 (fig. 36). Planimetering of figure 43 indicates that 

about 1.16 million acre-feet of subsidence had occurred 

within the 2-foot subsidence line, and an estimated 180 

thousand acre-feet had occurred outside the 2-foot line. 

Thus, the total volume of subsidence for the 28-year 

period, 1926-54, was about 1.34 million acre-feet. 

Roughly this same volume of water was permanently

VERTICAL SCALE GREATLY EXAGGERATED

6.0

FIGURE 42. Land-subsidence profiles Z-Z', 1935-64. For location, see figure 44.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B57

R 22 E 119°30'R 23 E R 24 E R 25 E 15 R 27 E H9°

 \ f fc/ 

10 MILES

I I I I

EXPLANATION

v/////7//////y////////////////^y/////:

Basement complex

Edge of foothills

Line of equal subsidence

Dashed where approximate.

Interval 2 feet

FIGURE 43. Land subsidence 1926-54. Compiled from topographic maps of the U.S. Geological Survey, surveyed in 1925-2:6 and 

in 1953-54, and leveling of the U.S. Coast and Geodetic Survey in 1953-54.

removed from ground-water storage owing to the compaction of the sediments.

Figure 44 shows the magnitude and areal extent of 

the subsidence between 1948 and 1954. The lines of equal 

subsidence are based on the change of altitude of about 

300 bench marks between the 1948 and 1954 levelings of the Coast and Geodetic Survey. In most of 

the area between Earlimart and Tulare, more subsidence 

occurred during this 6-year period than had occurred 

from 1926 to 1948 (fig. 39). The most rapid subsidence 

during the 6-year period was west of Richgrove, north

of Delano, and between Pixley and Earlimart. Also, an 

elongate subsidence trough developed along the highway 

southeast of Corcoran. About 780,000 acre-feet of subsidence (obtained by planimetering fig. 44) occurred in 

this 6-year period. Even though water levels in part of 

the Friant-Kern Canal service area started to rise in 

1951 (fig. 24), the rate of subsidence was only beginning 

to decrease by 1954. The 1953-54 leveling, therefore, 

marks the transition between the accelerating rate of 

subsidence that preceded this date and the decreasing 

rate that followed.
B58

R 22 E 119

STUDIES OF LAND SUBSIDENCE

>30'R 23 E R 24 E R 25 E 15' R 26 E R 27 E

EXPLANATION

Basement complex

Edge of foothills

Line of equal subsidence

Dashed where approximate. Interval 

1 foot except for 0.5-foot line

Compaction recorder and 

number

FIGURE 44. Land subsidence, 1948-54, and location of subsidence profiles. Compiled from leveling of the U.S. Coast and Geodetic

Survey, February to May 1948 and November 1953 to March 1954.

The water-level change map for 1948-54 (fig. 26) does 

not show centers of water-level decline to be coincident 

with the areas of subsidence north of Delano and west 

of Kichgrove (fig. 44). In fact, the 3-foot subsidence 

depression north of Delano is in an area where the 

waiter level in relatively shallow wells experienced a 

net recovery of as much as 40 feet from 1948 to 1954. 

This discrepancy suggests that compaction continued 

in the deeper, more confined, beds of the semiconfined 

system, which may not have recovered appreciable head 

by 1954. About one-quarter of the wells in this area

(SEi/4, T. 24 S., K. 25 E.) are more than 1,000 feet 

deep. West of Kichgrove, a number of deep wells drilled 

between 1948 and 1954 not only greatly increased the 

rate of pumpage from the deep part of the aquifer 

system but also tapped the underlying highly compactible marine beds (fig. 5) for the first time.

The effect of the sharp water-level recoveries that followed importation of surface waiter through the FriantKern Canal is shown in figure 45. This map, showing 

the amount of subsidence in the 3-year period, 1954-57, 

is based on leveling in the winter months of 1954 and
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

119°30' 15' 119°00'

B59

36° 00

35°45

EXPLANATION

Line of equal subsidence

Dashed where approximate. Interval 

0.2-foot, except for 0.1-foot line

Irrigation districts receiving 

water from the Friant-Kern 

Canal in 1956

FIGURE 45. Land subsidence, 1954r-57, and districts receiving irrigation water from the Friant-Kern Canal in 1956. Subsidence 

lines compiled from leveling of the U.S. Coast and Geodetic Survey, November 1953 to March 1954 and January to March 1957.

1957 (table 7). The shaded pattern in figure 45 shows 

the areal extent of irrigation districts receiving surfacewater diversions from the Friant-Kern Canal in 1956 

(table 3; fig. 13). Within these districts, the reduction 

in the rate of subsidence in the 3-year period 1954-57, 

compared to the 6-year period 1948-54, is striking. For 

example, in the area of historic maximum subsidence 

about-4 miles north of Delano, subsidence decreased 

from 3 feet in the 6-year period 1948-54 (0.5 ft per yr, 

fig. 44) to 0.1 foot in the 3-year period 1954-57 (0.03 ft 

per yr, fig. 45). Subsidence of more than 0.1 foot per

year (0.3 ft of subsidence during the 3 years, fig. 45), 

continued in the Pixley-Earlimart area, in a broad area 

between Alpaugh and Wasco, in a local area east of the 

Friant-Kern Ganal 6 miles north of Kichgrove, and at 

Richgrove. In the Pixley-Earlimart area and in the 

area north of Wasco, subsidence continued at a rate 

about equal to that of 1948-54 presumably because these 

areas did not receive surface-water imports in 1954- 

57, but rather were irrigated by ground water pumped 

from local wells.
B60 STUDIES OF LAND SUBSIDENCE

Figure 46 shows the amount of subsidence in the Tulare-Wasco area in the 2-year period from winter 1957 

to winter 1959. Although subsidence of more than 0.2 

foot per year (0.4 ft of subsidence during the 2 years) 

occurred in the Pixley-Earlimart area and in a small 

area 9 miles north of Richgrove, the rate in most of 

the area did not exceed 0.1 foot per year. In the vicinity 

of Delano and in an area of more than 100 square miles 

of farm land west of the Friant-Kern Canal, subsidence had ceased by 1957, owing to the appreciable rise 

in water levels that began in 1954 (fig. 27).

Surface-water supply was deficient in the 3 years 

from 1959 to 1962 (fig. 14), and withdrawal from 

wells increased (fig. 21). Water levels in deeper wells 

within the Friant-Kern Oanal service area again began 

to fall, although the water table in much of the canal 

service area continued to rise. Figure 47 shows the 

magnitude and extent of subsidence in this 3-year period between winter 1959 and winter 1962. Maximum 

subsidence was 2 feet in the Pixley-Earlimart area, and 

subsidence exceeded 1.4 feet midway between Tulare 

and Pixley on U.S. Highway 99 and 8 miles northwest

R 22 E 119°30'R 23 E R 24 E R 25 E 15' R 26 E R 27 E 119°00'

EXPLANATION

Basement complex

Edge of foothills

-0.2-

Line of equal subsidence

Interval 0.2 foot

FIGURE 46. Land subsidence, 1957-59. Compiled from leveling of the U.S. Coast and Geodetic Survey, January to March

1957 and February to March 1959.
R 22 E 119

LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

'30'R 23 E R 24 E R 25 E 15' R 26 E R 27 E. 119°00'

B61

EXPLANATION

Basement complex

Edge of foothills

-O.8 -

Line of equal subsidence

Dashed where approximate. Interval 

0.2 foot

FIGURE 47. Land subsidence, 195JM52. Compiled from leveling of the U.S. Coast and Geodetic Survey, February to March 1959

and January to April 1JM52.

of Delano. Subsidence exceeded 0.2 foot along 18 miles 

of the Friant-Kern Canal, as water deliveries from the 

canal decreased to less than half (table 3, 1961) their 

earlier maximums. More than half the Tulare-Wasco 

area again subsided at rates greater than 0.1 foot per 

year. Roughly 480,000 acre-feet of subsidence occurred 

in the area during the 3-year period 1959-62.

VOLUME OF SUBSIDENCE

The cumulative volume of subsidence in the TulareWasco area from 1926 to winter 1962, based on the 

subsidence maps of figures 36 and 43-47, was about

2.2 million acre-feet (fig. 48). Plotted points on the 

graph show the cumulative volume of subsidence as of 

the dates when control was available, and the connecting 

line indicates the estimated rate of cumulative increase 

in subsidence. The volumes of subsidence were obtained 

by using a planimeter to measure the areas of equal 

subsidence on the several subsidence maps.

The average rates of subsidence in thousands of acrefeet per year during the six periods of available data 

from 1926 to 1962 are shown in figure 49. The curved 

dashed line shows the probable subsidence during this 

period. The high rate of subsidence from 1948 to 1954
B62 STUDIES OF LAND SUBSIDENCE

0.5

1920 1950 1970

FIGURE 48. Cumulative volume of subsidence, 1926-62. Points indicate times of leveling control.

and again from 1959 to 1962, with an intervening 5-year 

period of reduced subsidence, is clearly shown in figure 

49 and roughly agrees with the trend of ground-water 

pumpage shown in figure 21.

Figure 50 shows the total amount of subsidence in 

the Tulare-Wasco area from 1926 to 1962. The map 

was compiled from a comparison of topographic maps 

for the period 1926-54 (fig. 43) and from leveling of 

the U.S. Coast and Geodetic Survey for the period 

1954-62. Subsidence was more than 10 feet in two 

centers: (1) 3 miles north of Delano and (2) between 

Pixley and Earlimart. In the southernmost of these 

centers (north of Delano), subsidence occurred almost 

entirely before 1954 (figs. 39, 43); from 1954 to 1962,

LL 

O

Iso >

"~ LJ

Lj' LJ

I- LJ

K LJ

LJ ce

oo 

z <

LlJ

C/5 m

1920

Pro

Average for period.

^Y

sable rate^

^ /

^y

/

r

\

 V,

\

\

\

\

\

\

\

i

^

1930 1940 1950 1960 19

FIGURE 49. Rate of subsidence, 1926-62.

the maximum subsidence during each period between 

levelings was between Pixley and Earlimart. As much 

as 11.5 feet of subsidence occurred in this area of continuous ground-water withdrawal between 1926 and 

1962, but most of this subsidence took place after 1948 

(fig. 39).

On the basis of planimetered areas of figure 50, the 

following relationships were obtained. By 1962, approximately 514,000 acres, or about 53 percent of the entire 

Tulare-Wasco area, had subsided more than 2 feet, and 

about 110,000 acres, or 11 percent of the area, had 

subsided more than 5 feet. One small area had subsided 

a maximum of 12.8 feet. These relationships are demonstrated in figure 51. The area under the curve represents 

the volume of subsidence, which is 2.2 million acre-feet 

for the period 1926-62 as measured from this plot. 

About 10 percent of the total volume of subsidence 

occurred in areas that subsided less than 2 feet.

POSSIBLE CAUSES OF LAND SUBSIDENCE

Three types of land subsidence due to man's activities have been recognized in or adjacent to the San 

Joaquin Valley: (1) subsidence due to the compaction of aquifer systems caused by a reduction of fluid 

pressures (Poland and Davis, 1956, 1969), (2) subsidence due to the hydrocompaction of moisturedeficient surficial deposits caused by wetting (InterAgency Committee, 1958; Bull, 1964; Lofgren, 1969), 

and (3), subsidence due to the oxidation and compaction of peat soils in the Sacramento-San Joaquin Delta 

areas as a result of drainage and cultivation (Weir, 

1950). Of these three types, only the first is known to 

be occurring in the Tulare-Wasco area.

The removal of fluids from oil and gas fields is a possible cause of local subsidence, but only two fields are 

of appreciable size in the Tulare-Wasco area the Trico 

gas field south of Alpaugh, in T. 24 S., K. 23 E., and 

the Semitropic oil field west of Wasco, in T. 27 S., 

K. 23 E. A comparison of leveling across the Trico 

gas field in 1948 and 1962 and across the Semitropic 

oil field in 1935 and 1962 indicates that withdrawals 

from these fields did not contribute appreciably to the 

areal subsidence.

Tectonic movement is another possible cause contributing to land subsidence in the Tulare-Wasco area. 

Davis and Green (1962, p. D-90) postulated that postdepositional downwarping was responsible for much 

of the structural closure of about 300 feet in the Corcoran Clay Member of the Tulare Formation beneath 

the Tulare Lake bed, which extends east into the western part of the Tulare-Wasco area (fig. 6). However, if 

structural downwarping has been occurring uniformly 

since the deposition of the Corcoran Clay Member in
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

R 22 E 119°30'R 23 E R 24 E R 25 E 15' R 26 E R 27 E H9°00'

B63

 U- ._AJ~- 

/I .1 ~... Q

EXPLANATION

Basement complex

Edge of foothills

Line of equal subsidence

Dashed where approximate. Interval 

2 feet, except for 1-foot line

33H1

o 2- 4

Observation well

Upper number- Well number 

Lower number-Subsidence/ headdecline ratio X 10^-(see table 15)

Reference bench mark and number

35°45'

T 25 S

i i i i

10 MILES

FIGURE 50. Land subsidence, 1926-62. Compiled from comparison of topographic maps, 1926-54, and leveling of the U.S. Coast

and Geodetic Survey, 1954-62.

Pleistocene time, the rate would have been so slow 

that it would not have appreciably affected the altitude 

of bench marks in the western part of the Tulare-Wasco 

area in the historic span of leveling control. There is 

no direct evidence of tectonic adjustment in the TulareWasco area since vertical control was first established. 

It is concluded, therefore, that tectonic movement has 

not contributed appreciably to the subsidence described 

in this report.

As stated earlier (B49), the causal relation of 

water-level decline to the subsidence of the land surface was recognized as early as 1935. Ingerson (1941)

also considered the possibility that vibrations of highway and rail traffic and shocks from explosive blasts 

were factors contributing to land subsidence. There is 

no evidence, however, that either natural or artificial 

vibrations have caused a measurable increase in the 

amount or the rate of subsidence.

The evidence is conclusive in time and place that 

subsidence is directly related to water-level decline and 

that it slows down or ceases in response to water-level 

recovery. This report concludes that water-level change 

is the cause of all measurable subsidence in the 

Tulare-Wasco area.
B64 STUDIES OF LAND SUBSIDENCE

5

\

\

X

2.2 million 

acre-feet

02468 

AREA, IN HUNDRED THOUSAND ACRES

FIGURE 51. Relation of magnitude to area of subsidence, 1926-62. 

Area under the curve equals the volume of subsidence.

ANALYSIS OF HYDRAULIC STRESSES 

CAUSING COMPACTION

Under natural conditions, unconsolidated deposits 

are generally in equilibrium with their overburden load. 

An increase in grain-to-grain stress, however, due to 

either surficial loading or a change in ground-water 

levels, causes a corresponding strain or compaction of 

the deposits. The magnitude of the strain is dependent 

on the compressibility of the deposits, which is related 

to their physical and chemical properties; the magnitude of the increased stress; possibly the type and rate 

of stress applied; and the stress history, that is, whether 

the increased stress is being applied for the first time 

or has been attained or exceeded previously.

Depending on the nature of the deposits, compaction 

may be (1) largely elastic, in which case stress and 

strain are proportional, independent of time, and reversible, or (2) principally nonelastic, in which case 

the granular structure is rearranged in such a way that 

the volume is permanently decreased. In general, if the 

deposits are coarse-grained sand and gravel, the compaction will be small, chiefly elastic, and thus reversible, 

whereas if they contain fine-grained clayey beds, the 

compaction will be much greater, chiefly inelastic, and 

thus permanent. In either type of compaction, subsidence of the land surface is due to a one-directional compression of the deposits.

Three different types of stresses cause compaction of 

an aquifer system. They are closely interrelated, yet are 

of such different nature that a clear distinction is of utmost importance. The first of these types is a gravitational stress, caused by the effective weight of overlying 

deposits and transmitted downward through the grainto-grain contacts in the deposits. The second type is a 

hydrostatic stress, caused by the weight of the interstitial 

water and transmitted downward through the water. 

The third type is a dynamic seepage stress exerted on 

the grains by the viscous drag of vertically moving interstitial water. The first and third types are additive 

in their effect and together compose the gram-to-grain 

stress which effectively changes the void ratio and mechanical properties of the deposit; this combined stress 

is commonly known as the "effective stress." The second 

type of stress, although it tends to compress each individual grain, has virtually no tendency to change the 

void ratio of the deposit and thus is referred to as a 

"neutral stress."

Only two of the various methods of analyzing the 

effect of these stresses in a compacting aquifer system 

(Taylor, 1948, p. 203) are considered here. They vary 

in their conceptual approach; however, both give the 

same mathematical results and can be used to check 

each other. The classical method, the approach more 

often used in practical soil mechanics problems, considers the combined total weight of grains and water 

(geostatic load) in the system and the neutral, hydrostatic stress. The second method considers the static 

gravitational stress of the grains, which comprises their 

true weight above the water table and submerged 

(buoyed) weight below the water table, and the vertical 

seepage stresses that may exist in the system. Inasmuch 

as changes in grain-to-grain effective stress, both gravitational stress and stress due to seepage, are directly responsible for the compaction of the deposits and are 

directly related to changes in head in an aquifer system, 

the latter method has proved simpler and clearer in analyzing subsidence in this investigation.

The Terzaghi theory of consolidation (Terzaghi and 

Peck, 1948, p. 233) commonly is used to estimate the 

magnitude and rate of compaction that will occur in 

fine-grained clayey deposits under a given change in 

stress. According to this theory of consolidation, compaction results from the slow escape of pore water from 

the stressed deposits, accompanied by a gradual transfer of stress from the pore water to the granular structure of the deposits. When an increment of loading 

stress is applied to a fine-grained interbed (aquitard), 

the entire stress increase, at first, is borne by the interstitial water; grain-to-grain stress can increase only 

as the interbed drains. A high hydraulic gradient at the 

surface of the interbed causes rapid drainage from the 

pores near the surface. Gradually, the excess pressure 

decreases, the intergranular stress increases, and the 

void ratio decreases. This gradual process always is in 

a more advanced state near the drainage surfaces of the
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B65

interbed and at a less advanced state near its center. Because of this hydrodynamic lag, strain cannot take place 

all at once in the interbed, but only as rapidly as drainage can occur. Coarse-grained beds, on the other hand, 

drain rapidly, and increased effective stresses quickly 

cause compaction of the beds and an adjustment of 

these beds to their new stress condition.

Water-level changes in subsidence areas may change 

effective stresses in two different ways:

1. A change in the position of the water table changes 

the effective stress, owing to the increase or decrease in buoyant support of grains in the zone of 

the change; this change in gravitational stress is 

transmitted downward to all underlying deposits.

2. A change in position of the water table or the piezometric surface (artesian head) or both that induces 

vertical hydraulic gradients across confining or 

semiconfining beds produces a seepage stress which 

is algebraically additive to gravitational forces and 

thereby changes the effective stress in the deposits. 

A change in effective stress also results if a natural 

preexisting seepage stress is altered in direction 

or magnitude by a change in head.

In the following analysis of stresses, compaction is 

considered under two different hydraulic regimes: (1) 

water-table (unconfined) conditions, in which no vertical hydraulic gradients exist, and (2) artesian (confined) conditions, in which vertical gradients exist and 

result in seepage stresses that usually represent the major part of the change in effective stress. Generally, the 

analysis of effective stress change involves both changes 

in buoyant support and changes in seepage forces, both 

with time and with depth.

Figure 52 shows the components of effective stress at 

three depths in an assumed hydrologic system involving 

a confined aquifer system with an interbedded aquitard 

and an overlying unconfined aquifer. For purposes of 

demonstration, a porosity, w, of 40 percent and an average specific gravity, G, of 2.7 for the individual mineral 

grains are assumed. All stresses in the system are expressed in units of feet of water (1 ft. of water equals 

0.43 psi) so that they are directly additive and are relatable to changes in hydraulic head. Thus, the unit 

weight of deposits above the water table (ignoring the 

contained moisture), y<z, may be expressed

7<z=(l n)-G-jw, 

where

7,0=unit weight of water.

Correspondingly, the buoyant (submerged) unit weight, 

7', of the deposits below the water table equals

If the numerical values assumed for n and G are used 

and if 7«, is expressed as 1 foot of water, the effective 

stress due to the weight of deposits above the water 

table equals about 1.6 feet of water per foot of thickness, 

and the effective stress due to the weight of deposits 

below the water table equals approximately 1.0 foot 

of water per foot of thickness.

UNCONFINED (WATER-TABLE) CONDITIONS

Before pumping lowers the water table in an unconfined aquifer, the deposits are generally in equilibrium 

with the natural effective stresses. For any element of 

the deposit, these effective stresses equal the true weight 

(per unit area) of the unsaturated deposits and the 

buoyant weight (per unit area) of the saturated deposits 

that overlie the element. As the water table is lowered, 

the effective unit weight of the deposits in the dewatered 

zone increases from the submerged unit weight, y', 

(weight of solids minus the weight of the displaced 

water) to the unit weight, yd, of the solids. The effective 

grain-to-grain stress in the aquifer below the dewatered 

zone is thus increased by the loss of buoyant support in 

the dewatered zone. The increase in effective stress at 

any depth below the lowered water table in an unconfined aquifer is equal to the increase in unit weight 

of the dewatered deposits multiplied by the dewatered 

thickness. Using the previously assumed unit weights, 

the effective stress below the lowered water table is 

calculated to increase 0.6 foot for each foot of watertable lowering.

CONFINED (ARTESIAN) CONDITIONS

Under simple hydrostatic conditions in a confined 

aquifer system (fig. 52^4), the hydraulic heads a'bove and 

below the confining layer stand at the same altitude. 

No hydraulic gradient exists across the confining layer; 

therefore, no seepage occurs through the confining layer. The effective stresses under these hydrostatic conditions are the same as in the unconfined aquifer; that is, 

they are equal to the gravitational stress of the overlying deposits.

If both the water table and the piezometric head in 

the confined aquifer are 200 feet below land surface (fig. 

52^4), the two components of effective stress exerted 

downward on the grains, owing to the weight of deposits 

above the water table (vector ps') and owing to the 

buoyant weight of deposits below the water table (vector 

pS) are as follows: 320 feet and 200 feet, respectively, on 

the top of the confining layer; 320 feet and 300 feet, on 

the top of the confined aquifer system; and 320 feet and 

500 feet on the top of the aquitard at a depth of 700 feet.

If from the hydrostatic condition of figure 52^4, the 

artesian pressure in a confined aquifer system is drawn
B66 STUDIES OF LAND SUBSIDENCE

1- u

UJ

u.

Z

u. 

K

ID

w

z

<

$

O

UJ 600 

m

i

t

Q 800

///<$!/[:X4$f/£

Unconfinec

aquifer

Aquiclude

Confined 

- aquifer 

system

Aquitard

 «

PS

A Water table

^v Piezometric'*

j x. surface

\5

Db' P:pb' Pfa'

\c ,

P,'

-\ Neutral,X. 

\ pressure \^

' 1

/ \

^ \ \ \l-D

P

A Water table^

^^ Piezometric

^\ surface x

\5

"Vri

|\

°b Pb>

p' 

j

.1

F \ £" N

\ s\

\. \

AP'

I

J Ap'

i I

\ IV^/

i i-/"\G Nl>

0 200 400 600 

PRESSURE, IN FEET OF WATER

A. Water table and piezometric 

surface common

0 200 400 600 

PRESSURE, IN FEET OF WATER

B. Water table constant; piezometric 

surface lowered

Water table^ 

Piezometric- 

\ surface

AP'

A

i' 2\

\

0 200 400 600 

PRESSURE, IN FEET OF WATER

C. Water table and piezometric 

surface lowered equally

<n a

W UJ «i 5; $

u. 

uj o

oJ

200 X- - - ^c-^ -

9 400

800

200 400 600 8 

PRESSURE, IN FEET OF WATER

D. Water table raised, piezometric 

surface constant

200 400 600 

PRESSURE, IN FEET OF WATER

E. Water table raised, piezometric 

surface lowered

800 0 200 400 600 

PRESSURE, IN FEET OF WATER

F. Water table lowered, piezometric 

surface constant

All stresses in feet of water; based on assumed porosity = 0.40 and specific gravity = 2.70 

p' =effective stress due to weight of unsaturated deposits 

Pt' =effective stress due to buoyant weight of submerged deposits 

J = seepage stress 

Ap' = change in total effective stress from condition A

FIGURE 52. Effective-stress diagrams for a confined aquifer system overlain by an unconfined aquifer.

down below an unchanging water table by pumping 

(fig. 52#), gravitational stresses remain the same; however. a downward hydraulic gradient which induces

downward seepage is developed across the confining 

layer (aquiclude). The loss of hydraulic head through 

the aquiclude represents the energy expended in moving 

the water through the pore passages. As head is dissipated by viscous flow through the confining layer, the

energy in the moving water is transferred by viscous 

drag to the granular skeleton of the deposit. The force 

corresponding to this energy transfer is exerted in the 

direction of flow and is algebraically additive with the 

gravitational stresses that tend to compact the deposits. 

As commonly used, the term "seepage force" refers 

to the energy transfer within the body through which 

the seepage takes place. As defined by Scott (1963, p. 96,
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B67

equation 4-20), the seepage force, /, exerted on the 

grains can be represented by the expression

f h-yw-A, 

in which

A.=head loss across an incremental thickness and 

A= cross sectional area.

Within an aquiclude compacting under the stress of 

downward seepage (fig. 525), the hydraulic gradient 

and therefore the seepage force per unit thickness vary 

from a minimum at the upper surface to a maximum 

at the lower surface until steady-state conditions are 

reached. The loading effect of the incremental seepage 

force developed through each unit volume vertically 

through the aquiclude is additive downstream. Thus, 

the net effect of these incremental units of seepage force 

at any point in the structure of the aquiclude is equal 

to the summation of the incremental forces upstream 

from that point. Although the distribution of these 

forces within the aquiclude may be indeterminate, the 

total seepage force accumulated through the aquiclude 

is equal to the total head differential across it. Thus, at 

the base of the aquiclude, the total seepage force, F» 

may be expressed as

F=H-yw.A.

The total seepage force per unit area, J, hereafter 

referred to as the seepage stress, is derived by

V

This seepage stress is transmitted downward through 

the intergranular structure of the aquifer system 

below the aquiclude.

In the assumed ground- water systems of figure 525, 

straight line ABCD represents the hydrostatic pressure (neutral pressure) gradient that existed before 

pumping began. The deposits are adjusted to the overburden load, which equals the actual weight of the deposits above the water table plus the buoyant weight of 

the submerged deposits. After pumping has lowered 

the head in the permeable members of the confined 

aquifer system to 300 feet, the effective stresses shown 

by vectors in figure 525 would prevail at the depths 

represented by the arrow points. The length CF represents the 100 feet of head decline, and FG represents 

the reduced pressure in the confined aquifer system. 

With a 100-foot head loss through the confining layer, 

a 100-foot seeepage stress is immediately developed 

across the confining layer and transmitted through 

grain-to-grain contacts to the underlying aquifer system. Even though normal hydrostatic pressure gradients 

exist both in the unconfined (line AB) and in the confined aquifer systems (line FG), through the confining 

aquiclude changing hydraulic gradients and transient 

flow conditions occur until a steady hydrodynamic 

gradient (line BF) is established between the heads at 

the upper and lower surfaces of the aquiclude. Initially, 

the head distribution through the confining clay approximates lines BC and CF. Curved line BEF represents a transient distribution of head in the confining 

layer at some intermediate time before steady flow is 

established.

As shown in figure 525, the length s indicates the 

magnitude of the seepage stress at a particular depth 

in the aquiclude, and the length u indicates the excess 

over steady-state head (Taylor, 1948, p. 221, 236) that 

remains in the interstitial voids at that depth. Also, the 

area BCFEB is proportional to the part of the ultimate 

compaction that has occurred, and area BEFB to the 

part of the ultimate compaction that has not taken 

place. Domenico and Mifflin (1965, p. 571) referred to 

the combined area BCFB as the effective-pressure area. 

As adjustment continues, excess pore pressures are reduced and compaction occurs within the aquiclude. 

After equilibrium conditions have been established, 

head distribution through the aquiclude follows 

straight line BF (assuming uniform permeability), and 

uniform flow conditions and a constant seepage gradient prevail through the aquiclude. Under these conditions, 1 foot of head is lost (transferred to the grains) 

through each foot of thickness of the aquiclude. The 

accumulated downward seepage thrust exerted on the 

grains by the moving water thus varies linearly from 

0 feet at the upper surface of the aquiclude to 100 feet 

at its lower surface. The total seepage stress, equal to 

the head differential across the aquiclude, is exerted on 

the granular structure of all underlying beds in the 

aquifer system. The time involved in reaching complete 

adjustment is dependent chiefly on the thickness, compressibility, and permeability of the confining layer.

At all times after the head in the confined aquifer 

system is lowered to 300 feet, the magnitude of the 

seepage stress (increased effective stress) exerted 

downward on all beds within the confined system (below the aquiclude) is 100 feet (distance CF, fig. 525). 

In the more permeable, less compactible, aquifers of 

the confined system, the increase in effective stress occurs 

rapidly. Within the aquitards, however, no change in 

effective stress can occur until water escapes from the 

slow-draining, compacting beds. The reduction in 

head in the permeable aquifers creates a two-directional hydraulic gradient outward from the center of 

the aquitard which induces seepage from and compaction of the aquitard. Two-directional drainage occurs 

from the aquitard and excess pore pressures are tran-
B68 STUDIES OF LAND SUBSIDENCE

sient (curved line HIJ, fig. 525) until equilibrium 

conditions (straight line HJ) are established. Although upward and downward seepage stresses occur 

within the aquitard during this adjustment, they have 

no net external effect on the rest of the aquifer system.

The open arrows (Ap') at two depths in the hydrologic section of figure 525 are vectors indicating the 

change in effective stress from the hydrostatic conditions of figure 52A. Thus, the net effect of lowering the 

piezometric head in the confined aquifer system 100 

feet below the water table is to create a seepage stress 

through the confining layer and ultimately to increase 

the effective stress in all beds in the confined aquifer 

system by 100 feet. No change in effective stress occurs 

in the unconfined aquifer overlying the confining 

layer. Although a small part of the resulting deformation of the confined aquifer system is elastic and thus 

reversible, most represents an irreversible rearrangement of fine particles in the clayey sediments to a 

more dense state.

Figure 52^7 represents a dual water-level lowering, 

with both the water table and piezometric surface 

lowered 100 feet below the level of figure 52A. A normal hydrostatic gradient of pressure with depth exists 

in the aquifers and is ultimately achieved in the aquiclude and aquitard as well. Effective stresses throughout the section, however, are considerably different 

from conditions of either figure 52J. or figure 525. 

Loss of buoyant support in the dewatered zone 

causes the effective stress changes shown in figure 52£7. 

The net change in stress from conditions of figure 52A 

is shown at three depths by the open arrow vectors. Although the effective stress throughout the section is 

increased from conditions of figure 52J. by the loss of 

buoyant support, the stresses in the confined aquifer 

system are less than those shown in figure 525 because 

there is no seepage stress component. If the head in the 

confined aquifer system had been drawn down to the 

condition shown in figure 525 before the hydrostatic 

conditions shown in figure 52(7 were established, rebound would tend to occur throughout the confined 

aquifer system as the water table was drawn down.

If the piezometric surface remains constant and the 

water table is raised 100 feet above the conditions of 

figure 52J., the effective stresses shown by the vectors 

in figure 52Z> are produced. A raised water table reduces the gravitational stress below the raised level by 

providing buoyant support of the grains in the zone 

of water-table rise; however, it also creates a downward seepage stress across the confining layer. The 

net change, therefore, from conditions of figure 52^4 

is an increase in effective stress throughout the confined

aquifer system. It is noteworthy that in changing from 

the conditions of figure 52(7 to the conditions of figure 

52Z>, rebound would occur in the unconfined aquifer, 

but no change in stress would occur in the underlying 

confined system.

If the water table is raised 100 feet above and the 

piezometric surface is lowered 100 feet below the hydrostatic conditions of figure 52^4, the effective stresses 

shown in figure 52# will prevail. An increase in 

buoyant support causes reduced gravitational stress 

in the unconfined aquifer, as it did under the conditions 

of figure 52Z>. The 200 feet of head differential across 

the confining layer represents a seepage stress of 200 

feet exerted downward on the deposits in the confined 

aquifer system. Under these conditions, the change in 

effective stress in the confined aquifer system, due to 

the combined changes in gravitational and seepage 

stress from the hydrostatic condition of figure 52^4, 

is 140 feet, a quantity considerably greater than that 

for conditions illustrated in figures 525-.Z?.

Figure 52F shows the effective stresses under the 

sixth general condition, in which the water table is 

lowered 100 feet below the piezometrie surface of figure 52^4. Here the effective stress in the unconfined 

aquifer is increased 60 feet, owing to the loss of buoyant support in the zone of the lowered water table. Because of upward seepage stresses that developed through 

the aquiclude, however, the effective stress throughout the confined aquifer system is reduced by 40 feet 

from the hydrostatic condition of figure 52A.

In summary, the following generalizations can be 

made with respect to effective stress analysis:

1. For purposes of stress analysis, a ground-water 

reservoir may act as an aquifer system if no 

significant vertical head differentials (seepage 

forces) occur within the reservoir under ordinary pumping stress. It may be considered to 

include one or more confined (artesian) systems if vertical head differentials within the 

reservoir are significant.

2. Under the conditions assumed for demonstration 

on page B68, the effective stress in an unconfined aquifer increases 0.6 foot for each foot of 

decline of the water table and decreases 0.6 

foot for each foot of rise of the water table. 

These values would change somewhat for different values of porosity. The change in effective 

stress equals the change in buoyant support of 

the deposits in the interval of water-table change 

and is independent of the specific gravity of the 

grains.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B69

3. The effective stress in a confined aquifer system 

is affected by changes in both the water table 

and the piezometric head in the confined system. For the values of porosity and specific 

gravity assumed in the analysis, a rise in the 

waiter table of 1 foot causes about 0.4 foot of 

increase in effective stress, whereas a decline of 

1 foot in the piezometric surface causes 1 foot 

of increase in effective stress.

COMPACTION OF THE WATER-YIELDING 

DEPOSITS

The amount of compaction at a given location depends 

on the thickness and compressibility of the deposits, the 

magnitude of the increase in effective stress, the time 

of stress application, and possibly the type of stress applied. The range of stress change, grain size, clay mineralogy, and geochemistry of the pore water all affect 

the compressibility of the deposits. Also, the effective 

stresses in a confined aquifer system are affected by (1) 

water-level changes in an overlying unconfined or semiconfined aquifer system and (2) by seepage stresses that 

may develop across the confined aquifer system.

This section includes a description of the recording 

equipment used to measure compaction to depths as 

great as 2,200 feet, a discussion of the measured compaction at several locations where sufficient data are 

available, and a computation of compaction at Pixley 

based on Terzaghi's theory of consolidation and field 

and laboratory data.

COMPACTION-RECORDER INSTALLATIONS

Subsidence of the land surface is measured by periodic 

leveling of a network of bench marks, whereas compaction of the deposits is measured by observing the change 

in thickness of a particular sequence of the deposits. For 

any given time interval, subsidence of the land surface 

should equal the sum of the incremental compaction of 

all strata between the land surface and the bottom of the 

compacting section. A special type of installation 

(Lofgren, 1961, p. B49) is being used to measure the 

rate and magnitude of compaction in the Tulare-Wasco 

area. As shown in figure 53, the assembly consists of a 

heavy weight emplaced in the formation below the bottom of a well casing and an attached cable stretched upward in the casing and counterweighted at the land 

surface to maintain constant tension. A monthly recorder (Stevens, type F, with battery-driven Elix clock) 

mounted over the open casing is used to measure directly 

the amount of cable that rises above the casing as compaction occurs. At the land surface during compaction, 

the bottom-hole weight appears to rise; actually, the

Metal table on 

concrete platform ^Recorder

Counterweight/ 

in 50-lb increments

Stainless steel cable 

1/8 inch, stranded

Anchor weight 

200 to 300 Ibs -Open hole

FIGURE 53. Compaction-recorder installation.

vertical distance from the land surface to the bottomhole weight shortens.

The success of this type of recorder installation depends largely on the durability and stretch characteristics of the down-hole cable and the minimization of 

down-hole friction between the cable and the well casing. The cable must remain at constant length during 

the period of record. If the length changes, due to temperature changes, fatigue elongation, or untwisting, this 

change is measured by the recorder and is indistinguishable from the record of actual compaction. Friction in 

the system, both down-hole and in the recording mechanism above the land surface, results in a stepped or interrupted record of compaction. This reduces the 

accuracy and resolution of the recorded data, especially 

during reversals in trend. Ball-bearing sheaves have 

been used in the installation to reduce frictional drag.

During the early phases of the investigation, a y$- 

inch, 7 by 7 stranded, preformed, galvanized steel aircraft cable was used. Eight recorder units were installed 

with this cable and, except for the Pixley recorder, 

23/26-16N1, all cables failed in 6-15 months because of 

corrosion. In general, failure due to corrosion occurred
B70 STUDIES OF LAND SUBSIDENCE

in the interval of water-level fluctuations in the well casing and was most rapid in wells that had excessive falling water. After experimentation with methods to 

prevent corrosion, a specially manufactured %-inch, 

stainless steel, 7 by 7 stranded, plastic coated preformed 

cable was selected, and four of the installations were rebuilt (table 8) with this cable in 1959. Further experimentation with an uncoated %-inch, 7 by 7 stranded, 

preformed stainless steel cable, and an uncoated %-inch, 

1 by 19 stranded, preformed stainless steel cable seemed 

to reduce the down-hole friction of the system; the 1 by 

19 stranded cable had even better performance characteristics than the 7 by 7 cable. Seven compactionrecorder installations in the Tulare-Wasco area were 

rebuilt in January 1966 with the 1 by 19 stranded cable 

and improved mechanical equipment to obtain a more 

precise record of compaction.

Compaction recorders were operated in 11 wells during the investigation, and eight of these were still in 

operation as of December 31, 1964. Companion waterlevel recorders were operated in five of these 11 wells 

and in one other observation well. The period of record 

of these recorders is given in table 8. The locations of the 

nine compaction recorders that have operated since 1958 

are shown in figure 44. Four of the recorder units were 

installed in specially drilled cased holes; the others were 

placed in unused irrigation wells which were cleaned 

o.ut and deepened about 20 feet to permit setting the 

anchor weights below the casing bottom. Two of the 

compaction recorders, 23/25-8J2 and 24/26-30P1, were 

not reinstalled after the cable failure in 1958, and their 

record was too short to be of use in computing compaction rates.

As shown in figure 44, the compaction recorders were 

installed in the two areas that subsided most rapidly 

from 1948 to 1954. At one site in each of these two 

subsidence centers, 23/25-16N1 near Pixley and 24/26-

TABLE 8. Water-level and compaction recorders in the 

Tulare-Wasco area

[Records dated 12-31-64 are last records available]

Well

(Unused irriga- Depth 

tion well unless (ft)

otherwise

marked)

Records available (month and year)

Water level Compaction

23/25- 8J2

16N32-- 

16N42-.. 

17Q1- 

17Q3 ..

24/26-30P1- 

34F1- 

36A2 i...

25/26-1A2- . 

1J3 

1K2 

270

760

430

260

615

355

- 1,150 

. 1,510

- 2,200 

892 

897

None ..............._-.. 9-57 to 4-58.

...-.do- .----------------- 4-58 to J2-31-64.

6-59 to 12-31-64.............. 6-59 to 12-31-64.

. .do Do.

None--_----------- 9-57 to 12-58.

9-57 to 12-31-64 --------- 9-57 to 1-59; 1-59 to 12-31-64.

None-.---------..--.- --- 9-57 to 3-58.

1-57 to 12-31-64 9-57 to 12-58; 1-59 to 12-31-64. 

None . 5-59 to 12-31-64.

9-57 to 9-58; 1-59 to 12-31-64. 9-57 to 6-58; 1-59 to 12-31-64. 

None__...._______ Do.

.. 2,200 4-60 to 12-31-64.............. None.

1 Cored test well.

2 Drilled test well.

36A2 at Eichgrove, test holes were cored and logged 

to obtain a detailed description of the type of deposits 

penetrated. Selected cored samples from these holes 

were tested in the laboratory to determine their physical and consolidation characteristics (Johnson and 

others, 1968).

At most of the sites, the compaction was recorded at 

a 1:1 scale, that is, 0.1 foot of compaction in the depth 

interval registered 0.1 foot of displacement on the recorder chart. At the Pixley site (23/25-16N1), however, as described later, the compaction was recorded 

at a 12:1 or 24:1 vertical amplification. This amplified compaction record and the corresponding waterlevel record permitted detailed correlation of the compaction with fluctuations in artesian pressure in the 

confined aquifer system.

COMPACTION OF DEPOSITS NEAR PIXLEY 

MEAUE.ED COMPACTION

Compaction recorders of the type shown in figure 

53 and companion water-level recorders were installed 

in two unused irrigation wells, 23/25-17Q1 and 17Q3 

(table 8), in the center of maximum subsidence near 

Pixley (fig. 44) in September 1957. A third compaction recorder was installed in a newly drilled nearby test 

well 23/25-16N1 in April 1958. These recorder units 

were anchored at three different depths, and each measured the amount of compaction between the land surface 

and the respective anchor depth. By comparing the 

compaction records of the three recorders during a 

common period, the amount of compaction in each of 

three depth zones has been computed. Two of the three 

compaction recorders failed, due to cable corrosion in 

the winter of 1958. Before the failure, however, several months of valuable record was obtained. The recorded compaction from June 1 through August 31, 

1958, is summarized in the following table :

Recorder Anchor depth Measured com- Compaction in depth interval 

(ft) paction(ff) peet Percent

23/25-17Q3- 

17Q1- 

16N1-

Surface 

355 

615 

760

0. 01 

.20 

.29

0.01 3

. 19 66

.09 31

Although these results apply to only part of one pumping season, it is concluded that during this period (1) 

essentially no compaction occurred in the upper 355 feet 

of deposits, (2) roughly two-thirds of the measured 

compaction occurred in the most heavily pumped zone 

between depths of 355 and 615 feet, and (3) about onethird of the measured compaction occurred in the
LAND .SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B71

615-760-foot depth zone. No record is available of the 

amount of compaction in the deposits below a depth 

of 760 feet.

Early in 1959 water-level and compaction recorders 

were reinstalled in unused irrigation well 23/25-17Q3 

to record water-level fluctuations in the semiconfined 

aquifer system and the compaction above 355 feet. Also, 

recorders were installed in two newly drilled test wells 

23/25-16N3 and 16N4 (table 8). Test well 16N3 was 

bottomed at a depth of 430 feet, and its casing was perforated between depths of 360 and 420 feet to record 

water-level fluctuations in the most heavily pumped 

part of the confined aquifer system. Test well 16N4 was 

drilled to a depth of 250 feet, and its casing was perforated between depths of 200 and 240 feet to record 

water-level fluctuations in the semiconfined aquifer system. Thus, four compaction recorders, three in a cluster 

at 16N1, 16N3, and 16N4 and a fourth 1,500 feet west 

at 17Q3, all in T. 23 S., K. 25 E. (fig. 44), and with 

anchor depths of 760, 430, 250, and 355 feet, respectively, below the land surface (fig. 56^4) have been in continuous operation since June 1959. The completion 

depth of 760 feet for test well 16N1 exceeded the depth

of the irrigation wells in the immediate vicinity and 

thus was inferred to span the depth range of most 

of the compacting deposits.

Figure 54 is a plot of land subsidence, compaction, 

water-level fluctuation, and change in effective stress 

in the subsidence center 3 miles south of Pixley. The 

graph shows the compaction measured in well 23/25- 

16N1 from May 1958 through 1964; the fluctuation of 

water level in the semiconfined aquifer system, as measured in well 23/25-16N4; the fluctuation of artesian 

head in the confined aquifer system, as measured in well 

23/25-16N3; the change in effective stress in the confined aquifer system, as computed from changes in 

water level in the semiconfined and confined aquifer 

systems (fig. 52); and the subsidence of bench mark 

Q945 at recorder site 16N1, determined by leveling of 

the Coast and Geodetic Survey from distant stable 

bench marks three times between January 1959 and 

February 1964.

The leveling of bench mark Q945 in January 1959, 

January 1962, and February 1964 permitted comparison 

of compaction to subsidence in the two intervening time 

periods. From January 1959 to January 1962, bench

Change in effective stress in the 

confined aquifer system

260

1958 1959 1960 1961 1962 1963 1964

FIGURE 54. Land subsidence, compaction, water-level fluctuations, and change in effective stress in the subsidence center 3 miles

south of Pixley.
B72 STUDIES OF LAND SUBSIDENCE

mark Q945 subsided 2.08 feet, and measured compaction 

in well 23/25-16N1 was 1.60 feet. Thus, the measured 

compaction to a depth of 760 feet in the 3-year period 

was 77 percent of the total subsidence. From January 

1962 to February 1964, bench mark Q945 subsided 0.46 

foot, and measured compaction in well 16N1 was 0.30 

foot. Compaction thus equaled 65 percent of the total 

subsidence during this second period. For the 5-year 

span, the total compaction of 1.90 feet was 75 percent 

of the total subsidence of 2.54 feet. Thus, 0.64 foot of 

vertical shortening, or about 25 percent of the subsidence 

during the 5-year period, was due to compaction of deposits in the confined aquifer system below a depth of 

760 feet. This compaction below 760 feet indicates that 

the drawdown effects of pumping extended to depths 

considerably below the deepest irrigation wells in the 

immediate vicinity, but whether the pumping effects 

were from distant or nearby wells is not known.

Comparison of the compaction rate with fluctuations 

in water level in the semiconfined and confined aquifer 

systems indicates that compaction beg'an each year during the period of rapid head decline in the confined 

aquifer system, continued through the pumping season, 

and ceased during the early stages of head recovery. 

Also, the magnitude of compaction each year is related 

to the magnitude of seasonal head drawdown. This relation is illustrated clearly by the increase in head decline and compaction in 1964 'as compared to 1963. Each 

year from 1959 to 1964, the water level in the semiconfined aquifer system (16N4) registered a seasonal fluctuation less than 10 percent of the artesian-head change 

in the confined aquifer system (16N3) and, after 1961, 

it showed a gradual rise. The change in piezometric head 

in the confined system, therefore, was the dominant 

component of the change in effective stress that caused 

compaction in the confined zone.

The center graph of figure 54 shows the change in 

effective stress in the permeable aquifers of the confined aquifer system for the period 1959-64, as computed 

from the hydrographs of wells 23/25-16N3 and 16N4 

(fig. 52). The changes in effective stress in the compactible fine-grained beds of low permeability are less, 

but the magnitudes are not known. During this period, 

the effective-stress change fluctuated annually through a 

range of 60 feet to more than 100 feet, and being dominated by the changes in piezometric head in the confined aquifer system, was nearly parallel to the hydrograph of well 23/25-16N3. Dashed line A-A', with a 

slight change in slope in 1962, approximates the trend 

of winter crests (low effective stress) of the effectivestress graph and indicates a winter-minimum stress 

increase of about 4 feet of water (1.7 psi) per year from 

1960 to 1962. Although the 1963 crest failed to reach line 

A-A', the 1964 crest was about equal to that of 1962. 

Dashed straight line B-B' approximates the declining 

trend of summer troughs (high stress) of the effectivestress graph for all years except 1962 and 1963. The 

summer-maximum stress increased at an average rate 

of about 7 feet of water (3.0 psi) per year.

Of special interest in relating compaction to changes 

in effective stress is the position of straight line G-G' 

(fig. 54). Vertical dashed lines have been drawn downward to the effective-stress graph from points marking 

the beginning and end of most rapid compaction in well 

23/25-16N1. Straight line G-G' is drawn as near as 

possible through the points on the effective-stress curve 

where compaction began each season. Most of the compaction occurred when the effective stress was below 

(higher stress) line C-C''; little or no compaction occurred when the effective stress was above (lower stress) 

line C-C'. Compaction continued for several weeks after 

the maximum effective stress was attained but always 

terminated before line C-C' was reached on the recovery limb of the stress curve. In general, the amount of 

compaction in any year was related to the area below 

line C-C' bounded by the effective-stress curve.

Figure 55 shows the record of four compaction recorders and subsidence of nearby bench mark Q945, 

3 miles south of Pixley, for the period 1960-64. These 

recorders were anchored at different depths (table 8; 

fig. 564), and the installations had stabilized during 

several months of operation prior to January 1960. The

^^"S-" .

^ ==

- ___

- ^

^ *^Ss^

Bench mark Q945'""''"*

N 23/25-l

\23/25-16N3 (depth

^23/25-16Nl (death

* . ______ 

O . . __

6N4 and 17Q3 (Depths: 250

430 feet)

i 760 feet)

 

*^^ w

and 355 feet, respectively)

 *^

-O

0.8

1.6

2.4

1960 1961 1962 1963 1964 

FIGUEB 55. Record of four compaction recorders and> subsid ence of a nearby bench mark, 3 miles south of Pixley, 1960-64.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B73

observed subsidence of bench mark Q945 is a measure 

of the total compaction of deposits at the site as of January 1962 and January 1964 (this bench mark was also 

leveled in January 1959; see fig. 54). By computing 

the difference in amount of compaction measured by the 

various recorders, the compaction in each of the three 

depth zones was obtained; these results are summarized in table 9.

The water level in the semiconfined aquifer system 

(fig. 54, hydrograph 16N4) rose from 1961 through 

1964; so, effective stresses did not increase in the deposits above the confining clay layers. Compaction 

recorders 16N4 (250 feet) and 17Q3 (355 feet) registered only a few hundredths of a foot of compaction 

during this period. However, compaction recorders 

16N1 and 16N3, with anchor depths of 760 and 430 

feet, respectively, recorded significant compaction 

(table 9). Unit compaction in the 355-430-foot zone 

was greater than in the 430-760-foot zone in each 

of the 5 years; it ranged from 1.2 times the unit 

rate of the lower zone in 1960, when compaction in 

the aquifer system was the greatest, to 2.5 times that

TABLE 9. Compaction rate of unconsolidated deposits in the Pixley area in four depth

zones during 5 years of record

[Symbols used: VS, very small]

Depth zone (ft)

Measured compaction (ft) Unit compaction (XNH ft per ft) Specific unit compaction (seasonal) 

(XlO-s ft per ft 2)

0-355 .....

355-430........

430-760 ...-.

0-760 .

1960

...... 0.02

 .- .13

...... .45

... ... .60

1961

0.01

.13

.37

.51

1962

0.03

.05

.10

.18

1963

0

0.04

.07

.11

1964

0.02

.08

.26

.36 .

1960

VS

1.7

1.4

1961

VS

1.7

1.1

1962

VS

0.7

.3

1963

VS

0.5

.2

1964

VS1.1

0.8

1960

VS

2.5

2 1

1961

VS

2.4

1.6

1962

VS

2.5

1.1

1963

VS

1 Q

0.7

1964

VS1 <*

O

n

i Based on only the change in effective stress during the period of compaction, that is, below line C-C', fig. 54.

16N4 17Q3 16N3 16N1 UNIT COMPACTION, IN FEET X 10" 3 PER FOOT PER YEAR

0.5 1.0 1.5 2.0

- 400 

800 > 

B

FIGURE 56. Annual rate of compaction ofl deposits in four depth zones, 3 miles south of Pixley, 196O-64. A, Relation of recorders to the 

hydrologic units. B, Measured compaction rate in four depth zones for 5 years of record.
B74 STUDIES OF LAND SUBSIDENCE

of the lower zone in 1963, when compaction was the 

least. Specific unit compaction (seasonal),5 which is the 

unit compaction per foot of seasonal change in effective 

stress (fig. 54), ranged during these 5 years from 2.5 

to 1.3 X 10-5 foot per foot2 in the 355-430-foot zone and 

from 2.1 to 0.7 X 10~5 foot per foot2 in the 430-760-foot 

zone.

Figure 56 shows the relation of the four compaction 

recorders to the confining clay layers and the unit compaction in each of the depth intervals for the period 

1960-64. Inasmuch as most of the nearby pumping was 

from wells tapping only the confined aquifer system, it 

is not surprising that virtually all the measured compaction was below 355 feet and that 75 percent of the observed subsidence (1960-64) was caused by compaction 

in the 355-760-foot zone. It is also noteworthy that the 

highest unit compaction was in the micaceous silty sands 

containing clayey interbeds in the 355-430-foot depth 

zone (fig. 7).

The relationship between seasonal unit compaction 

in two depth zones near Pixley (table 9) and the change 

in stress during the period of compaction which produced the vertical shortening is shown graphically in 

figure 57 for 5 years, 1960-64. Thus, the upper left end 

of each stress-strain line of figure 57 represents the stress 

at which seasonal compaction was first recognized, and 

the coordinates of the lower right end represent the 

maximum compaction and stress that was attained that 

year. Stress changes are based on the arbitrary scale of 

figure 54, where zero change in stress was assumed for 

the high point of the stress curve during the first year 

of continuous record. The slope of each year-line of 

figure 57, representing the stress-strain relationship for 

a particular depth zone, is inversely proportional to 

corresponding values of specific unit compaction 

(table 9).

The effect of slow drainage from the fine-grained 

beds on the rate of compaction of the two depth zones 

is illustrated by the progressive increase in slope of 

the stress-strain lines of figure 57. During the 4%-year 

period from January 1960 to June 1964, the effective 

stresses in the confined aquifer system exceeded the 

July 1960 stress for only 5 weeks in 1961 (center graph, 

fig. 54). Slow drainage and associated compaction continued at a diminishing rate (steeper slope, fig. 57) 

throughout the part of the period that stresses were

5 The values of effective-stress change used in deriving numerical 

values of specific unit compaction are those measured in the permeable 

beds during the period of compaction. The effective-stress change in the 

fine-grained compactible beds is less by the amount of the residual excess 

pore pressure, which is not known. Stress change in the permeable beds 

is the best evidence available of changes in the less permeable, compactible beds. After all excess pore pressures are dissipated, the effective stress in the permeable and less permeable beds is the same.

below line C-C' (fig. 54). When previous maximum 

stresses were exceeded in June 1964, renewed compaction occurred throughout the aquifer system. The increased compaction rate during 1964 for the 430-760- 

foot depth zone is particularly noticeable in figure 

57.Z?, where the 1964 stress-strain line falls above the 

1963 line.

To obtain a detailed correlation between the measured compaction and the related fluctuations of the 

piezometric surface of the confined aquifer system, an 

amplifying compaction recorder was installed at well 

23/25-16N1 in May 1961. This recorder was geared to 

the direct-reading recorder to give a 12:1 or 24:1 vertical amplification of the compaction record as compaction ocurred. The center graph of figure 58 shows the 

direct 1:1 record of compaction measured by recorder 

23/25-16N1 during 12 months of 1962 and 1963. The 

lower graph, which is the 12:1 amplified compaction 

record, shows an excellent correlation with the waterlevel fluctuations in well 23/25-16N3 (top graph). During this 12-month period, the water level in the semiconfined aquifer system rose slightly; thus head changes 

in the confined aquifer system approximately equaled 

the changes in effective stress in the compacting deposits. The continuous rise in water level in well 16N3 

from late July 1962 (fig. 54) to January 2,1963, caused 

a slight expansion of the aquifer system (fig. 58^7). 

About 0.0022 foot of expansion was measured during 

October, November, and December of 1962 during a 

water-level recovery. Pumping during March caused the 

water level to fall again, and after it had declined about 

5 feet below its March high, measurable compaction was 

observed in the amplified record. Rapid compaction occurred for 10 days (March 10 to March 20), during 

which the water level in well 16N3 dropped 48 feet.

Compaction during this 10-day period amounted to 

0.031 foot, at a rate of 0.65 X 10' 3 foot per foot of water-level decline. During the straight-line part of the 

declining record, March 12-17, a water-level decline of 

7.3 feet per day caused compaction of 5.5 X 10~ 3 foot 

per day, at a rate of about 0.76 X 10' 3 foot per foot of 

water-level decline. For 9 days of water-level recovery 

after reaching the spring low of March 21, compaction 

continued at a diminishing rate. It was not until the 

water level had recovered 35 feet from the March 21 

low that compaction stopped. Through April, May, and 

early June, the water level remained above the March 

29 level, at which compaction stopped, and water-level 

fluctuations resulted in little or no observed compaction. 

Soon after the water level had fallen below the March 

29 level, however, rapid compaction resumed, and thereafter, each minor fluctuation of the water level in the
50

100

150

LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

0 rB75

50

100

150

1.0 2.0 0 1.0 

^4 SEASONAL UNIT COMPACTION, IN FEET X 10~~ 3 PER FOOT £>

2.0

FIGURE 57. Relation of seasonal unit compaction to stress1 change during the compaction period in two depth zones of the confined 

aquifer system near Pixley, 1960-64. A, 355-480-foot depth zone. B, 430-760-foot depth zone.

confirmed aquifer system had an observable effect on the 

rate of compaction (fig. 58#, O). From June 24 to August 31, 28 feet of water-level decline caused 0.068 foot 

of compaction, at a rate of 2.4 X 10' 3 foot per foot of 

water-level decline. Mechanical difficulties during August and September 1963 resulted in a broken record 

in both the hydrograph of well 23/25-16N3 and the 

amplified compaction record of well 23/25-16N1 (fig. 

58).

The delicate sensitivity of the aquifer system to 

changes in effective stress is readily apparent in the 

graphs of figure 58. Under certain conditions, compaction of the deposits may begin within minutes after 

pumping affects the pressure in the confined aquifer 

system. Compaction continues as long as excess pore 

pressures remain in the aquitards and thus may continue at a diminishing rate even during the early stages 

of water-level recovery. A very small part of the compaction is elastic in nature, and rebound may occur 

when the stress is decreased (Oct.-Dec. 1962, fig. 58). 

Most of the compaction, however, is nonelastic in nature and represents a permanent decrease in the volume 

of the stressed deposits.

As shown in figure 59, rebound occurred in the compaction record of well 23/25-16N1 during periods of 

water-level recovery that preceded and followed a major water-level decline in March 1963. The water-level 

in the confined aquifer system rose continuously from 

mid-January to the end of February (hydrograph 

23/25-16N3, fig. 54). During February, the water level 

rise of 11 feet (fig. 59) resulted in a measured rebound 

of about 8 X 10'4 foot, or a rebound of 7.5 X 10' 5 foot 

per foot of water-level rise. From March 9 to March 21, 

a water-level decline of roughly 50 feet produced an 

abrupt compaction of 0.034 foot, or 0.68 X lO" 3 foot 

of compaction per foot of water-level decline. Waterlevel recovery of 26 feet from March 23 to March 30 

resulted in cessation of compaction, which was followed 

by more than a month of continued water-level recovery 

and rebound. From March 30 to April 24, water levels 

in the confined aquifer system rose 16 feet, and about 

9.4 X 10-* foot of rebound, for a rebound of 5.9 X 10' 5 

foot per foot of water-level rise, occurred. During the 

3-month period from February to April (1963), the 

water level in the overlying semiconfined aquifer system rose slightly, and no measurable compaction was
B76 STUDIES OF LAND SUBSIDENCE

140

210

T

fc -TT

z 

g

o 

<

o. 

^ 

o

O o

B

1962 1963

C

FIGDKE 58. Correlation of compaction and water-level fluctuations near Pixley. A, Hydrograph of well 23/25-16N3. B, Compaction in 

well 23/25-16N1 (1:1 scale). O, Compaction in well 23/25-16N1 (12 :1 amplification).

recorded by either the 250-foot or the 355-foot compaction recorders.

Assuming that all the measured rebound and compaction of the 760-foot recorder occurred in the 355- 

760-foot depth zone, the February 1-March 9 rebound 

represented 1.8 X 10' 7 foot of rebound per foot of water-level rise per foot of aquifer thickness, the March 

9-March 21 compaction represented 1.7 X 10' 6 foot of

compaction per foot of water-level decline per foot of 

thickness, and the March 30-April 24 rebound represented 1.5 X 10' 7 foot of expansion per foot of waterlevel rise per foot of thickness. Table 10 summarizes the 

computed compaction and rebound of figures 58 and 59. 

It is noteworthy that the specific unit rebound is at least 

an order of magnitude smaller than the specific unit 

compaction. Rebound and compaction are largely elas-
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B77

140

180

220

i

0.1

T

i

1 ""*" N-_____l ] i

i i i i

1 !

B

X

J_L I I I I I I I I I I I I I I I I I I I I I I I I I I l I I I I I I I I I I I I I

FEBRUARY MARCH APRIL

1963

c

FIGURE 59. Observed rebound and compaction near Pixley. A, Water-level fluctuations well 23/25-16N3. B, Compaction record well 

23/25-16N1. 0, Compaction record well 23/25-10N1 (24:1 vertical amplification).

tic through this range of water-level fluctuation, and the 

specific unit values are one to two orders of magnitude 

smaller than the value of specific unit compaction shown 

in table 9.

Summary of measured compaction,

Results obtained at the Pixley recorder site in relating compaction and subsidence to changes in effective 

stress and water-level fluctuations are of significance 

not only for Pixley and the Tulare-Wasco area but also 

for other subsidence areas where similar stress-strain 

relationships apply. Multiple-compaction and waterlevel recorders at this site, through 5 years (1959-64) 

of continuous operation, have supplied the most detailed record of compaction and water-level change in 

the San Joaquin Valley.

The seasonal fluctuations of the piezometric head in 

the confined aquifer system, between winter highs of 

about 140 feet below land surface and summer lows of 

200-260 feet, depended on the amount of pumpage required to augment the limited and variable supply of 

surface water. Except in 1962 and 1963, the summer 

lows tended to deepen several feet each successive year. 

Annual fluctuations in the semiconfined system were 

about 10 percent as great as those in the confined system, and from 1961 to 1964 the water level gradually 

rose. Only minor increases in effective stress occurred in 

the semiconfined aquifer system from 1959 through 1961, 

and little or no compaction was measured in the upper 

355 feet of deposits. Because changes in the semiconfined 

water level were small, piezometric fluctuations in the 

confined system were the dominant factor in computing
B78 STUDIES OF LAND SUBSIDENCE

TABLE 10. Compaction and rebound characteristics of the confined aquifer system near Pixley

Compaction Rebound

Date Figure 

reference compaction:

Specific unit 

compaction 2

Specific 

rebound'

Specific unit 

rebound 4

10- 1-62 to 12-31-62....................

3- 7-63 to 3-12-63...... ..............

6-24-63 to 8-12-63....... ............

6- 5-62 to 6-11-62....................

6-22-62 to 6-24-62....................

7- 5-62 to 7-10-62.... ................

2- 1-63 to 2-28-63....................

3- 9-63 to 3-21-63....................

3-30-63 to 4-24-63 .................

.......... 57 ..

.......... 57

.......... 57

.......... 58

.......... 58

.......... 58

.......... 59 ..

.......... 59

.......... 59 ..

0. 67X10-3

2.4 X10-3

. 83X10-3

. 42XHH

. 62X10-3

. 68XWH

1.7X10-' ...

5.9X10-8 ...

2.0X10-' ... i.oxio-« ...

1.5X10-« ...

1.7X10-« 

6.9X10-5

7. 6X10-5

fi QV1ft-5

1. 7X10-'

1. 8X10-7

1. 5X10-'

1 Feet of compaction per foot of increase in effective stress.

2 Feet of compaction per foot of compacting deposits per foot of increase in effective stress.

3 Feet of expansion per foot of decrease in effective stress.

4 Feet of expansion per foot of expanding deposits per foot of decrease in effective stress.

changes in effective stress in the confined aquifer system. The graph of effective-stress change, therefore, resembles closely the hydrograph of well 23/25-16N3 

(fig. 54), both in magnitude and configuration.

The average rate of subsidence at the Pixley site 

(bench mark Q945) diminished from 0.69 foot per year 

(1959-62) to 0.23 foot per year (1962-64) in response 

to a marked, though temporary, change in the pumping 

pattern. Significant compaction in the confined aquifer 

system occurred only when the effective stress was in 

the lower (greater stress) two-thirds of its annual cycle. 

The amount of compaction each year was roughly proportional to the area bounded by the effective-stress 

curve under the C-C' line (fig. 54). Of the 2.54 feet 

of subsidence from January 1959 to February 1964, 

little or none represented compaction in the 0-355-foot 

depth zone of the semiconfined system; 1.90 feet of compaction, or 75 percent of the subsidence, was above 760 

feet.

Because of differences in drainage characteristics, the 

individual fine-grained beds in the confined aquifer 

system are at different stages of compaction at each 

level of effective stress below line C-C' (fig. 54). The 

rate of compaction of each bed and of the depth interval as a whole varies as the effective stress changes. An 

empirical correlation can be made, however, between 

the rate of change in effective stress and the rate of compaction or subsidence after a sufficiently long period of 

comparable record is available to establish a long-term 

trend for these interrelated variables. From 1959 to 

1961, for example, the trend of water levels and subsidence continued roughly downward as it had for several 

years. During this period, the effective stress increased 

at a rate of about 9 feet per year (trend of summer 

troughs, fig. 54), while bench mark Q945 subsided at 

a 3-year average rate of 0.69 foot per year, a ratio of 

0.077 foot of subsidence per foot of effective stress increase. Eeduced pumping during 1962 and 1963 caused 

a marked reduction in the rate of subsidence during

these years, and even though heavy pumping in 1964 

caused the effective stress in the confined aquifer system to decline to the projected trend line B-B', the 

subsidence rate from 1962 to 1964, as inferred from the 

compaction graph of well 23/25-16N1 (fig. 54), was 

much less than during the 1959-61 period.

The thickness and compressibility of the compacting 

deposits vary greatly, both areally and with depth, 

throughout the Tulare-Wasco area. Also, the seasonal 

fluctuations and trend of water levels in the confined 

and semiconfined aquifer system vary from place to 

place. The measured rates of compaction and subsidence 

at the Pixley site, therefore, do not apply to other parts 

of the area. The general stress-strain relationships, however, do apply. Compaction is directly related to change 

in effective stress, which in turn is computed from 

changes in hydraulic head in the confined and the semiconfined aquifer systems. To establish a relationship 

between compaction, subsidence, and water-level change 

at any location, one or both of the following two types 

of data can be used:

1. Field measurements of compaction, subsidence, and 

water-level change in the principal hydrologic 

units, from which the overall transient response 

of the sequence of deposits to changes in effective 

stress can be analyzed for several years of record.

2. Detailed records of thickness and character of beds 

in the compacting zone, as obtained from electric 

logs, and a measure of the compressibility of the 

individual beds, as obtained from consolidation 

tests on selected cored samples, from which .a rough 

estimate of the ultimate compaction of the system 

can be made for a given change in effective stress. 

The application of the first type of data at one location has been presented in preceding pages. The application of the second type of data for the same Pixley 

site is considered in the following pages. In few locations in the Tulare-Wasco area are sufficient data available to apply either of the two procedures.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B79

COMPUTED COMPACTION

On the basis of Terzaghi's theory of consolidation 

(Taylor, 1948, p. 208), the amount of compaction that 

would occur at a particular site in a subsidence area resulting from a given water-level decline, can be computed from laboratory test data taken at that site. By 

using a procedure outlined by Gibbs (1960) and applied 

in another subsidence area by Miller (1961), the amount 

of compaction that could be expected at the Pixley core 

hole (23/25-16N1) under the historic changes in water 

levels was computed. Water-level declines approximating the actual changes at the Pixley site from 1905 

to 1964 were used in these computations. This method 

of computation requires that the lithology and hydraulic history of the aquifer system be known. Also, laboratory test data must be available for sufficient core

samples to give a representative measure of the compressibility of the individual lithologic zones under a 

given change in loading stress.

As shown in figure 60, the 760 feet of unconsolidated 

deposits penetrated by the Pixley core hole, 23/25-16N1, 

was subdivided into 10 zones, on the basis of a study 

of the electric log and the core samples. The individual 

depth zones were selected to include deposits of similar 

lithology and physical character, insofar as possible. 

Laboratory consolidation tests were available for six 

cored samples from this sequence (table 11); the test 

results of four of these samples were used to represent 

the compressibility of the deposits in the 10 depth zones 

(fig. 60). Thus, the consolidation data for a sample 

considered most representative of the deposits of that 

zone were used in the following computations, even 

though the sample may not have come from that zone.

TABLE 11. Results of consolidation tests on samples from the Pixley core hole, 23/2G-16N1 

[Data from Earth Laboratory, U.S. Bur. Reclamation, Denver, Colo.]

Sample Depth

(ft)

Description

Grain size

(percent) Load Compression Coefficient 

 range index consolidation

Silt (psi) Cc cv 

Sand and . (ft2 per yr) 

clay

23L-226.. .......

227.........

228 ». ....

229.........

232 .........

234.........

261.7-261.9

283.5-283.9

292.0-292.4

450.1-450.5

630.3-630.7

723.5-723.8

brown.

55

10

20

5

55

40

45 200-400

on 9nft_4nn

80 20Q 400

95 300-600

45 ..........

60 ..........

0.17

.62

.. 53

.40

.25 ....

.35 ....

311.0

O Q

192 7

4 a

1 Not used in computations.

The laboratory data from 47 core samples tested by 

the Geological Survey (Johnson and others, 1968, table 

4) were used to compute the average specific gravity, 

G, and the average porosity, w, for deposits in each of 

the 10 depth zones. Table 12 gives the depths to water 

in the confined and semiconfined aquifer systems and 

the seepage stresses used in computing compaction at 

the Pixley core hole. From these data, the dry unit 

weight (Ib per cu ft) or the buoyant unit weight (Ib 

per cu ft) was computed for each zone (dry unit weight 

for deposits above the water table and buoyant unit 

weight for deposits below the water table). These 

unit weights were used to compute the total effective 

overburden load (in psi) for the midpoint of each of 

the 10 zones for each of 5 years. Even though the weight 

of the deposits above the water table exceeds the dry 

unit weight by the amount of retained moisture, the 

moisture retention of the deposits was not known, and 

thus the dry weight was used as an approximation of the

actual weight of the deposits. The increase in effective 

stress due to seepage stress exerted through the confining 

clay of zone 4 (equal to the head differential, in psi) was 

added to the computed effective overburden load. Thus, 

the total effective stress tending to compact the deposits 

was obtained for the midpoint of each zone for each of 

the 5 years (table 13).

TABLE 12. Depths to water in the confined and semiconfined 

aquifer systems and seepage stresses used in computing compaction at the Pixley core hole, 1905-64

Depth to water below land 

surface, in feet

Semiconflned Confined

1905- _.__

1931_ ____

1948___.._

1959 _____

1964______

10 

59 

91 

110 

95

_ e

64 

125 

232 

260

Feet Pounds per 

square inch

-15 

5 

34 

122 

165

-6.5 

2.2 

14.7 

52.9 

71.5
TABLE 13. Effective stress, void ratio, and computed compaction for each of the lithologic zones at the Pixley core hole

1905 1931 1948 1959 1964 

Zone (ft) ness (ft) ing thick- specific porosity Effective 

ness i (ft) gravity (n) stress 2 

(0) (psi)

I...... .......... 0-280 280

2 . ......... _ 280-296 16

3.-. ... .... 296-330 34

4 ............. 330-360 30

5.... 360-420 60

6. .. . 420-620 200

7 . _ .- ..-_ 620-660 40

8..... ........ 660-680 20

9. _ ........ __ 680-710 30

10... ............ 710-760 50

Total... ...... ................

80 

16 

34 

30 

0 

160 

40 

10 

30 

30

2.68 

2.68 

2.69 

2.70 

2.72 

2.70 

2.68 

2.73 

2.69 

2.68

0.36 

.56 

.40 

.38 

.42 

.42 

.41 

.37 

.40 

.43

68.6 

136.9 

146.9 

154.8

230.5 

282.1 

295.4 

306.7 

324.5

Void Effective 

ratio 3 stress 

(«) (Psi)

0.498 

1.112 

.745 

.769

.677 

.670 

.640 

.656 

.624

81.7 

150.0 

160.0 

176.9

252.6 

304.2 

317.5 

328.8 

345.6

Void Effective 

ratio stress 

(«) (Psi)

Void Effective 

ratio stress 

(«) (Psi)

0. 481 90. 3 0. 470 

1. 085 158. 6 1. 072 

. 732 168. 6 . 724 

.744 197.7 .727 

Assumed no compaction 

.665 273.4 .651 

.658 325.0 .645 

. 628 338. 3 . 617 

. 641 349. 6 . 629 

.613 366.4 .603

95.5 

163.8 

173.8 

241.1

316.8 

368.4 

381.7 

400.0 

409.8

Void Effective 

ratio stress 

(«) (Psi)

0.469 

1.063 

.719 

.696

.629 

.619 

.596 

.602 

.584

91.4 

159.7 

169.7 

255.6

331.3 

382.9 

396.2 

407.5 

424.3

Void 

ratio 

<«)

» 0.469 

 1.083 

«.719 

.687

.620 

.611 

.590 

.599 

.578

1905-31

0.91 

.20 

.25 

.42 

0 

1.15 

.29 

.07 

.27 

.20

3.76

1 Estimated from electric log; fig. 60.

2 Computed for midpoint of zone.

8 From consolidation curve of representative sample.

4 Compaction estimated to occur ultimately as a result o

period indicated. 

8 Assumed no rebound.
ZONE

1

2 

3

4 

5

6

7

8

9

10

DEPTH 

(feet)

0-280 

280-296

330-360 

360-420

420-620

620-660

660-680

680-710

710-760

CONSOLIDATION TEST 

USED

23L-226 

23L-227

23L-229

23L-229

23 L- 234

23L-229

23 L- 234

Cc

0.17

0.62 

0.35

0.40 

0.35

0.40

0.35

0.40

0.35

DEPTH, 

IN FEET 

BELOW 

Cv LAND 

SURFACE

311.0 

9.9

4.8

4.8

-

4.8

-

100

200 

300

400 

500 

600

700

SPONTANEOUS 

POTENTIAL 

(millivolts)

10

- (-1 + (

^

3<r

r

-<

f

5. 

:

iI*

a

}

\_

\

5

I t I

\

RESISTIVITY 

16-in. normal 

(ohms m 2 /m)

) 20 40

t^

,<§=

^_^r~ :

) 

GRAPHIC 

LOG

l^i^7.

^±^t!±^

i^iaai

.V.V.V.VA

XvX-X-iX

E^rd

$$$

^::^v

GENERALIZED LITHOLOGIC DESCR

(from core descriptions and electr

30-80 Silt, sandy, loose to plastic, micaceous, yellowish-brown.

80-115 Sand, silty, loose to plastic, fine to coarse, yellowish brow

115-138 Silt, sandy, loose to plastic, gravelly, calcareous, micaceo

138-258 Sand, silty, loose to plastic, fine to coarse, micaceous, ye

258-280 Sand, silty, clayey, fine, some coarse, calcareous near bo

280-296 Clay, plastic, silty, micaceous, pale brown to bluish-gray 

330-360 Clay, sandy, silty, plastic, micaceous, calcareous streaks, 

360-420 Sand, silty, fine to coarse, gravelly, micaceous, yellowish-

420-520 Sand, silty, clayey, fine to coarse, some gravel, calcareo

ish-brown; clay, silt interbeds.

520-560 Clay, sandy, silty, plastic, gravelly, calcareous streaks, 

ceous, yellowish-brown; thin sand interbeds.

560-620 Sand, silty, loose to friable, fine to coarse, gravelly some 

620-660 Silt, sandy, loose to plastic, some carbonaceous mate

ceous, yellowish-brown; thin sand and clay interbeds

660-680 Sand, silty, clayey, loose, fine to coarse, carbonaceous m

680-710 Clay, plastic, massive, calcareous nodules, micaceous.ye

710-752 Sand, loose, friable, massive, fine to coarse, micaceous.

^orcoran Clay Member of Tulare Formation. 

2 Principal confining layer.

FIGURE 60. Lithologic subdivision of the Pixley core hole, 23/25-16N1, for application of consolidation test data. Cc, compression index; c», conso

per year.
B82 STUDIES OF LAND SUBSIDENCE

As shown in figure 22, artesian wells still flowed in 

the vicinity of the Pixley core hole in 1905 (Mendenhall and others, 1916). By 1929, however, the shallow 

water level was 56 feet below the land surface, and in 

1931, the confined water level was 64 feet below the land 

surface in a deep Pixley municipal well. Continued 

pumping caused continued decline, but the artesian 

head declined more rapidly than the semiconfined water 

level.

Figure 61 shows the generalized trend of water levels 

in the shallow semiconfined aquifer system and in the 

underlying confined aquifer system in the vicinity of 

the Pixley core hole. These plots, in general, represent 

the spring high-water level, except for the confined 

system in which the seasonal pumping drawdown is 

assumed to have increased consistently from about 1945 

to 1960, as shown. Although some summer-pumping 

drawdown must have occurred in the confined aquifer 

system prior to 1944, it is assumed to have been small 

compared to the summer drawdown in later years of 

more intensive pumping; it was roughly equivalent to 

the summer drawdown in the semiconfined system prior 

to 1944. Prior to 1944, the seepage force was computed 

as the difference between the spring high-water levels 

in the two systems, which was, in turn, assumed to be 

about equal to the difference between the summer lowwater levels. After 1944, accelerated pumping caused 

rapidly increasing summer drawdowns in the confined 

aquifer system, and the seepage force was computed 

as the maximum head differential during the pumping 

season. Although these maximum stresses were directly 

applicable only during a short summer period, they 

did apply during the part of the year when subsidence 

was most rapid (fig. 57).

50

100

0150

:200

£250

Bench mark 274.875 

^X,

10 9

1910 1920 1960

FIGURE 61. Trend of water levels in the semiconfined and confined 

aquifer systems at the Pixley core hole, 23/25 16N1, and observed 

subsidence of nearby bench marks. The vector F, wtich changes with 

time, indicates the magnitude of the seepage force that was used in 

computing the increases in effective stress due to pumping.

As of 1943 (fig. 61), 82 feet of water-level decline in 

the semiconfined aquifer system and a corresponding 

95 feet of decline in the deeper confined-aquifer system 

had caused roughly 1.2 feet of subsidence at bench mark 

274.875. With continued water-level decline, subsidence 

at this location in 1947 was about 2.0 feet (bench mark 

M829 replaced bench mark 274.875 after 1947) . As a result of accelerated seasonal drawdown in the confined 

aquifer system, however, the subsidence rate increased 

sharply after 1948. Under the new pumping regimen 

(1948-62), water levels in the semiconfined and confined aquifers fell roughly 1.3 and 9.0 (summer low 

level) feet per year, respectively. The subsidence rate 

during this period increased to 0.67 foot per year 

more than 20 times the 1905^13 rate. Since 1948, the accelerated downward trend of artesian head during each 

successive summer pumping season seems to be the 

determining factor in the increased rate of subsidence.

By using the computed effective stress for each zone 

(table 13), and the one- dimensional consolidation curve 

of the sample considered representative of the zone (fig. 

60), the theoretical void ratio of each zone was determined for each year being considered. Figure 62 is a 

plot of the consolidation data for core sample 23L-229, 

used for estimating void ratios in zones 4, 7, and 9. The 

left graph (fig. 62 A) is a semilogarithmic plot of the 

data, as determined by the Bureau of Eeclamation ; the 

right graph, figure 62#, is an arithmetic replot of part 

of the same data, prepared to facilitate interpolating 

intermediate points on the graph. Figure 62 B indicates 

the effective stress (load, in psi) in 1905 and 1931 for 

zone 4 and the corresponding void ratios for these two 

years. In a similar way, the void ratios for each of the 

lithologic zones for each of the 5 years (table 13) were 

computed from the consolidation curve selected as representative for that zone. Because of its coarse sandy 

texture (fig. 60), zone 5 was assumed to have undergone no appreciable compaction, even though some 

compaction was measured between 1959 and 1964 for a 

somewhat thicker interval (table 9) .

The amount of compaction in a particular zone that 

results from the computed change in void ratio is expressed by the following equation :

in which

AA= vertical shortening or compaction of the zone

in feet,

61= initial void ratio, 

e2=void ratio after loading, and 

h= thickness of the compacting zone, in feet.

Values of e{ and e2 were obtained for each zone from the 

particular e-log curve as just described. On this basis, the
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B83

0.90 

0.80

0 0.70

1 

a 0.60

0

0.50 

0.40

0.30 

0

-

_

-

-

-

-

-

^-^^

\*

\

\

" -^^

^ N

"~^

-

CC = OAO _ 

V

^ "

\ _

\

^^ \

-

1 1.0 10 100 10(

LOAD, IN POUNDS PER SQUARE INCH

1.2

0.8

0.6

0.4 r v

100 200 300 400 500

LOAD, IN POUNDS PER SQUARE INCH

B

FIGURE 62. One-dimensional consolidation data for core siample 

23L-229, Pixley core hole. A, Semilogarithmic plot. B, Arithmetic 

plot. Test by Earth Laboratory, U.S. Bureau of Reclamation, 

Denver, Colo.

ultimate compaction that would occur in each of the 10 

depth zones under the effective stress conditions of 

1931, 1948, 1959, and 1964 was estimated (table 13). In 

these computations, the thickness used for each of the 

zones was reduced to include only that part of the zone 

considered to be compactible, as estimated from the 

electric log (fig. 60). The values of computed compaction indicate the ultimate compaction that would occur 

under the hydrologic conditions of the given time 

periods, even though come of the compaction would be 

delayed many years because of slow drainage.

The estimated ultimate compaction that would occur 

as a result of the effective stress changes from 1905 to 

1964 is 12.99 feet (table 13). Of this amount, 1.45 feet 

of compaction would be due to stress increases incurred

from 1959 to 1964. Although no information is available as to the amount of compaction that actually occurred from 1905 to 1959, 1.90 feet of compaction was 

measured at the Pixley core hole from spring 1959 to 

spring 1964. Thus, for the 5-year period 1959-64, compaction measured by the 760-foot recorder exceeded the 

computed ultimate compaction for the same period 

by 0.45 foot, or about 24 percent.

From the data of table 13, a rough measure of the 

compressibility of the confined aquifer systems can be 

obtained for use in predicting future subsidence at the 

Pixley recorder site. Considering zones 4 through 10 

(table 13) as a single hydrologic unit, the ultimate 

specific unit compaction for the measured part of the 

confined aquifer system was obtained for four periods 

of record from the following values of stress change and 

compaction:

Period

1905-31.- 

1931-48 

1959-64

Compaction 

(ft)

..... 2.40

2.42

..... 4.29

..... 1.45

Stress 

change 

(psi)

22.1

20.8

43.4

14.5

Stress 

change 

(ft of water)

50.8

47.8

99.9

33.4

Ultimate 

specific unit 

compaction 

(XKHftper 

W)

1.1

1.1

1.0

1.0

1905-64. 10.56 100.8 231.8 1.1

Change in effective stress at the time of ultimate compaction for each period was assumed to be common for all 

beds of zones 4 through 10 and was converted to "feet 

of water" units for the computation. It is significant that 

ultimate specific unit compaction as here computed is 

the same parameter as Terzaghi's (Terzaghi and Peck, 

1948, p. 64) coefficient of volume compressibility (mv). 

As noted in the table, the computed value of specific 

unit compaction for the overall confined aquifer system 

was about 1.1 X lO4 foot per foot2 for the four periods 

of water-level decline. This value suggests that if unconfined water levels remain nearly unchanged in the 

future and confined water levels follow the same declining trend, roughly 1.1 X 10-4 foot of compaction will 

occur in each foot of aquifer-system thickness for each 

foot of increase in effective stress beyond the 1964 value.

TIME LAG OF COMPACTION

One complicating condition that must be considered 

when comparing computed ultimate compaction with 

actual measured compaction is the time delay for compaction to occur, referred to here as time lag of compaction. Because of the slow rate of drainage from finegrained deposits, particularly those that are thick and 

of very low permeability, years or even centuries may 

be required for ultimate compaction to be completed for
B84 STUDIES OF LAND SUBSIDENCE

a given change in effective stress; this period, based on 

the Terzaghi theory of consolidation (Terzaghi and 

Peck, 1948, p. 241), can be computed from the consolidation test data by the equation

t=

Th2

in which

£=time since application of increased stress, in

years, 

T= time factor that varies with the percentage of

ultimate compaction completed, 

h=thickness of the compacting layer, in feet, and 

cv=coefficient of consolidation, in square feet per 

year.

If the stress is assumed to have been instantaneously 

and fully applied at #=0, T=0.0076 for 10 percent compaction, about 0.2 for 50 percent compaction, and 1.0 

for about 93 percent compaction. If a compacting layer 

is free to drain through both its upper and lower surfaces, as is a clay interbed within an aquifer system, the 

thickness used in the preceding equation is k/2. If a 

compacting layer drains through only one surface, as 

does a confining layer over a drawdown aquifer system, 

the full thickness of the confining layer, h, is used.

Values of the coefficient of consolidation were determined for only four samples from the Pixley core hole 

(table 11). From these determinations, however, an 

estimation was made of the length of time required for 

compaction to occur in the Pixley area after an assumed 

water-level lowering. The preceding equation states 

that the time required for excess pore water to drain 

from a compacting layer varies as the square of the 

thickness. Also, the time varies inversely as the coefficient of consolidation, which, at the Pixley site, ranged 

from 4.8 to 9.9 for the silty clay aquitards to 311 for a 

clayey sand (sample 23L-226, table 11). Undoubtedly, 

untested beds in the deposits at the Pixley core hole 

have coefficients of consolidation both larger and smaller 

than these values. The coefficients for the tested samples, 

however, give some indication of the range of time required for compaction to occur in the slow-draining 

beds.

The substitution of the parameters of the Pixley deposits in the time equation shows that only the thickest 

finest-grained layers have compaction times of more 

than a few weeks or months. In the sandy sequence of 

zone 1 (fig. 60), few of the finer silt beds are more than 

10 feet thick, and only two are 23 feet thick or more. 

Even these thicker beds probably include thin sandy 

stringers which reduce greatly the time required for 

drainage. Considering, for example, the silt bed from 

115 to 138 feet below land surface and assuming

cy =311 feet2 per year and two-directional drainage 

(A/2=11.5 ft), the time required for 10 percent compaction under any given effective-stress increase is roughly 

3.2 X10-3 years, or about 1 day. About 1 month of 

drainage would be required to complete 50 percent of 

the compaction and roughly 5 months to complete 93 

percent.

By similar computations, the compaction time for the 

16-foot thick Corcoran Clay Member (depth 280-296 

ft; assume cv =9.9 ft2 per yr for the entire thickness 

and two-directional drainage) would range from 0.05 

year for 10 percent compaction, to 1.3 years for 50 percent compaction, to about 6.5 years for 93 percent compaction. Correspondingly slow drainage would occur 

in the other fine-grained beds, particularly those that 

are more than 10 feet thick. The computed compaction 

time for the four slowest draining beds, assuming onedirectional drainage for zone 4, the principal confining 

bed at this site, and two-directional drainage for zones 

2,7, and 9, follows:

Zone

2-___-

4

?___ _

9_____

c

Depth Thickness o 

(ft) (ft)

(f

280-296 

330-360 

620-660 

680-710

16 

30 

40 

30

oefflcient 

' consoliTime, in years, for percentage 

of compaction to occur

< 10 percent 60 percent 93 percent 

t2 per yr)

9.9

4.8 

48 

48

0.05 

1.4 

. 6 

.3

1.3 

38 

17 

9

6.5 

187 

83 

46

From table 13 and figure 60, it is noted that about 

60 percent of the ultimate compaction occurs in relatively permeable zones, which drain probably within a 

few days or weeks. This rapid response undoubtedly 

represents the "short term" compaction observed at the 

Pixley recorder site (figs. 54, 59), but probably 40 percent of the compaction occurs in beds with compaction 

lags comparable to those summarized in the preceding 

table. Figure 63 shows the estimated time delay, or lag

50

I 25

0 20 40 60 80 

TIME, IN YEARS

FIGURE 63. Estimated time required for compaction of deposits to 

760-foot depth at Pixley following an increase in effective stress.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B85

effect, for compaction of the 760 feet of unconsolidated 

deposits penetrated by the Pixley core hole after an increase in effective press is applied. The figure suggests 

that as much as 60 percent of the ultimate compaction 

under a given stress increase might occur within the 

first several months but that 75 percent of the ultimate 

compaction would require 10 years. During periods of 

sustained water-level decline, the delayed residual, or 

lag, compaction from previous stress increases is cumulative ; thus, the percentage of the actual measured compaction that is residual compaction changes with time 

and with changes in effective stress.

CORRELATION OF SUBSIDENCE, COMPACTION, AND 

WATER-LEVEL CHANGE

Measured compaction of the upper 760 feet of deposits at the Pixley core hole, as mentioned previously, 

composed 75 percent of the subsidence for the 5-year 

period from 1959 to 1964; therefore, 25 percent of the 

total compaction in the 5 years probably occurred at 

depths below 760 feet. Also, as suggested by figure 63, 

about 75 percent of the ultimate compaction due to 

effective stress increase to 1964 had occurred by 1964. 

These results suggest three limitations in relating 

water-level fluctuations to measured and computed compaction and to observed subsidence 'at this site:

1. Compaction and subsidence are directly related to 

changes in effective stress, which in turn are caused 

by water-level changes. Water-level changes must 

be converted to effective-stress changes in each of 

the compacting beds before a direct correlation can 

be made. The effective-stress changes are known 

only for the aquifers, not for the aquitards.

2. The compaction characteristics of the deposits below 

the 760-foot depth and also the changes in effective 

stress in this deep zone may be considerably different from conditions above the 760-foot depth. 

Therefore, the compaction below 760 feet may not 

always parallel the compaction above 760 feet.

3. Because of the slow drainage of fine-grained beds 

and the associated delay in the compaction of these 

deposits, subsidence at a particular time may be 

more closely related to past water-level changes 

than to current changes. Certainly, after a given 

change in effective stress has occurred in the coarsegrained beds and these beds have fully adjusted to 

the new stress, any further vertical shortening of 

the aquifer system would result from delayed compaction of the fine-grained beds. The ratio of subsidence to head decline, therefore, is meaningful 

in anticipating future subsidence only when residual compaction represents only a small part of

the total subsidence or the ratio is related to a 

sufficiently long period of uniform water-level decline that the component of residual compaction is 

nearly constant.

Figure 64 shows the relationship between observed 

subsidence at the Pixley site and the computed ultimate 

compaction of the deposits to a depth of 760 feet for 

the estimated stress changes from 1905 to 1964, as given 

in table 13. Also shown is the measured compaction of 

the upper 760 feet of deposits from 1958 to 1964. Since 

25 percent of the ultimate compaction represents residual compaction as of 1964 which had not yet resulted 

in subsidence, and since about 25 percent of the measured subsidence is due to compaction below 760 feet, the 

amount of computed ultimate compaction and the measured subsidence should be about equal for any stress 

change, as long as this approximate relationship is 

maintained. Even though the total amount of computed 

compaction during the 59-year period roughly approximates the observed subsidence, the two curves do not 

look alike. The hydrograph for the confined system from 

which compaction was computed (fig. 61) had only one 

control point between 1905 and 1958. If the confined 

head at this site had actually declined slower before 

1944 and faster after 1944 than figure 61 indicates, the 

computed compaction and subsidence graphs would be 

more parallel.

On the other hand, if the hydrograph for the confined 

system (fig. 61) is accepted as approximately correct, 

the small amount of observed subsidence prior to 1944 

in response to water-table and artesian-head declines of 

nearly 100 feet suggests that the deposits may have been 

consolidated at some prehistoric time under a greater 

effective stress than that which existed in 1905. The 

deficient record for the artesian head precludes a conclusion as to which interpretation is the more likely one.

fc QLU

LJ 4

°z 

6

-i i i i r 

Subsidence B M 274.875-

i_____i_____i_____i_____i______i

0 u u

1900 1910 1920 1930 1940 1950 1960 1970'

FIGURE 64. Computed ultimate compaction, measured compaction, and 

observed subsidence at .the Pixley core hole, 1902-64. About 25 

percent of subsidence is due to compaction below 760 feet. About 

25 percent of computed ultimate compaction represents residual lag.
B86 STUDIES OF LAND SUBSIDENCE

COMPACTION IN THE VICINITY OF RICHGROVE

Prior to 1945 most of the irrigation wells in the vicinity of Bichgrove were less than 1,000 feet deep. Pumping 

of these early wells had lowered water levels as much 

as 40 feet below the virgin condition by 1930 (fig. 65), 

and increased pumping during the 1930's steepened the 

downward trend of water levels. Following World War 

II, increased ground-water development, including the 

drilling of deeper wells, caused water levels in the Richgrove area to fall even more rapidly. This long-term 

decline of water levels, notably accelerated since about 

1946, resulted in extensive land subsidence in the Richgrove area. Subsidence was most rapid between 1948 and 

1954 (figs. 44, 65).

Beginning in 1952, imports of surface water from the 

Bureau of Reclamation's Friant-Kern Canal caused a 

marked reversal in water-level trend. By spring 1959, 

water levels in the deeper part of the semiconfined aquifer system had recovered as much as 100 feet from their 

1951 low levels (fig. 65). During this recovery period,

< 360

480

1910 1960

FIGURE 65. Relation of subsidence to water-level decline at Richgrove, 1905-64. Source of water-level data: 1905, water-level map 

of Mendienhall (1916, pi. 1) ; 1920, water-level maip of California 

Division of Engineering and Irrigation (California Department of 

Public Works, 1922) ; 1929, water-level map of California Division 

of Water Resources (Department of Public Works, 1934) ; 1934, 

measurement, well 25/26-1J3 ; 1946-60, hydrograph, well 25/26- 

1J3 ; 1959-64, hydrograph, well 25/26-1A2.

many of the larger irrigation wells were idle, and seasonal water-level fluctuations were less than half as 

large as during the late forties.

Surface-water supply was deficient in 1959-61 (fig. 

21), and most of the idle pumps were again turned on 

to supply irrigation needs. Although water levels rose to 

about the same level during the early spring of each 

year, the amplitude of the seasonal fluctuation (fig. 65) 

increased. These 3 years of deficient runoff were followed 

by 2 years of above normal surface-water supply (fig. 

14), resulting in a marked recovery of the seasonal low.

The upper right plot of figure 65 shows the subsidence 

at bench mark U288 (for location, see figure 66) in 

response to the long-term water-level decline in the Richgrove area. Little subsidence apparently occurred prior 

to 1940 (fig. 42), by which time water levels in wells 

600-1,100 feet deep had fallen more than 100 feet. The 

rate of water-level decline had greatly increased by 

1946, when the earliest continuing records were available. Leveling control was not available in 1951 when 

the water level was lowest; however, the water-level 

trend suggests that the subsidence rate was probably 

even higher than the dashed line indicates for the 

period 1947-51 and lower than the dashed line indicates 

for the succeeding 3 years. From 1954 to 1959, the subsidence rate decreased markedly in response to the 

rising water level. The effect of the intensified pumping 

of 1959-61 followed by reduced pumping in 1962 and 

1963 is clearly reflected in the subsidence trend of bench 

mark U288. (See also, lower graph, fig. 68.)

The hydrograph in figure 66 shows in detail the waterlevel fluctuations in observation well 25/26-1A2, 892 

feet deep and perforated below 200 feet. During the 

spring of each year from 1959 through 1963, the water 

level returned to about the same high level, even though 

yearly pumpage varied greatly. The amplitude of the 

seasonal fluctuations, however, increased from 96 feet in 

1959 to 148 feet in 1960 and to 198 feet in 1961. During 

this 3-year span, bench marks U822, U288, V822, and 

V288 subsided 0.72,0.62,0.59, and 0.44 foot, respectively. 

During the succeeding 2 years of reduced pumping and 

relatively high water levels, 1962 and 1963, summer 

drawdown was more irregular and varied from 75 feet 

in 1962 to about 115 feet for a month in the spring of 

1963. Subsidence of bench marks U822, U288, V822, and 

V288 for the 2 years was 0.15, 0.13, 0.10, and 0.15 foot, 

respectively.

Heavy pumping during the summer of 1964 caused a 

wsiter-level drawdown of about 200 feet. Bench-mark 

control during this last year, however, was not available 

to determine the rate of subsidence that accompanied 

this renewed seasonal water-level decline.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B87

i

T

"CA

\__ -3P-fU288 LI 

25/26-1A2 ./T945

lichgrove

' TULA RE CO

'KERN 7x1 

EXPLANATION

.25/26-1A2

Recorder well and 

number

XU822

Bench mark

Line of equal subsidence 

in feet, 1959-62

o b

Hydrograph,25/26-lA2

560

1959 1960 1961 1962 1963 1964

FIGURE 66. Correlation of water-level fluctuations in an 892-foot well with subsidence of four bench marks near Richgpove, 1959-64.

Three compaction recorders were maintained in the 

Richgrove area from 1959 through 1964 (table 8) 

two in unused irrigation wells about 900 feet deep and 

the third in the 2,200-foot Richgrove core hole in 

an area that had been actively subsiding (fig. 44). The 

recorders were similar to those operating near Pixley 

(fig. 53) and were installed to measure the magnitude 

and rate of compaction within two depth zones. The 

two 900-foot wells (25/26-1A2 and 1J3) span the continental deposits from the Sierra Nevada and about 150 

feet of the underlying marine siltstone. The deep recorder (24/26-36A2) spans the continental deposits, 

the entire marine siltstone sequence (744-1,900 feet below the land surface), and the underlying sand aquifer 

of the Santa Margarita Formation as used by Diepenbrock (1933). Thus, it spans all the deposits tapped by

water wells in the Richgrove area. Because of mechanical complications, the record obtained from each of 

the three installations is only an approximation of the 

actual compaction at the site and thus cannot be analyzed in detail. For this reason, the compaction graphs 

have not been included in this report.

MEASURED COMPACTION AT 24/26-36A3

Compaction recorder 24/26-36A2 (for location, see 

fig. 66, insert) was installed in the Richgrove core hole 

in May 1959 (table 8), with the bottom-hole anchor set 

at a depth of 2,200 feet. Because of excessive friction 

between the compaction cable and the 4-inch casing, 

however, the recorder registered compaction only when 

the cable was oscillated manually, and therefore the record is not amenable to detailed quantitative analysis.
B88 STUDIES OF LAND SUBSIDENCE

The following qualitative conclusions, however, were obtained from the continuous record of compaction at 36 

A2 and water-level change in well 25/26-1A2:

1. After adjustment for mechanical problems, the 

compaction measured by recorder 24/26-36A2, 

spanning 2,200 feet of unconsolidated and semiconsolidated deposits, roughly equaled the total 

subsidence of 0.87 foot (bench mark U822) during 

the period of leveling control, February 1959-February 1964. This agreement indicates that compaction due to change in effective stress in the 

deposits tapped by water wells has been the principal and probably the sole cause of subsidence 

near Kichgrove since February 1959.

2. A definite correlation exists between the measured 

compaction in well 24/26-36A2 and the water-level 

trend in observation well 25/26-1A2 (fig. 66). The 

rate of compaction was greatest during March 

through June each year when the water level in 

well 1A2 was falling most rapidly. The compaction curve flattened abruptly during periods of 

water-level rise. Little or no compaction occurred 

during 5 to 7 months each year when the waterlevel was relatively high.

3. Water-level fluctuations in well 25/26-1A2 are not 

representative of the entire thickness of compacting deposits at the Kichgrove core hole. Not only 

is the observation well more than a mile from the 

core hole where subsidence rates are much less (fig. 

66, inset), but also it penetrates only the upper 892 

feet of the 2,200-foot sequence of deposits spanned 

by recorder 24/26-36A2. Furthermore, the marine 

siltstone unit that extends from a depth of 744- 

1,900 feet at the Kichgrove core hole has permeability and compressibility characteristics that are 

markedly different from the deposits above 744 

feet. When tested in the consolidometer, samples 

of this marine siltstone were consistently highly 

compressible. No well casings are perforated solely 

in the siltstone, and thus little information is available regarding changes in effective stress that have 

occurred in the siltstone beds.

MEASURED COMPACTION AT 25/26-1A2 AND 1J3

In September 1957, compaction recorders were installed in two unused irrigation wells, 25/26-1A2 and 

1J3, 892 and 897 feet deep, respectively. These wells are 

0.3 mile apart and about 1.5 miles southwest of the 

Richgrove core hole (fig. 66, inset). A water-level recorder also was placed on well 1A2, which is perforated 

from 200 feet to bottom. Because of installation complications, the recorders were placed on wooden platforms,

which swelled in the wet winter months causing an 

inaccuracy of as much as 0.05 foot in the record. This 

seasonal deflection due to wetting and drying has somewhat masked the true compaction record at both sites, 

especially during years of little subsidence.

Measured compaction at these sites from 1959 to 1964 

(February) was equal to about half the total subsidence 

of 0.69 foot (bench mark V822, fig. 66) as determined 

by leveling. Inasmuch as compaction occurred only in 

the deposits below the water table (depth about 250 

ft), the compacting interval measured in these wells 

included about 500 feet of continental deposits and 150 

feet of the underlying marine siltstone. It is concluded 

that compaction occurred also in the thick and highly 

compressible marine siltstone deposits below 900 feet 

(tapped by a few deeper wells), where it is thought 

about half the subsidence occurred from 1959 to 1964.

The magnitude and rate of measured compaction at 

both sites correlate with water-level fluctuations in well 

25/26-1A2 (fig. 66), which is perforated through the 

same depth interval as the compacting deposits spanned 

by these two recorders. Compaction occurred in the 5 

months from March through July when the water level 

in well 1A2 was declining rapidly, but was negligible 

the rest of the year. There was little time delay in the 

compaction response to water-level decline or for a 

water-level rise to stop compaction.

LABORATORY CONSOLIDATION TESTS

The composite logs for the Richgrove core hole are 

shown in figure 8, and the depths from which selected 

samples were tested in the laboratory for consolidation 

characteristics are given in table 14. The subsidence at 

the Richgrove site was due to compaction of the waterbearing deposits as the pore pressures were reduced by 

pumping. No compaction was expected within the upper 

200 feet of deposits, which has been above the water 

table in recent years. Also, little compaction was expected within the Santa Margarita below 1,900 feet, 

because pumping from these sands did not commence 

until 1954; furthermore, clean sands generally do not 

compact appreciably under increased effective stress. 

Most of the subsidence .at Richgrove, therefore, has 

resulted from the compaction of the deposits between 

depths of 200 and 1,900 feet, which include the interbedded sand, silt, and clay of the continental deposits 

above 744 feet and the underlying marine siltstone with 

thin interbedded sands (fig. 8). Table 14 gives a brief 

description of the consolidation test data for samples 

from the Richgrove core hole.

The compression index, Cc, is the numerical value of 

the slope of the straight-line segment of the void ratiologarithm of load curve obtained from a consolidation
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B89

test (fig. 62). Because a straight-line segment of the 

curve was not attained in eight of the 15 samples tested 

(table 14) values of Cc are available for only seven 

samples between depths of 840 and 1,450 feet, in the 

marine siltstone. Within this depth range, however, the 

average value of Cc for plastic clay samples (claystone 

in the lithologic description of fig. 8) is about 2i/£ times 

higher than for samples from the Pixley core hole (table 

11). The Cc values in the sandy deposits above 744 feet 

would be considerably less than those for the plastic 

clays. Without more detailed laboratory consolidation 

data, however, and specific information on the head 

decline that has occurred in the marine siltstone 

sequence, the amount of compaction in each depth zone 

during the successive periods of subsidence cannot be 

calculated.

TABLE 14. Description of consolidation test data for samples

from the Richgrove core hole 

[Data from Earth Laboratory, U.S. Bur. Reclamation, Denver, Colo.]

Compression 

Sample Description Depth (ft) index,

Cc

23L-237 . Sand...................... 157.1 (»)

239.... . Sand-..-.----......... ... 443.0 0)

240 -. Silty clay. --.-.--- -. ... 516.0 (»)

241....... Silt.----.-----..---.- _ .. 607.2 0)

243 Clay, plastic. . ______ 843.0 0.76 

244....... Clay, plastic.............. 916.1 .63 

246--.-.. Clay, plastic--.----. _ ... 1,115.7 1.18 

247... -. Clay, plastic.. __ . __ . 1,155.1 .86

251 - Clay, plastic.............. 1,526.2 (») 

252... Clay, plastic.- __ ........ 1,687.0 (i) 

253 . ... Clay, plastic ........... 1,826.2 (»)

1 Not calculated because of pronounced curvature and insufficient 

segment of void ratio-logarithm of load curve from consolidation test.

Consolidation coefficient, c, 

(ft2 per yr)

55.9

120.7

94 ^

120.7

n

o

6.6 

4.8 

6.4 

12.5

7.2

4.5

1.5

18.1

2 K

straight-line

MEASURED COMPACTION AT 24/26-34F1

Compaction and water-level recorders were installed 

in 1957 in reconditioned unused irrigation well 

24/26-34F1, located 2i/2 miles west of Kichgrove (fig. 

44). The anchor weight (fig. 53) was set at a depth of 

1,510 feet, about 550 feet below the top of the upper 

Pliocene marine siltstone (fig. 5). About half the active 

irrigation wells in sections 25-27 and 34-36 of T. 24 S., 

K. 26 E., have been drilled to the depth range of 1,300- 

1,600 feet and thus tap the deposits spanned by this 

compaction recorder. Nearly all the other active wells 

in these sections are less than 1,000 feet deep.

The hydrograph and compaction record of well 

24/26-34F1 and the subsidence trend of two nearby 

bench marks (for location, see figure 32) are shown in 

figure 67 for the 8-year period 1957-64. The compaction 

record was interrupted twice due to equipment failure 

in December 1958 and again in July 1964.

During the 3 years 1959-61, for which comparable 

records are available, a correlation existed between 

compaction, subsidence, and the downward trend of 

water levels in the heavily pumped aquifer system. During this period of deficient surface-water supply, the 

summer low level in well 34F1 fell about 18 feet per 

year. The decline caused subsidence of 0.33 foot from 

March 1959 to February 1962 at bench mark G758, 

about half a mile northwest of the recorder well, as 

determined by leveling. The measured compaction in 

well 34F1 (1,510 ft. deep) in this same period was 

approximately equal to the measured subsidence at 

bench mark G758. The subsidence rate at bench mark 

U822, about 2i/£ miles to the east of recorder

z

0 i

t:W 1

RELATIVE COMPAC SUBSIDENC AND 

«~|0.8 ft.j- 

- ft

Compaction rec

Equipment failure^

order, 24/26-34F

Bench mark

Bench mark

^*- - -

1 (1,510 feet)

U822

G758

' .

" o

 &

 X

Hydrograph of well 24/26-34F1

FIGUBE 67. Correlation of subsidence and compaction with water-level fluctuations, 2% miles west of Richgrove, 1957-64.
B90 STUDIES OF LAND SUBSIDENCE

24/26-34F1, was about twice the rate at bench mark 

G758 from March 1959 to February 1962.

From 1962 through 1964, water levels remained relatively high in well 24/26-34F1, and little compaction 

was recorded. No leveling was done in this vicinity 

during the 1964 resurvey of a few level lines in the 

Tulare-Wasco area (table 7, line 108), but the compaction record indicates that subsidence was very small.

The long-term trend of water levels in the vicinity 

of well 24/26-34F1 is shown in the upper graph of 

figure 68. Here, the hydrographs of wells 24/26-33H1 

(1930-54) and 24/26-28Q1 (1952-57) extend the waterlevel record back to 1930 and show the marked effect 

that imports of surface water from the Friant-Kern 

Canal during the fifties had on ground-water levels in 

the area. This same general pattern of long-term waterHydrograph, 25/26-6H1 

(Depth 505 feet) /

FIGUEE 68. Correlation of water-level fluctuations in wells northeast of Delano with 

subsidence of nearby bench marks. For location, see figure 32.
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B91

level decline to about 1950, followed by a recovery to 

about their earlier levels during the fifties, is indicated 

by the hydrographs of three observation wells about 3 

miles west of 24/26-34F1 (center graphs, fig. 68).

RELATION OF SUBSIDENCE TO 

WATER-LEVEL CHANGE

Subsidence in the study area is due to compaction of 

the desposits that is caused by changes in effective stress 

resulting from water-level changes. For a given waterlevel change in the coarse-grained beds of a complex 

aquifer system, some beds may compact, other beds may 

expand, and still other beds may remain virtually unchanged in thickness. Compaction of an individual bed 

ocqurs only as rapidly as pore water can escape from 

the deposits. Coarse-grained beds yield water rapidly 

and may adjust to an increased effective stress within 

minutes, whereas a thick fine-grained slow-draining bed 

might take tens of years or centuries to reach hydraulic 

adjustment, that is, for all excess pore pressures to dissipate. Subsidence of the land surface, therefore, is the 

net change in thickness of all the individual beds.

According to the estimate represented by figure 63, 

about 60 percent of the ultimate compaction at the 

Pixley recorder site that would result from the change 

in water levels from 1959 to 1964 occurred in the same 

months as the. responsible water-level decline. About 

25 percent of the computed kiltimate compaction would 

occur more than 10 years after the water-level change. 

Time delay occurs to some degree in all compacting 

aquifer systems and seriously complicates the direct relationship between subsidence and water-level change.

During periods when water-level declines produce 

new maximum effective stresses in the aquifer system, 

all beds tend to compact. Each bed responds to the increased stress at a rate determined by its permeability, 

compressibility, and thickness, but probably no two 

beds respond in exactly the same manner. Some beds 

reach adjustment quickly; others drain slowly and will 

have compacted only slightly when the next seasonal 

water-level recovery occurs. As water levels rise from 

the seasonal lows and the effective stress in the individual beds is reduced, again each bed responds independently. Some beds may have attained ultimate 

compaction under the maximum stress and may tend to 

expand elastically under the reduced stress. Other slowdraining beds may have compacted only slightly and 

might continue to compact through much of the recovery period. The change at the land surface is the 

composite change of all the individual beds. The response of the overall aquifer system can be estimated 

either by assuming an average response for all the beds

combined or by considering each bed separately under 

the change in effective stress.

The actual change in head in each of the beds of the 

semiconfined and confined aquifer systems since groundwater development began in the Tulare-Wasco area 

is not clearly defined. Water levels in both the semiconfined and confined aquifer systems generally declined throughout the area from 1905 to about 1950. 

Since 1950, however, water levels in the eastern part 

of the area served by the Friant-Kern Canal have generally risen, whereas water levels in the western part 

have continued their downward trend. For the western 

part of the area, water-level data are restricted to the 

hydrographs of a few wells which indicate the change 

in head in the principal aquifer system during only a 

few years of record. For most of the area, the change in 

water level, shown by the hydrographs, depends on the 

well depth.

Because of inadequate water-level control, computation of long-term changes in effective stress was possible at only a few localities. For most of the area, only 

gross changes in water levels for the principal waterproducing zone are available, and little information is 

available to indicate long-term changes in the water 

table or in the piezometric head in the less productive 

zones. Inasmuch as the changes in head in the principal 

aquifers are the best data available and as they are 

related to changes in effective stress at a given location, 

they have been used to derive ratios between subsidence 

and head decline at nine locations. These ratios are a 

rough approximation of the response of the aquifer 

system under a given change in stress.

Table 15 gives the rate of subsidence, the rate of head 

decline, and the corresponding subsidence to head-decline ratio for eight wells of figures 33, 34, and 35, 

and also for one nearby well of figure 68. The locations 

of the nine sites involved and the respective subsidence 

to head-decline ratios are shown in figure 50.

In computing the subsidence to head-decline ratios of 

table 15, only the long-term trend of declining 

water levels in deep wells tapping the principal aquifer 

system was considered. The ratios at the nine locations 

ranged from 0.5X10'2 to 5.0 XlO' 2 . As shown in figure 

50, the subsidence to head'-decline ratio is smallest in 

areas of least subsidence and is greatest where subsidence has continued for many years and where the 

amount of subsidence is the greatest. In general, this 

ratio is a rough measure of the response of the aquifer 

system to changes in stress, but it may also be used to 

approximate future subsidence, provided the ratio is 

applied only to water-level declines in excess of prior 

historic low levels.
B92 STUDIES OF LAND SUBSIDENCE

TABLE 15. Relationship between subsidence and head decline at nine locations

Well (for location see fig. 32)

23/23-33A1 (No. 3) __ ____

23/27-28J1 __ ___

24/24-9Ql______-___--___

24/26-30R1. _____________

24/26-33H1. __..____-___

24/27-17Ll________ _______

25/23-29A1, _____________

26/24-3Hl_______________

26/25-19Pl_______________

Reference 

figure

34 

33 

35 

35 

33 

68 

33 

34 

34 

35 

33

Nearby Average rate of Average rate of Subsidence to 

Period bench mark head decline subsidence head-decline ratio 

(ft per yr) (ft per yr) (X 10-2)

1952-59 

1926-62 

1950-59 

1959-62 

1930-46 

1943-51 

1935-57 

1952-59 

1959-62 

1948-62 

1948-59

2PT27S 

PT4S 

PT44S 

PT44S 

302. 847 

G758 

S288 

A755 

A755 

Q754 

W754

5.9 (')

3. 1 

5.3 (')

16. 0

(') 

8. 0 

12.0 

5. 7 

44

0. 17

o

. 13 

.25

0) 

.38

0) 

. 10 

.21 

.25 

.08

2.9 

.5 

42 

47 

5.0 

2.4 

2.5 

1.2 

1.8 

44 

1.8

 Changing rate; parallelism of graphs indicates constant ratio.

In an attempt to relate subsidence to water-level decline on an area! basis, a rough approximation of longterm water-level change and subsidence was made for 

that part of the Tulare-Wasco area where these data 

were available. From these rough data, the lines of equal 

subsidence to head-decline ratio of figure 69 were obtained. For the part of the area east of the boundary of 

the confining Corcoran Clay Member, the head decline in 

deep wells from 1928 to 1948 (fig. 25) and the subsidence 

as of 1954 (fig. 43) were used to compute the longterm subsidence to head-decline ratio. For the area west 

of the Corcoran Clay Member boundary, the change in 

head in the confined aquifer system from about 1905 to 

1959 was related to the subsidence that had occurred to 

1962 (fig. 50). Little information is available as to 

water-level conditions in the western part of the area in 

1905 other than that artesian wells flowed throughout 

much of the area (fig. 22). For this computation, the 

1905 piezometric head was assumed to be at land surface ; thus the 1905-59 change in head was computed as 

the difference between the topographic map contours 

and the 1959 piezometric contours of figure 30. The 

water-level changes used in the computations are, of 

course, only a rough approximation of the actual head 

changes in the aquifer system; also, these computations 

do not take into account the changes in effective stress 

that resulted from fluctuations in the water table. The 

gross effect of these discrepancies, however, is probably 

within 30 percent of the actual, but indeterminate, 

values, and the subsidence to head-decline ratios thus 

obtained are as good a measure of the response of the 

aquifer system to changes in stress as is available.

Figure 69 shows on an areal basis the subsidence to 

head-decline ratios for that part of the area where longterm water-level change and subsidence could be approximated. Also shown are the point values of subsidence to head-decline ratio of table 15 (see also fig. 50).- 

It is significant that five of the point values are in reasonable agreement with the areal lines of equal subsidence to head-decline ratio, even though two of the point 

values are considerably high and two are considerably 

low. These subsidence to head-decline ratios, rough as 

they are, are probably the best parameter available for 

estimating future subsidence for water-level declines 

below historic low levels.

PARAMETERS FOR ESTIMATING SUBSIDENCE UNDER ASSUMED HYDROLOGIC 

CHANGE

Three parameters are of prime significance in estimating the amount of subsidence that will occur under assumed hydrologic change: (1) the change in effective 

stress, (2) the compressibility of the deposits, and (3) 

the thickness of the compacting beds. The time rate of 

compaction, or coefficient of compaction (cv, fig. 60), of 

the slow-draining beds must also be known if the 

rate of subsidence is of concern. If these parameters are 

known, estimates of future subsidence can be made.

The following general criteria can be applied in relating subsidence to head decline:

1. Where little or no increase in effective stress has 

occurred, no compaction is expected.

2. Where increased effective stress has caused measurable subsidence, further increases in effective stress 

will cause continued subsidence.

3. Delayed, or "lag," compaction of slow-draining beds 

may represent a major part of the ultimate subsidence at a location. Such compaction, and related 

subsidence, may continue for many months or 

years after water levels become stabilized at a 

lower level.

4. In areas where both subsidence and water-level decline have been observed for a sufficiently long 

period to establish a long-term relationship, the 

ratio between these two parameters can be pro-
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA

R 22 E 119°30'R 23 E. R 24 E R 25 E 15' R 26 E R 27 E 119°00'

B93

EXPLANATION

Basement complex

Edge of foothills

Approximate eastern boundary 

of the confining Corcoran 

Clay Member of the Tulare 

Formation

Line of equal subsidence/headdecline ratio; equals

subsidence (feet) .

head decline (feet)

X 10"

Dashed where approximate. Interval 

2 units

33H1 

O 2.4

Observation well

Upper number- Well number 

Lower number-Subsidence/ headdecline ratio X 10~2 (see table 15)

0 5 

I i

10 MILES

FIGURE 69. Subsidence to head-decline ratios for that part of the Tulare-Wasco area where data on long-term water-level change 

and subsidence were available. For area west of Corcoran Clay Member boundary, based on head change in confined aquifer 

system, 1905-59, and subsidence in 1962. For area east of Corcoran Clay Member boundary, based on head change in deeper 

wells tapping the semiconflned aquifer system, 1928 48, and subsidence to 1954.

jected into the future as far as the projected 

water-level trend justifies. This relationship does 

not take into account residual "lag" effects; thus 

minimum values of subsidence are determined by 

this means. Where water levels have declined and 

then partially recovered, the subsidence to headdecline ratio has little significance until water levels 

return to their former low levels. 

As in most ground-water reservoirs, neither the semiconfined nor the confined aquifer systems of the TulareWasco area are simple hydrologic units. Intercalated 

silt and clay lenses within these aquifer systems create a 

diverse range of pore pressures in the various beds. An 

analysis of effective stresses and compaction rates at any 

location, therefore, is not a simple relationship. Effective-stress computations generally must be made for 

each of the subunits of the aquifer system, using either 

known or assumed hydrologic data. Also, the only 

places in the Tulare-Wasco area where the compressibility of some of the compacting beds has been meas-
B94 STUDIES OF LAND SUBSIDENCE

ured directly are at Pixley and at Richgrove where 

cored samples have been tested in the laboratory. Because of the rapid areal change in lithology, it is impractical to consider obtaining the hydrologic and compressibility field data on a regional basis that would be 

necessary to compute subsidence using the conventional 

soil-mechanics approach.

The practical method of estimating future subsidence 

areally is to utilize, an approximate parameter based 

on the historic response of the sediments to increase 

in stress (water-level change). The approximate parameter most effective in this study is the ratio of subsidence to head decline that can be derived from subsidence and water-level change maps, together with 

graphs showing subsidence and water-level change at 

specific locations (fig. 69). To derive meaningful ratios 

of subsidence to head decline, great care is needed in 

selecting water-level declines representative of the 

stress change in the principal compacting zone. This 

ratio is most meaningful for long periods of continuous 

water-level decline and has little significance unless 

water levels at the end of the period are at their lowest 

level.

EXAMPLES OF APPLICATION OF PARAMETERS 

AT FOUR SITES

The following four examples of the application of 

available parameters, rough as they are, to estimate 

future subsidence under assumed water-level decline 

not only give projected values at these sites, but outline 

the method of predicting subsidence for other parts of 

the area. Since no attempt has been made to forecast 

future water-level trends, subsidence is herein estimated 

in terms of head decline in the principal aquifer system, 

as measured by water levels in selected observation 

wells.

At Pixley, a compressibility parameter for the confined aquifer system, derived from laboratory consolidation tests and computations made earlier in this report (p. B83), is applied directly to obtain an estimate 

of ultimate subsidence. At the other three sites, subsidence to head-decline ratios are applied to derive 

rough estimates of subsidence that would be expected 

from additional long-term head decline below historic 

low levels at these sites. For other parts of the area, 

the best available data for deriving crude estimates of 

the subsidence that would occur if water levels in the 

principal aquifer system were lowered below historic 

minimum levels are values of subsidence to head-decline 

ratios from figure 69, applied as for the three sites.

AT THE PIXLEY CORE HOLE, 23/25-16N1

From the data of table 13, a rough measure of the 

compressibility of the confined aquifer system was obtained which is here used to estimate future subsidence 

at the Pixley core hole for assumed head decline. Thus, 

as tabulated on page B83, the ultimate specific unit compaction (compressibility) for the 60 years from 1905 

to 1964 was 1.1 X 10~ 4 foot of compaction per foot of 

aquifer-system thickness for each foot of increase in 

effective stress. If the water level in the semiconfined 

aquifer system is assumed to remain nearly constant in 

the future, as it has since 1962, then the water-level 

trend of wells tapping the confined system will approximate the effective-stress trend for the compacting 

system.

By using 1.1 X 10~4 foot per foot2 as the measure of 

compressibility and an estimated compacting thickness 

of 600 feet, the following amounts of ultimate subsidence (compaction) are estimated for various assumed 

head declines in the confined aquifer system at Pixley:

Piezometric head 

decline below 

1964 levels 

(ft)

10

50

100

200

Estimated 

ultimate 

subsidence ' 

(ft)

0.7

3. 3

6. 6

13. 2

Estimated 

short-term 

subsidence l 

(ft)

0. 5

2.5

5.0

9. 9

1 Assuming a constant water table at 100 feet below the land surface.

Inasmuch as short-term subsidence (less than 10 years) 

represents about three-quarters of the ultimate subsidence, these estimates are also tabulated. It is significant that if the piezometric level at Pixley is drawn 

down 100 feet below the 1964 level, it will be below the 

base of the confining layer for a short period each year, 

and if it is drawn down 200 feet below the 1964 level, 

it will be below the confining layer continuously. Under 

the unconfined condition thus developed in the compacting aquifer system, the amount of subsidence per foot 

of water-level decline would be only about two-thirds 

as great as under confined conditions.

These values apply specifically to the Pixley site and 

to the conditions of 1964 as a reference base. If deeper 

wells are drilled in the area and thereby compaction occurs at greater depths, or if the shallow water level 

changes appreciably from the 1964 level, the estimated 

amounts of subsidence would be changed accordingly. 

No attempt is made to anticipate the rate at which water 

levels may decline in the future. If confined water levels 

should decline significantly below the 1964 level, however, the amount of subsidence would probably be ap-
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B95

proximately that which is indicated in the table. It is 

noteworthy that when similar computations are applied 

to the stress changes that occurred from 1948 to 1964, 

confirmatory results of subsidence are obtained. For example, a 1948-64 piezometric lowering of about 130 feet 

resulted in 9.5 feet of subsidence (bench mark N88 reset) , as compared to 8.6 feet computed from the value of 

1.1 X 10~4 foot'1 for ultimate specific unit compaction. 

(Seep. B94.)

Relating 9.5 feet of subsidence to 130 feet of head 

decline for the 1948-64 period gives a subsidence to headdecline ratio of 7.3 X 10~2 . This value is in close agreement with the value obtained from figure 69. This ratio, 

if multiplied by an assumed 100 feet of future head decline, would indicate about 7.3 feet of ultimate subsidence, which also is in reasonable agreement with the 6.6 

feet of subsidence of the preceding tabulation.

AT ALPAUGH, 23/23-33A1

As shown in the upper graphs of figure 34, the water 

level in the semiconfined aquifer system (well 23/23- 

33 Al, piezometer 1) at Alpaugh declined about 2 feet 

per year (average decline of seasonal low levels) from 

1952 through 1964. Also, the piezometric head in both 

the upper and lower zones of the confined aquifer system 

(piezometers 2, 3, respectively), although much more 

irregular and unmeasured during the last part of the 

period, declined roughly 5 feet per year. This decline 

suggests an average increase in effective stress in the confined aquifer system (fig. 52) equivalent to about 4 feet 

of water per year. Subsidence for the period averaged 

about 0.18 foot per year. Assuming that all the subsidence at this location is due to compaction of the confined aquifer system, a reasonable approximation, 

considering the depth of the producing wells and the 

depth of the confining clay layer, the ratio of subsidence 

to effective-stress increase roughly equals 4.5 X 10~2 . 

This ratio suggests that as long as present trends continue, 1 foot of subsidence will occur for each 22 feet 

of increased effective stress.

For the following tabulation this ratio was used to 

estimate the subsidence that would occur at Alpaugh 

if the 1952-62 water-level trends continued :

Water-level decline

Confined

system (ft)

10

50

100

150

200

300

Semiconfined

system (ft)

4

20

40

60

80

120

Increase in 

effective stress 

(ft of water)

8

40

80

120

160

240

subsidence 

(feet)

0.4 

1.8 

3.6 

5. 5 

7.3 

10. 9

The estimates represent only a minimum value for 

ultimate subsidence resulting from the specified change 

in effective stress because the amount of time lag and 

residual compaction (subsidence) as of 1962 is unknown. 

On the basis of theoretical considerations of figure 52, 

if shallow water levels remained constant, while confined water levels continued downward, the subsidence 

would be about 25 percent greater than that shown in the 

preceding table.

AT WELL 25/23-29A1, 11 MILES SOUTHWEST OF 

ALPAUGH

As at Alpaugh, water levels in both the semiconfined 

and confined aquifer systems at well 25/23-29A1, 11 

miles southwest of Alpaugh, maintained a downward 

trend during the 1952-64 period of record (fig. 34). The 

shallow, semiconfined water level declined an average 

of 1.5 feet per year (trend of summer low levels) during 

this period, the upper confined level declined about 2.5 

feet per year, and the lower confined level declined 

roughly 9 feet per year. Nearby subsidence (bench mark 

A755) averaged about 0.13 foot per year from 1952 to 

1962. If these generalized downward water-level trends 

were to continue at the same proportional rates, 0.1 foot 

of subsidence would occur for each 7 feet of head decline 

in the deep confined zone. The following tabulation indicates the estimated subsidence at this location if the 

1952-64 water-level trends continue:

Water-level

decline,

confined system, 

deep zone

(ft)

7

50

100

200

300

Estimated 

subsidence

(ft)

0. 1

.7

1. 4

2.9

4. 3

Because of the complexity of the hydraulic conditions 

in the compacting confined-aquifer system and the scant 

amount of water-level data (p. B48), the change in effective stress at the site can only be approximated. There 

is little basis for estimating subsidence during periods 

when water levels are significantly above the 1964 

conditions.

FIVE MILES NORTHEAST OF DELANO

As shown by the upper and center graphs of figure 

68, water levels in the semiconfined aquifer system 5 

miles northeast of Delano generally declined until about 

1951, and then recovered during the following 9 years. 

Water levels in deep wells (24/26-33H1, 28Q1, 34F1,
B96 STUDIES OF LAND SUBSIDENCE

and 30K1), intermediate wells, e.g. 24/26-32G1 (470 ft 

deep), and shallow wells, e.g. 25/26-6H1 (297 ft deep) 

followed the same general pattern, except that the 

shallow water level was 20-100 feet higher than the 

deeper water levels.

Subsidence in this area, as indicated by the graphs 

of bench marks G758 and F758 (for location, see fig. 

32), continued at a rate of from 0.3 to 0.5 foot per year 

for 2-3 years after deep water levels began to recover 

and then abruptly abated. During the late fifties, when 

water levels were considerably above their earlier lows, 

and thereby effective stresses in the semiconfined aquifer 

system were less than their previous maxima, little or 

no subsidence occurred. During the dry years of 1959- 

61 (fig. 14), when water levels in deep wells again declined, subsidence recommenced (bench mark F758) or 

the rate increased (bench mark G758), even though 

effective stresses were much lower than 10 years earlier.

The progressive compaction of the various beds of the 

semiconfined aquifer system was interrupted by the 

water-level recovery of the fifties, but more subsidence 

will probably occur if water levels again fall through 

the range of previous decline. No method is known, 

however, for estimating the amount of subsidence that 

will occur at this location until effective stresses are 

again as great as they were in 1950. It is reasonable to 

conclude that during the second cycle of effective-stress 

increase the subsidence would be considerably less than 

during the first cycle, but how much less is not known. If 

effective stresses should exceed their 1950 maximum 

values, it is anticipated that subsidence would continue 

at about its pre-1950 rate, that is, about 1 foot of subsidence for each 30 feet of water-level decline.

As shown in figure 69, the subsidence to head-decline 

ratios at wells 24/26-30K1 and 33H1 are considerably 

lower when derived from the hydrographs of figure 

68 than from the water-level change map (fig. 26). Apparently, water levels in these wells have been drawn 

down deeper than the regional water-level contours indicate. By using a subsidence to head-decline ratio of 

3.8 X 10"2 (fig. 69), the following amounts of subsidence 

at well 24/26-33H1 were calculated for the listed drawdowns below historic low levels:

Water-level decline, principal

aquifer system

(ft)

10

50

100

200

Estimated

subsidence

(ft)

0. 4

1.9

3.8

7.6

METHODS OF DECREASING OR 

STOPPING SUBSIDENCE

Theoretically, subsidence will continue at a given 

location as long as excess pore pressures exist within 

the underlying deposits, but will stop as soon as excess 

pore pressures are dissipated. Thus, as long as declining 

water levels continue to produce increasing effective 

stresses, subsidence will continue. When the rate of effective-stress increase is reduced, or the effective stresses 

in the system are significantly reduced by water-level 

recovery, subsidence will slow down or eventually stop. 

Inasmuch as a small part of the compaction in a subsiding area is elastic in nature and will be recovered 

when the applied stress is removed, slight rebound of 

the land surface should occur when water levels recover. Slight rebound has been measured at several 

locations in the Tulare-Wasco area during periods of 

water-level recovery.

SEASONAL CHANGES IN WATER LEVELS

As shown by the stepped record of compaction 

recorder 23/25-16N1 (fig. 54, upper), little or no compaction occurs at this location during about one-third 

of each year when water levels are high. In fact, slight 

rebound has been measured during periods of seasonal 

high water levels (fig. 59). This rebound indicates that 

the process of aquifer-system compaction is effectively 

stopped by raising the water levels in the confined 

aquifer system enough to bring effective stresses above 

the C-C' line.

The magnitude of the seepage stress in an aquifer 

system (difference in head between the confined and 

overlying semiconfined aquifer systems) plays a dominant role in producing subsidence (fig. 52). As shown 

in figure 54, the rate of subsidence at Pixley is greatly 

increased during periods of increased seasonal drawdown. Inasmuch as the seepage stress is the principal 

component of effective stress in much of the TulareWasco area, the rate of subsidence can be reduced by 

decreasing the seasonal range of water-level fluctuations 

in the confined aquifer system. It is significant that 

changes in effective stress are only about half as great 

in the confined aquifer system when water levels in the 

confined and semiconfined aquifer systems are lowered 

together, as when the semiconfined water level is held 

constant and the confined water level is drawn down 

seasonally by pumping. Therefore, additional compaction of the confined aquifer system could be reduced by
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B97

planned lowering of the water level in the overlying 

semiconfined system to conform with head decline in the 

confined system.

LONG-TERM WATER-LEVEL CHANGES

The long-term graphs of figures 33, 34, 35, and 68 

show the correlation between water-level trend and subsidence in various parts of the area. Of particular interest is the marked change in the rate of subsidence 

north and east of Delano (fig. 68) during periods of 

water-level recovery. Thus, from 1954 to 1957 little 

subsidence occurred in the area of imported surface 

water (fig. 45) where water levels recovered as much 

as 150 feet. Also, in the Delano-Famoso-Wasco area, 

where 1948-54 subsidence rates were as much as 0.5 foot 

per year, no subsidence occurred from 1957 to 1959 (fig. 

46) in response to continued water-level recovery.

As shown in figure 49, the subsidence rate in the 

Tulare-Wasco area decreased from about 150,000 acrefeet per year (1950) during a period of maximum 

water-level decline to about 40,000 acre-feet per year 

during maximum water-level recovery. This decrease 

is shown graphically in figure 48, where the slope of the 

curve denoting the volumetric rate of subsidence was 

about the same in the late fifties as it was in about 1946.

To sum up, any method that could be employed to reduce the ground-water pumpage of an area would tend 

to reduce the subsidence. Also, centers of intense subsidence could be eliminated by distributing the withdrawal wells more uniformly.

CONCLUSIONS AS TO METHODS OF DECREASING OR 

STOPPING SUBSIDENCE

1. Inasmuch as the thickness and compressibility of deposits in a subsiding area change only slightly as 

subsidence increases, the rate of subsidence at any 

location is directly related to the change in effective stress that results during ground-water development. Continued increase in effective stress will 

cause continued subsidence. Subsidence can be 

slowed, however, by reducing the rate of increase 

in effective stress or by permitting water levels to 

stabilize and thereby stopping further increase in 

effective stress. Subsidence can be stopped altogether by raising water levels sufficiently to eliminate all residual excess pore pressures in the 

aquitards.

2. In the western part of the Tulare-Wasco area, the 

subsidence rate under continued pumping can be 

reduced by increasing withdrawal from the semiconfined aquifer system, so that water levels in the 

confined and semiconfined systems are drawn down 

at about the same rate. This method would reduce 

the seepage stresses in the confined system and

thereby reduce the rate of compaction of that 

system.

3. Also, throughout the study area the subsidence 

rate can be markedly decreased by reducing the 

seasonal head decline in the confined aquifer system. This method might be accomplished by wider 

spacing of pumping wells, by moving some of the 

large pumping wells outside of areas of maximum 

summer drawdown, or by holding canal deliveries 

during years of deficient surface supply until 

midseason.

4. The mining of ground water in subsiding (as well 

as nonsubsiding) areas is ultimately limited by 

economic considerations. When the practical range 

of water-level fluctuations in the ground-water 

basin is established for optimum cyclic storage, the 

basin can be precompacted by creating maximum 

effective stresses in the basin by pumping, and then 

permitting water levels to recover to their predetermined operating range.

5. Slight rebound of the land surface was observed in 

several areas of large water-level recovery. Measured rebound at Pixley during recovery represented 1 or 2 percent of the earlier compaction 

during a corresponding period of drawdown. 

Northeast of Delano, as much as 0.05 foot of rebound was observed at several bench marks from 

1957 to 1959; the rebound resulted from widespread water-level recovery.

SUMMARY AND CONCLUSIONS

Intensive pumping of ground water in the TulareWasco area since 1905 has resulted in extensive land 

subsidence. As of 1962, 800 square miles of irrigable 

land had undergone more than 1 foot of subsidence, and 

as much as 12 feet of subsidence had occurred locally. 

Although subsidence has continued for more than 40 

years, it has occurred so gradually and over such a 

broad area that it has gone unnoticed to most local residents. Many well casings have been severely damaged 

by the subsidence, however, and its detrimental and 

costly effects have been of serious concern to surveyors, 

design and construction engineers, irrigation districts, 

and some landowners for more than 20 years.

The deposits penetrated by wells in the TulareWasco area and the underlying sediments and bedrock, 

include the following, in descending order of occurrence: (1) A thick sequence of unconsolidated continental deposits of late Tertiary and Quaternary age derived from the Sierra Nevada, that constitute the principal ground-water reservoir, (2) semiconsolidated 

and consolidated upper Pliocene and Pliocene(?) marine strata, tapped by water wells in the eastern part
B98 STUDIES OF LAND SUBSIDENCE

of the area, (3) the Santa Margarita Formation as 

used by Diepenbrock (1933), a thin marine sand, tapped 

by water wells near Richgrove, (4) an undifferentiated sequence of lower Tertiary sand and siltstone, not 

tapped by water wells, and (5) the crystalline basement 

complex. A well-sorted diatomaceous lake clay the 

Corcoran Clay Member of the Tulare Formation 

within the continental deposits in the western half of 

the area forms an effective ground-water confining bed.

The unconsolidated continental deposits, derived almost wholly from the Sierra Nevada, dip gently westward, and the underlying marine deposits dip more 

steeply westward beneath the study area. Most of the 

ground water is pumped from the unconsolidated continental deposits, which for the most part are moderately permeable.

Usable ground water occurs in two principal aquifer 

systems: (1) a semiconfined system that underlies the 

entire area and that extends downward from the water 

table to the top of the Corcoran Clay Member in the 

western part of the area and to the top of the marine 

strata or to the base of the fresh-water body in the eastern part and (2) a confined aquifer system beneath the 

confining Corcoran Clay Member in the western part 

of the area that extends down to the base of the freshwater body. In addition, a deep confined aquifer the 

Santa Margarita Formation as used by Diepenbrock 

(1933) is tapped only in the vicinity of Richgrove.

Four natural streams enter the Tulare-Wasco area 

from, the Sierra Nevada on the east. Tule River has 

long been an important source of irrigation supply, 

whereas Deer Creek, Poso Creek, and White River flow 

only intermittently and in most years supply only small 

quantities of water to the area. Also, canal diversions 

from the Kern and Kaweah Rivers and, since 1950, from 

the Friant-Kern Canal have been an important source 

of irrigation supply. Imports from the Friant-Kern 

Canal since 1953 have far exceeded all other surfacewater sources and have greatly reduced the groundwater pumpage in the canal service area. Recharge to 

the ground-water reservoir is principally from deep 

percolation from the Sierran streams and canal diversions, but also comes from underflow in the foothill 

recharge area.

Little ground water was used in the Tulare-Wasco 

area prior to the introduction of electrically powered 

pumping plants in about the year 1900. Since the early 

twenties, however, the use of ground water has accelerated and has resulted in severe water-level declines in 

much of the area. By 1940, water levels had declined 125 

feet between Delano and Richgrove, and extensive subsidence was recognized. Water levels continued to decline throughout the area until the early 1950's, when

surface-water imports via the Friant-Kern Canal reversed the downward trend of water levels in the canal 

service area. Since the early 1950's, therefore, two different trends have prevailed: (1) in the western half of 

the area, water levels both above and below the confining layer have continued to decline, the shallow levels 

trending downward at a slower rate than the deeper 

levels, and (2) in the eastern half of the area, shallow 

water levels have generally remained constant or risen 

slightly,' while the levels in deeper wells rose during the 

fifties and leveled off or declined during the early sixties.

Estimated ground-water pumpage for agricultural 

use from 1950 through 1962 ranged from 0.7 million 

acre-feet in 1958 to 1.4 million acre-feet in 1961.

Subsidence was first recognized in the Tulare-Wasco 

area in 1935, when leveling showed definite changes in 

altitude of the land surface from 1926 topographic 

maps. In 1940, surveys indicated that an area of more 

than 200 square miles had experienced more than 1 foot 

of subsidence since 1902. Repeated leveling of a network 

of bench marks throughout the subsidence area in 1947- 

1948, 1953-54, 1957, 1959, 1962, and partial releveling 

in 1964, have provided the data for a series of subsidence maps and profiles that define the extent and magnitude of the subsidence. The annual volumetric rate of 

subsidence, which is directly related to seasonal pumping, varied from a 1948-54 average of about 136,000 

acre-feet to 45,000 acre-feet in 1957-59 and a maximum 

of 173,000 acre-feet in 1959-62. As of 1962, at least 600.- 

000 acres had subsided more than 1 foot, and 10,000 

acres had subsided more than 10 feet. The cumulative 

volume of subsidence from 1926 to winter 1962 was 

about 2.2 million acre-feet. Subsidence will continue as 

long as ground-water levels are drawn down below 

prior low levels.

During the 13 years from 1950 to 1962, 1.4 million 

acre-feet of subsidence occurred as a result of pumping 

13.5 million acre-feet of ground water. The volume of 

subsidence, therefore, represented about 10 percent of 

the total ground-water pumpage.

Subsidence is due to the compaction of the wateryielding deposits as intergranular effective stresses are 

increased by lowered ground-water levels. The amount 

of compaction at a given locality depends on the thickness and compressibility of the deposits and the magnitude of the effective stress change.

Specially designed compaction recorders, measuring 

the vertical shortening of the stratigraphic section to 

depths as great as 2,200 feet, were operated in 11 wells 

during the investigation. Of these recorders, eight were 

still in operation as of December 31, 1964. Companion 

water-level recorders were operated in five of these 

wells and also in one other observation well. At Pixley,
LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B99

where the most detailed measurements of compaction 

are available, little or no compaction occurred in the 

0-355-foot depth zone from January 1959 to February 

1964, whereas 1.90 feet of compaction, or 75 percent of 

the total subsidence, occurred in the 355-760-foot zone; 

about 0.64 foot of vertical shortening, or 25 percent of 

the subsidence, occurred in the confined deposits below 

760 feet. The rate of subsidence at this site varied from 

0.69 foot per year (1959-62) to 0.23 foot per year (1962- 

64), in response to a marked, though temporary, change 

in the pumping pattern. The computed compaction at 

this site, based on laboratory consolidation tests of representative core samples and Terzaghi's theory of consolidation, agreed reasonably well with the measured 

compaction for the given change in effective stress.

It is concluded that water-level change is the cause 

of the subsidence in the Tulare-Wasco area and that 

neither tectonic movement nor hydrocompaction have 

been contributing factors to the land subsidence. Also, 

there is no evidence that either natural or artificial 

vibrations have caused a measurable increase in either 

the amount or the rate of subsidence.

The direct cause of the subsidence is the change in 

effective stress in the deposits due to a change in groundwater levels. Water-level changes in subsidence areas 

may change effective stresses in two different ways: (1) 

a change in the position of the water table changes the 

effective stress because of the change in buoyant support of grains in the zone of the change or (2) a change 

in position of the water table or the piezometric surface 

(artesian head) or both that induces hydraulic gradients 

across confining or semiconfining beds produces a seepage stress which is algebraically additive to gravitational stresses.

If the artesian head remains unchanged, a rise in the 

water table reduces effective stresses in the unconfined 

parts of the aquifer system but increases the effective 

stress in the confined parts, due to the increased downward seepage stress. A decline in the water table, on 

the other hand, increases the effective stresses in the 

saturated part of the unconfined aquifer system, but 

decreases the effective stress in the confined beds. A decline in piezometric head in a confined aquifer system, 

however, has no effect on stresses in an overlying unconfined system, but increases the stress in the confined 

beds. The magnitude of the change in effective stress 

is nearly twice as great for a given head change in a 

confined system as for the same head change in an 

unconfined system.

Based on the findings of this investigation, the following criteria may be applied to anticipate the amount 

of subsidence that will occur under assumed hydrologic 

change:

1. Inasmuch as changes in ground-water levels are 

responsible for subsidence, little subsidence would 

be expected if little change in ground-water level 

had occurred.

2. If subsidence is known to have occurred in response 

to a given increase in effective stress (water-level 

change), future increases in effective stress will 

cause roughly proportional subsidence provided 

the time intervals are comparable.

3. For this hydrologically complex area, the subsidence 

to head-decline ratios established during periods 

of continuing subsidence and water-level decline 

are the best means for deriving crude estimates 

of the subsidence that would occur if water levels 

in the principal aquifer system were lowered below historic minimum levels. Subsidence to headdecline ratios range from about 0.5 XlO"2 foot of 

subsidence per foot of head decline in areas where 

little subsidence has occurred to more than 6.0 

X 10~2 feet of subsidence per foot of head decline 

where subsidence has been the greatest. Where the 

water-level trend has been reversed, however, and 

effective stresses have been decreased sufficiently 

to stop subsidence, little future subsidence would 

be anticipated unless prior maximum effective 

stresses were exceeded.

4. Because of the slow drainage from the thicker less 

permeable beds in an aquifer system, subsidence 

may continue long after maximum effective 

stresses have been imposed on the permeable beds 

(aquifers).

It has been clearly demonstrated in the service area 

of the Friant-Kern Canal that subsidence can be effectively stopped by raising ground-water levels sufficiently high to eliminate all excess pore pressures in 

the aquitards. Also, it is concluded that if water levels 

are held at a constant low level, subsidence will stop 

after all lag, or residual, compaction has been accomplished. As long as excess pore pressures exist in any of 

the compactible beds, drainage from these beds will 

occur and subsidence will continue.

No method is known for stopping subsidence other 

than that of raising the head in the aquifers sufficiently 

to eliminate the excess pore pressures in the aquitards. 

This method can be effected either by decreasing 

pumpage, increasing recharge, or both. If neither is 

practicable, however, under favorable circumstances 

subsidence rates may be substantially reduced by redistributing the total pumpage in time and in space so as to 

reduce local seasonal head declines and minimize the 

development of seepage stresses (hydraulic gradients) 

across confining beds within the ground-water reservoir.
B100 STUDIES OF LAND SUBSIDENCE

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LAND SUBSIDENCE, TULARE-WASCO AREA, CALIFORNIA B101

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INDEX

Page 

Acknowledgments.._-. . ....__ ._ B6

AUuvialdeposits.---................... 7,8,9.10,11

Alpaugh...... ___.. 8,9,10,11,13,25,28, 48,62,95

Aquiclude______.-_... _.-.--...... 66,67,68

defined...........__.................... vi

Aquifer, defined--.-----...-----......--.-.... vi

Aquifer system, confined..._._____- _ - 23,

25, 28, 30, 34, 48, 53, 68, 72, 77, 78, 79, 91, 

94,95, 96, 98, 99 

confined, hydraulic stresses............... 65

piezometric head..................... 45,

48,49, 65,67, 70, 72, 74, 77,95,99 

piezometric surface....._........... 36,

39,40, 43, 68, 69, 71, 74, 82 

See also Santa Margarita Formation

as used by Diepenbrock. 

defined......_.-.-----................. vi

semiconfined . . _ _ _ _ __ 23,

25, 30, 44, 46, 53, 69, 72, 78, 79, 91, 94. 96, 98

piezometric surface.......... 28,39,40, 4$, 53

water level... 26,28,34,38,39, 40, 71,74,82,88 

unconfined, hydraulic stresses. -------- 65, 68,99

Aquitard................ 23,30,64,65,67,68,75,84,99

defined.--_....-_---.._--.-.--..--..-...-- vi

Arvin-Maricopa area__..................... 1,4

Basement complex...................... 8,18,25,98

Cable, down-hole..-.._..._.-...-..-.....-.. 69,70

Galloway Canal...._................___ 19

Chlorite..______._..__...._.__._ 19

Clay-mineral assemblage..................... 18

Climate..__._____.__...._._.... 2

Coefficient of volume compressibility. -------- 83

defined-.,................................ vi

Collection of data___........._.___... 6

Compaction, computed_.--.----..-........ 79

defined_..______________....... vi

elastic and nonelastic.................. 64,68,75

near Pixley............___._......... 70,99

near Richgrove_..__ _.___ __ 86

recorder installations.............-----. 6,69,88

time lag.............._.._....._..._ 83

Compressibility_.___.........._._,._ 78

Compression index..-........................ 88

Cone of depression___...._.__.. 35,38,39,56

Confining beds.._...__......11,23,28, 45, 66, 73, 74, 98

Consolidation................................ 79,89

defined.-._............................. vi

Corcoran................................___ 18,57

Corcoran Clay Member of the Tulare Formation...__.____________. 9,10, 

11, 23,25,26,28,34,42,43,46,48,62,84, 92,98 

Corcoran Lake...__....................... 12

Deer Creek.......................2,8,19,23,25,41,98

Delano. .2,12,25,34, 39,48, 52,53, 56, 57,58,59, 62,95, 98 

Deposits, continental...... .7,8,23,25, 26, 87,88,97,98

marine......___.--__------._--_____..__ .7,28,98

Tertiary sedimentary undiflerentiated 8,

J8.98

upper Pliocene and Pliocene(?) siltstone strata_................... 8,

IS, 23,25,26, 28,29,45,87,88,89,97 

See also Santa Margarita Formation as

used by Diepenbrock. 

Diatoms.....................................9,13,98

[Italic page numbers indicate major references!

Page 

Earlimart----------------~----Bll, 39,53,56,57,62

Eflective stress......____.._........... 34,

45, 64,66, 67, 68, 69, 71, 72, 73, 75, 77, 78, 79, 

82,83,84,85,88,91,94,95, 96,98,99 

defined.._....._. .. ......-..--. . vi

Electric log..-.---.------.-_-------... . 9

Flood-plain deposits....------_---.--.-. .7,8,9,10,11

Freeman-Jewett Silt__ ... ...... .-.-.. - 18

Friant-Kern Canal......-.------..-.----.. 2,

19, 22, 23, 24, 31, 39, 41, 43, 46, 47, 49, 53, 57, 

61,90,98

Gravitational stress._.........___... 64,66

Ground water, pumpage...... .10,23,24, SO, 36,39,86

recharge........--.-------_._---.-20,23,41,45,53

Hall,W. H., cited...........................5,23,24

Hanford-Visalia area.-................ 5

Hydraulic stresses........_.....- .--..--.. 64,78

Hydrostatic stress..-----._-_.-._-----.-----54,67,68

Illite-.--- .-..- ----.------ - - 18,19

Irrigation...................2, 5,18, 19, 23,26,28, 30,35

Kaweah River...................2,8,21,23,35,!

Kern River........._-__-._......-...2, 8,21,24,47, 98

Kern River Series of Diepenbrock.. _....... 8

Kings River..,.-._....._-__.._..----....--... 8

Lacustrine deposits_.-----.____-_.----_--.__ 7,8,9

Lerdo Canal......._...........__.- ..... 19

Leveling data.-------.-----.----------------- 60

Lindsay.._----.----_---_-----_---..--------_. 35

Los Banos-Kettleman City area........... _ 1,4

Millerton Lake.--...-..-......... .... 19

Montmorillonite...-_.... .. ._....... 4,18,19

Mount Poso oil field...-_.....-._.----__---._- 17

Mya......................................... 13,16

Neutral pressure. 

defined.-----.

Olcese Sand. 18

Piezometers......................... 12,28,34,47,48

Pine Flat Dam_. __............. __. __ 8

Pixley............. 12,18,25, 53, 56, 57,62, 70, 71,72,94

computed compaction....._............ 79,85

measured compaction__................ 70,85

rebound________.__.........._... 75

time lag of compaction.................... 83

Pixley core hole....__...._.. -...-.-..- 6,

9,12,16,18,19, 79,82, 83,84,85, 89,94 

Pixley-Earlimart area.-...................... 59

Porosity _..__._ - --__-- . 65,68,79 

Porterville- ...-......_-__.._....- 18,26,35,39,52

Poso Creek.............................. 2,19,23,98

Purpose of report--.-.-.----__----_---..---..- 2

Pyramid Hill Sand........................... 18

Richgrove...........__._......._.__ 13,

18,25,29, 38,39,47, 56, 57,58, 59, 70,94,98 

measured compaction_.......-.---.- 87,88,89

Richgrove core hole. ...... 4, 6,10,13,17,18,19,87,88

Round Mountain Silt._............-.---..- 18

Page 

Saline water body..... B16,18,28,29

San Emigdio Mountains .. 7 

San Joaquin Formation.--- -- - --- 13 

San Joaquin River.--- --- .- 8,24

San Joaquin Valley 2,4,5,7,11,62

Santa Margarita Formation as used by

Diepenbrock......... 8, 16, 23,25,28,98

piezometric surface ... .. 29,40,45 

Seepage force... . - - - 66,67 

stress. .- 64, 65,67, 69, 79,82,96

defined.-- - vii

Sierra Nevada basement complex.-...--. 8,^8,25,98 

Sierra Nevada block . . ... 7 

Specific compaction, defined vii

Specific gravity...... ... - 65,68,79

Specific rebound, defined - . . vii 

Specific unit compaction ..... 73,74,83,94

defined.___.. - - vii

Specific unit rebound 76 

defined. .---- - vii

Specific yield 10,18

Storage coefficient-. 30

Subsidence, causes 88,91

estimation by parameters 02,04

leveling data.... -- 50

magnitude 1,2,22,34,52,56, 61, 72,89,97,98 

maps. s6 

methods of decreasing or stopping .... 96

profiles .... 53

rate... - 22,53,57,59,60,78,89,95,96,97

Subsidence to head-decline ratio.. 85, 91, 94,95,96,99

defined vii

Success Dam... . - - 21

Success Reservoir - - 19

Surface water, supply 2,^0,20,60,86

Tectonic movement 7,62 

Tehachapi Mountains 7 , 

Terra Bella.... .... . - .-.- 53

Terra Bella-Lost Hills area 5,8

Terzaghi theory of consolidation... 4, 64, 69,79,84,99 

Tipton 47> 53

Transmissibility - !6.30

Tulare 2,11,34,36,53,57

Tulare Formation..... 8,9

Tulare Lake 7,8,9,21,24,35,62

Tulare-Wasco area, ground water reservoir 23,39

location and general features #

physiography 7

Tule River..... 2,8,19,21,23,25,35,36,41,98

Ultimate compaction_ 78,83,84,85,91 

Unit compaction, defined vii 

Unit compaction to head-decline ratio,

defined vii

Vedder Sand...-- --------------------- 18

Vermiculite. 18' 19 

Void ratio .... - 64,82,88

Walker Formation.... 18

Wasco -..... H.12,47,59

Water level, changes ^ 

36, 39, 46, 47, 48, 53, 58, 66, 74, 78, 86, 90, 

91,96,97

history of trends. . 2,24,32,33,34,45 

recorders... -- --- - 70> 88

Well-numbering system...--- ---------- s

Wells, depth. . 26,28,39,42,46,47,58,70,71,86,89 

White River. - - 2,19,23,25,88

B103

U. S. GOVERNMENT PRINTING OFFICE : 1969 O 332-133