U.S. Geological Survey

Water-Resources Investigations

Report 02-4239

Prepared in cooperation with the Coachella Valley Water District

Detection and Measurement of Land Subsidence Using

Global Positioning System and Interferometric Synthetic

Aperture Radar, Coachella Valley, California, 1998–2000

Detection and Measurement of Land Subsidence 

Using Global Positioning System and 

Interferometric Synthetic Aperture Radar, 

Coachella Valley, California, 1998–2000

By Michelle Sneed1, S.V. Stork1, and Marti E. Ikehara2

Prepared in cooperation with the

COACHELLA VALLEY WATER DISTRICT

Sacramento, California

2002

Water-Resources Investigations Report 02-4239

U.S. GEOLOGICAL SURVEY 7417-14

1

U.S. Geological Survey, Placer Hall, 6000 J Street, Sacramento, CA 95819-6129

2National Geodetic Survey, 1727 30th Street, MS35, Sacramento, CA 95816
For additional information write to:

District Chief

U.S. Geological Survey

Placer Hall, Suite 2012

6000 J Street

Sacramento, California 95819-6129

http://ca.water.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director
Contents iii

CONTENTS

Abstract ................................................................................................................................................................ 1

Introduction .......................................................................................................................................................... 2

Purpose and Scope ...................................................................................................................................... 4

Description of Study Area........................................................................................................................... 4

Acknowledgments....................................................................................................................................... 4

Geohydrologic Setting.......................................................................................................................................... 5

Mechanics of Pumping-Induced Land Subsidence .............................................................................................. 7

Global Positioning System (GPS) Surveys .......................................................................................................... 8

Land-Subsidence Monitoring Network....................................................................................................... 8

Determination of Ellipsoid Heights ............................................................................................................ 8

1998 GPS Survey ............................................................................................................................... 11

2000 GPS Survey ............................................................................................................................... 11

GPS Results................................................................................................................................................. 12

Ground-Water Levels.................................................................................................................................. 15

Interferometric Synthetic Aperture Radar (InSAR) ............................................................................................. 15

InSAR Results............................................................................................................................................. 19

Comparison with GPS Results........................................................................................................... 22

Areas of Land Subsidence.................................................................................................................. 23

Ground-Water Levels.................................................................................................................................. 27

Future Monitoring ................................................................................................................................................ 27

Summary And Conclusions.................................................................................................................................. 27

References Cited .................................................................................................................................................. 28
iv Figures

FIGURES

Figure 1. Map showing location of study area and of six Continuously Operating Reference 

Stations (CORS) in or near Coachella Valley, California. ................................................................ 3

Figure 2. Map showing generalized geology of the Coachella Valley, California ........................................... 6

Figure 3. Map showing network of Global Positioning System (GPS) stations and wells used to 

monitor vertical changes in land surface and ground-water levels, respectively, in the 

lower Coachella Valley, California.................................................................................................... 9

Figure 4. Graphs showing water-surface elevations for selected wells near the three uplifted monuments 

in the lower Coachella Valley, California.......................................................................................... 14

Figure 5. Interferograms showing areas of subsidence and locations of GPS stations in the 

land-subsidence monitoring network in Coachella Valley, California. Area of figure 5 is 

shown on figure 1............................................................................................................................... 16

Figure 6. Amplitude image processed from SAR scenes showing land-surface features and selected 

production wells in Coachella Valley, California.............................................................................. 17

Figure 7. Interferograms showing areas of subsidence and profiles showing vertical changes in 

land surface in Coachella Valley, California, for (A) June 17, 1998, through June 2, 1999, 

and (B) November 24, 1999, through October 4, 2000 ..................................................................... 20

Figure 8. Hydrographs showing water-surface elevations for selected production wells in areas where 

InSAR-generated maps show subsidence in the Coachella Valley, California ................................. 24
Tables v

TABLES

Table 1. Horizontal position, elevation change prior to 1996, ellipsoid heights for 1998 and 2000, and 

ellipsoid-height change for 1998–2000 of geodetic network monuments, and water-level 

changes for 1998–2000 in selected wells in the Coachella Valley, California.................................. 13

Table 2. Vertical change measured using interferometric synthetic aperture radar (InSAR) 

and Global Positioning System (GPS) for selected monuments in the Coachella 

Valley, California............................................................................................................................... 22
vi Conversion Factors, Vertical Datum, and Abbreviations

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

CONVERSION FACTORS

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Vertical displacements determined by InSAR and coordinates determined by global positioning system (GPS) surveying generally are reported in metric units. The industry standard for GPS usage is

that field measurements and subsequent computations, including standard error determinations, are

done in the metric system. The use of dual units in this report is intended to facilitate application of the

data by maintaining the integrity of the original units of measurement for GPS surveying.

Vertical Datum

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of

1929)—a geodetic datum derived from a general adjustment of the first-order level nets of both the

United States and Canada, formerly called Sea Level Datum of 1929.

Ellipsoid heights: In this report, Global Positioning System (GPS) measurements of ellipsoid heights

are based on the North American Datum of 1983 (NAD83). 

Abbreviations

CORS Continuously Operating Reference Station

CSRC California Spatial Reference Center

CVWD Coachella Valley Water District

DEM digital elevation model

GPS Global Positioning System

InSAR interferometric synthetic aperture radar

NAD83 North American Datum of 1983

NGS National Geodetic Survey

SAR synthetic aperture radar

SCIGN Southern California Integrated GPS Network

USGS U.S. Geological Survey

Multiply By To obtain

kilometer (km) 0.6214 mile (mi)

square kilometer (km2) 0.3861 square mile (mi2)

meter (m) 3.281 foot (ft)

millimeter (mm) 0.03937 inch (in.)

millimeter (mm) 0.003281 foot (ft)
Well-Numbering System vii

WELL-NUMBERING SYSTEM

Wells are identified and numbered according to their location in the rectangular system for the subdivision of 

public lands. Identification consists of the township number, north or south; the range number, east or west; and the 

section number. Each section is divided into sixteen 40-acre tracts lettered consecutively (except I and O), 

beginning with "A" in the northeast corner of the section and progressing in a sinusoidal manner to "R" in the 

southeast corner. Within the 40-acre tract, wells are sequentially numbered in the order they are inventoried. The 

final letter refers to the base line and meridian. In California, there are three base lines and meridians; Humboldt 

(H), Mount Diablo (M), and San Bernardino (S). All wells in the study area are referenced to the San Bernardino 

base line and meridian (S). Well numbers consist of 15 characters and follow the format 006S008E02D001S. In 

this report, well numbers are abbreviated and written 6S/8E-2D1. Wells in the same township and range are 

referred to only by their section designation, 2D1 The following diagram shows how the number for well 

6S/8E-2D1 is derived.

R1W R1EMeridian San Bernardino

 T5S

 T6S

T7S

RANGE

TOWNSHIP

 R7E R8E R9E

27

R8E

T6S

Well-numbering diagram

6 5 4 3 2 1

7

18 13

8 9 10 11 12

17 16 15 14

19 24

30 25

31 36

20 21 22 23

29 28 26

32 33 34 35

6S/8E-2D1

2

SECTION 2

D C B A

EFGH

M L K J

N P Q R
Abstract 1

Detection and Measurement of Land Subsidence Using 

Global Positioning System and Interferometric Synthetic 

Aperture Radar, Coachella Valley, California, 1998–2000

By Michelle Sneed, S.V. Stork, and Marti E. Ikehara

ABSTRACT

Land subsidence associated with groundwater-level declines has been recognized as a 

potential problem in Coachella Valley, California. 

Since the early 1920s, ground water has been a 

major source of agricultural, municipal, and 

domestic supply in the valley. Pumping of ground 

water resulted in water-level declines as large as 

15 meters (50 feet) through the late 1940s. In 

1949, the importation of Colorado River water to 

the lower Coachella Valley began, resulting in a 

reduction in ground-water pumping and a recovery 

of water levels during the 1950s through the 

1970s. Since the late 1970s, demand for water in 

the valley has exceeded deliveries of imported 

surface water, resulting in increased pumping and 

associated ground-water-level declines and, 

consequently, an increase in the potential for land 

subsidence caused by aquifer-system compaction.

The location, extent, and magnitude of the 

vertical land-surface changes in Coachella Valley 

between 1998 and 2000 were determined using 

Global Positioning System (GPS) and 

interferometric synthetic aperture radar (InSAR) 

methods. GPS measurements made at 15 geodetic 

monuments in the lower Coachella Valley indicate 

that –34 to +60 millimeters ± 45 millimeters (–

0.11 to +0.20 foot ± 0.15 foot) of vertical change 

in the land surface occurred during the 2-year 

period. Changes at three of the monuments 

exceeded the maximum uncertainty of 

± 45 millimeters (± 0.15 foot) at the 95-percent 

confidence level, which indicates that small 

amounts of uplift occurred at these monuments 

between October 1998 and August 2000. 

Water-level measurements made at wells near the 

three uplifted monuments during this 2-year 

period indicate that the water levels fluctuate 

seasonally; water-level measurements made at 

these wells in September 1998 and September 

2000 indicate that the water levels rose slightly 

near two monuments and declined slightly near the 

third. The relation between the seasonally 

fluctuating, but fairly stable, water levels between 

September 1998 and September 2000 and the 

slight uplift at the monuments may indicate that 

the water levels are fluctuating in the elastic range 

of stress and that the preconsolidation stress of the 

aquifer system was not exceeded during the 2-year 

period.
2 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Results of the InSAR measurements made 

between June 17, 1998, and October 4, 2000, 

indicate that land subsidence, ranging from about 

40 to 80 millimeters (0.13 to 0.26 foot), occurred 

in three areas of the Coachella Valley; near Palm 

Desert, Indian Wells, and La Quinta. 

Measurements made between June 17, 1998, and 

June 2, 1999, indicate that about 15 millimeters 

(0.05 foot) occurred southeast of Lake Cahuilla. 

All the subsiding areas coincide with or are near 

areas where ground-water levels declined between 

1998 and 2000; some water levels in 2000 were at 

the lowest levels in their recorded histories. The 

coincident areas of subsidence and declining water 

levels suggest that aquifer-system compaction may 

be causing subsidence. If the stresses imposed by 

the historically lowest water levels exceeded the 

preconsolidation stress, the aquifer-system 

compaction and associated land subsidence may 

be permanent. Although the localized character of 

the subsidence signals look typical of the type of 

subsidence characteristically caused by localized 

pumping, the subsidence also may be related to 

tectonic activity in the valley.

INTRODUCTION

Ground water has been a major source of 

agricultural, municipal, and domestic water supply in 

Coachella Valley, California (fig. 1), since the early 

1920s. Pumping of ground water resulted in water-level 

declines as large as 15 m (50 ft) between the early 

1920s and late 1940s. In 1949, the importation of 

Colorado River water through the Coachella Branch of 

the All-American Canal to the lower Coachella Valley 

began. As a result of the importation of surface water, 

pumping of ground water decreased in the lower 

Coachella Valley during the 1950s through the 1970s, 

and water levels in some wells in the lower valley 

recovered as much as 15 m (50 ft). Since the late 

1970s, however, the demand for water in the lower 

Coachella Valley has exceeded the deliveries of the 

imported surface water, pumping has increased, and 

water levels have again declined. By 2000, water levels 

in many wells in the lower Coachella Valley had 

declined 15 to 30 m (50 to 100 ft); some wells were at 

their lowest recorded water levels.

Declining water levels can contribute to or 

induce land subsidence in aquifer systems that consist 

of a significant fraction of unconsolidated fine-grained 

sediments (silts and clays). Ikehara and others (1997) 

reported that as much as 150 mm ± 90 mm (0.5 ft ± 0.3 

ft) of subsidence occurred in the southern parts of the 

Coachella Valley between 1930 and 1996. Land 

subsidence can disrupt surface drainage; cause earth 

fissures; and damage wells, buildings, roads, and utility 

infrastructure. A large earth fissure was discovered in 

1948 about 3 km (2 mi) north of Lake Cahuilla; 

because subsidence had not been documented in the 

southern parts of the Coachella Valley prior to the 

report by Ikehara and others (1997), it isn’t known if 

this fissure formed in response to differential land 

subsidence during the earlier period (early 1920s–late 

1940s) of ground-water-level declines. 

Subsidence-related earth fissures and reactivated 

surface faults have been identified in many other 

ground-water basins in the western United States 

(Holzer, 1984).

The Coachella Valley Water District (CVWD) is 

responsible for managing the water supply for a large 

part of the Coachella Valley (fig. 1). As part of their 

water-management strategy, the CVWD plans to 

monitor vertical changes in land surface to determine 

whether land subsidence may be occurring. In 1996, 

the CVWD entered into a cooperative agreement with 

the U.S. Geological Survey (USGS) to establish a 

geodetic network of monuments to monitor vertical 

changes in land surface in the lower Coachella Valley 

using Global Positioning System (GPS) surveys and to 

establish baseline values for comparisons with results 

of future surveys.
Introduction 3

Figure 1. Location of study area and of six Continuously Operating Reference Stations (CORS) in or near Coachella Valley, California.

San

Francisco

Los

Angeles

EXPLANATION

Continuously Operating Reference Station (CORS) and name

Area of

enlargement

Colorado

River

Cottonwood Mts

San Jacinto Mts

Little San Bernardino Mts

San Bernardino Mts

San Gorgonio Pass

PIN1

COTD

Point

Happy

COACHELLA BRANCH OF

THE ALL-AMERICAN CANAL

WHITEWATER

STORMWATER

CHANNEL

Yucaipa

Indio

Durmid

DHLG

TMAP

HNPS

DHLG

Salton Sea

Base prepared by U.S. Geological Survey

from digital elevation data, 1:1,000,000, 1987

North American Datum 1927

0

0

50 Miles

50 Kilometers

Coachella Valley

Water District boundary

Area of figure 5

Lake

Cahuilla

33°00'

33°30'

34°00'

117°00' 116°30' 116°00' 115°30'

C A L I F O R N I A

111

Santa Rosa Mts

Palm

Springs

Indian

Wells Thermal

10

Whitewater

River

Palm

Desert

Cathedral

City Coachella

Mecca Hills

WIDC

La

Quinta

Coachella

Valley

10

111

111

Mecca

86

86

Indio Hills
4 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

This study is the third in a series of landsubsidence studies that began in 1996. Ikehara and 

others (1997) documented the development of the 

geodetic monitoring network and areas of possible land 

subsidence in Coachella Valley by comparing historical 

leveling measurements with GPS surveying 

measurements made in 1996. The vertical changes in 

land surface between 1996 and the earliest 

measurements at monuments in the monitoring 

network do not exceed 150 mm (0.5 ft) (Ikehara and 

others, 1997). The range of uncertainty (±90 mm or 

±0.3 ft) of these calculated vertical changes in land 

surface, however, is large because the historical 

leveling surveys were done at different times and 

sometimes by different agencies using different 

methods. Furthermore, the methods used for the 

leveling surveys had different standards of accuracy 

and the networks were of different geographic extents 

(Ikehara and others, 1997). Sneed and others (2001) 

reported that small amounts of subsidence occurred 

between 1996 and 1998 at some monuments in the 

monitoring network; they used interferometric 

synthetic aperture radar (InSAR) to detect and quantify 

land subsidence throughout much of the Coachella 

Valley. InSAR measurements made between 1996 and 

1998 indicate that as much as 70 mm (0.23 ft) of land 

subsidence occurred in areas near Palm Desert, Indian 

Wells, and Lake Cahuilla.

Purpose and Scope

This study supports part of the watermanagement strategy of CVWD to monitor changes in 

land surface to determine where changes may be 

occurring in Coachella Valley. This report presents the 

results of comparisons between GPS data collected at 

the monuments in the monitoring network during 

surveys in 1998 and 2000 and spatially detailed maps 

of vertical land-surface changes generated using 

InSAR. The InSAR-generated maps extend from near 

Palm Springs to near the Salton Sea (fig. 1). Groundwater-level change data for 1998–2000 were examined 

and compared with the GPS measurements and the 

InSAR-generated maps to determine if the vertical 

changes in land surface may be related to the changes 

in ground-water levels.

Description of Study Area

The Coachella Valley is a 100-km (65 mi) long, 

northwest-trending valley in southeastern California 

(fig. 1). The valley covers about 1,000 km2 (400 mi2)

(California Department of Water Resources, 1964) and 

includes the cities and communities of Palm Springs, 

Palm Desert, Indio, and Coachella. The valley is 

bordered by the San Jacinto and Santa Rosa Mountains 

on the west, the San Bernardino and the Little San 

Bernardino Mountains on the north, the Cottonwood 

Mountains and the Mecca Hills on the east, and the 

Salton Sea on the south (fig. 1). The Coachella Valley is 

drained primarily by the Whitewater River, which 

flows into the Whitewater Stormwater Channel and 

eventually discharges into the Salton Sea (fig. 1). 

Land-surface elevations vary from more than 3,000 m 

(10,000 ft) above sea level at the peaks of the 

surrounding mountains to more than 70 m (230 ft) 

below sea level at the Salton Sea.

The climate of the Coachella Valley floor is arid. 

Average annual rainfall ranges from 80 mm (3 in.) on 

the valley floor to more than 760 mm (30 in.) on the 

crests of the mountains to the west and north of the 

valley (California Department of Water Resources, 

1964). Temperatures range from about 50°C (120°F) 

on the valley floor in the summer to below 0°C (32°F) 

in the surrounding mountains in the winter.

Acknowledgments

Daniel C. Aguirre and Luis G. Luna of the 

Coachella Valley Water District are gratefully 

acknowledged for their help in finding suitable 

locations for, and installation of, bench marks and for 

their help during the 1998 and 2000 GPS surveys. 

Successful completion of the fieldwork would not have 

been possible without the support of the CVWD Chief 

Surveyor and creative problem solver, Tim Lytsell. We 

acknowledge the Southern California Integrated GPS 

network (SCIGN) and its sponsors, the W.M. Keck 

Foundation, the National Aeronautics and Space 

Administration, the National Science Foundation, the 

USGS, and the Southern California Earthquake Center 

for providing data used in this study. Radar data used to 

produce the interferograms shown in this report were 

obtained from the European Space Agency, distributed 

through Eurimage Corporation for purposes of research 

and development.
Geohydrologic Setting 5

GEOHYDROLOGIC SETTING

The Coachella Valley is the northernmost extent 

of the Salton Trough, which is the landward extension 

of a ridge/transform fault system (the East Pacific Rise) 

of the Gulf of California (McKibben, 1993). Near the 

end of the Miocene, a spreading center separating the 

western Farallon plate from the eastern Pacific plate 

was obliquely subducted under the North American 

continent (McKibben, 1993). The modern Gulf of 

California and the Salton Trough formed about 

12 million years ago during a period when subduction 

ceased and when the formation of an inland belt of 

east–west extension, alkali basalt volcanism, and 

crustal-spreading induced subsidence and basin 

sedimentation began (McKibben, 1993). Prior to about 

6 million years ago, the shear zone constituting the 

principal tectonic boundary between the Pacific and 

North American plates appears to have shifted about 

250 km (155 mi) inland into this belt initiating the 

formation of the modern Gulf of California and the 

Salton Trough. As the Salton Trough opened, it was 

filled with sediment from the delta of the Colorado 

River. The river has been building its delta from the 

east into the trough since about 5 million years ago, 

and sedimentation has apparently kept pace with the 

crustal-spreading induced subsidence (McKibben, 

1993). The relation between subsidence that has 

occurred on a geologic time scale and vertical landsubsidence changes measured during this study are 

unknown.

The Coachella Valley is filled with as much as 

3,700 m (12,000 ft) of sediments; the upper 610 m 

(2,000 ft) are water-bearing (California Department of 

Water Resources, 1979). In this report, the waterbearing deposits are referred to as the aquifer system, 

which consists of a complex unconsolidated to partly 

consolidated assemblage of gravel, sand, silt, and clay 

of alluvial and lacustrine origins (fig. 2). Sediments 

tend to be finer grained (contain more silt and clay) in 

the southern part of the valley than in the northern part 

because of the greater depositional distance from 

mountain runoff and lacustrine deposition from ancient 

Lake Cahuilla. In the lower Coachella Valley, the 

aquifer system consists of a semiperched zone that is 

fairly persistent southeast of Indio, an upper aquifer, a 

confining layer, and a lower aquifer (California 

Department of Water Resources, 1964, 1979).

The lower aquifer is the most productive source 

of ground water in the lower Coachella Valley; it 

consists of unconsolidated and partly consolidated silty 

sands and gravels with interbeds of silt and clay. The 

top of the lower aquifer is about 90 to 180 m (300 to 

600 ft) below land surface. Available data indicate that 

it is at least 150 m (500 ft) thick and may be as much as 

600 m (2,000 ft) thick (California Department of Water 

Resources, 1964, 1979). This thick aquifer is overlain 

by a confining layer that is 30 to 60 m (100 to 200 ft) 

thick. The upper aquifer overlies this confining layer 

and is similar in lithology to the lower aquifer, 

although it is only about 45 to 90 m (150 to 300 ft) 

thick. The near-surface semiperched zone consists of 

silts, clays, and fine sand; is as much as 30 m (100 ft) 

thick; and generally is an effective barrier to deep 

percolation (California Department of Water 

Resources, 1964, 1979).

Geologic structures in the Coachella Valley have 

a marked influence on the occurrence and movement of 

ground water. The principal structural features of 

Coachella Valley are faults, and fault-related drag and 

compressional folds. The most notable fault system is 

the northwest-trending San Andreas Fault Zone that 

flanks the eastern side of the valley (fig. 2). Although 

movement within the San Andreas Fault Zone is 

predominantly right lateral (across the fault, movement 

is to the right), vertical displacement has downdropped 

the southwest block (California Department of Water 

Resources, 1964).
6 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Figure 2. Generalized geology of the Coachella Valley, California. Figure modified from Tyley (1971).

0 5

0 5 10 Kilometers

10 Miles

San

Francisco

Los

Angeles

SALTON SEA

Unconsolidated deposits

Fault

Partly consolidated deposits

Consolidated rock

EXPLANATION

SAN

JACINTO

MOUNTAINS

SAN BERNARDINO MOUNTAINS

SANTA

ROSA

MOUNTAINS

LITTLE

SAN

BERNARDINO

MOUNTAINS

C O A C H E L L A

V A L L E Y

116°45'

34°00'

33°45'

33°30'

116°30'

116°15'

116°00'

Palm

Desert

Palm

Springs

La

Quinta

Indio

Mecca

Coachella

Thermal

COACHELLA BRANCH OF THE ALL-AME RICAN CANAL

Aquifer system

Indian

Wells

Lake

Cahuilla

86

111

111

San Andreas Fault Zone

10

INDIO

HILLS
Mechanics of Pumping-Induced Land Subsidence 7

MECHANICS OF PUMPING-INDUCED 

LAND SUBSIDENCE

Land subsidence is known to occur in valleys 

containing aquifer systems that are at least in part made 

up of fine-grained sediments and that have undergone 

extensive ground-water development. The pore 

structure of a sedimentary aquifer system is supported 

by a combination of the granular skeleton of the aquifer 

system and the pore-fluid pressure of the ground water 

that fills the intergranular pore space (Meinzer, 1928). 

For a constant total stress on the aquifer system 

(equivalent to a constant total weight of the overlying 

sediments and pure fluid—the overburden), when 

ground water is withdrawn in quantities that result in 

reduced pore-fluid pressures and water-level declines, 

the reduction of the pore-fluid pressure support 

increases the intergranular stress, or effective stress, on 

the skeleton. A change in effective stress deforms the 

skeleton—an increase in effective stress causes some 

degree of skeletal compression and a decrease in 

effective stress causes some degree of expansion. The 

vertical component of this deformation sometimes 

results in irreversible compaction of the aquifer system 

and land subsidence. An aquifer-system skeleton that 

primarily consists of fine-grained sediments, such as 

silt and clay, is much more compressible than one that 

primarily consists of coarse-grained sediments, such as 

sand and gravel.

Aquifer-system deformation is elastic 

(recoverable) if the effective stress imposed on the 

skeleton is smaller than any previous effective stress 

(Leake and Prudic, 1991). The largest historical 

effective stress imposed on an aquifer system—

sometimes as a result of the lowest ground-water 

level—is the “preconsolidation stress.” If a stress 

imposed on the skeleton is greater than the 

preconsolidation stress, the pore structure (granular 

framework) of the granular matrix of the fine-grained 

sediments is rearranged; this new configuration results 

in a reduction of pore volume and, thus, inelastic 

(largely irreversible) compaction of the aquifer system. 

Furthermore, the compressibility of the fine-grained 

sediments and any resulting compaction under stresses 

greater than the preconsolidation stress are 20 to more 

than 100 times greater than they are under stresses less 

than the preconsolidation stress (Riley, 1998). Inelastic 

compaction of coarse-grained sediment is negligible.

For an aquifer-system skeleton that contains an 

appreciable thickness of fine-grained sediments, a 

significant part of the total compaction may be residual 

compaction [delayed compaction that occurs in thick 

fine-grained interbeds and confining layers while heads 

equilibrate with heads in the adjacent aquifers 

(Terzaghi, 1925)]. Depending on the thickness and the 

vertical hydraulic diffusivity of a confining layer, 

pressure equilibration—and thus compaction—lags 

behind pressure, or head, changes in the adjacent 

aquifers. For a more complete description of aquifersystem compaction, see Poland (1984), and for a 

review and selected case studies of land subsidence 

caused by aquifer-system compaction in the United 

States, see Galloway and others (1999).
8 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

GLOBAL POSITIONING SYSTEM (GPS) 

SURVEYS

GPS is a U.S. Department of Defense satellitebased navigation system designed to provide 

continuous worldwide positioning and navigation 

capability. For this study, GPS surveys were done to 

determine the position of monuments in the geodetic 

monitoring network. The network was established in 

1996 by the USGS to determine changes in landsurface elevations in the network (Ikehara and others, 

1997) and to establish baseline values for comparisons 

with results of future surveys.

Land-Subsidence Monitoring Network

The geodetic monitoring network, henceforth 

referred to as the land-subsidence monitoring network, 

consists of geodetic monuments used as GPS stations 

(fig. 3A). Geodetic monuments are markers that are 

anchored in the ground or to a structure and can be 

used to make repeat surveying measurements of 

horizontal or vertical positions. During the 1996 study 

by Ikehara and others (1997), historical data for 

monuments in the lower Coachella Valley were 

compiled and reviewed to determine the location and 

the quality of the vertical-control data. Sources of the 

data include the National Geodetic Survey [NGS 

(formerly the U.S. Coast and Geodetic Survey)], the 

California Department of Transportation (Caltrans), the 

U.S. Bureau of Reclamation, and the Coachella Valley 

Water District (Ikehara and others, 1997). The geodetic 

monuments were examined at the beginning of the 

1996–98 study (Sneed and others, 2001) and this study 

(1998–2000) to determine whether any had been 

damaged or destroyed and to evaluate their suitability 

for GPS observations.

The original subsidence monitoring network in 

the lower Coachella Valley was established in 1996 and 

consisted of 17 geodetic monuments. The network was 

modified for the 1998 GPS survey by replacing two 

monuments that had been destroyed with two nearby 

monuments [G70 1928 (G70) and Caltrans 13.2 1986 

(C132)]. The network was also modified for the 2000 

GPS survey because monument 54JA was horizontally 

unstable; the replacement monument (JA54) was 

installed about 6 m (20 ft) northwest of monument 

54JA. In addition, four new monuments—MAGF, 

MANI, OSDO, and DEEP—were added in the Palm 

Desert and Indian Wells areas (fig. 3) because the 

InSAR maps processed for 1996–98 showed 

subsidence in these areas (Sneed and others, 2001). 

The spacing between the monuments meets the 

generalized network design criterion established by 

Zilkoski and others (1997), which requires that the 

distance between local network points not exceed 10 

km (6 mi).

Determination of Ellipsoid Heights

GPS measurements were made at the geodetic 

monuments to determine their horizontal positions and 

ellipsoid heights. Ellipsoid height is the vertical 

coordinate relative to a geodetically defined reference 

ellipse; the ellipsoid that closely approximates the 

Earth’s shape in the study area is the North American 

Datum of 1983 (NAD83). To determine changes in 

ellipsoid heights, the heights from successive GPS 

surveys are compared, and the differences in the 

heights are used to determine the location and 

magnitude of any vertical land-surface changes. The 

vertical land-surface changes between the 1998 and 

2000 GPS surveys were calculated by differencing the 

ellipsoid heights of the geodetic monuments 

determined for the two surveys.
Global Positioning System (GPS) Surveys 9

Figure 3. Network of Global Positioning System (GPS) stations and wells used to monitor vertical changes in land surface and ground-water levels, 

respectively, in the lower Coachella Valley, California. A, Locations and status of GPS stations in 2000 and locations of wells. B, Vertical changes at GPS 

stations and water-level changes in wells between 1998 and 2000.

Salton

 Sea

Point Happy

A

EXPLANATION

0 5 10 Miles

0 5 10 Kilometers

New (2000) GPS station and identifier 

Abandoned GPS station and identifier

GPS station and identifier used in the 1998 and 2000 surveys

Geodetic monuments—

Well and identifier

GPS control station for 1998 and 2000 surveys and identifier

GPS control station for 2000 survey and identifier

















111

86

111

10

10

Coachella

Indian

Wells

 Palm

Desert

116°30' 20' 10' 115°50'

 45'

33°50'

33°30'

40'

35'

116°00'

5S/7E-9F1

5S/7E-8Q1

5S/8E-17N1

5S/8E-20C2

6S/7E-23D3

6S/8E-19D1

6S/8E-5P1

6S/8E-5R2

6S/8E-2D1

6S/8E-2F1

6S/8E-12Q1

6S/8E-27C1

6S/8E-32R1 7S/7E-1C1 7S/9E-7H2

7S/9E-17K1

7S/9E-23N1

7S/9E-30M1

7S/8E-20H1 7S/8E-22K1

7S/8E-28G1

7S/8E-34G1

8S/8E-11A4

8S/8E-24A1

8S/8E-24L1

8S/8E-24L1

7S/10E-27A1

San Andreas Fault Zone

DUNE

COCH

R70R

JA54 54JA 5211

CAHU

S753

C132

PAIN

K572

JOHN

C101

C101

C427

C427

P572 SWC

K70

54JA

G70

MAGF

DEEP

DEEP

OSDO MANI

MANI
10 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Point Happy

B 0 5 10 Miles

0 5 10 Kilometers

111

86

111

10

10

Coachella

 Palm 

Desert

 Indian

 Wells

116°30' 20' 10' 115°50'

 45'

33°50'

33°30'

40'

35'

116°00'

5S/7E-9F1

5S/7E-8Q1

5S/8E-17N1

5S/8E-20C2

6S/7E-23D3

6S/8E-19D1

6S/8E-5P1 6S/8E-5R2

6S/8E-2D1

6S/8E-2F1

6S/8E-12Q1

6S/8E-27C1

6S/8E-32R1 7S/7E-1C1 7S/9E-7H2

7S/9E-17K1

7S/9E-23N1

7S/9E-30M1

7S/8E-20H1 7S/8E-22K1

7S/8E-28G1

7S/8E-34G1

8S/8E-11A4

8S/8E-24A1

8S/8E-24L1

7S/10E-27A1

San Andreas Fault Zone

DUNE

COCH

R70R

JA54

5211

5211

CAHU

S753

C132

PAIN

K572

JOHN

C101

C101 7S/8E-34G1

8S/8E-24L1

C427

C427

P572

SWC

SWC

K70

G70

MAGF

DEEP

OSDO

MANI

EXPLANATION

Vertical change not computed 

Possible land uplift [less than 45 millimeters 

 (0.15 foot)]

Decline of 0–2.2 meters (0.0–7.3 feet)

Rise of 0–2.0 meters (0.0–6.6 feet)

 

Possible land subsidence [less than 45 millimeters 

 (0.15 foot)]

Land uplift [46–60 millimeters (0.15–0.2 foot)]

 

Vertical changes at GPS stations between

 October 1998 and August 2000. (Number

 is station identifier)

Water-level changes in wells between late summer/early 

 autumn 1998 and late summer/early autumn 2000.

 (Number is well identifier. The abbreviated well

 number is given in the explanation) 

Note: The late summer/early autumn 2000 measurement 

 for wells 5S/7E-8Q1, 5S/8E-20C2, and 7S/8E-22K1 was

 interpolated or estimated to compute water-level change

Salton

 Sea

Figure 3.—Continued.
Global Positioning System (GPS) Surveys 11

1998 GPS Survey

GPS measurements for the 1998 survey were 

made using five dual-frequency, full-wavelength, Pcode GPS receivers (Ashtech MD-XII) and choke-ring 

antennas (Ashtech Dorne–Margolin). The 

measurements were made to determine the horizontal 

positions and the ellipsoid heights of the 17 geodetic 

monuments in the land-subsidence monitoring network 

during October 5–9, 1998. The GPS survey was done 

in accordance with version 4.3 of “Guidelines for 

Establishing GPS-Derived Ellipsoid Heights” by 

Zilkoski and others (1997). The GPS measurements 

were made at the monuments on at least 2 different 

days, and data were recorded during 45-minute 

observation periods. Five of the 17 geodetic 

monuments were used as network control stations—

COCH, CAHU, PAIN, C101, and G70

(fig. 3). GPS measurements were made at these five 

stations on 3 additional days, and data were recorded 

during 4.5-hour observation periods. The only variation 

from the guidelines established by Zilkoski and others 

(1997) was that single-baseline, rather than multibaseline, processing software was used for 

postprocessing. There are no known conclusive tests 

that permit an objective evaluation of the effect of 

using single-baseline, rather than multi-baseline, 

processing software (Craymer and Beck, 1992); singlebaseline processing software was used for this study 

because it was readily available. The software used for 

the postprocessing (baseline and relative-positioning 

computations) was GPSurvey version 2.30 (Trimble).

Determining the ellipsoid heights of the 17 

geodetic monuments in the 1998 network involved two 

phases of relative positioning. During the first phase, 

the horizontal coordinates and the ellipsoid heights of 

the five Coachella Valley network control monuments 

were determined by processing the GPS measurements 

made at these monuments with measurements made 

simultaneously at three Continuously Operating 

Reference Stations [CORS (DHLG, PIN1, and WIDC)] 

in southern California (fig. 1) and by using precise 

satellite orbital data and accurate coordinates of the 

CORS produced by the California Spatial Reference 

Center (CSRC). The GPS measurements for the CORS 

were recorded continually (at 30-second intervals) and 

archived by members of the SCIGN. The network 

control monuments were selected on the basis of their 

geographic distribution (they are located at the 

perimeter of the monitoring network). For the second 

phase of relative positioning, the positions of the 5 

Coachella Valley network control monuments were 

held fixed at the positions determined during the first 

phase, and the positions and ellipsoid heights of the 

other 12 monuments were determined. The accuracy of 

the ellipsoid heights is ±20 mm (±0.07 ft) at the 95-

percent confidence level. An accuracy at the 95-percent 

confidence level means that 95 percent of the repeat 

measurements are expected to be within ±20 mm 

(±0.07 ft) of their true value.

2000 GPS Survey

GPS measurements for the 2000 survey were 

made using six dual-frequency, full-wavelength, Pcode GPS receivers (5 Trimble 4000SSIs and 1 Trimble 

4000SSE) and compact L1/L2 Trimble antennas (with 

groundplane). The measurements were made to 

determine the horizontal positions and the ellipsoid 

heights of the 21 geodetic monuments in the landsubsidence monitoring network between August 28 and 

September 1, 2000. The GPS survey was done in 

accordance with version 4.3 of “Guidelines for 

Establishing GPS-Derived Ellipsoid Heights” by 

Zilkoski and others (1997). The GPS measurements 

were made at the monuments on at least 2 different 

days, and data were recorded during 35-minute 

observation periods. Six of the 21 geodetic monuments 

were used as network control stations—COCH, DEEP, 

CAHU, PAIN, C101, and G70 (fig. 3). GPS 

measurements were made at these six stations on 3 

additional days, and data were recorded during 5-hour 

observation periods. The only variation from the 

guidelines established by Zilkoski and others (1997) 

was that single baseline, rather than multi-baseline, 

processing software was used for postprocessing. The 

software used for the postprocessing (baseline and 

relative-positioning computations) was GPSurvey 

version 2.30 (Trimble).
12 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Determining the ellipsoid heights of the 21 

geodetic monuments in the network involved two 

phases of relative positioning. During the first phase, 

the horizontal coordinates and the ellipsoid heights of 

the six Coachella Valley network control monuments 

were determined by processing the GPS measurements 

made at these monuments with measurements made 

simultaneously at five CORS (DHLG, PIN1, COTD, 

TMAP and HNPS) in southern California (fig. 1) and 

by using precise satellite orbital data and accurate 

coordinates of the CORS produced by CSRC. The GPS 

measurements of the CORS were recorded continually 

(at 30-second intervals) and archived by members of 

the SCIGN. Because of the addition of monuments in 

the Palm Desert and Indian Wells areas since the 1998 

survey, a new network control monument, DEEP, was 

added to the network (fig. 3) to provide control for the 

new part of the network. During the second phase of 

relative positioning, the positions of the 6 previously 

established network control monuments were held 

fixed at the positions determined during phase 1, and 

the horizontal positions and ellipsoid heights of the 

other 15 monuments were determined. The accuracy of 

the ellipsoid heights is ±40 mm (±0.13 ft) at the 95-

percent confidence level. The uncertainty of the 

ellipsoid heights determined from data collected during 

the 2000 survey is larger, by a factor of two, than that 

determined from the GPS data collected during the 

1998 survey because the GPS data collected during the 

2000 survey was of lower quality. The lower quality of 

the GPS data collected in 2000 may have been due to 

flawed GPS equipment, environmental factors (such as 

solar flares), and (or) other factors.

GPS Results

The ellipsoid heights of the monuments 

determined from the 2000 GPS survey were compared 

with those from the 1998 GPS survey to determine the 

location and magnitude of vertical land-surface 

changes in the lower Coachella Valley (fig. 3B; table 1). 

Because five new monuments were added to the GPS 

network in 2000 (DEEP, MANI, MAGF, OSDO, and 

JA54) and because of the poor quality (large 

discrepancies between the repeat measurements) of the 

GPS measurements made at monument C427 in 2000, 

the ellipsoid heights of only 15 of the 21 monuments 

surveyed in 2000 were suitable for comparison with the 

heights determined from the 1998 survey (fig. 3B; 

table 1). Data collected at monument C427 during the 

1996 survey also were of poor quality and, thus, were 

not compared with data collected at this monument 

during the 1998 survey (Sneed and others, 2001). This 

monument may be unstable or otherwise unsuitable for 

GPS surveying. The ellipsoid heights determined for 

the five new monuments can serve as baseline 

measurements for future surveys.

The calculated vertical changes between 1998 

and 2000 ranged from –34 to +60 mm ± 45 mm (–0.11 

to +0.20 ft ± 0.15 ft) at the 15 monuments that were 

suitable for comparison (table 1). The ellipsoid-height 

differences for three of the monuments (K572, JOHN, 

and SWC) exceeded the uncertainty of ±45 mm (±0.15 

ft), which indicates that small amounts of uplift [46 to 

60 mm ± 45 mm (0.15 to 0.20 ± 0.15 ft)] occurred 

between 1998 and 2000 at these monuments (fig. 3B, 

table 1). The vertical changes at these three monuments 

were small or insignificant between 1996 and 1998 

(Sneed and others, 2001). Prior to 1996, vertical 

change at monument K572 was –120 mm ± 90 mm 

(–0.4 ft ± 0.3 ft) and insignificant at monuments JOHN 

and SWC (Ikehara and others, 1997). (See table 1 for 

measurement intervals.) The ellipsoid-height 

differences between 1998 and 2000 for the remaining 

12 monuments suitable for comparison (DUNE, 

COCH, R70R, 5211, CAHU, S753, PAIN, C132, 

C101, K70, P572, and G70) did not exceed the 

uncertainty of ±45 mm (±0.15 ft). The vertical changes 

at these monuments ranged from –34 to +36 mm ±45 

(–0.11 to +0.12 ft ± 0.15 ft) (table 1). The ellipsoidheight differences calculated for 10 of these 12 

monuments during the 1996–98 study by Sneed and 

others (2001) indicate vertical changes ranging from 

–13 to –67 mm ± 45 mm (–0.04 to –0.22 ft ± 0.15 ft). 

The ellipsoid-height differences for the remaining two 

monuments (G70 and C132) for 1996–98 were not 

calculated because the monuments had not been 

surveyed in 1996. Prior to 1996, vertical changes 

ranged from –150 to +30 mm ± 90 mm (–0.50 to 

+0.1 ft ± 0.3 ft) at 7 of the 12 monuments; the 5 other 

monuments had no vertical-change data prior to 1996 

(Ikehara and others, 1997) (table 1).
Global Positioning System (GPS) Surveys 13

Table 1. Horizontal position, elevation change prior to 1996, ellipsoid heights for 1998 and 2000, and ellipsoid-height change for 1998–2000 of geodetic network monuments, and water-level 

changes for 1998–2000 in selected wells in the Coachella Valley, California

[Latitude, longitude, and ellipsoid height are referenced to the North American Datum of 1983. Elevation-change data from Ikehara and others, 1997. Negative values for elevation change and ellipsoidheight change indicate subsidence. Uncertainty for elevation change is ±90 millimeters (±0.3 foot). Uncertainty for ellipsoid-height change is ±45 millimeters (±0.15 foot). Negative values for water-level 

change indicate decline. ft, foot m, meter; mm, millimeter; —, no data]

1 Value is within measurement error indicating relative vertical stability. 2Measurement was interpolated or estimated for the water-level change computation. 3Network control monument for 1998 and 2000 surveys.4 Network control monument for 2000 survey. 5Suitability for GPS survey questionable because of poor quality data from each survey. 6Comparison includes available water-level measurements collected late summer/early autumn 1998 and late summer/early autumn 2000.

Global

Positioning

System 

(GPS)

station

Monument

name 

Latitude Longitude

Elevation change

Measurement

interval

Status

of

monument

for 2000

GPS

survey

Ellipsoid height Ellipsoid-height change

Well 

near

GPS 

station

Water-level change, 

1998 –20006

(mm) (ft)

October

1998

(m) 

August

2000

(m)

October 1998 to 

August 2000

(mm (ft)) 

(m) (ft)

DUNE DUNEPORT Azimuth 33°44′46′′ 116°16′10′′ 1 −90 1 −0.3 1991–96 Suitable −17.388 –17.382 1 6 (0.02) 5S/7E-8Q1 2

5S/7E-9F1

−1.8−1.8

−6.0−5.9

COCH 3 CO

ACH 1931 33°44′25′′ 116°09′30′′ —

—

— Suitable 33.417 33.418 11 (.00) 5S/8E-17N1

5S/8E-20C2 2

–.8

 +2.0

–2.5

+6.6

MAGF Magnesium Falls Drive 33°44′11′′ 116°23′27′′ —

—

— Ne

w

— 27.748

—

—

—

—

MANI Manitou Drive 33°43′11′′ 116°19′03′′ —

—

— Ne

w

— 2.972

—

—

—

—

OSDO Osage Trail and El 

Dorado Drive

33°43′06′′ 116°20′19′′ —

—

— Ne

w

— 13.496

—

—

—

—

R70R R70 Reset 1958 33°40′49′′ 116°10′26′′ 1 −60 1 −.2 1956–96 Suitable −54.453 –54.445 1 8 (.03) 6S/8E-5P1

6S/8E-5R2

–.3–.1

–.8–.2

DEEP 4 Deep Canyon 33°40′21′′ 116°22′34′′ —

—

— Ne

w

— 190.404

—

—

—

—

5211 USBR 52.11 33°40′17′′ 116°06′43′′ 1 −90 1 −.3 1946–96 Suitable −32.721 –32.754 1 –34 (–.11) 6S/8E-2D1

6S/8E-2F16S/8E-12Q1

+.1

+1.3

+.6

+.3

+4.3+1.8

54JA Avenue 54 and Jackson 33°39′24′′ 116°13′00′′ —

—

— Replaced −46.415

—

— 6S/7E-23D3

6S/8E-19D1

−2.2

−.2

−7.3

−.5

JA54 Jackson and Avenue 54 33°39′24′′ 116°13′00′′ —

—

— Ne

w

— –46.904

—

—

—

—

CAHU 3 Lake Cahuilla 33°38′19′′ 116°16′25′′ —

—

— Suitable −30.807 –30.805 1 2 (.01)

—

—

—

S753 S753 1945 33°38′13′′ 116°09′49′′ 1 −90 1 −.3 1945–96 Suitable −68.253 –68.248 15 (.02) 6S/8E-19D1

6S/8E-27C1

−.2

–1.4

–.5

–4.7

PAIN 3 Painted Canyon 33°36′43′′ 116°00′30′′ —

—

— Suitable 93.339 93.355 1 16 (.05)

—

—

—

C132 Caltrans 13.2 1986 33°34′59′′ 116°10′54′′ —

—

— Suitable −74.029 –74.025 1 4 (.01) 6S/8E-32R1

7S/7E-1C1

−1.6−1.3

−5.2

–4.4

K572 K572 1939 33°34′09′′ 116°05′42′′ −120 −.4 1939–96 Suitable −91.543 –91.483 60 (.20) 7S/9E-7H2 +.2 +.7JOHN Johnson 33°33′03′′ 116°03′18′′ 1 −90 1 −.3 1991–96 Suitable −94.178 –94.131 47 (.15) 7S/9E-17K1 +1.1 +3.6C101 3 Caltrans 10.1 1986 33°32′44′′ 116°09′16′′ 130 1.1 1986–96 Suitable −50.425 –50.410 1 15 (.05) 7S/8E-20H1

7S/8E-22K1 27S/8E-28G1

−1.6

−.6

−1.3

−5.1−1.9−4.2

K70 K70 1928 33°32′09′′ 116°00′21′′ −150 −.5 1928–96 Suitable −91.525 –91.495 1 30 (.10) 7S/9E-23N1 +1.2 +3.9P572 P572 1939 33°31′32′′ 116°06′46′′ −150 −.5 1939–96 Suitable −91.286 –91.251 1 36 (.12) 7S/8E-34G1 +.6 +1.9SWC Stormwater channel 33°31′27′′ 116°04′42′′ 1 −30 1 −.1 1967–96 Suitable −100.313 –100.267 46 (.15) 7S/9E-30M1 –1.2 –3.8G70 3 G70 1928 33°30′27′′ 115°54′51′′ —

—

— Suitable −93.093 –93.080 1 13 (.04) 7S/10E-27A1 –.1 –.2

C427 Caltrans 4.27 1987 33°28′25′′ 116°06′27′′ 1 0 1 .0 1987–96 (

5) −73.356

—

— 8S/8E-11A4

8S/8E-24A18S/8E-24L1

+.2−.7

−2.1

+.7

−2.2−6.8
14 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Figure 4. Water-surface elevations for selected wells near the three uplifted monuments in the lower Coachella Valley, California.

-355

-335

-315

-90

-80

-70

-100

-60

-50

-275

-295

-255

-235

-215

-195

-175

-155

-250

-240

-230

-220

-210

-75

-70

-200

-190

-180

-170

-160

-150

-275

1955 1926

19311936194119461951195619611966197119761981198619911996

2001

1960

1965

1970

197519801985199019952000

-265

-255

-245

-235

-225

-215

-205

-195

-185

-175

-50

-55

-60

-65

-65

-60

-55

-70

-75

-80

7S/9E-7H2, screened in the upper aquifer

 (near monument K572)

7S/9E-17K1, screened in the upper and

 lower aquifers

 (near monument JOHN)

7S/9E-30M1, screened in the perched and

 upper aquifers

 (near monument SWC)

WATER-SURFACE ELEVATION, IN FEET ABOVE SEA LEVELWATER-SURFACE ELEVATION, IN METERS ABOVE SEA LEVEL

YEAR

10/5/98–8/28/00

10/5/98–8/28/00

10/5/98–8/28/00
Interferometric Synthetic Aperture Radar (InSAR) 15

Ground-Water Levels

In general, water levels declined in the western 

part of the geodetic network during 1998–2000 and 

recovered in the eastern part of the network (fig. 3B). 

Water levels in wells 7S/9E-7H2 and 17K1, near two of 

the three uplifted monuments, rose slightly between 

late September 1998 and late September 2000, but the 

water level in well 7S/9E-30M1, near the third uplifted 

monument, declined slightly (fig. 4). The water level in 

well 7S/9E-7H2 rose 0.2 m (0.7 ft) during the 2-year 

period; this well is located near monument K572 at 

which 60 mm ± 45 mm (0.20 ft ± 0.15 ft) of uplift was 

measured. The water level in well 7S/9E-17K1 rose 1.1 

m (3.6 ft) during the 2-year period; this well is near 

monument JOHN, which had a slight uplift [47 mm 

± 45 mm (0.15 ft ± 0.15 ft)]. The September 2000 

water level in well 7S/9E-30M1 declined 1.2 m (3.8 ft) 

from the September 1998 measurement; however, the 

other measurements collected after September 1998 

and before September 2000 were higher (fig. 4). This 

well is near monument SWC, which also had a slight 

uplift [46 mm ± 45 mm (0.15 ft ± 0.15 ft)]. The slight 

uplift at these monuments and the small changes in 

water levels in the nearby wells indicate that the water 

levels fluctuated in the elastic range of stress (that is, 

they did not exceed the preconsolidation stress) and 

therefore the vertical changes at these monuments were 

elastic (recoverable). The water levels in the three wells 

near the uplifted monuments were more than 10 m (30 

ft) higher than the historical lows of the mid-1990s

(fig. 4) which further suggests that water levels were 

fluctuating in the elastic range of stress during the 2-

year period. The inverse relation of the water-level 

decline in well 7S/9E-30M1 during this period and the 

slight uplift at monument SWC suggests that residual 

deformation may have occurred. However, because 

water levels in wells 7S/9E-7H2, 17K1, and 30M1 

fluctuated significantly during short periods, the water 

levels measured in late September 1998 and in late 

September 2000 most likely do not represent the 

precise water-level changes that occurred between the 

weeks of October 5, 1998, and August 28, 2000 (fig. 4).

INTERFEROMETRIC SYNTHETIC 

APERTURE RADAR (INSAR)

InSAR is a powerful technique that uses the 

differences in the reflected phases between two 

reflected satellite radar images acquired at different 

times to measure ground-surface deformation that 

occurred between the two acquisitions. This technique 

has been used to investigate deformation resulting from 

earthquakes (Massonnet and others, 1993), volcanoes 

(Massonnet and others, 1995), and land subsidence 

related to the extraction of subsurface fluids 

(Massonnet and others, 1997; Fielding and others, 

1998; Galloway and others, 1998; Amelung and others, 

1999). Interferograms, maps of relative ground-surface 

displacement constructed from InSAR data, have 

demonstrated great potential for high-density spatial 

mapping of ground-surface displacement (Galloway 

and others, 2000). Two interferograms were developed 

for a part of the Coachella Valley using synthetic 

aperture radar (SAR) scenes acquired from the 

European Earth Remote-Sensing satellites (ERS-1 and 

-2). Four SAR scenes (two pairs) that had nearly 

identical acquisition geometries were combined to 

form two “change” interferograms. One interferogram 

has a temporal baseline of 350 days (June 17, 1998, to 

June 2, 1999) and the other interferogram has a 

temporal baseline of 315 days (November 24, 1999, to 

October 4, 2000) (fig. 5).

The amplitude component of the change 

interferogram (fig. 6) shows land-surface features such 

as mountains, roads, drainage ways, and engineered 

structures. The phase component shows the coherent 

displacements imaged by radar and it shows a residual 

topographic component. The topography was removed 

from the image using a 30-m resolution digital 

elevation model (DEM) (fig. 5). However, it was not 

possible to completely remove the topographic 

component from the image for the mountainous terrain 

northeast and southwest of Coachella Valley because 

the 30-m resolution DEM was inadequate for 

accurately describing this terrain characterized by large 

topographic gradients.
16 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Figure 5. Areas of subsidence and locations of GPS stations in the land-subsidence monitoring network in Coachella Valley, California. A, June 17, 1998, 

to June 2, 1999. B, November 24, 1999, to October 4, 2000. Boxes indicate areas of subsidence. Displacement is in millimeters (mm). Area of figure 5 is 

shown on figure 1.

A

B

111

111

111

111

111

10

111

10

10

10

1

2

3

4

— Palm Desert Area

— Indian Wells Area

— La Quinta Area

— Lake Cahuilla Area

— GPS station (Number is station

 identifier)

S a n

N

A n d r e a s F a u l t Z o n e

S a n A n d r e a s F a u l t Z o n e

4

3

3

1

2

1

2

86

86

10 Miles

5 

5 

10 Kilometers

0

0

 Lake Cahuilla

 Palm Desert

 Indian Wells

Cathedral City 

Palm Springs 

 La Quinta

 Coachella

-28 mm 0 +28 mm

relative 

subsidence uplift

DUNE

COCH

R70R

JA54 5211

CAHU

S753

C132

PAIN

K572 JOHN

C101

P572

P572

SWC

K70

MAGF

DEEP

OSDO MANI

DUNE

COCH

R70R

JA54 5211

CAHU

S753

C132

PAIN

K572 JOHN

C101

P572 SWC

K70

MAGF

DEEP

OSDO MANI

EXPLANATION
Interferometric Synthetic Aperture Radar (InSAR) 17

Figure 6. Amplitude image processed from SAR scenes showing land-surface features and selected production wells in Coachella Valley, California. 

Boxes indicate areas of subsidence (see figures 5 and 7). Hydrographs for labeled wells are shown in figure 8.

 Area 1 in

 figures 5A

 and 7A

 Area 2 in

 figures 5

 and 7

 Area 1 in

 figures 5B

 and 7B

Palm Desert Area

N

PORTOLA AVENUE

33°40'

45'

33°50'

116°30'

25'

116°20'

5S/6E-17M2

5S/6E-9M1

5S/6E-8N3

5S/6E-7M1

1

San Jacinto Mountains

Santa Rosa Mountains

10

COUNTRY CLUB DRIVE

5S/6E-16M1

 FRED WARING DRIVE

5S/6E-5Q1 5S/6E-6M2 111

Whitewater River

Palm

Springs

Well

Well and identifier 5S/6E-7M1
18 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Figure 6.—Continued.

2

3

4

Coachella

Indio

Lake Cahuilla Area

La Quinta Area

Lake

Cahuilla

Indian Wells Area

111

86

10

5 Miles

0 5 Kilometers

0

15'

116°10'

5S/6E-24F1 5S/6E-22B1

5S/6E-23K2

5S/6E-23N1

5S/6E-27C2 5S/6E-25A1

5S/7E-31A1

6S/6E-12G1

5S/7E-31Q2

6S/7E-6B1

6S/7E-16D1 6S/7E-16A2

6S/7E-16R2

6S/7E-21D1

golf

course

MANITOU DRIVE

EL DORADO

DRIVE

Area 3 in

figures 5

and 7

Area 4 in

figures 5A

and 7A
Interferometric Synthetic Aperture Radar (InSAR) 19

For landscapes with radar reflectors (such as 

buildings or other engineered structures, or undisturbed 

rocks and ground surfaces) that are fairly stable over 

time, it is possible to make high-precision 

measurements (±5 to ±10 mm or ±0.02 to ±0.03 ft) of 

the changes in the positions, or the displacements, of 

the reflectors (Galloway and others, 1998; Galloway 

and others, 2000). Displacements are computed from 

the phase change at each point in the interferogram. 

The phase change is determined by “interfering” 

(differencing) two radar images made of the same area 

at different times (Galloway and others, 2000).

Because the phase of the radar echo is 

proportional to the distance traveled by the pulse, any 

motion of the ground surface between two SAR scenes 

causes a phase difference, or shift, in the interferogram. 

Propagation delays of the radar signal, such as the 

delays caused by variable water vapor content in the 

atmosphere, also can cause a phase shift (Zebker and 

others, 1997). The phase shifts (0–2 pi) are scaled over 

one-half the wavelength of the radar signal—from 0 to 

28 mm (0 to 0.09 ft) for the C-band radar used by ERS1 and -2. Because the phase shifts are ambiguous, that 

is, shifts of 2, 4, and 6 pi or equal fractions thereof, are 

indistinguishable, the first product of the 

interferometric process is termed the “wrapped” 

interferogram—meaning the phase shifts from pixel to 

pixel are ambiguous and mapped modulo 2 pi. Figure 5

shows wrapped interferograms for the Coachella 

Valley. Phase shifts are “unwrapped” by a procedure 

that results in a continuous map of phase shifts and, 

thus, of displacement over the extent of the image for 

areas where it was possible to resolve potential 

ambiguities (Rosen and others, 2000). Figure 7 shows 

the unwrapped interferograms for each of the areas 

previously demarcated in the Coachella Valley where it 

was possible to unwrap the interferogram. The areas 

that are decorrelated (the areas where the data are not 

smooth and continuous) are not shown on the 

unwrapped interferogram (the white areas in figure 7).

Except for the atmospheric variations associated 

with altitude in the mountainous regions fringing the 

Coachella Valley, all coherent phase shifts shown on 

the interferograms (fig. 5) were attributed to range 

displacements of the ground surface, which were 

assumed vertical. An area of coherent displacements is 

shown by color fringes that define a shape. More color 

fringes indicate more change; in figures 5 and 7, one 

color cycle—for example, blue to blue—indicates 28 

mm (0.09 ft) of range change. The direction of 

change—subsidence or uplift—is indicated by the 

color progression of the fringes toward the center of the 

shape. For interferograms in this report, the colorfringe progression of blue-green-yellow-orange-redpurple indicates subsidence; the opposite progression 

indicates uplift.

InSAR techniques cannot be used for landscapes 

without substantial stable radar reflectors, such as 

agricultural land where farming practices disturb the 

ground surface. The colors on the interferograms of 

such landscapes do not show a defined shape, but 

instead, show an incoherent speckled pattern similar to 

that shown, for example, for the area along much of 

Highway 86 in figure 5, where the land use is 

predominantly agricultural.

InSAR Results

The InSAR-generated maps of the Coachella 

Valley show at least four areas with coherent signals; 

these signals indicate that significant subsidence 

occurred between June 17, 1998, and June 2, 1999 (fig. 

5A). The maps also show at least three areas with 

coherent signals indicating subsidence between 

November 24, 1999, and October 4, 2000 (fig. 5B). 

These signals are located in the vicinities of Palm 

Desert (area 1), Indian Wells (area 2), La Quinta (area 

3), and Lake Cahuilla (area 4). The interferograms 

show that other areas in the Coachella Valley also may 

have deformed (fig. 5), but the extent of these areas and 

the amount of deformation generally are small. 
20 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Figure 7. Areas of subsidence and profiles showing vertical changes in land surface in Coachella Valley, California, for (A) June 17, 1998, through June 

2, 1999, and (B) November 24, 1999, through October 4, 2000. See figure 5 for locations of areas of subsidence. White areas on interferograms and line 

breaks on land-surface profiles indicate no data. White circles and numbers are well locations and identifiers, respectively.

0

-10

-20

-30

-40

10

-50

10

20

-30

0

-10

-20

0 2 3.7

10

-10

-20

20

30

-30

-40

0

Relative vertical land-surface  change, in millimeters

Relative vertical land-surface  change, in millimeters

Relative vertical land-surface  change, in millimeters

02468

024 6 8 9.2

8.9

Distance from A, in kilometers

Distance from C, in kilometers

Distance from B, in kilometers

A — June 17, 1998, through June 2, 1999

AREA 1. Palm Desert Area

AREA 2. Indian Wells Area

 AREA 3.

La Quinta Area

 AREA 4.

Lake Cahuilla Area

A A'

C C'

D D'

B B' Lake

Cahuilla

5S/7E-31A1

6S/6E-12G1

5S/7E-31Q2

6S/7E-6B1

5S/6E-24F1

5S/6E-22B1

5S/6E-23K2

5S/6E-23N1

5S/6E-27C2

5S/6E-25A1

5S/6E-17M2

5S/6E-9M1

5S/6E-8N3 5S/6E-7M1

5S/6E-16M1

-28 mm 0 +28 mm

relative 

subsidence uplift

0 2 3.7

 Relative vertical land-surface change,  in millimeters

Distance from D, in kilometers

0

-10

-20

-30
Interferometric Synthetic Aperture Radar (InSAR) 21

Figure 7.—Continued.

0

-10

10

-20

-30

-40

-50

0

-10

10

-20

20

-30

Relative vertical land-surface  change, in millimeters

Relative vertical land-surface  change, in millimeters

Relative vertical land-surface  change, in millimeters

02468

0 2 4 6 8 9.2

8.9

Distance from A, in kilometers

Distance from C, in kilometers

Distance from B, in kilometers

AREA 1. Palm Desert area

AREA 2. Indian Wells area

 AREA 3.

La Quinta area

A A'

C C'

B B'

0

-10

10

-20

20

-30

30

-40

0 2 3.7

5S/7E-31A1

6S/6E-12G1

5S/7E-31Q2

6S/7E-6B1

5S/6E-24F1

5S/6E-22B1

5S/6E-23K2

5S/6E-23N1

5S/6E-27C2

5S/6E-25A1

5S/6E-17M2

5S/6E-9M1

5S/6E-5Q1

5S/6E-8N3

5S/6E-7M1

5S/6E-6M2

5S/6E-16M1

B — November 24, 1999, through October 4, 2000

-28 mm 0 +28 mm

relative 

subsidence uplift
22 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Comparison with GPS Results

The vertical changes measured using InSAR are 

comparable to the vertical changes measured using 

GPS for at least five of the monuments surveyed during 

the 1998 and 2000 GPS surveys (table 2). Four of the 

monuments (DUNE, COCH, 5211, and R70R) 

surveyed during the 1998 and 2000 GPS surveys are in 

the areas that have coherent signals on the June 17, 

1998, to June 2, 1999, interferogram. Five of the 

monuments (DUNE, COCH, 5211, R70R, and S753) 

surveyed during the 1998 and 2000 GPS surveys are in 

the areas that have coherent signals on the November 

24, 1999, to October 4, 2000, interferogram. The 

vertical changes at the remaining monuments (CAHU, 

PAIN, C132, K572, JOHN, C101, K70, P572, SWC, 

G70, and C427) are not comparable because they either 

are in decorrelated areas of the interferograms or are 

not within the areal extent of the interferograms. The 

vertical movement shown on the interferograms agrees 

reasonably well with that determined from the GPS 

surveys for DUNE, COCH, 5211, and R70R 

monuments, especially considering that the 

measurement intervals are different for InSAR and 

GPS and that about a 6-month period (June 2, 1999, to 

November 24, 1999) is not represented in the 

interferograms. The June 17, 1998, to June 2, 1999, 

interferogram (fig. 5A) shows that less than 5 to 10 mm 

(0.02 to 0.03 ft) of relative uplift occurred at 

monuments DUNE and COCH and that less than 5 to 

10 mm (0.02 to 0.03 ft) of subsidence occurred at 

monuments 5211 and R70R. The November 24, 1999, 

to October 4, 2000, interferogram (fig. 5B) shows that a 

small amount of subsidence (5 mm or 0.02 ft) occurred 

at monument DUNE and that monuments COCH, 

5211, R70R, and S753 were fairly stable. The GPS 

results indicate that uplifts of 8 mm (0.03 ft) or less 

occurred at monuments DUNE, COCH, R70R, and 

S753 between October 1998 and August 2000 and that 

subsidence of about 34 mm (0.11 ft) occurred at 

monument 5211 (table 1). It should be noted that the 

GPS processing results for monument 5211 indicated 

significantly larger errors than the results for any other 

monument in the network. The discrepancy between 

the InSAR and GPS measurements for this location 

probably is the result of the poor GPS data for 

monument 5211.

Table 2. Vertical change measured using interferometric synthetic aperture radar (InSAR) and Global Positioning System (GPS) for selected monuments in 

the Coachella Valley, California

[mm, millimeter; ft, foot. —, no data]

Measurement 

type

Measurement 

interval

Vertical change

DUNE COCH 5211 R70R S753

InSAR June 17, 1998–

June 2, 1999

5 to 10 mm

(0.02 to 0.03 ft)

5 to 10 mm

(0.02 to 0.03 ft)

−5 to −10 mm

(−0.02 to −0.03 ft)

−5 to −10 mm

(−0.02 to −0.03 ft)

—

InSAR November 24, 1999–

October 4, 2000

−5 mm

(−0.02 ft)

0 0 0 0

GPS October 5, 1998–

August 28, 2000

6 mm

(0.02 ft)

1 mm 

(0.00 ft)

−34 mm

(−0.11 ft)

8 mm

(0.03 ft)

5 mm

(0.02 ft)
Interferometric Synthetic Aperture Radar (InSAR) 23

Areas of Land Subsidence

A subsidence signal was detected in the 

northwestern part of Palm Desert (area 1 in figures 5

and 7); this signal was previously detected by Sneed 

and others (2001) using InSAR methods. The part of 

the signal that has the largest magnitude is nearly 

circular (slightly elongated north to south); it is about 

1 km (0.6 mi) in diameter and covers an area of about 

1 km2 (0.4 mi2) (area 1 in figures 5 and 7). This part of 

the signal is approximately bounded by Country Club 

Drive on the north, Fred Waring Drive on the south, 

Highway 111 and the San Jacinto and Santa Rosa 

Mountains on the west, and Portola Avenue on the east 

(figs. 6). The part of the signal that is smaller in 

magnitude extends to the north and east (area 1 in 

figure 5) and has a pronounced northwest–southeast 

elongation. The interferogram for June 17, 1998, to 

June 2, 1999, shows that the signal extends northwest 

from Palm Desert to near Palm Springs and southeast 

from Palm Desert to Indian Wells (fig. 5A). The 

interferogram for November 24, 1999, to October 4, 

2000, shows that the signal extends northwest from 

Palm Desert toward Cathedral City and southeast from 

Palm Desert almost to Indian Wells (fig. 5B). The San 

Jacinto and Santa Rosa Mountains, which are 

outcropping consolidated rock, may act as a barrier to 

subsidence farther to the southwest; and the Indio Hills, 

which are outcropping partly consolidated deposits, 

(fig. 2) may act as a barrier to subsidence farther to the 

northeast. A lack of barriers to the northwest and 

southeast may explain the pronounced elongation of 

the subsidence signal in these directions.

A maximum of about 30 mm (0.1 ft) of 

subsidence occurred in the center of the northwestern 

part of the Palm Desert between June 17, 1998, and 

June 2, 1999 (area 1 in figure 7A). About 30 mm (0.1 

ft) of subsidence also occurred in this area between 

November 24, 1999, and October 4, 2000 (area 1 in 

fig. (7B). Consequently, if no recovery occurred 

between June 2, 1999, and November 24, 1999, a 

minimum of 60 mm (0.2 ft) of subsidence occurred in 

the center of the subsidence bowl between June 17, 

1998, and October 4, 2000.

Two distinct subsidence signals were detected in 

the Indian Wells area near a golf course (area 2 in 

figures 5, 6, and 7), and a small subsidence signal was 

detected about 1 km (0.6 mi) southeast of the distinct 

subsidence bowl to the east of the golf course. The 

existence and magnitude of the small subsidence 

signal, however, are suspect because of the proximity 

of this area to steep topographic terrain; thus, this 

subsidence signal is not discussed further in this report. 

The western subsidence bowl is in the Indian Wells 

area and is approximately bounded by Highway 111 on 

the north, the San Jacinto and Santa Rosa Mountains 

on the south, El Dorado Drive on the west, and a golf 

course on the east (fig. 6). The eastern subsidence bowl 

is approximately bounded by Highway 111 on the 

north, the San Jacinto and Santa Rosa Mountains on 

the south, a golf course on the west, and Manitou Drive 

on the east (fig. 6). The bowl to the west, which is 

elongated northwest–southeast, is about 1.6 km (1 mi) 

long and about 0.8 km (0.5 mi) wide (northeast–

southwest) and has an area of about 1.3 km2 (0.5 mi2). 

The bowl to the east, which is elongated west–east, is 

about 1.5 km (0.9 mi) long and about 0.8 km (0.5 mi) 

wide (north–south) and has an area of 1.2 km2 (about 

0.5 mi2) (area 2 in figures 5 and 7). The maximum 

subsidence for the two bowls was about 20 mm 

(0.07 ft) for both the June 17, 1998, through June 2, 

1999, and the November 24, 1999, through October 4, 

2000, periods (area 2 in figure 7). If no recovery 

occurred between June 2, 1999, and November 24, 

1999, then a minimum of about 40 mm (0.13 ft) of 

subsidence occurred in the centers of each of the 

subsidence bowls between June 17, 1998, and October 

4, 2000.

A third area of subsidence was detected in the 

area extending from near La Quinta on the northwest to 

just southeast of Lake Cahuilla (areas 3 and 4 in figure 

5A). This area is about 10 km (6 mi) in length and 

ranges from about 1.5 to 2 km (0.9 to 1.2 mi) wide 

(areas 3 and 4 in figure 5A). The northwestern-most 

extent of this subsidence signal is fairly coherent 

(area 3 in figures 5 and 7), but the southeastern part of 

the signal southeast of Lake Cahuilla was detected only 

in the June 17, 1998, to June 2, 1999, interferogram 

(area 4 in figures 5A and 7A), which shows that at least 

15 mm (0.05 ft) of subsidence occurred there. A 

maximum of about 40 mm (0.16 ft) of subsidence 

occurred in the northwestern part of the signal between 

June 17, 1998, to June 2, 1999, and between November 

24, 1999, and October 4, 2000 (area 3 in figure 7). If no 

recovery occurred between June 2, 1999, and 

November 24, 1999, then a cumulative minimum of 80 

mm (0.26 ft) of subsidence occurred in the 

northwestern part of the signal between June 17, 1998, 

and October 4, 2000.
24 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Figure 8. Water-surface elevations for selected production wells in areas where InSAR-generated maps show subsidence in the Coachella Valley, 

California. A, Palm Desert (area 1). B, Indian Wells (area 2). C, La Quinta/Lake Cahuilla (areas 3 and 4). (See figures 6 and 7 for well locations.)

0 0

20

40

15

10

 5

 5

20 60

80

20

40

15

30

25

20

10

10

60

80

100

-20

0 0

20

40

15

 -5

 5

60

19801982198419861988199019921994199619982000

-20

0

0

0 0

0

0

20

40

15

15

15

10

10

 5

 5

 -5

 -5

10

 5

 -5

60

-20

20

40

60

-20

20

40

60

0 0

20

40

15

20

10

60

19661968

1970

1972

1974

197619781980

1982

1984

1986

19881990

1992

1994

19961998

2000

5S/6E-16M1, screened in the upper aquifer

 

5S/6E-7M1, screened interval unknown

5S/6E-5Q1, screened in the upper and

 lower aquifers

5S/6E-8N3, screened in the upper and

 lower aquifers

5S/6E-6M2, screened in the upper and

 lower aquifers

5S/6E-17M2, screened in the upper and

 lower aquifers

5S/6E-9M1, screened in the upper and

 lower aquifers

WATER-SURFACE ELEVATION, IN METERS ABOVE SEA LEVEL

WATER-SURFACE ELEVATION, IN METERS ABOVE SEA LEVEL

WATER-SURFACE ELEVATION, IN FEET ABOVE SEA LEVEL

WATER-SURFACE ELEVATION, IN FEET ABOVE SEA LEVEL

YEAR

YEAR

A

6/17/98–6/2/99

11/24/99–10/4/00

6/17/98–6/2/99

11/24/99–10/4/00
Interferometric Synthetic Aperture Radar (InSAR) 25

Figure 8.—Continued.

-20

0 0

20

40

15

60

19661968

1970

1972

1974

1976

1978

1980

1982

1984

19861988

1990

1992

1994

1996

1998

2000

-40

-20

20

-40

-20

0

0 0

0

-15

-5

-10

20

-40

-20

0 0

20

19801982198419861988199019921994199619982000

-55

-35

-15

5

25

-10

0

10

10

10

20

-5

0

 5

-10

-15

30

15 50

 5

 5

 -5

70

5

-15

-5

-10

5

-15

-5

-10

5

5S/6E-23K2, screened in the upper aquifer

5S/6E-23N1, screened in the upper aquifer 5S/6E-27C2, screened in the upper aquifer

5S/6E-24F1, screened in the upper 5S/6E-22B1, screened in the upper aquifer

 and lower aquifers

5S/6E-25A1, screened in the upper 

 and lower aquifers

YEAR YEAR

B

6/17/98–6/2/99

11/24/99–10/4/00

6/17/98–6/2/99

11/24/99–10/4/00

WATER-SURFACE ELEVATION, IN METERS ABOVE SEA LEVELWATER-SURFACE ELEVATION, IN METERS ABOVE SEA LEVEL

WATER-SURFACE ELEVATION, IN FEET ABOVE SEA LEVEL

WATER-SURFACE ELEVATION, IN FEET ABOVE SEA LEVEL
26 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

Figure 8.—Continued.

-120

-100

-100

-30

-35

-80

-60

-15

-20

-25

-35

-20

-25

-40

-120

-30

-20

-25

-30

-30

-25

-35

-40

-80

-60

-15

-15

-40

-103

-83

-63

-43

-23

1966

1968

1970

1972

1974

197619781980

1982

1984

198619881990

1992

1994

1996

1998

2000

-115

-95

-75

-55

-35

-45 -150

-130

-110

-90

-70

-120

-30 -100

-35

-80

-60

-15

-20

-25

-40

-45 -150

-130

-110

-30

-40

-35

-25

-40

-35

-25

-90

-70

-45 -150

-130

-110

-30

-90

-70

19801982198419861988199019921994199619982000

19801982198419861988199019921994199619982000

-15

-25

-20

-10

-30

6S/6E-12G1, screened in the upper aquifer

6S/7E-16D1, screened in the upper and

 lower aquifers

6S/7E-16R2, screened in the upper and

 lower aquifers

6S/7E-21D1, screened in the upper and

 lower aquifers

5S/7E-31A1, screened in the upper and

 lower aquifers

5S/7E-31Q2, screened in the upper and

 lower aquifers

6S/7E-16A2, screened in the upper and

 lower aquifers

6S/7E-6B1, screened in the lower aquifer 

YEAR

YEAR

YEAR

C

6/17/98–6/2/99

11/24/99–10/4/00

6/17/98–6/2/99

11/24/99–10/4/00

6/17/98–6/2/99

11/24/99–10/4/00

WATER-SURFACE ELEVATION, IN METERS ABOVE SEA LEVEL

 WATER-SURFACE ELEVATION, IN METERS ABOVE SEA LEVEL

WATER-SURFACE ELEVATION, IN METERS ABOVE SEA LEVEL

WATER-SURFACE ELEVATION, IN FEET ABOVE SEA LEVEL

WATER-SURFACE ELEVATION,  IN FEET ABOVE SEA LEVEL

WATER-SURFACE ELEVATION, IN FEET ABOVE SEA LEVEL
Summary and Conclusions 27

Ground-Water Levels

All the areas where significant subsidence was 

detected using InSAR—Palm Desert, Indian Wells, and 

La Quinta/Lake Cahuilla—coincide with or are near 

areas where ground-water pumping generally caused 

ground-water levels to decline between 1998 and 2000. 

In 2000, many of these wells were at the lowest levels 

in their recorded histories (fig. 8). The coincident areas 

of the subsidence signals and the declining water levels 

and the localized character of the subsidence signals 

typical of subsidence caused by localized pumping 

strongly suggests a relation between subsidence and 

ground-water-level declines. If the stresses imposed by 

the historically lowest water levels exceeded the 

preconsolidation stress, the subsidence may be 

permanent.

FUTURE MONITORING

Continued monitoring in the lower Coachella 

Valley is warranted because ground-water levels 

continue to decline in some areas of the valley and, 

therefore, the small amounts of land subsidence 

documented by this study are likely to increase. 

Because the changes in the vertical positions of the 

monuments in the GPS network during 1998–2000 

generally were negligible (less than or equal to the 

expected error in GPS measurements), future GPS 

surveys could be done less frequently than biannually. 

Measurement intervals of 3 to 5 years may be adequate 

for detecting changes significantly larger than the 

expected GPS measurement error. Spatially detailed 

InSAR-derived maps of ground displacements, 

however, could continue to be processed annually 

(depending on data availability) because InSAR can 

detect changes in vertical position as small as 5 mm 

(0.02 ft) (Hoffmann and others, 2001). Because the 

areas of subsidence detected using InSAR spatially 

overlap the GPS network, future monitoring of the GPS 

network could be used to provide ground truth for the 

more spatially detailed and higher resolution InSAR 

measurements.

SUMMARY AND CONCLUSIONS

Ground water has been a major source of 

agricultural, municipal, and domestic water supplies in 

the Coachella Valley since the early 1920s. Groundwater levels declined throughout the Coachella Valley 

from the 1920s until 1949. In 1949, the importation of 

surface water from the Colorado River to the lower 

Coachella Valley began, resulting in decreased 

pumping and a recovery of water levels in some areas. 

Since the 1970s, the demand for water in the lower 

Coachella Valley has exceeded the deliveries of 

imported surface water, and ground-water levels have 

again declined. The declining water levels have the 

potential to induce or renew land subsidence in the 

Coachella Valley. Results of a previous study by the 

U.S. Geological Survey indicate that land subsidence 

may have been as much as about 150 mm (0.5 ft) in the 

southern parts of the valley between about 1930 and 

1996.

The location and magnitude of vertical landsurface changes during 1998–2000 were determined 

using GPS and InSAR techniques. The geodetic 

network used for the GPS measurements described in 

this report covers the area from the Salton Sea on the 

south to Palm Desert on the north. The extent of the 

maps processed using InSAR overlaps the part of the 

geodetic network west of Coachella and north of Lake 

Cahuilla and includes the Palm Desert area. The 

InSAR-generated maps were more useful for 

determining land-surface changes in urban 

(nonagricultural) areas than were the GPS 

measurements, and the GPS measurements were more 

useful for determining changes in agricultural areas. 

The InSAR-generated maps also were useful for 

determining land-surface changes in areas where the 

changes had not previously been detected when only 

the relatively sparse monuments and GPS methods had 

been used. Five locations had GPS and InSAR 

measurements that were comparable; these 

measurements agree reasonably well.
28 Detection and Measurement of Land Subsidence using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, CA

GPS measurements made at 15 geodetic 

monuments in the lower Coachella Valley indicate that 

–34 to +60 millimeters ± 45 millimeters (–0.11 to 

+0.20 foot ± 0.15 foot) of vertical change in the land 

surface occurred during the 2-year period. Changes at 

three of the monuments exceeded the maximum 

uncertainty of ± 45 millimeters (± 0.15 foot) at the 

95-percent confidence level, which indicates that small 

amounts of uplift occurred at these monuments 

between October 1998 and August 2000. Water-level 

measurements made at wells near the three uplifted 

monuments during this 2-year period indicate that the 

water levels fluctuate seasonally; water-level 

measurements made at these wells in September 1998 

and September 2000 indicate that the water levels rose 

slightly near two monuments and declined slightly near 

the third. The relation between the seasonally 

fluctuating, but fairly stable, water levels between 

September 1998 and September 2000 and the slight 

uplift at the monuments may indicate that the water 

levels are fluctuating in the elastic range of stress and 

that the preconsolidation stress of the aquifer system 

was not exceeded during the 2-year period.

Results of the InSAR measurements made 

between June 17, 1998, and October 4, 2000, indicate 

that land subsidence, ranging from about 40 to 80 

millimeters (0.13 to 0.26 ft), occurred in three areas of 

the Coachella Valley—near Palm Desert, Indian Wells, 

and La Quinta. In addition, measurements made 

between June 17, 1998, and June 2, 1999, indicate that 

about 15 millimeters (0.05 ft) of subsidence occurred 

just southeast of Lake Cahuilla. All the subsiding areas 

coincided with areas that are in or near areas where 

ground-water levels declined during the 2-year period, 

which suggests that subsidence and declining water 

levels are related. If the stresses imposed by the 

declining water levels exceeded the preconsolidation 

stress, then the subsidence may be permanent. 

Although the localized character of the subsidence 

signals look typical of the type of subsidence 

characteristically caused by localized pumping, the 

subsidence also may be related to tectonic activity in 

the valley. Future monitoring of land surface change is 

needed to determine if the land subsidence is the result 

of localized pumping or tectonic activity. 

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