Application of Geographic Information System Methods to 

Identify Areas Yielding Water that will be Replaced by 

Water from the Colorado River in the Vidal and Chemehuevi 

Areas, California, and the Mohave Mesa Area, Arizona 

Scientific Investigations Report 2007–5284

Prepared in cooperation with the Bureau of Reclamation 

U.S. Department of the Interior

U.S. Geological Survey

Well

River

aquifer

boundary

River aquifer

boundary

Flood plain

Water table

Accounting

surface

Sediments and sedimentary rocks

Modified from Wilson and Owen-Joyce (1994)

River aquifer Bedrock

Reservoir

Dam

Tributary wash

Water table

Bedrock

Accounting

surface

Colorado

River
Cover: Schematic diagram showing river aquifer and accounting surface along 

the lower Colorado River, California and Arizona.
Application of Geographic Information System 

Methods to Identify Areas Yielding Water that 

will be Replaced by Water from the Colorado 

River in the Vidal and Chemehuevi Areas, 

California, and the Mohave Mesa Area, Arizona

By Lawrence E. Spangler, Cory E. Angeroth, and Sarah J. Walton

Prepared in cooperation with the Bureau of Reclamation

Scientific Investigations Report 2007–5284

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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World Wide Web: http://www.usgs.gov

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Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Spangler, L.E., Angeroth, C.E., and Walton, S.J., 2008, Application of Geographic Information System methods to 

identify areas yielding water that will be replaced by water from the Colorado River in the Vidal and Chemehuevi 

areas, California, and the Mohave Mesa area, Arizona: U.S. Geological Survey Scientific Investigations Report 

2007–5284, 38 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................2

Description of Study Areas .................................................................................................................2

Vidal, California ............................................................................................................................2

Chemehuevi, California...............................................................................................................4

Mohave Mesa, Arizona...............................................................................................................4

The Colorado River Aquifer and Accounting Surface ....................................................................4

Methods...........................................................................................................................................................5

Water Levels and Land-Surface Elevations .....................................................................................5

Geographic Information System Methods .......................................................................................6

Application of Geographic Information System Methods ......................................................................7

Vidal Area...............................................................................................................................................7

Well Selection and Water-Level Measurements ..................................................................7

Delineation of Areas ...................................................................................................................8

Chemehuevi Area ...............................................................................................................................13

Well Selection and Water-Level Measurements .................................................................13

Delineation of Areas..................................................................................................................13

Mohave Mesa Area............................................................................................................................18

Well Selection and Water-Level Measurements .................................................................18

Delineation of Areas..................................................................................................................19

Summary and Conclusions.........................................................................................................................24

References Cited..........................................................................................................................................25
iv

Figures

Figure 1. Map showing location and geology of the Vidal, Chemehuevi, and Mohave

Mesa study areas along the lower Colorado River, California and Arizona ......... 3

Figure 2. Schematic diagram showing river aquifer and accounting surface along

the lower Colorado River, California and Arizona ....................................... 5

Figure 3. Map showing areas interpolated above, below, and near the accounting

surface in the Vidal area of California by using the Triangulated Irregular

Network Contour tool ..................................................................... 9

Figure 4. Map showing areas interpolated above, below, and near the accounting

surface in the Vidal area of California by using the Natural Neighbor tool ......... 10

Figure 5. Map showing areas interpolated above, below, and near the accounting

surface in the Vidal area of California by using the Inverse Distance

Weighted (power of 2) tool ............................................................... 11

Figure 6. Map showing areas interpolated above, below, and near the accounting

surface in the Vidal area of California by using the Spline (weight of 0.1) tool ...... 12

Figure 7. Map showing areas interpolated above, below, and near the accounting

surface in the Chemehuevi area of California by using the Triangulated

Irregular Network Contour tool ............................................................ 14

Figure 8. Map showing areas interpolated above, below, and near the accounting

surface in the Chemehuevi area of California by using the Natural Neighbor

tool............................................................................................. 15

Figure 9. Map showing areas interpolated above, below, and near the accounting

surface in the Chemehuevi area of California by using the Inverse Distance

Weighted (power of 2) tool ............................................................... 16

Figure 10. Map showing areas interpolated above, below, and near the accounting

surface in the Chemehuevi area of California by using the Spline (weight of

0.1) tool ....................................................................................... 17

Figure 11. Map showing areas interpolated above, below, and near the accounting

surface in the Mohave Mesa area of Arizona by using the Triangulated

Irregular Network Contour tool ............................................................ 20

Figure 12. Map showing areas interpolated above, below, and near the accounting

surface in the Mohave Mesa area of Arizona by using the Natural Neighbor

tool............................................................................................. 21

Figure 13. Map showing areas interpolated above, below, and near the accounting

surface in the Mohave Mesa area of Arizona by using the Inverse Distance

Weighted (power of 2) tool ............................................................... 22

Figure 14. Map showing areas interpolated above, below, and near the accounting

surface in the Mohave Mesa area of Arizona by using the Spline (weight

of 0.1) tool .................................................................................... 23

Tables

Table 1. Data for selected wells in the Vidal area, California..................................... 26

Table 2. Data for selected wells in the Chemehuevi area, California ........................... 32

Table 3. Data for selected wells in the Mohave Mesa area, Arizona ........................... 36
v

Conversion Factors and Datums

Multiply By To obtain

gallon per minute (gal/min) 0.0631 liter per second

inch per year (in/yr) 25.4 millimeter per year

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

square mile (mi2

) 2.590 square kilometer

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

°F = (1.8 × °C) + 32.

Datums

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29). 

Elevation, as used in this report, refers to distance above the vertical datum.

Land-Net Numbering System for Wells in the Vidal, Chemehuevi, and Mohave Mesa 

Study Areas

The land-net numbering system for wells in the Vidal, Chemehuevi, and Mohave Mesa study 

areas is based on the cadastral land-survey system of the U.S. Government. The number, in 

addition to designating the site, describes its position in the land net. The land-survey system 

divides a section of land within a township into four quadrants or quarter sections that are 

designated in counterclockwise order by the uppercase letters NE, NW, SW, and SE, which 

indicate, respectively, the northeast, northwest, southwest, and southeast quadrants. Each 

quadrant is further subdivided into quarter-quarter and quarter-quarter-quarter sections, 

equivalent to a 10-acre tract, using the same designation. Numbers that designate the section, 

township, and range, in that order, follow the third-level quadrant designation. Thus, a well in 

the Vidal area with a land-net designation of SWSENES29 T01S R24E identifies its location in the 

SW 1⁄4 of the SE 1⁄4 of the NE 1⁄4 of Section 29, Township 1 South, Range 24 East. 

R. 24 E.

Well SWSENES29 T01S R24E

9

6 5 4 3

7 8 10 11 12

12

T.

1

S.

18 16 15 13

19 20

30 29 27 26 25

31 32 33 34

21

17

22 24

28

3635

23

14

NW

SW

NE

SW SE

SE

NW

NE

SW SE

NW

NE

29 SE

SE

SW

29

Land-net location system for Vidal, Chemehuevi, and Mohave Mesa study areas.
vi

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Application of Geographic Information System Methods to 

Identify Areas Yielding Water that will be Replaced by 

Water from the Colorado River in the Vidal and 

Chemehuevi Areas, California, and the Mohave 

Mesa Area, Arizona

By Lawrence E. Spangler, Cory E. Angeroth, and Sarah J. Walton

Abstract

Relations between the elevation of the static water level 

in wells and the elevation of the accounting surface within the 

Colorado River aquifer in the vicinity of Vidal, California, the 

Chemehuevi Indian Reservation, California, and on Mohave 

Mesa, Arizona, were used to determine which wells outside 

the flood plain of the Colorado River are presumed to yield 

water that will be replaced by water from the Colorado River. 

Wells that have a static water-level elevation equal to or below 

the elevation of the accounting surface are presumed to yield 

water that will be replaced by water from the Colorado River. 

Geographic Information System (GIS) interpolation tools were 

used to produce maps of areas where water levels are above, 

below, and near (within ± 0.84 foot) the accounting surface.

Calculated water-level elevations and interpolated 

accounting-surface elevations were determined for 33 wells in 

the vicinity of Vidal, 16 wells in the Chemehuevi area, and 35 

wells on Mohave Mesa. Water-level measurements generally 

were taken in the last 10 years with steel and electrical 

tapes accurate to within hundredths of a foot. A Differential 

Global Positioning System (DGPS) was used to determine 

land-surface elevations to within an operational accuracy 

of ± 0.43 foot, resulting in calculated water-level elevations 

having a 95-percent confidence interval of ± 0.84 foot. 

In the Vidal area, differences in elevation between the 

accounting surface and measured water levels range from 

-2.7 feet below to as much as 17.6 feet above the accounting 

surface. Relative differences between the elevation of the 

water level and the elevation of the accounting surface 

decrease from west to east and from north to south. In the 

Chemehuevi area, differences in elevation range from -3.7 feet 

below to as much as 8.7 feet above the accounting surface, 

which is established at 449.6 feet in the vicinity of Lake 

Havasu. In all of the Mohave Mesa area, the water-level 

elevation is near or below the elevation of the accounting 

surface. Differences in elevation between water levels and the 

accounting surface range from -0.2 to -11.3 feet, with most 

values exceeding -7.0 feet. 

In general, the ArcGIS Triangulated Irregular Network 

(TIN) Contour and Natural Neighbor tools reasonably 

represent areas where the elevation of water levels in wells 

is above, below, and near (within ± 0.84 foot) the elevation 

of the accounting surface in the Vidal and Chemehuevi study 

areas and accurately delineate areas around outlying wells 

and where anomalies exist. The TIN Contour tool provides 

a strict linear interpolation while the Natural Neighbor tool 

provides a smoothed interpolation. Using the default options 

in ArcGIS, the Inverse Distance Weighted (IDW) and Spline 

tools also reasonably represent areas above, below, and 

near the accounting surface in the Vidal and Chemehuevi 

areas. However, spatial extent of and boundaries between 

areas above, below, and near the accounting surface vary 

among the GIS methods, which results largely from the 

fundamentally different mathematical approaches used by 

these tools. The limited number and spatial distribution of 

wells in comparison to the size of the areas, and the locations 

and relative differences in elevation between water levels 

and the accounting surface of wells with anomalous water 

levels also influence the contouring by each of these methods. 

Qualitatively, the Natural Neighbor tool appears to provide the 

best representation of the difference between water-level and 

accounting-surface elevations in the study areas, on the basis 

of available well data.
2 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Introduction

A cooperative effort by the Bureau of Reclamation 

(Reclamation) and the U.S. Geological Survey (USGS) has 

been under way since the early 1990s to inventory all wells 

located within the river aquifer along the lower Colorado River 

from the area surrounding Lake Mead to the Mexican border. 

Information obtained from the well inventory will be used 

by Reclamation to determine if wells located within the river 

aquifer outside of the flood plain are pumping water that will 

be replaced by water from the Colorado River. Initial attempts 

to identify these wells by using well inventory and water-level 

data have encountered several problems, including substantial 

water-level differences in adjacent wells, long time spans 

between water-level measurements, and the precision with 

which water levels and elevations are measured. In addition, 

the data often include a range of natural and anthropogenicinduced variations that must be considered when determining 

static water levels under current hydrologic conditions.

Accounting for use of water from the Colorado River 

is decreed by the Consolidated Decree of the United States 

Supreme Court in Arizona v. California (United States 

Supreme Court, 2006). Water pumped from wells located 

within the flood plain of the river is presumed to be river 

water and is accounted for as Colorado River water. Water 

pumped from wells outside the flood plain of the river but still 

within the bounds of the river aquifer, however, may or may 

not be accounted for as Colorado River water. A method for 

identifying which wells outside the flood plain of the river will 

yield water that will be replaced by water from the Colorado 

River by determining the relation between the elevation of the 

static water level in wells and the elevation of the accounting 

surface is documented in Wilson and Owen-Joyce (1994) 

and Owen-Joyce and others (2000). Wells that have a static 

water-level elevation equal to or below the elevation of the 

accounting surface at the location of the well are presumed to 

yield water that will be replaced by water from the Colorado 

River. Wells that have a static water-level elevation above 

the elevation of the accounting surface are presumed to yield 

water that will be replaced by water from precipitation and 

inflow from tributary valleys. 

Purpose and Scope

This report describes the application of selected 

Geographic Information System (GIS) methods to determine 

differences between water-level and accounting-surface 

elevations and to identify areas that yield water that will be 

replaced by water from the Colorado River. The report (1) 

evaluates the well-inventory data set in three test basins along 

the lower Colorado River, (2) compares water-level elevations 

in selected wells with the elevation of the accounting surface 

in these areas, and (3) examines selected interpolation tools 

that can be used to identify areas that yield water that will be 

replaced by water from the Colorado River. Data from wells 

in the Vidal, California; Chemehuevi Indian Reservation, 

California; and Mohave Mesa, Arizona areas are stored in the 

USGS National Water Information System (NWIS) database. 

Description of Study Areas

Three areas along the lower Colorado River downstream 

from Davis Dam were selected to determine the relation 

between static water levels in wells and the accounting 

surface: the area in the vicinity of Vidal, California; the area 

that includes the Chemehuevi Indian Reservation (herein 

termed Chemehuevi), California; and the area in the vicinity 

of Bullhead City, Arizona, and to the south on Mohave Mesa 

(fig. 1). These areas were selected on the basis of having a 

sufficient number of wells for analysis, had static water levels 

that had been measured within the last 10 years, and had landsurface elevations that had been determined by a Differential 

Global Positioning System (DGPS). 

Vidal, California

The Vidal study area is located along the western side of 

the Colorado River, in San Bernardino and Riverside Counties, 

California, and east of the small community of Vidal (fig. 1). 

The area lies roughly between lat 34°02' and 34°13' and long

114°21' and 114°31' and includes about 45 mi2 of the Colorado 

River aquifer. The area is situated on an alluviated terrace that 

slopes toward the river at an elevation ranging from about 

325 ft along the river to 530 ft in the western part of the area, 

about 3 mi from the river. Land use primarily consists of 

residential areas interspersed with undeveloped areas. The 

area is sparsely populated and most water use is for domestic 

purposes. Reported well yields in the Vidal area range from 

10 to 1,800 gal/min, and depth to water below land surface 

ranges from about 14 ft along the Colorado River to 184 ft in 

the western part of the area (U.S. Geological Survey, unpub. 

data, 2006). No perennial surface streams cross the study 

area. Precipitation in the vicinity of Vidal averages 5.3 in/yr 

and mean temperature is 22.8°C, calculated on the basis of 

monthly normals for 1971–2000 at Parker, Arizona (Western 

Regional Climate Center, 2007).
Introduction 3

CLARK COUNTY

SAN BERNARDINO COUNTY

LA PAZ COUNTY

MOHAVE COUNTY

SAN BERNARDINO COUNTY

RIVERSIDE COUNTY

95

72

62

95

66 68 93 95

153

10

40

163

Mohave Mesa

Chemehuevi

Vidal

Wash

35°04'

114°42'

NEVADA

Mohave Mesa

113°56'

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

ARIZONA

EXPLANATION

Geology

Younger Alluviums

Older Alluviums

Bouse Formation

Fanglomerate

Bedrock

Boundary of river aquifer

Boundary of Chemehuevi 

Indian Reservation

Wells

0 6 12 KILOMETERS 3

0 3 6 12 MILES

Colorado

River

34°24'

CALIFORNIA

Colorado

River

Chemehuevi

Bullhead City

Davis Dam

Needles

Desert Hills

Lake Havasu City

Parker

Vidal

Topock

Piute

Wash

Mackenzie Wash

Buck Mountain

Sacramento Wash

Chemehuevi Wash

Colorado River Aqueduct

Bouse Wash

Mohave Wash

Castanada

Wash

Bill WilliamsRiver

Lake

Havasu

V idal

Mohave

Mesa

Chemehuevi

Vidal

Lake

Meade

40

Arizona

Utah

California

Nevada

15

1 0

93

93

Figure 1. Location and geology of the Vidal, Chemehuevi, and Mohave Mesa study areas along the lower Colorado River, 

California and Arizona (modified from Wilson and Owen-Joyce, 1994).
4 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Chemehuevi, California

The Chemehuevi study area is located along the western 

side of the Colorado River (Lake Havasu), in San Bernardino 

County, California, and across the river from Lake Havasu 

City, Arizona (fig. 1). The area lies roughly between lat 34°25' 

and 34°37' and long 114°17' and 114°29' and includes about 

50 mi2 of the river aquifer. Elevation ranges from about 450 ft 

along the river to about 625 ft in the northern part of the area. 

Land that is developed in the area primarily is for residential 

use. The area is sparsely populated and most water use is for 

domestic purposes. Reported well yields in the Chemehuevi 

area range from 15 to 550 gal/min, and depth to water below 

land surface ranges from about 3 ft along the Colorado River 

to 180 ft in higher-elevation areas west of the river (U.S. 

Geological Survey, unpub. data, 2006). No perennial surface 

streams cross the study area, but Chemehuevi Wash forms the 

southern boundary of the area. Precipitation in the vicinity 

of Chemehuevi averages 2.9 in/yr and mean temperature 

is 24.7°C, calculated on the basis of monthly normals for 

1971-2000 at Lake Havasu City, Arizona (Western Regional 

Climate Center, 2007).

Mohave Mesa, Arizona

The Mohave Mesa study area is located along the 

eastern side of the Colorado River, in Mohave County, 

Arizona, south of Bullhead City (fig. 1). The area lies roughly 

between lat 34°55' and 35°13' and long 114°25' and 114°44' 

and includes about 111 mi2. Elevation ranges from about 

1,225 ft northeast of Bullhead City to 530 ft in the southern 

part of the area, near the river. Land use primarily consists 

of residential areas among undeveloped areas. The area 

is sparsely populated and most water use is for domestic 

purposes. Reported well yields in the Mohave Mesa area 

range from 12.5 to 650 gal/min, and depth to water below 

land surface ranges from about 71 ft near the Colorado River 

to 731 ft in the northeastern part of the area, near Bullhead 

City (U.S. Geological Survey, unpub. data, 2006). No 

perennial surface streams cross the study area. Precipitation 

in the vicinity of Mohave Mesa averages 6.6 in/yr and mean 

temperature is 23.4°C, calculated on the basis of monthly 

normals for 1971-2000 at Bullhead City, Arizona (Western 

Regional Climate Center, 2007). 

The Colorado River Aquifer and Accounting 

Surface

The Colorado River aquifer consists of permeable, 

partly saturated sediments and sedimentary rocks that are 

hydrologically connected to the Colorado River (fig. 2). These 

sediments consist of unconsolidated to semi-consolidated 

sands, silts, gravels, and clays that interfinger with similar 

materials that make up the adjacent alluvial slopes. These 

materials have highly variable transmissivity values and 

serve as the principal aquifer in this region. In the Vidal, 

Chemehuevi, and Mohave Mesa study areas, the river aquifer 

generally includes younger and older alluviums of Miocene 

to Holocene age; Pliocene-age sediments of the Bouse 

Formation; and a Miocene- to Pliocene-age fanglomerate 

unit (Metzger and others, 1973; Wilson and Owen-Joyce, 

1994) (fig. 1). The river aquifer is bounded by relatively 

impermeable bedrock along the bottom and margins of the 

basins that underlie the valley of the Colorado River (fig. 2). 

Total thickness of the river aquifer is as much as 5,000 ft in 

some areas.

Water levels in the Colorado River aquifer respond to 

changes in elevation of the Colorado River, withdrawals 

from the aquifer, and runoff from precipitation that infiltrates 

downward to the aquifer from the river channel, tributary 

washes, canals, and reservoirs. Nearly all of the water in 

the river aquifer is derived from the Colorado River. The 

accounting surface represents the elevation and slope of the 

unconfined static water table in the river aquifer outside the 

flood plain of the Colorado River that would exist assuming 

the only source of water to the aquifer is the Colorado River. 

This surface was generated by using profiles of the Colorado 

River or the water-surface elevation of agricultural drains 

near the outer edge of the flood plain where available, or in 

the case of reservoirs, the annual high water-surface elevation 

used by Reclamation to operate reservoirs under normal flow 

conditions. Water-surface profiles were computed for the 

highest median monthly projected discharge in the river for 

1992-2001 and were determined by using hydraulic routing 

and step-backwater methods (Bureau of Reclamation, 1989a, 

1989b, and 1990). The accounting surface extends outward 

from the edge of the flood plain to the subsurface boundary 

of the river aquifer along the margins of the basins (fig. 2). 

Accounting-surface contours generally are perpendicular to 

the Colorado River and increase in elevation from south to 

north. Contour intervals are variable along the lower Colorado 

River; accounting-surface contours are established at 4-ft 

intervals in the Vidal area and 2-ft intervals in the Mohave 

Mesa area. Because the Colorado River has been impounded 

to form Lake Havasu in the Chemehuevi area, the accounting 

surface is presumed to be essentially level and thus is 

represented by a single elevation value.
Methods 5

River

aquifer

boundary

Alluvial slope

Flood plain

Water table

Drainage ditch

Accounting

surface

Sediments and sedimentary rocks

R

EXPLANATION

Well—The symbol "R" denotes a well that has a static water-level elevation 

equal to or below the accounting surface and is presumed to yield water that 

will be replaced by water from the river. The symbol "T" denotes a well that 

has a static water-level elevation above the accounting surface and is 

presumed to yield water that will be replaced by water from precipitation and 

inflow from tributary valleys.

Modified from Wilson and Owen-Joyce (1994)

River aquifer Bedrock

Reservoir

Dam

Tributary wash

Water table

Bedrock

T

T

R

Accounting

surface

Colorado

River

Figure 2. River aquifer and accounting surface along the lower Colorado River, California and Arizona.

Methods

Measured depths to water in feet below land surface were 

subtracted from land-surface elevations to determine waterlevel elevations for selected wells in the Vidal, Chemehuevi, 

and Mohave Mesa study areas. These water-level elevations 

were then compared with the elevation of the accounting 

surface at each of the wells. On the basis of relations between 

the water-level and accounting-surface elevations, ArcGIS 

Triangulated Irregular Network (TIN) Contour, Natural 

Neighbor, Inverse Distance Weighted (IDW), and Spline 

interpolation tools were used to delineate areas where waterlevel elevations are presumed to be above, below, and near 

(within ± 0.84 ft) the elevation of the accounting surface in the 

study areas.

Water Levels and Land-Surface Elevations

Data for inventoried wells in the study areas were 

obtained from the USGS (Arizona Water Science Center) 

NWIS database. Information that was obtained included 

elevation of the land surface at the well, depth to water 

below land surface, pumping status of the well at the time of 

measurement, date of measurement, and elevation and waterlevel measurement methods and accuracies. These data were 

used to determine water-level elevations that could then be 

compared with one another to evaluate anomalies. Historical 

examinations of water levels for selected wells also were done 

to evaluate variability in water levels over time in comparison 

to water levels measured during the study period and used for 

analysis. 

Land-surface elevations for wells stored in the NWIS 

database were determined by several different methods. For 

this project, only those wells for which the land-surface 

elevation was determined by DGPS were used. The DGPS 

unit used to determine the land-surface elevation at each of 

the wells has a manufacturers’ reported accuracy of ± 0.10 ft. 

This accuracy results in a 95-percent confidence interval of 

about ± 0.20 ft. In practice, the accuracy of the DGPS unit 

was determined to be ± 0.43 ft (Sandra Owen-Joyce, U.S. 

Geological Survey, written commun., 2006), resulting in a 

95-percent confidence interval of ± 0.84 ft with respect to 

land-surface elevation. Thus, with 95-percent confidence, 
6 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

wells with a difference between the water-level elevation and 

accounting-surface elevation of greater than ± 0.84 ft have 

water levels that are either above or below the accounting 

surface, and wells with a difference of less than ± 0.84 ft have 

water levels that may be either above or below (cannot be 

distinguished from) the accounting surface. 

Geographic Information System Methods

Interpolation tools available within the ArcGIS 3D 

and Spatial Analyst tool box include TIN Contour, Natural 

Neighbor, IDW, and Spline (Environmental Systems Research 

Institute, 2007a and b). These tools commonly are used to 

determine values of points at locations where no data are 

available by mathematically interpolating between points with 

known values. All of the tools are designed to work best where 

data sets are sufficiently large (dense) and where data are 

evenly distributed. Limited and irregularly distributed data sets 

may substantially affect the usefulness of the tools to be able 

to generate accurate interpolations.

TIN Contour is a linear interpolation tool that represents 

a surface as a network of triangles (Environmental Systems 

Research Institute, 2007a). A TIN can be constructed by 

triangulating a set of vertices with x, y, and z values. The 

vertices are connected with a series of edges to form a network 

of triangles, where each triangle is treated as a plane. The 

edges of a TIN form contiguous, nonoverlapping triangular 

facets. The resulting triangulation ensures that no vertex lies 

within the interior of any of the triangles in the network. 

Contours are generated directly from the TIN within its zone 

of interpolation. Portions of individual contours generated by 

the tool within a triangle are straight. Any change in direction 

occurs only when a contour passes from one triangle into 

another. As a result, the resulting contours are not smooth. 

This type of contouring produces an exact linear interpretation 

of the surface, which may not be realistic. 

Natural Neighbor is an exact triangulation interpolation 

tool for multivariate datasets. The value for an interpolation 

point is estimated by using weighted values of the closest 

surrounding points in a triangulation rather than distances 

between points (Sibson, 1981). These points, termed the 

natural neighbors, are connected to the interpolation point 

when inserted into the triangulation. The Natural Neighbor 

tool can efficiently handle large numbers of input points and 

works equally well with regularly and irregularly distributed 

data sets (Watson, 1992). The Natural Neighbor tool has 

been shown to consistently outperform other techniques both 

quantitatively and qualitatively when applied to generating 

surfaces (Owen, 1993; Abramov and McEwen, no date, 

accessed November 2007). No weighting or power options are 

available for the Natural Neighbor tool within ArcGIS.

The Natural Neighbor tool also was used to calculate 

the elevation of the accounting surface at each well location 

by using the principal contours established by Reclamation. 

Assuming a linear relation between the established 

accounting-surface contours, 10-meter grid cells were used 

to generate values of the elevation of the accounting surface 

between the principal contours and at each well location. The 

elevation of the accounting surface could then be compared 

with the water-level elevation at that location. 

Inverse Distance Weighted is a method of interpolation 

that estimates cell values by averaging (weighting) the values 

of sample data points in the neighborhood of each cell. The 

weight is a function of inverse distance and is not affected by 

the spatial arrangement of the data. The closer a point is to 

the center of the cell being estimated, the more influence, or 

weight, it has in the averaging process; likewise, the farther a 

sampled point is from the cell being evaluated, the less weight 

it has in the calculation of the cell’s value. IDW makes the 

assumption that values closer to the unsampled location are 

more representative of the value to be estimated than samples 

farther away (Collins, 1996). Distance-based weighting 

methods have been used to interpolate climatic data (Legates 

and Willmont, 1990). 

The IDW tool tends to generate bull’s eye patterns. In 

addition, all interpolated values lie within the range of the 

data point values and may not accurately represent valleys 

and peaks in the surface (de Smith, Goodchild, and Longley, 

2007). The choice of power option in the IDW tool also can 

substantially affect the interpolation results. As the power 

option is increased, the interpolated value takes on the value 

of the closest sample point. Thus, nearby points will have 

the most influence, and the surface will have more detail (be 

less smooth). Specifying a lower value for the power option 

provides more influence to surrounding points farther away. 

For this project, the default option (power of 2) was used to 

simplify and streamline the method for potential users. 

The Spline tool uses a deterministic technique to 

represent two-dimensional curves on three-dimensional 

surfaces (Eckstein, 1989; Hutchinson and Gessler, 1994). 

The tool uses an interpolation method that estimates values 

by using a mathematical function that minimizes the total 

curvature of the surface, resulting in a smooth surface that 

passes exactly through the input points. Because rapid changes 

in gradient or slope may occur in the vicinity of the data points 

(edge effects), however, this tool is not suitable for estimating 

curvature. Splines can be used for generating gently varying 

surfaces such as the elevation of the water surface and have 

the advantage of creating curves and contour lines that are 

visually appealing. Some of the disadvantages of using Spline 

are that no estimates of error are given and that splines may 

mask uncertainty present in the data (Collins, 1996). Splines 
Application of Geographic Information System Methods 7

are typically used for creating contour lines from dense 

regularly spaced data, but may be used for interpolation of 

irregularly spaced data. The basic (regularized) interpolation 

tool within ArcGIS can be applied by assigning a weight value 

of 0 to 0.5 in the Spline function, with higher values of weight 

resulting in smoother surfaces. For this project, the default 

option (weight of 0.1) was used to simplify and streamline the 

method for potential users.

Application of Geographic Information 

System Methods

Data from the USGS NWIS database were imported 

into ArcGIS to determine the relation between water-level 

elevations and the elevation of the accounting surface along 

the lower Colorado River. The elevation of the accounting 

surface was compared with the elevation of water levels in 

selected wells to determine which wells yield water that will 

be replaced by water from the Colorado River. Wells in areas 

in which the elevation of the water level is above the elevation 

of the accounting surface are presumed to pump water that 

will be replaced by water from precipitation or tributary 

inflow. Wells in areas in which the elevation of the water level 

is below the elevation of the accounting surface are presumed 

to pump water that will be replaced by water from the 

Colorado River. Wells in areas in which the elevation of the 

water level is within ± 0.84 ft of the accounting surface cannot 

be determined with sufficient confidence to be either above 

or below the accounting surface. These wells may or may not 

pump water that will be replaced by water from the Colorado 

River.

Maps for each of the study areas have been produced 

showing the contoured relations between areas where waterlevel elevations are above, below, and near the accounting 

surface using TIN Contour, Natural Neighbor, IDW, and 

Spline interpolation tools. Contour intervals were established 

at -2, -0.84, 0.84, 2, 4, and 8 ft to span the range of difference 

between water-level and accounting-surface elevations. The 

boundary of the river aquifer along the edge of the Colorado 

River in the Vidal and Mohave Mesa study areas and Lake 

Havasu in the Chemehuevi study area was represented by 

a series of points where the elevation of the river and the 

elevation of the water table in the river aquifer are assumed to 

be equal. For contouring purposes, these points were assigned 

a value of zero so that the interpolation tools could define 

more accurately the boundaries between areas above, below, 

and near the accounting surface between well locations and 

the river. 

Vidal Area

Well Selection and Water-Level Measurements 

Data for 81 wells completed in the river aquifer in the 

Vidal area were compiled from the NWIS database, of which 

17 wells did not have a measured static water level because 

of well obstructions, well status such as pumping, or because 

a measurement was not possible (landowner restriction, well 

had been destroyed, etc.). Water-level measurements in the 

remaining 64 wells were further evaluated on the basis of the 

date of measurement and land-surface elevation accuracy. 

Most of the water levels in the data set were measured 

during 1961-64, 1972, 1990, 1995-97, and 2000-01. The 

number of measurements taken in each well ranged from 

1 to 13; most wells had 5 or less measurements that were 

made throughout at least a 10-year period. Water levels in all 

wells were measured with calibrated steel or electrical tapes 

that are accurate to within tenths or hundredths of a foot. 

Water-level measurements that were reported only to within 

1-ft accuracy were not used. Water-level measurements that 

were determined to be substantially influenced by the effects 

of pumping of the well or a nearby well were not used. All 

elevation measurement accuracies in the 1972 data set (which 

included 12 wells) were 10 ft, as determined from topographic 

map contour intervals, and none of these wells were included 

in the analysis. The selection process yielded 33 wells with 

water levels that were measured during 2000-01. 

Calculated water-level elevations and interpolated 

accounting-surface elevations for the 33 selected wells in the 

Vidal area are shown in table 1; at back of report. Water levels 

measured from November 2000 through March 2001 were 

used to calculate elevations to maintain consistency in method 

of measurement of water levels and elevations, and minimize 

variations resulting from natural (climatic) and anthropogenic 

effects over time. Nonetheless, in some locations, such as at 

wells 7 and 8, water-level elevations in adjacent wells were 

substantially different and no apparent explanation for these 

discrepancies could be determined. In some areas where 

wells are sparse or recent water-level data are not available, 

older water-level data were used to help evaluate relations 

between the elevation surfaces. For example, water-level 

and accounting-surface elevation differences determined for 

several wells for which only 1990 measurements are available 

were observed to be consistent with elevation differences 

determined for nearby wells measured in 2000-01. Water-level 

variations of more than 10 ft were noted for several wells 

in which multiple measurements had been taken over time 

(table 1). These large “apparent” water-level fluctuations, 

however, may be the result of measurements being made 

during or shortly after pumping of the well or pumping effects 

from nearby wells, rather than from natural variations, and 

thus, probably do not represent static water-level conditions. 
8 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Although not selected for use in analysis because an 

obstruction had prevented water levels from being measured 

since 1993, the water-level fluctuation in a well located at 

NESESES10 T01S R24E may be more representative of 

natural (seasonal) effects over time. Thirteen measurements 

made every 1 to 2 months from December 1961 through June 

1963 showed a variation of only 1.59 ft between the highest 

and lowest values (standard deviation of 0.46 ft). Other wells 

with fewer measurements taken over longer time periods 

showed fluctuations of less than 1 ft (table 1).

Delineation of Areas 

When the 95-percent confidence interval (± 0.84 ft) 

is taken into account, relative differences between waterlevel elevations and accounting-surface elevations for the 

selected wells show distinct areas where the elevation of the 

water level is above (higher than), below (lower than), and 

within the 95-percent confidence interval (within ± 0.84 ft) 

of the accounting surface. On the basis of the availability 

and distribution of wells within the river aquifer, these 

generalized areas were delineated between the accountingsurface elevation contours of 320 and 336 ft by using the TIN 

Contour, Natural Neighbor, IDW, and Spline tools (figs. 3-6).

The area where the elevation of the water level is above 

the elevation of the accounting surface generally lies more 

than 1 mi from the river and between the 324- and 332-ft 

elevation contours of the accounting surface. Differences 

in elevation range from 1.4 to 17.6 ft above the accounting 

surface, with a substantial increase in difference and thus, 

gradient toward the northwest. This area likely extends past 

the 332-ft contour interval to the east, but relations to areas 

where water-level elevations are lower than accounting-surface 

elevations between the 332 and 336-ft intervals are uncertain. 

An area where the water-level elevation also is substantially 

above the accounting-surface elevation (5.6 ft) appears to 

be localized around well 14. Although wells along the river 

generally have water-level elevations near or below the 

accounting surface, calculated elevation differences for wells 

with older water-level data in the vicinity of this well (not 

shown) also indicate that an elevated water-table surface may 

exist in this area.

The area where the water-level elevation is below the 

elevation of the accounting surface lies in the southern part of 

the study area where the accounting-surface elevation is lower 

than about 325 ft and also along the river in the eastern part 

of the area between the 332- and 336-ft contours. Differences 

in elevation range from -0.9 to -2.7 ft below the accounting 

surface. A small area where the water-level elevation is also 

below the elevation of the accounting surface is localized 

around wells 19 and 20. Water-level elevations in this area are 

more than 2 ft below the elevation of the accounting surface 

whereas elevations in surrounding wells are slightly above the 

accounting-surface elevation of about 327 ft. The area where 

the elevation of the water level may be above or below the 

elevation of the accounting surface (on the basis of ± 0.84 ft at 

the 95-percent confidence interval) generally lies within 1.5 mi 

of the river and between the accounting-surface elevations 

of 324 and 328 ft, with localized areas to the northeast. The 

boundary defining this area will change over time as additional 

information becomes available. Overall, in the Vidal area, 

relative differences between the elevation of the water level 

and the elevation of the accounting surface decrease from west 

to east (toward the river) and from north to south (along the 

river). 

The TIN Contour and Natural Neighbor tools appear 

to reasonably portray areas where water-level elevations 

are above, below, and near (within ± 0.84 ft) the accounting 

surface, except in areas where well data are sparse, and 

adequately delineate areas where anomalies in the surface 

exist, such as in the vicinity of wells 19 and 20, and around 

well 14 (figs. 3 and 4). Boundaries between areas where waterlevel elevations may be above or below the elevation of the 

accounting surface (on the basis of ± 0.84 ft at the 95-percent 

confidence interval) and areas that are above (greater than 

0.84 ft) and below (less than -0.84 ft) the accounting surface 

also appear to be reasonable, although contours delineated 

by Natural Neighbor are considerably smoother than those 

delineated by TIN Contour. 

The default power option of 2 in the IDW tool was 

used to delineate areas where water-level elevations are 

above, below, and near the accounting surface and is shown 

in figure 5. In general, these areas are reasonably portrayed, 

although the area near (within ± 0.84 ft) the accounting 

surface is substantially larger than that delineated by either 

the TIN Contour or Natural Neighbor tool, and the area below 

the accounting surface in the vicinity of wells 27 to 32 is 

noticeably different. 

The default weight option of 0.1 in the Spline tool was 

used to delineate areas above, below, and near the accounting 

surface as shown in figure 6. In general, the area near (within 

± 0.84 ft) the accounting surface is considerably reduced 

in size from that delineated by the IDW tool and relations 

between the surfaces between about the 322 and 328-ft 

accounting-surface contours are substantially different. 

Anomalous areas around well 14 and wells 19 and 20 appear 

to be accurately represented. Although boundaries between all 

three areas are smooth, anomalies (inliers) within the area near 

(within ± 0.84 ft) the accounting surface are shown where well 

control is not available, such as that in the vicinity of well 15 

(fig. 6). 
Application of Geographic Information System Methods 9

Figure 3. Areas interpolated above, below, and near the accounting surface in the Vidal area of California by using the 

Triangulated Irregular Network Contour tool. 

336

332

328

324

320

30 333.0 333.7

-0.7 32 332.6

333.8

-1.2

29 331.3

333.6

-2.3

27 331.6 333.1

-1.5

31 332.8

333.7

-0.9 28 332.6

333.6

-1.0

33 342.2

330.5

11.7

26 337.0

329.9

7.1

24 330.6

330.2

0.4

25 339.0 329.5

9.5

21 327.7

327.5

0.2 22 329.1

327.7

1.4

23 345.0

327.4

17.6 20 325.1

327.3

17 327.7 -2.2

327.0

0.7

16 327.6

326.9

0.7

14 332.6

327.0

5.6

15 327.1

326.7

0.4

19 324.8

327.2

-2.4

18 328.0

326.6

1.4

12 327.9

326.3

1.6

13 328.2

326.3

1.9

11 324.7

325.3

-0.6 10 324.7

325.3

8 330.3 -0.6

324.4

5.9 9 323.7

324.9

-1.2

5 321.8

323.6

-1.8 4 321.7

323.2

-1.5 2 321.8

322.8

-1.0

1 320.1

322.8

-2.7

3 321.4

323.1

-1.7

6 321.5

323.5

-2.0

7 322.9

324.1

-1.2

95

62

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

CALIFORNIA ARIZONA

Colorado

River

114°30' 114°22'

34°10'

34°04'

1

3 2

3

2

0 1 2 KILOMETERS 0.5

0 0.5 1 2 MILES

Vidal

Boundary of river aquifer

Boundary of river aquifer

EXPLANATION

1

2

3

0.84

2

336

Well ID Elevation of water level in well

Elevation of accounting surface 

—interpolated

Difference in elevation between 

water level and accounting 

surface

4

8

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 

95-percent confidence interval)

Below accounting surface

Accounting surface

River aquifer

Accounting-surface contours—Number represents 

elevation of Colorado River within adjacent river 

aquifer

Contour—Number represents difference, in feet, 

between water-level and accounting-surface 

elevations

-2

 -0.84

Well— 14 332.6

327.0

5.6
10 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

336

332

328

324

320

30 333.0 333.7

-0.7 32 332.6 333.8

-1.2

29 331.3

333.6

-2.3

27 331.6

333.1

-1.5

31 332.8 333.7

-0.9 28 332.6

333.6

-1.0

33 342.2

330.5

11.7

26 337.0

329.9

7.1

24 330.6

330.2

0.4

25 339.0 329.5

9.5

21 327.7

327.5

0.2

22 329.1

327.7

1.4

23 345.0

327.4

17.6 20 325.1

327.3

17 327.7 -2.2

327.0

0.7

16 327.6

326.9

0.7

14 332.6

327.0

5.6

15 327.1

326.7

0.4

19 324.8

327.2

-2.4

18 328.0 326.6

1.4

12 327.9

326.3

1.6

13 328.2

326.3

1.9

11 324.7

325.3

-0.6

10 324.7 325.3

-0.6 8 330.3

324.4

5.9 9 323.7

324.9

-1.2

5 321.8

323.6

-1.8 4 321.7

323.2

-1.5 2 321.8

322.8

-1.0

1 320.1

322.8

-2.7

3 321.4

323.1

-1.7

6 321.5

323.5

-2.0

7 322.9

324.1

-1.2

95

62

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

CALIFORNIA ARIZONA

Colorado

River

114°30' 114°22'

34°10'

34°04'

1

3

2

3

2

0 1 2 KILOMETERS 0.5

0 0.5 1 2 MILES

Vidal

Boundary of river aquifer

Boundary of river aquifer

EXPLANATION

1

2

3

0.84

2

336

Well ID Elevation of water level in well

Elevation of accounting surface 

—interpolated

Difference in elevation between 

water level and accounting 

surface

4

8

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 

95-percent confidence interval)

Below accounting surface

Accounting surface

River aquifer

Accounting-surface contours—Number represents 

elevation of Colorado River within adjacent river 

aquifer

Contour—Number represents difference, in feet, 

between water-level and accounting-surface 

elevations

 -2

 -0.84

Well— 14 332.6

327.0

5.6

Figure 4. Areas interpolated above, below, and near the accounting surface in the Vidal area of California by using the 

Natural Neighbor tool.
Application of Geographic Information System Methods 11

336

332

328

324

320

30 333.0

333.7

-0.7

32 332.6

333.8

-1.2

29 331.3

333.6

-2.3

27 331.6

333.1

-1.5

31 332.8

333.7

-0.9 28 332.6

333.6

-1.0

33 342.2

330.5

11.7

26 337.0

329.9

7.1

24 330.6

330.2

0.4

25 339.0

329.5

9.5

21 327.7 327.5

0.2

22 329.1

327.7

1.4

23 345.0

327.4

17.6

20 325.1

327.3

-2.2

17 327.7 327.0

0.7

16 327.6

326.9

0.7

14 332.6 327.0

5.6

15 327.1

326.7

0.4

19 324.8

327.2

-2.4

18 328.0 326.6

1.4

12 327.9

326.3

1.6

13 328.2 326.3

1.9

11 324.7

325.3

-0.6 10 324.7

325.3

-0.6

8 330.3

324.4

5.9

9 323.7

324.9

-1.2

5 321.8

323.6

-1.8 4 321.7

323.2

-1.5

2 321.8

322.8 1 320.1 -1.0 322.8

-2.7

3 321.4

323.1

-1.7

6 321.5

323.5

-2.0

7 322.9

324.1

-1.2

95

62

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

CALIFORNIA ARIZONA

Colorado

River

114°30' 114°22'

34°10'

34°04'

1

3

2

3

2

0 1 2 KILOMETERS 0.5

0 0.5 1 2 MILES

Vidal

Boundary of river aquifer

Boundary of river aquifer

EXPLANATION

1

2

3

0.84

2

336

Well ID Elevation of water level in well

Elevation of accounting surface 

—interpolated

Difference in elevation between 

water level and accounting 

surface

4

8

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 

95-percent confidence interval)

Below accounting surface

Accounting surface

River aquifer

Accounting-surface contours—Number represents 

elevation of Colorado River within adjacent river 

aquifer

Contour—Number represents difference, in feet, 

between water-level and accounting-surface 

elevations

 -2

 -0.84

Well— 14 332.6

327.0

5.6

Figure 5. Areas interpolated above, below, and near the accounting surface in the Vidal area of California by using the 

Inverse Distance Weighted (power of 2) tool.
12 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

336

332

328

324

320

30 333.0 333.7

-0.7

32 332.6

333.8

-1.2

29 331.3

333.6

-2.3

27 331.6

333.1

-1.5

31 332.8

333.7

-0.9 28 332.6

333.6

-1.0

33 342.2

330.5

11.7

26 337.0

329.9

7.1

24 330.6

330.2

0.4

25 339.0

329.5

9.5

21 327.7

327.5

0.2

22 329.1

327.7

1.4

23 345.0

327.4

17.6

20 325.1

327.3

-2.2 17 327.7

327.0

0.7

16 327.6

326.9

0.7

14 332.6

327.0

5.6

15 327.1

326.7

0.4

19 324.8

327.2

-2.4

18 328.0

326.6

1.4

12 327.9

326.3

1.6

13 328.2

326.3

1.9

11 324.7

325.3

-0.6 10 324.7

325.3

8 330.3 -0.6

324.4

5.9

9 323.7

324.9

-1.2

5 321.8

323.6

-1.8

4 321.7

323.2

-1.5 2 321.8

322.8

-1.0

1 320.1

322.8

-2.7

3 321.4

323.1

-1.7

6 321.5

323.5

-2.0

7 322.9

324.1

-1.2

95

62

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

CALIFORNIA ARIZONA

Colorado

River

114°30' 114°22'

34°10'

34°04'

1

3

2

3

2

0 1 2 KILOMETERS 0.5

0 0.5 1 2 MILES

Vidal

Boundary of river aquifer

Boundary of river aquifer

EXPLANATION

1

2

3

0.84

2

336

Well ID Elevation of water level in well

Elevation of accounting surface 

—interpolated

Difference in elevation between 

water level and accounting 

surface

4

8

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 

95-percent confidence interval)

Below accounting surface

Accounting surface

River aquifer

Accounting-surface contours—Number represents 

elevation of Colorado River within adjacent river 

aquifer

Contour—Number represents difference, in feet, 

between water-level and accounting-surface 

elevations

 -2

 -0.84

Well— 14 332.6

327.0

5.6

Figure 6. Areas interpolated above, below, and near the accounting surface in the Vidal area of California by using the 

Spline (weight of 0.1) tool. 
Application of Geographic Information System Methods 13

Representations of areas above, below, and near (within 

± 0.84 ft) the accounting surface in the Vidal area are 

substantially different among the Natural Neighbor, IDW, 

and Spline tools, and result largely from the fundamentally 

different mathematical approaches used by each of these tools. 

Variations in the representations of these surfaces by these 

tools also are likely influenced by the limited number of wells 

(interpolation points) in comparison to the size of the area, 

the spatial distribution of the wells, and the location of wells 

with anomalous water-level elevations. Although all of the 

tools portray an area along the Colorado River where waterlevel elevations may be above or below (within ± 0.84 ft) 

the accounting surface, as might be expected, well control is 

sparse or nonexistent. Qualitatively, the Natural Neighbor tool 

appears to provide the best representation of the difference 

between the water-level elevation and the accounting surface 

in the Vidal area.

Chemehuevi Area 

Well Selection and Water-Level Measurements

Data for 39 wells in the Chemehuevi study area were 

compiled from the NWIS database, of which 6 wells did 

not have a measured static water level because of well 

obstructions, well status such as pumping, or because a 

measurement was not possible (landowner restriction, well 

had been destroyed, etc.). Water-level measurements in the 

remaining 33 wells were further evaluated on the basis of the 

date of the measurement and land-surface elevation accuracy. 

Most of the water levels in the data set were measured in 1996 

and 2000-01, with the oldest but most recent measurements for 

two wells made in 1962. The number of measurements taken 

in each well ranged from one to four. Water levels in all wells 

were measured with calibrated steel or electrical tapes that 

are accurate to within tenths or hundredths of a foot. Waterlevel measurements that were reported only to within 1-ft 

accuracy were not used. Water-level measurements that were 

determined to be substantially influenced by the effects of 

pumping of the well or a nearby well were not used. Wells that 

were reported to be pumped recently however, were evaluated 

on a well by well basis. As a result, 16 wells with water levels 

that were measured in 1996 and 2000-01 were selected for 

analysis. 

Calculated water-level elevations and interpolated 

accounting-surface elevations were determined for the 

16 selected wells completed in the river aquifer north of 

Chemehuevi Wash (table 2; at back of report). Water levels 

were measured in 11 wells between November 2000 and 

March 2001; however, because of the scarcity of wells in the 

area and the absence of recent water-level data, older waterlevel data were used to help understand relations between the 

elevation surfaces. Therefore, water-level elevations in the 

remaining five wells were based on measurements taken in 

1996. These water levels were observed to be consistent with 

elevation differences determined for nearby wells measured 

during 2000-01. Variations as large as 7 ft were noted for 

wells in which multiple measurements (at least three) had 

been taken, but variations for most wells generally were within 

about 2 ft over intervals of at least 10 years. Some fluctuations 

in water level may be the result of measurements being made 

shortly after pumping of the well or possibly from effects of 

pumping of nearby wells, and thus, may not represent static 

water-level conditions. 

Delineation of Areas

When the 95-percent confidence interval (± 0.84 ft) is 

taken into account, relative differences between water-level 

elevations and the accounting surface for the selected wells 

show distinct areas where the elevation of the water level is 

below the elevation of the accounting surface and where the 

elevation of the water level may be above or below (within 

± 0.84 ft) the elevation of the accounting surface. Areas 

where the elevation of the water level is above the elevation 

of the accounting surface appear to be localized. Because the 

accounting surface is presumed to be level in the vicinity of 

Lake Havasu, only one value, 449.6 ft, was used to represent 

the elevation of the accounting surface throughout the area 

(fig. 7). On the basis of the availability and distribution of 

wells within the river aquifer, these generalized areas were 

delineated between Chemehuevi Wash and the northern 

boundary of the river aquifer by using TIN Contour, Natural 

Neighbor, IDW, and Spline techniques (figs. 7-10). 

The area where the water-level elevation is above the 

elevation of the accounting surface is based only on two 

wells that are located in the southern part of the study area, 

just north of Chemehuevi Wash. The difference in elevation 

between the water level in well 3 and the accounting surface 

is 8.7 ft; this relation between the surfaces probably extends 

to the west where land-surface elevation is higher. An area 

where the water-level elevation also is above the accounting 

surface appears to be localized around well 4 just west of 

Lake Havasu. Calculated elevation differences for wells in 

the vicinity of well 4 however, are substantially below the 

elevation of the accounting surface. No apparent reason could 

be found for this anomalous difference using the available 

data. 
14 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

16 448.8

449.6

-0.8

15 448.5

449.6

-1.1

13 447.6

449.6

-2.0

14 449.4

449.6

-0.2

12 448.6

449.6

-1.0

10 448.9

449.6

-0.7 11 449.3

449.6

-0.3

9 450.0

449.6

0.4 8 450.4

449.6

0.8

7 447.2

449.6

-2.4

6 449.4

449.6

-0.2

4 452.2

449.6

2.6

5 447.0

449.6

-2.6

2 445.9

449.6

-3.7

1 447.4

449.6

-2.2

3 458.3

449.6

8.7

95

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

CALIFORNIA

ARIZONA

Colorado River

Boundary of river aquifer

EXPLANATION

1

2

3

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 95-percent 

confidence interval)

Below accounting surface

Accounting surface

Contour—Number represents difference, in feet, between 

water-level and accounting-surface elevations

 -2

 -0.84

Well—

1

2

3

Chemehuevi Indian Reservation boundary

34°30'

Chemehuevi Wash

Lake Havasu Lake Havasu

City

ARIZONA

CALIFORNIA

114°28' 114°20'

3

34°34'

Desert Hills

0 0.5 1 2 MILES

0 1 2 KILOMETERS 0.5

0.84

2

Well ID Elevation of water level in well

Elevation of accounting surface —interpolated

Difference in elevation between water level and 

accounting surface

4

8

16 448.8

449.6

-0.8

Figure 7. Areas interpolated above, below, and near the accounting surface in the Chemehuevi area of California by using 

the Triangulated Irregular Network Contour tool.
Application of Geographic Information System Methods 15

16 448.8

449.6

-0.8

15 448.5

449.6

-1.1

13 447.6

449.6

-2.0

14 449.4

449.6

-0.2

12 448.6

449.6

-1.0

10 448.9

449.6

-0.7 11 449.3

449.6

-0.3

9 450.0

449.6

0.4

8 450.4

449.6

0.8

7 447.2

449.6

-2.4

6 449.4

449.6

-0.2

4 452.2

449.6

2.6

5 447.0

449.6

-2.6

2 445.9

449.6

-3.7

1 447.4

449.6

-2.2

3 458.3

449.6

8.7

95

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

CALIFORNIA

ARIZONA

Colorado River

Boundary of river aquifer

EXPLANATION

1

2

3

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 95-percent 

confidence interval)

Below accounting surface

Accounting surface

Contour—Number represents difference, in feet, between 

water-level and accounting-surface elevations

 -2

 -0.84

Well—

1

2

3

Chemehuevi Indian Reservation boundary

34°30'

Chemehuevi Wash

Lake Havasu Lake Havasu

City

ARIZONA

CALIFORNIA

114°28' 114°20'

3

34°34'

Desert Hills

0 0.5 1 2 MILES

0 1 2 KILOMETERS 0.5

16 448.8

449.6

-0.8

0.84

2

Well ID Elevation of water level in well

Elevation of accounting surface —interpolated

Difference in elevation between water level and 

accounting surface

4

8

Figure 8. Areas interpolated above, below, and near the accounting surface in the Chemehuevi area of California by using 

the Natural Neighbor tool. 
16 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

16 448.8

449.6

-0.8

15 448.5

449.6

-1.1

13 447.6

449.6

-2.0

14 449.4

449.6

-0.2

12 448.6

449.6

-1.0

10 448.9

449.6

-0.7 11 449.3

449.6

-0.3

9 450.0

449.6

0.4 8 450.4

449.6

0.8

7 447.2

449.6

-2.4

6 449.4

449.6

-0.2

4 452.2

449.6

2.6

5 447.0

449.6

-2.6

2 445.9

449.6

-3.7

1 447.4

449.6

-2.2

3 458.3

449.6

8.7

95

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

CALIFORNIA

ARIZONA

Colorado River

Boundary of river aquifer

EXPLANATION

1

2

3

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 95-percent 

confidence interval)

Below accounting surface

Accounting surface

Contour—Number represents difference, in feet, between 

water-level and accounting-surface elevations

 -2

 -0.84

Well—

1

2

3

Chemehuevi Indian Reservation boundary

34°30'

Chemehuevi Wash

Lake Havasu Lake Havasu

City

ARIZONA

CALIFORNIA

114°28' 114°20'

3

34°34'

Desert Hills

0 0.5 1 2 MILES

0 1 2 KILOMETERS 0.5

0.84

2

16 448.8

449.6

-0.8

Well ID Elevation of water level in well

Elevation of accounting surface —interpolated

Difference in elevation between water level and 

accounting surface

4

8

Figure 9. Areas interpolated above, below, and near the accounting surface in the Chemehuevi area of California by using 

the Inverse Distance Weighted (power of 2) tool. 
Application of Geographic Information System Methods 17

16 448.8

449.6

-0.8

15 448.5

449.6

-1.1

13 447.6 449.6

-2.0

14 449.4

449.6

-0.2

12 448.6

449.6

-1.0

10 448.9

449.6

-0.7 11 449.3 449.6

-0.3

9 450.0

449.6

0.4

8 450.4

449.6

0.8

7 447.2

449.6

-2.4

6 449.4

449.6

-0.2

4 452.2

449.6

2.6

5 447.0

449.6

-2.6

2 445.9

449.6

-3.7

1 447.4

449.6

-2.2

3 458.3

449.6

8.7

95

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

CALIFORNIA

ARIZONA

Colorado River

Boundary of river aquifer

EXPLANATION

1

2

3

16 448.8

449.6

-0.8

Well ID Elevation of water level in well

Elevation of accounting surface —interpolated

Difference in elevation between water level and 

accounting surface

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 95-percent 

confidence interval)

Below accounting surface

Accounting surface

Contour—Number represents difference, in feet, between 

water-level and accounting-surface elevations

 -2

 -0.84

Well—

1

2

3

Chemehuevi Indian Reservation boundary

34°30'

Chemehuevi Wash

Lake Havasu Lake Havasu

City

ARIZONA

CALIFORNIA

114°28' 114°20'

3

34°34'

Desert Hills

0 0.5 1 2 MILES

0 1 2 KILOMETERS 0.5

0.84

2

4

8

Figure 10. Areas interpolated above, below, and near the accounting surface in the Chemehuevi area of California by using 

the Spline (weight of 0.1) tool.
18 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

The area where the water-level elevation is below the 

elevation of the accounting surface is in the southeastern part 

of the study area just north of Chemehuevi Wash and adjacent 

to Lake Havasu, and also in the northern part of the area 

(fig. 7). Well 7 may also represent an area where the water 

level is substantially below the accounting surface. Differences 

in elevation range from about -1.0 to -3.7 ft in well 2; however, 

the large difference associated with this well may be attributed 

to its close proximity to the lake where water levels may be 

influenced by lake fluctuations. The area where the elevation 

of the water level may be above or below the elevation of the 

accounting surface (on the basis of ± 0.84 ft at the 95-percent 

confidence interval) is located primarily in the northern part of 

the study area and along the western margin of the delineated 

area, on the basis of available well data. The boundary 

defining this area will change or shift over time as water levels 

fluctuate. Overall, in the Chemehuevi study area, the elevation 

of the water level in most wells is below or near (within ± 0.84 

ft) the elevation of the accounting surface. 

The TIN Contour and Natural Neighbor tools appear 

to accurately portray areas where water-level elevations are 

above, below, and near (within ± 0.84 ft) the accounting 

surface, and delineate areas where anomalies in the surface 

exist, such as around well 4 (figs. 7 and 8). Boundaries 

between areas where the elevation of the water level may be 

above or below the elevation of the accounting surface (on the 

basis of ± 0.84 ft at the 95-percent confidence interval) and 

areas that are above (greater than 0.84 ft) and below (less than 

-0.84 ft) the accounting surface also appear to be reasonably 

defined, on the basis of the distribution of wells in this area. 

However, well data are insufficient in a large part of the area to 

accurately portray relations between these surfaces. Contours 

delineated by the Natural Neighbor tool are considerably 

smoother than those delineated by TIN Contour.

The IDW tool using the default power option of 2 is 

represented in figure 9. The area that may be above or below 

(within ± 0.84 ft) the accounting surface is portrayed as 

larger than that delineated by the TIN Contour or Natural 

Neighbor tools, with a consequent decrease in size of the area 

where water-level elevations are below (less than -0.84 ft) 

the accounting surface, especially in the vicinity of well 7. 

However, well data are insufficient to accurately portray 

relations between the surfaces in much of the area. The IDW 

tool delineates the anomalous area around well 4, but the 

area around well 15, with a water-level elevation below the 

accounting surface, is not well defined. 

Boundaries delineated by the Spline tool using the default 

weight option (0.1) (fig. 10) are substantially different from 

those delineated by using the IDW, TIN, and Natural Neighbor 

tools, with a larger component of the area represented as 

where the water-level elevation is below (less than -0.84 ft) 

the accounting surface, with a consequent reduction in size of 

the area near (within ± 0.84 ft) the accounting surface. This 

substantial difference appears to be influenced by well 7, 

where the water-level elevation is 2.4 ft below the accounting 

surface. The Spline tool accurately delineates the anomalous 

area around well 4 and around wells in the northern part of the 

area where water-level elevations are below the accounting 

surface, but generates inliers (closed contours) in areas for 

which no well data are available.

Areas above, below, and near (within ± 0.84 ft) the 

accounting surface in the Chemehuevi area are represented 

differently among the TIN Contour, Natural Neighbor, IDW, 

and Spline tools. Although all of the tools portray a sizeable 

area where water-level elevations may be above or below 

(within ± 0.84 ft) the accounting surface, well control is 

sparse or nonexistent. Variations in the representations by 

each of these tools result in large part, from the fundamentally 

different mathematical approaches used by these tools. The 

relatively small number of wells (interpolation points) in 

comparison to the size of the area, the spatial distribution of 

the wells (most wells located in the northern and southern 

parts of the area), and the location of wells with anomalous 

water-level elevations also influence relations between the 

contoured surfaces. On the basis of the very limited data 

set, the Natural Neighbor tool appears to provide the best 

qualitative representation of the difference between the waterlevel elevation and the accounting surface in the Chemehuevi 

area.

Mohave Mesa Area

Well Selection and Water-Level Measurements

Data for 79 wells in the Mohave Mesa area were 

compiled from the NWIS database, of which 28 wells 

completed in the river aquifer did not have a measured 

static water level or else had a measured water level that 

was not static because of well obstructions or pumping 

effects. Four wells had anomalous water-level elevations 

that were substantially above or below calculated values for 

surrounding wells. Water-level measurements in the remaining 

47 wells were further evaluated on the basis of the date of 

the measurement and land-surface elevation accuracy. In the 

Mohave Mesa area, the most recent water-level measurements 

were made in 2006 in 30 of the wells. All of the water-level 

measurements in the vicinity of Bullhead City were made in 

1998. A few additional measurements were made in 1999, 

2002, 2003, and 2005. Land-surface elevation accuracies for 

six wells ranged from 5 to 20 ft (one-half the topographic map 

contour interval) and were not used for determining waterlevel elevations. Water levels for an additional six wells were 

reported only to an accuracy of 1 ft and were not used. Water 

levels in the remaining 35 wells were measured by using 

calibrated steel or electrical tapes that are accurate to within 

tenths or hundredths of a foot.
Application of Geographic Information System Methods 19

Calculated water-level elevations and interpolated 

accounting-surface elevations were determined for the 35 

selected wells completed in the river aquifer in the Mohave 

Mesa area (table 3; at back of report). Most of the water 

levels selected for analysis were measured in 2006 and in 

many instances, were the only values available. However, in 

some areas where recent water-level data are not available, 

such as in the vicinity of Bullhead City, older water-level data 

were used to help understand relations between the elevation 

surfaces. These data were observed to be consistent with 

measurements determined for nearby wells measured in 2006, 

or to be consistent with measurements taken in other wells in 

the area at the same time. 

Water-level variations observed in some wells are likely 

the result of measurements being made during or shortly after 

pumping of the well or pumping effects from nearby wells, 

and thus, do not represent static water-level conditions. The 

significance of these effects on a well-by-well basis was 

used in evaluating whether a well was selected for analysis. 

Measurements made sequentially on August 30, 2006, in a 

well located at NESENWS14 T19N R22W that likely shows 

the effects of pumping of a nearby well indicated depth to 

water of 154.75, 156.65, and 158.12 ft, showing a steady 

decline in the water level (U.S. Geological Survey, unpub. 

data, 2006). Water levels measured in another well located 

at SWNWNES15 T19N R22W on August 31, 2006, also 

show the effects of pumping, with sequential values of 82.68, 

83.72, and 85.96 ft. (U.S. Geological Survey, unpub. data, 

2006). Because these values do not represent static water-level 

conditions, they were not used in the analysis.

Delineation of Areas

 When the 95-percent confidence interval (± 0.84 ft) is 

taken into account, relative differences between water-level 

elevations and the accounting surface for the selected wells 

show that in virtually all of the study area, the elevation of the 

water level is below the elevation of the accounting surface. A 

small area is located near highway 153 where the elevation of 

the water level may be above or below (within ± 0.84 ft) the 

elevation of the accounting surface. Areas where the elevation 

of the water level is above the elevation of the accounting 

surface may not be present in the Mohave Mesa area. On the 

basis of the availability and distribution of wells within the 

river aquifer, these generalized areas were delineated between 

the accounting-surface elevations of 470 and 502 ft by using 

TIN Contour, Natural Neighbor, IDW, and Spline techniques 

(figs. 11-14).

In virtually all of the Mohave Mesa study area, the 

water-level elevation is below the elevation of the accounting 

surface. This includes the area near Bullhead City between 

the accounting-surface elevations of 488 and 502 ft and all 

wells between the accounting-surface elevations of 472 and 

478 ft, which generally are within a short distance of the river. 

Water-level elevations for selected wells between the contour 

intervals of 470 and 472 ft and more than 5 mi east of the river 

also are below the accounting surface. Differences in elevation 

between water levels in wells and the accounting surface range 

from about -2.0 to -11.3 ft, with most values exceeding -7.0 ft. 

However, water levels in a number of wells were reported to 

have been measured after the well had been recently pumped 

and therefore, may not represent static water-level conditions. 

Effects from nearby pumping wells may also result in 

differences between water-level elevations and the accounting 

surface that are considerably lower (more negative) than 

would exist under normal static conditions. The magnitude of 

the difference between elevations in this area indicates that 

water-level elevations in many wells may still be below the 

accounting surface when pumping effects are neglected.

An area where the elevation of the water level may be 

above or below the elevation of the accounting surface (on the 

basis of ± 0.84 ft at the 95-percent confidence interval) occurs 

between the 470- and 472-ft accounting-surface contours in 

the southern part of Mohave Mesa (fig. 11). This localized 

area is represented by wells 4 and 5, which have differences 

in elevation of -0.2 and -0.4 ft, respectively. An area where 

the elevation of the water level is above the elevation of the 

accounting surface may be present immediately to the north 

of these wells. A reported water-level measurement (1-ft 

accuracy) made in 1999 in one well in this area (not shown) 

results in a difference in elevation of about 6.0 ft, substantially 

higher than the 472-ft accounting-surface contour. The 

close proximity of wells in this area, and hence, potential 

interference between wells during pumping, may explain the 

range in variability (-0.1 to -7.9 ft) of differences between 

water-level and accounting-surface elevations. 

The TIN Contour and Natural Neighbor tools accurately 

delineate the small area where water-level elevations may 

be above or below (within ± 0.84 ft) the elevation of the 

accounting surface and also delineate a narrow area along 

the Colorado River west of Bullhead City (figs. 11 and 12). 

Power option 2 (default) in the IDW tool shows a considerably 

larger (wider) area along the Colorado River where the 

water-level elevation may be above or below the elevation 

of the accounting surface (fig. 13). This delineated area 

along the river likely results from the interpolation between 

the boundary of the river aquifer along the edge of the river 

(where the elevation of the river and the elevation of the water 

table in the river aquifer are assumed to be equal) and the 

considerably lower (more negative) water-level elevations in 

wells east of the river. However, no well data exist in this area 

to substantiate whether water-level elevations are near (within 

± 0.84 ft) the accounting surface. 
20 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

502

500

504

502

500

496

498

494

492

490

488

486

484

482

480

478

476

474

472

470

468

466

464

462

460

498

496

490

488

486

484

482

480

478

476

474

472

470

468

35 493.8

500.4

-6.6 34 497.0

501.6

-4.6

33 492.3

498.4

-6.1

32 487.3

498.1

-10.8

31 491.3

496.8

-5.5 29 485.1

493.9

-8.8

30 485.4

494.4

-9.0

28 480.7

490.6

-9.9

27 478.3

489.3

-11.0

20 469.3

476.5

-7.2

22 468.9

476.7

-7.8

21 469.6

476.7

-7.1

24 469.2

476.7

-7.5

18 469.3 476.5

-7.2

26 469.6

477.2

-7.6

23 466.0

476.8

-10.8

25 468.2

477.0

-8.8

19 468.6

476.5

-7.9

16 466.6

474.5

-7.9

15 467.0

474.5

-7.5

14 465.4

474.5

-9.1

17 468.5 476.2

-7.7 13 465.4

474.3

-8.9

12 466.4

473.8

-7.4

9 463.1

473.0

-9.9

11 465.5

473.6

-8.1

10 463.3

473.4

-10.1

8 461.5

472.8

-11.3

2 462.5

471.4

-8.9

7 469.7

471.7

-2.0

6 468.8

471.1

-2.3

1 468.6

470.8

-2.2

3 463.1

471.0

-7.9

4 470.7

470.9

-0.2

5 470.5

470.9

-0.4

153

68 163

95

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

NEVADA

CALIFORNIA

Colorado

River

Boundary of river aquifer

EXPLANATION

1

2

3

502

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 95-percent 

confidence interval)

Below accounting surface

Accounting surface

River aquifer

Accounting-surface contours—Number represents elevation of 

Colorado River within adjacent river aquifer

Contour—Number represents difference, in feet, between 

water-level and accounting-surface elevations

 -2

 -0.84

Well—

35°10'

114°40' 114°28'

2

3

3

2

35°00'

0 1 2 4 MILES

0 1 2 4 KILOMETERS

Davis Dam

Bullhead City

Piute Wash

0.84

2

4

8

34 497.0

501.6

-4.6

Well ID Elevation of water level in well

Elevation of accounting surface—interpolated

Difference in elevation between water level and 

accounting surface

CALIFORNIA

ARIZONA

NEVADA

ARIZONA

Boundary of river aquifer

Figure 11. Areas interpolated above, below, and near the accounting surface in the Mohave Mesa area of Arizona by using 

the Triangulated Irregular Network Contour tool.
Application of Geographic Information System Methods 21

502

500

504

502

500

496

498

494

492

490

488

486

484

482

480

478

476

474

472

470

468

466

464

462

460

496

498

490

488

486

484

482

480

478

476

474

472

470

468

35 493.8

500.4

-6.6 34 497.0

501.6

-4.6

33 492.3

498.4

-6.1

32 487.3

498.1

-10.8

31 491.3

496.8

-5.5

29 485.1

493.9

-8.8

30 485.4

494.4

-9.0

28 480.7

490.6

-9.9

27 478.3

489.3

-11.0

20 469.3

476.5

-7.2

22 468.9

476.7

-7.8

21 469.6

476.7

-7.1

24 469.2

476.7

-7.5

18 469.3

476.5

-7.2

26 469.6

477.2

-7.6

23 466.0

476.8

-10.8

25 468.2

477.0

-8.8

19 468.6

476.5

-7.9

16 466.6

474.5

-7.9 15 467.0

474.5

-7.5

14 465.4 474.5

-9.1

17 468.5

476.2

-7.7

13 465.4

474.3

-8.9

12 466.4

473.8

-7.4

9 463.1

473.0

-9.9

11 465.5

473.6

-8.1

10 463.3

473.4

-10.1

8 461.5

472.8

-11.3 2 462.5

471.4

-8.9

7 469.7

471.7

-2.0

6 468.8

471.1

-2.3 1 468.6

470.8

-2.2

3 463.1

471.0

-7.9

4 470.7

470.9

-0.2

5 470.5

470.9

-0.4

153

68 163

95

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

NEVADA

CALIFORNIA

Colorado

River

Boundary of river aquifer

EXPLANATION

1

2

3

502

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 95-percent 

confidence interval)

Below accounting surface

Accounting surface

River aquifer

Accounting-surface contours—Number represents elevation of 

Colorado River within adjacent river aquifer

Contour—Number represents difference, in feet, between 

water-level and accounting-surface elevations

 -2

 -0.84

Well—

35°10'

114°40' 114°28'

2

3

3

2

35°00'

0 1 2 4 MILES

0 1 2 4 KILOMETERS

Davis Dam

Bullhead City

Piute Wash

0.84

2

4

8

34 497.0

501.6

-4.6

Well ID Elevation of water level in well

Elevation of accounting surface—interpolated

Difference in elevation between water level and 

accounting surface

CALIFORNIA

ARIZONA

NEVADA

ARIZONA

Boundary of river aquifer

Figure 12. Areas interpolated above, below, and near the accounting surface in the Mohave Mesa area of Arizona by using 

the Natural Neighbor tool.
22 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

502

500

504

502

500

496

498

494

492

490

488

486

484

482

480

478

476

474

472

470

468

466

464

462

460

498

496

490

488

486

484

482

480

478

476

474

472

470

468

35 493.8

500.4

-6.6 34 497.0

501.6

-4.6

33 492.3

498.4

-6.1

32 487.3

498.1

-10.8

31 491.3

496.8

-5.5 29 485.1 493.9

-8.8

28 480.7

490.6

-9.9 27 478.3

489.3

-11.0

20 469.3

476.5

-7.2

22 468.9

476.7

-7.8

21 469.6

476.7

-7.1

24 469.2

476.7

-7.5

18 469.3

476.5

-7.2 23 466.0

476.8

-10.8

25 468.2

477.0

-8.8

16 466.6

474.5

-7.9

15 467.0 474.5

-7.5

14 465.4 474.5

-9.1

17 468.5 476.2

-7.7 13 465.4

474.3

-8.9

12 466.4

473.8

-7.4

9 463.1

473.0

-9.9

11 465.5

473.6

-8.1

10 463.3

473.4

-10.1

8 461.5

472.8

-11.3

2 462.5

471.4

-8.9

7 469.7

471.7

-2.0

6 468.8

471.1

-2.3

3 463.1

471.0

-7.9

4 470.7

470.9

-0.2

5 470.5

470.9

-0.4

30 485.4 494.4

-9.0

26 469.6

477.2

-7.6

19 468.6

476.5

-7.9

1 468.6

470.8

-2.2

153

68 163

95

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

NEVADA

CALIFORNIA

Colorado

River

Boundary of river aquifer

EXPLANATION

1

2

3

502

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 95-percent 

confidence interval)

Below accounting surface

Accounting surface

River aquifer

Accounting-surface contours—Number represents elevation of 

Colorado River within adjacent river aquifer

Contour—Number represents difference, in feet, between 

water-level and accounting-surface elevations

 -2

 -0.84

Well—

35°10'

114°40' 114°28'

2

3

3

2

35°00'

0 1 2 4 MILES

0 1 2 4 KILOMETERS

Davis Dam

Bullhead City

Piute Wash

0.84

2

4

8

34 497.0

501.6

-4.6

Well ID Elevation of water level in well

Elevation of accounting surface—interpolated

Difference in elevation between water level and 

accounting surface

CALIFORNIA

ARIZONA

NEVADA

ARIZONA

2

Boundary of river aquifer

Figure 13. Areas interpolated above, below, and near the accounting surface in the Mohave Mesa area of Arizona by using 

the Inverse Distance Weighted (power of 2) tool.
Application of Geographic Information System Methods 23

502

500

504

502

500

496

498

494

492

490

488

486

484

482

480

478

476

474

472

470

468

466

464

462

460

498

496

490

488

486

484

482

480

478

476

474

472

470

468

35 493.8

500.4

-6.6 34 497.0

501.6

-4.6

33 492.3 498.4

-6.1

32 487.3 498.1

-10.8

31 491.3

496.8

-5.5 29 485.1

493.9

-8.8

28 480.7

490.6

-9.9

27 478.3

489.3

-11.0

20 469.3 476.5

-7.2

22 468.9

476.7

-7.8

21 469.6

476.7

-7.1

24 469.2

476.7

-7.5

18 469.3 476.5

-7.2 23 466.0

476.8

-10.8

25 468.2

477.0

-8.8

16 466.6

474.5

-7.9

15 467.0

474.5

-7.5

14 465.4

474.5

-9.1

17 468.5

476.2

-7.7

13 465.4

474.3

-8.9

12 466.4

473.8

-7.4

9 463.1

473.0

-9.9

11 465.5

473.6

-8.1

10 463.3

473.4

-10.1

8 461.5

472.8

-11.3

2 462.5

471.4

-8.9

7 469.7

471.7

-2.0

6 468.8

471.1

-2.3

3 463.1

471.0

-7.9

4 470.7

470.9

-0.2

5 470.5

470.9

-0.4

30 485.4

494.4

-9.0

26 469.6

477.2

-7.6

19 468.6 476.5

-7.9

1 468.6

470.8

-2.2

153

68 163

95

Base from U.S. Geological Survey,1:100,000, digital data

Universal Transverse Mercator projection, Zone 11

NEVADA

CALIFORNIA

Colorado

River

Boundary of river aquifer

EXPLANATION

1

2

3

502

Area where elevation of water level in well is:

Above accounting surface

Above or below accounting surface (+/- 0.84 foot at 95-percent 

confidence interval)

Below accounting surface

Accounting surface

River aquifer

Accounting-surface contours—Number represents elevation of 

Colorado River within adjacent river aquifer

Contour—Number represents difference, in feet, between 

water-level and accounting-surface elevations

 -2

 -0.84

Well—

35°10'

114°40' 114°28'

2

3

3

2

35°00'

0 1 2 4 MILES

0 1 2 4 KILOMETERS

Davis Dam

Bullhead City

Piute Wash

0.84

2

4

8

34 497.0 501.6

-4.6

Well ID Elevation of water level in well

Elevation of accounting surface—interpolated

Difference in elevation between water level and 

accounting surface

CALIFORNIA

ARIZONA

NEVADA

ARIZONA

2

1

Boundary of river aquifer

Figure 14. Areas interpolated above, below, and near the accounting surface in the Mohave Mesa area of Arizona by using 

the Spline (weight of 0.1) tool.
24 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Areas delineated along the river where the water-level 

elevation may be above or below (within ± 0.84 ft) the 

accounting surface by using the default weight option (0.1) 

in the Spline tool are similar to those delineated by the IDW 

tool (fig. 14). The Spline tool also delineates the area between 

the 470- and 472-ft accounting-surface contours where the 

water-level elevation may be above or below the accounting 

surface. However, several other areas on Mohave Mesa, 

such as between the 474- and 476-ft and 482- and 484-ft 

accounting-surface contours, are delineated by the Spline tool 

as where the water-level elevation may be above (greater than 

0.84 ft) the accounting surface, but for which no well data 

exist (fig. 14). 

The observed patterns resulting from the application 

of the TIN Contour, Natural Neighbor, IDW, and Spline 

tools to delineate areas below the accounting surface in the 

Mohave Mesa area result largely from the fundamentally 

different mathematical approaches used by these tools. The 

spatial distribution of the wells, particularly the lack of well 

control in the area between the 478- and 488-ft accountingsurface contours, and the considerable range in difference in 

elevations between the water-level and accounting surfaces, 

also may contribute to the observed anomalies and variation 

in contouring among the interpolation tools. Qualitatively, 

the Natural Neighbor tool appears to provide the best 

representation of the difference between the water-level 

elevation and the accounting surface in the Mohave Mesa area.

 Summary and Conclusions

The U.S. Geological Survey, in cooperation with the 

Bureau of Reclamation, began this study to determine if 

wells located within the Colorado River aquifer outside the 

flood plain are pumping water that will be replaced by water 

from the Colorado River. Water pumped from wells along the 

flood plain of the river is presumed to be river water and is 

accounted for as Colorado River water. Water pumped from 

wells outside the flood plain of the river may or may not be 

accounted for as Colorado River water. Relations between the 

elevation of the static water level in wells and the elevation of 

the accounting surface within the Colorado River aquifer were 

used to determine which wells outside the flood plain of the 

river will yield water that will be replaced by water from the 

Colorado River. Wells that have a static water-level elevation 

equal to or below the elevation of the accounting surface are 

presumed to yield water that will be replaced by water from 

the Colorado River. 

Calculated water-level elevations and interpolated 

accounting-surface elevations were determined for 33 

wells completed in the river aquifer in the vicinity of Vidal, 

California, 16 wells on and adjacent to the Chemehuevi Indian 

Reservation, California, and 35 wells on Mohave Mesa, 

Arizona. Well data were obtained from the U.S. Geological 

Survey NWIS database. Water-level measurements generally 

were taken during the last 10 years with steel and electrical 

tapes accurate to within tenths or hundredths of a foot. A 

Differential Global Positioning System (DGPS) was used to 

determine land-surface elevations to within an operational 

accuracy of ± 0.43 ft, resulting in calculated water-level 

elevations having a 95-percent confidence interval of ± 0.84 ft. 

Thus, wells with a difference between the water-level elevation 

and accounting-surface elevation of greater than ± 0.84 ft have 

water levels that are either above or below the accounting 

surface, and wells with a difference of less than ± 0.84 ft have 

water levels that cannot be determined with at least 95-percent 

confidence, to be either above or below the accounting surface. 

ArcGIS Triangulated Irregular Network (TIN) Contour, 

Natural Neighbor, Inverse Distance Weighted (IDW), and 

Spline interpolation tools were used to create contours of the 

difference between the water-level and accounting-surface 

elevations. The contours delineate areas where water-level 

elevations are above, below, and near (within ± 0.84 ft at the 

95-percent confidence interval) the elevation of the accounting 

surface, on the basis of available well data.

In the Vidal area, differences in elevation range from 

1.4 to 17.6 ft above the accounting surface and range 

from -0.9 to -2.7 ft below the accounting surface. Relative 

differences between water-level elevations and the elevation 

of the accounting surface decrease from west to east (toward 

the river) and from north to south (along the river). In the 

Chemehuevi area just north of Chemehuevi Wash, differences 

in elevation in the area where the water-level elevation is 

below the elevation of the accounting surface range from about 

-1.0 to -3.7 ft. In the vicinity of Lake Havasu, the accounting 

surface is established at 449.6 ft. In most of the Mohave Mesa 

study area, the water-level elevation is below the elevation of 

the accounting surface. Differences in elevation between water 

levels and the accounting surface range from about -2.0 to 

-11.3 ft, with most values exceeding -7.0 ft. 

The TIN Contour and Natural Neighbor tools reasonably 

represent areas where the elevation of water levels in wells 

is above, below, and near (within ± 0.84 ft) the elevation of 

the accounting surface in the Vidal and Chemehuevi study 

areas and accurately delineate areas around outlying wells 

and where anomalous differences between water-level and 

accounting-surface elevations exist. Using the default options 

in ArcGIS, the IDW and Spline tools also reasonably represent 

areas above, below, and near the accounting surface in the 

Vidal and Chemehuevi areas. However, spatial extent of 

and boundaries between areas above, below, and near the 

accounting surface vary substantially between the IDW and 

Spline tools and those delineated by the TIN Contour and 

Natural Neighbor tools. Variations in the representations by 

the TIN Contour, Natural Neighbor, IDW, and Spline tools 

result largely from the fundamentally different mathematical 

approaches used by each of these tools. The limited number 

of wells selected for analysis, and hence interpolation points, 

in comparison to the size of the areas, the spatial distribution 

of the wells, and the locations and relative differences in 

elevation between water levels and the accounting surface 

of wells with anomalous water levels also influence the 

contouring variations observed among the methods. 
References Cited 25

Qualitatively, the Natural Neighbor tool appears to 

provide the best representation of the difference between 

water-level and accounting-surface elevations in the study 

areas when compared with the TIN Contour, IDW, and Spline 

tools in ArcGIS. Additional work to determine quantitatively 

which tool provides the best representation could be done 

and should include other tools available in ArcGIS as well 

as interpolation methods not available in ArcGIS. Semivariograms or sensitivity analysis on residuals also could be 

done for each of the study areas using geostatistical methods 

such as kriging. 

References Cited

Abramov, O., and McEwen, A., no date, An evaluation of 

interpolation methods for Mars Orbiter Laser Altimeter 

(MOLA) data: available on the World Wide Web, accessed 

October 2007, at http://pirlwww.lpl.arizona.edu/~abramovo/

MOLA_interpolation/MOLA_ interpolation_submitted_

paper.pdf

Bureau of Reclamation, 1989a, Flood frequency 

determinations of the lower Colorado River–Volume 1: 

Supporting hydrologic documents of the Colorado River 

Floodway Protection Act of 1986, 26 p.

Bureau of Reclamation, 1989b, Supporting hydrologic 

and hydraulic studies–Volume 2: Supporting hydrologic 

documents of the Colorado River Floodway Protection Act 

of 1986. 

Bureau of Reclamation, 1990, Flood routing and mapping 

procedures for the lower Colorado River–Summary report: 

Supporting hydrologic documents of the Colorado River 

Floodway Protection Act of 1986, 41 p.

Collins, Jr., F.C., 1996, A comparison of spatial interpolation 

techniques in temperature estimation: Third International 

Conference on Integrating GIS & Environmental Modeling, 

Santa Fe, New Mexico, January 21-25, 1996, conference 

proceedings available on the World Wide Web, accessed 

November 2007, at http://www.ncgia.ucsb.edu/conf/

SANTA_FE_CD-ROM/sf_papers/collins_fred/collins.html

de Smith, M.J., Goodchild, M.F., Longley, P.A., 2007, 

Geospatial analysis: A comprehensive guide to 

principles, techniques, and software tools: available 

on the World Wide Web, accessed November 2007, 

at http://www.spatialanalysisonline.com/output/html/

Comparisonofsamplegriddingandinterpolationmethods.html

Eckstein, B.A., 1989, Evaluation of spline and weighted 

average interpolation algorithms: Computers & 

Geosciences, v. 15, no. 1, p. 79-94.

Environmental Systems Research Institute, 2007a, ArcGIS 

desktop help, ArcGIS 3D analyst, release 9.2: available 

on the World Wide Web, accessed October 2007, 

at http://webhelp.esri.com/arcgisdesktop/9.2/index.

cfm?TopicName=How%20TIN%20Contour%20(3D%20

Analyst)%20works

Environmental Systems Research Institute, 2007b, ArcGIS 

desktop help, ArcGIS spatial analyst, release 9.2: available 

on the World Wide Web, accessed January 31, 2007, 

at http://webhelp.esri.com/arcgisdesktop/9.2/index.

cfm?TopicName=An_overview_of_the_ Interpolation_tools

Hutchinson, M.F., and Gessler, P.E., 1994, Splines—More 

than just a smooth interpolator: Geoderma, v. 62, p. 45-67.

Legates, D.R., and Willmott, C.J., 1990, Mean seasonal 

and spatial variability in global surface air temperature: 

Theoretical Applied Climatology, v. 41, p. 11-21.

Metzger, D.G., Loeltz, O.J., and Irelan, B., 1973, 

Geohydrology of the Parker-Blythe-Cibola area, Arizona 

and California: U.S. Geological Survey Professional Paper 

486-G, 130 p.

Owen, S., 1993, Subsurface characterization with threedimensional natural neighbor interpolation: available on the 

World Wide Web, accessed October 2007, at http://www.

andrew.cmu.edu/user/sowen/natneigh/index.html

Owen-Joyce, S.J., Wilson, R.P., Carpenter, M.C., and Fink, 

J.B., 2000, Method to identify wells that yield water 

that will be replaced by water from the Colorado River 

downstream from Laguna Dam in Arizona and California: 

U.S. Geological Survey Water-Resources Investigations 

Report 00-4085, 31 p., 3 pls.

Sibson, R., 1981, A brief description of natural neighbor 

interpolation, in Barnett, V., ed., Interpreting multivariate 

data: New York, John Wiley & Sons, p. 21–36.

United States Supreme Court, 2006, Consolidated Decree in 

Arizona v. California, 547 U.S. 150.

Watson, D., 1992, Contouring: A guide to the analysis and 

display of spatial data: Pergamon Press, London, England.

Western Regional Climate Center, 2007, Arizona 1971-2000 

monthly normals: Data from the National Climatic Data 

Center, available on the World Wide Web, accessed January 

31, 2007, at http://www.wrcc.dri.edu/summary/Climsmaz.

html

Wilson, R.P., and Owen-Joyce, S.J., 1994, Method to identify 

wells that yield water that will be replaced by Colorado 

River water in Arizona, California, Nevada, and Utah: U.S. 

Geological Survey Water-Resources Investigations Report 

94-4005, 36 p. 
26 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Table 1. Data for selected wells in the Vidal area, California—Continued.

Map ID Site ID Latitude Longitude

Land-net 

location

(Section-Township-Range)

Elevation of 

land surface

(feet above 

sea level)

Well depth

(feet below 

land surface)

Water-level 

measurement

date 

(year/month/day)

1 340330114282801 340329.73 1142828.79 SWSENES29 T01S R24E 415.6 110 19900919 

20010213 

2 340332114282801 340331.92 1142827.85 SWSENES29 T01S R24E 418 19900918 

20010213 

3 340335114285301 340334.58 1142854.37 SESENWS29 T01S R24E 426.8 20010208 

4 340340114283301 340339.65 1142833.16 NWSENES29 T01S R24E 426.2 132 20010213 

5 340342114282701 340343.7 1142825.65 SENENES29 T01S R24E 426.9 166 19900918 

20010208 

6 340347114284301 340348.86 1142840.7 NENWNES29 T01S R24E 438.9 19900920 

20010215 

7 340406114285301 340406.96 1142855.9 NESESWS20 T01S R24E 473.8 19900918 

20010208 

8 340414114285301 340414.52 1142853.14 SENESWS20 T01S R24E 488 185 19920731 

19920731 

20010208 

9 340422114274301 340422.46 1142743.63 SWSWNES21 T01S R24E 438.7 142 19900921 

19970425 

20010125 

10 340443114274901 340444.41 1142748.37 NENENWS21 T01S R24E 456.1 154.8 19900921 

19970425 

20010125 

11 340445114274701 340445.03 1142747.05 NWNWNES21 T01S R24E 455.2 20010125 

12 340525114274701 340525.99 1142746.62 NWSWNES16 T01S R24E 469.8 225 19640616 

19900921 

20001129 

20001129 

13 340526114274801 340525.76 1142747.86 NESENWS16 T01S R24E 470.8 224 20001129 

20001129 

14 340529114261601 340527.15 1142617.72 SENENES15 T01S R24E 418 19870917 

19900921 

19970425 

20001116 

15 340533114270601 340532.5 1142706.44 NENWNWS15 T01S R24E 448.4 234 19900922 

19970425 

20001114 

16 340538114265301 340538.59 1142652.71 NWNENWS15 T01S R24E 444.2 205 19611214 

19620223 

19620329 

19620523 

19900915 

19970610 

20001114 

Table 1. Data for selected wells in the Vidal area, California.

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level 

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Waterlevel method: S, steel tape; V, calibrated electric tape; U, unknown; Water-level elevation: Determined by difference between land-surface elevation at well and 

depth to water below land surface; Elevation of accounting surface: Refer to description in text; Difference in elevation: Determined by subtracting elevation 

of accounting surface from water-level elevation at each well]
Table 1 27

Map ID Site ID

Water level

(feet below 

land surface)

Water-level

accuracy

Water-level 

status

Water-level 

method

Water-level 

elevation

(feet above 

sea level)

Elevation of 

accounting 

surface

(feet above 

sea level)

Difference in 

elevation

(feet)

1 340330114282801 95.79 2 S

95.53 2 R V 320.1 322.8 -2.7

2 340332114282801 110.26 2 S

96.22 2 V 321.8 322.8 -1.0

3 340335114285301 105.43 2 V 321.4 323.1 -1.7

4 340340114283301 104.47 2 V 321.7 323.2 -1.5

5 340342114282701 105.11 2 S

105.13 2 V 321.8 323.6 -1.8

6 340347114284301 117.33 2 S

117.37 2 S 321.5 323.5 -2.0

7 340406114285301 155.69 2 R S

150.89 2 V 322.9 324.1 -1.2

8 340414114285301 157.02 2 S

157.03 2 S

157.67 2 V 330.3 324.4 5.9

9 340422114274301 114.73 2 S

113.86 2 V

115 2 V 323.7 324.9 -1.2

10 340443114274901 130.85 2 S

130.28 2 V

131.42 2 V 324.7 325.3 -0.6

11 340445114274701 130.51 2 V 324.7 325.3 -0.6

12 340525114274701 141.5 1 S

141.9 1 V

141.87 2 R S

141.87 2 R S 327.9 326.3 1.6

13 340526114274801 142.59 2 R S

142.61 2 R S 328.2 326.3 1.9

14 340529114261601 86.7 2 S

85.21 2 S

84.15 2 V

85.38 2 V 332.6 327.0 5.6

15 340533114270601 120.56 2 S

120.3 2 V

121.35 2 V 327.1 326.7 0.4

16 340538114265301 115.28 2 S

115.53 2 S

118.42 2 P S

121.36 2 S

115.57 2 S

115.35 2 V

116.6 2 V 327.6 326.9 0.7

Table 1. Data for selected wells in the Vidal area, California.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level 

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Waterlevel method: S, steel tape; V, calibrated electric tape; U, unknown; Water-level elevation: Determined by difference between land-surface elevation at well and 

depth to water below land surface; Elevation of accounting surface: Refer to description in text; Difference in elevation: Determined by subtracting elevation 

of accounting surface from water-level elevation at each well]
28 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Map ID Site ID Latitude Longitude

Land-net 

location

(Section-Township-Range)

Elevation of 

land surface

(feet above 

sea level)

Well depth

(feet below 

land surface)

Water-level 

measurement

date 

(year/month/day)

17 340546114271501 340545.72 1142715.83 NWSWSWS10 T01S R24E 462.3 306 19611214 

19620223 

19620329 

19620523 

19621107 

19630104 

19900922 

20001104 

18 340541114273801 340540.44 1142741.62 SWSWSES09 T01S R24E 467.5 19900922 

19970612 

20001129 

19 340551114271501 340552.1 1142715.64 NWSWSWS10 T01S R24E 461.6 19620223 

19620329 

19620523 

19620718 

19900922 

20001114 

20 340559114270001 340558.18 1142659.61 SWNESWS10 T01S R24E 448.7 19870917 

19900915 

19950412 

19950412 

19970610 

20001115 

21 340608114264901 340607.87 1142700.25 SESWNWS10 T01S R24E 460.6 241.5 19900917 

20001115 

20001115 

22 340614114270001 340614.23 1142700.24 NWSENWS10 T01S R24E 465.4 224 19610524 

19611213 

19640617 

19870917 

19900914 

19950412 

19970610 

20001115 

20001115 

23 340625114274301 340622.05 1142747.17 SWNWNES09 T01S R24E 502.8 365 19611213 

19900922 

20001129 

24 340654114251301 340653.65 1142513.14 NENESES02 T01S R24E 430.6 174 20001130 

20001130 

25 340706114261501 340709.89 1142612.33 NWSWNWS02 T01S R24E 480.3 20010213 

26 340707114254801 340707.46 1142547.53 NESENWS02 T01S R24E 457.9 202 20000211 

20010207 

27 340712114230201 340710.25 1142303.38 NESENES06 T01S R25E 350.4 19900914 

19950406 

20010207 

Table 1. Data for selected wells in the Vidal area, California.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level 

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Waterlevel method: S, steel tape; V, calibrated electric tape; U, unknown; Water-level elevation: Determined by difference between land-surface elevation at well and 

depth to water below land surface; Elevation of accounting surface: Refer to description in text; Difference in elevation: Determined by subtracting elevation 

of accounting surface from water-level elevation at each well]
Table 1 29

Map ID Site ID

Water level

(feet below 

land surface)

Water-level

accuracy

Water-level 

status

Water-level 

method

Water-level 

elevation

(feet above 

sea level)

Elevation of 

accounting 

surface

(feet above 

sea level)

Difference in 

elevation

(feet)

17 340546114271501 135.14 2 S

135.5 2 S

143.14 2 P S

152.58 2 P S

138.58 2 S

138.98 2 S

134.54 2 S

134.58 2 V 327.7 327.0 0.7

18 340541114273801 139.46 2 S

143.2 1 V

139.5 2 V 328.0 326.6 1.4

19 340551114271501 137.69 2 S

144.57 2 P S

149.02 2 P S

153.79 2 S

136.78 2 S

136.84 2 V 324.8 327.2 -2.4

20 340559114270001 121.6 1 V S

123.93 2 S

131.9 2 V S

132.8 2 V S

124.4 1 V V

123.59 2 V S 325.1 327.3 -2.2

21 340608114264901 133.03 2 S

132.92 2 S 327.7 327.5 0.2

132.97 2 V

22 340614114270001 148.14 2 S

138.61 2 S

141.6 1 S

134.9 2 S

136.51 2 S

138.67 2 S

136.35 2 V

136.06 2 S

136.26 2 S 329.1 327.7 1.4

23 340625114274301 159.32 2 S

158.14 2 S

157.77 2 V 345.0 327.4 17.6

24 340654114251301 99.95 2 S

99.96 2 S 330.6 330.2 0.4

25 340706114261501 141.31 2 V 339.0 329.5 9.5

26 340707114254801 123 0 U

120.86 2 V 337.0 329.9 7.1

27 340712114230201 16.91 2 S

16.36 2 S

18.78 2 S 331.6 333.1 -1.5

Table 1. Data for selected wells in the Vidal area, California.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level 

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Waterlevel method: S, steel tape; V, calibrated electric tape; U, unknown; Water-level elevation: Determined by difference between land-surface elevation at well and 

depth to water below land surface; Elevation of accounting surface: Refer to description in text; Difference in elevation: Determined by subtracting elevation 

of accounting surface from water-level elevation at each well]
30 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Map ID Site ID Latitude Longitude

Land-net 

location

(Section-Township-Range)

Elevation of 

land surface

(feet above 

sea level)

Well depth

(feet below 

land surface)

Water-level 

measurement

date 

(year/month/day)

28 340713114224601 340713.01 1142246.06 SWNENWS05 T01S R25E 350.8 19900914 

19950406 

20010207 

29 340713114224602 340713.84 1142246.17 SWNENWS05 T01S R25E 351.1 19900914 

20010207 

30 340714114224201 340713.46 1142242.72 SWNENWS05 T01S R25E 347.8 100 20010207 

31 340714114224301 340713.39 1142242.02 SWNENWS05 T01S R25E 347.5 20010207 

32 340714114224001 340714.16 1142240.13 SWNENWS05 T01S R25E 347.8 90 20010207 

33 340738114254301 340738.23 1142543.00 SENESWS35 T01N R24E 476 218 19611213 

19661018 

19900907 

19900924 

19950412 

20010206 

Table 1. Data for selected wells in the Vidal area, California.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level 

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Waterlevel method: S, steel tape; V, calibrated electric tape; U, unknown; Water-level elevation: Determined by difference between land-surface elevation at well and 

depth to water below land surface; Elevation of accounting surface: Refer to description in text; Difference in elevation: Determined by subtracting elevation 

of accounting surface from water-level elevation at each well]
Table 1 31

Map ID Site ID

Water level

(feet below 

land surface)

Water-level

accuracy

Water-level 

status

Water-level 

method

Water-level 

elevation

(feet above 

sea level)

Elevation of 

accounting 

surface

(feet above 

sea level)

Difference in 

elevation

(feet)

28 340713114224601 17.64 2 S

18.79 2 S

18.21 2 X V 332.6 333.6 -1.0

29 340713114224602 17.75 2 S

19.80 2 X V 331.3 333.6 -2.3

30 340714114224201 14.85 2 X V 333.0 333.7 -0.7

31 340714114224301 14.74 2 X V 332.8 333.7 -0.9

32 340714114224001 15.23 2 X V 332.6 333.8 -1.2

33 340738114254301 132.83 2 S

145.35 2 S

133.65 2 S

133.69 2 S

133.79 2 S

133.83 2 V 342.2 330.5 11.7

Table 1. Data for selected wells in the Vidal area, California.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level 

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Waterlevel method: S, steel tape; V, calibrated electric tape; U, unknown; Water-level elevation: Determined by difference between land-surface elevation at well and 

depth to water below land surface; Elevation of accounting surface: Refer to description in text; Difference in elevation: Determined by subtracting elevation 

of accounting surface from water-level elevation at each well]
32 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Table 2. Data for selected wells in the Chemehuevi area, California.

Map ID Site ID Latitude Longitude Land-net location

(Section-Township-Range)

Elevation of 

land surface

(feet above 

sea level)

Well depth

(feet below 

land surface)

Water-level 

measurement

date 

(year/month/day)

1 342846114243601 342845.83 1142435.29 SESESES36 T05N R24E 554.8 20010510 

2 342855114241501 342855.10 1142414.73 SENWSWS31 T05N R25E 457.4 19960313 

3 342857114253001 342857.17 1142530.22 SWNWSWS36 T05N R24E 612 400 19910130 

19910130 

19960314 

20010425 

20010425 

4 342859114243101 342858.82 1142430.37 SENESES36 T05N R24E 479.6 19960327 

20010522 

5 342902114244001 342901.65 1142439.46 NWNESES36 T05N R24E 520.1 19910202 

19910202 

19910202 

19960328 

20010522 

6 342931114241501 342930.98 1142415.18 NENWNWS31 T05N R25E 458.4 19960313 

20010508 

7 343030114242701 343029.87 1142426.81 SWSWSWS19 T05N R25E 512.4 19960312 

20000607 

8 343146114254101 343146.46 1142541.34 SWSENES14 T05N R24E 613 350 19960312 

20010524 

20010524 

20010524 

9 343159114254401 343158.76 1142543.79 SWNENES14 T05N R24E 618.2 300 19960206 

20000607 

10 343253114252601 343252.66 1142525.65 SWNWNWS12 T05N R24E 603.5 369 19950418 

19960206 

19960329 

20000606 

11 343258114251401 343257.92 1142514.30 NWNENWS12 T05N R24E 589.5 310 19950331 

19950418 

19960206 

19960315 

12 343307114251901 343306.76 1142518.40 SESWSWS01 T05N R24E 597.2 220 19910202 

19910202 

19960314 

20010508 

20010508 

13 343312114252101 343312.67 1142520.21 NESWSWS01 T05N R24E 604.1 198 19910202 

19910202 

19960313 

20010424 

20010424 

Table 2. Data for selected wells in the Chemehuevi area, California.

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Water-level 

method: S, steel tape; V, calibrated electric tape; R, reported; Water-level elevation: Determined by difference between land-surface elevation at well and depth 

to water below land surface; Elevation of accounting surface: For all wells, based on average stage of Lake Havasu; Difference in elevation: Determined by 

subtracting elevation of accounting surface from water-level elevation at each well]
Table 2 33

Map ID Site ID

Water level

(feet below 

land surface)

Water-level

accuracy

Water-level 

status

Water-level 

method

Water-level 

elevation

(feet above 

sea level)

Elevation of 

accounting 

surface

(feet above 

sea level)

Difference in 

elevation

(feet)

1 342846114243601 107.44 2 V 447.4 449.6 -2.2

2 342855114241501 11.47 2 V 445.9 449.6 -3.7

3 342857114253001 146.74 2 V 465.3

146.87 2 S 465.1

146.86 2 V 465.1

153.5 2 S 458.5

153.7 2 S 458.3 449.6 8.7

4 342859114243101 27.9 1 V 451.7

27.42 2 R V 452.2 449.6 2.6

5 342902114244001 74.96 2 V 445.1

75.07 2 S 445.0

75.07 2 S 445.0

74.01 2 V 446.1

73.15 2 V 447.0 449.6 -2.6

6 342931114241501 11.48 2 V 446.9

9.04 2 V 449.4 449.6 -0.2

7 343030114242701 64.67 2 V 447.7

65.21 2 S 447.2 449.6 -2.4

8 343146114254101 161.56 2 V 451.4

162.63 2 S 450.4

162.63 2 S 450.4 449.6 0.8

162.65 2 V 450.4

9 343159114254401 167.39 2 V 450.8

168.19 2 V 450.0 449.6 0.4

10 343253114252601 154.5 1 R 449.0

154.2 2 S 449.3

154.6 2 S 448.9 449.6 -0.7

158.35 2 V V 445.2

11 343258114251401 142 0 R 447.5

140 1 R 449.5

139.88 2 S 449.6

140.25 2 V 449.3 449.6 -0.3

12 343307114251901 148.97 2 V 448.2

149 2 S 448.2

148.65 2 V 448.6 449.6 -1.0

149.95 2 R S 447.3

149.97 2 R S 447.2

13 343312114252101 155.68 2 V 448.4

155.73 2 S 448.4

155.22 2 V 448.9

156.5 2 S 447.6

156.5 2 S 447.6 449.6 -2.0

Table 2. Data for selected wells in the Chemehuevi area, California.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Water-level 

method: S, steel tape; V, calibrated electric tape; R, reported; Water-level elevation: Determined by difference between land-surface elevation at well and depth 

to water below land surface; Elevation of accounting surface: For all wells, based on average stage of Lake Havasu; Difference in elevation: Determined by 

subtracting elevation of accounting surface from water-level elevation at each well]
34 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Map ID Site ID Latitude Longitude Land-net location

(Section-Township-Range)

Elevation of 

land surface

(feet above 

sea level)

Well depth

(feet below 

land surface)

Water-level 

measurement

date 

(year/month/day)

14 343312114250501 343312.86 1142504.88 NESESWS01 T05N R24E 572 200 19910202 

19910202 

19960328 

15 343320114242301 343319.53 1142422.58 SWNWSWS06 T05N R25E 466.5 250 19960312 

20010424 

20010424 

20010424 

16 343339114243001 343339.21 1142429.51 NESENES01 T05N R24E 467.4 88 20010425 

20010425 

Table 2. Data for selected wells in the Chemehuevi area, California.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Water-level 

method: S, steel tape; V, calibrated electric tape; R, reported; Water-level elevation: Determined by difference between land-surface elevation at well and depth 

to water below land surface; Elevation of accounting surface: For all wells, based on average stage of Lake Havasu; Difference in elevation: Determined by 

subtracting elevation of accounting surface from water-level elevation at each well]
Table 2 35

Map ID Site ID

Water level

(feet below 

land surface)

Water-level

accuracy

Water-level 

status

Water-level 

method

Water-level 

elevation

(feet above 

sea level)

Elevation of 

accounting 

surface

(feet above 

sea level)

Difference in 

elevation

(feet)

14 343312114250501 123.23 2 V 448.8

123.28 2 S 448.7

122.57 2 V 449.4 449.6 -0.2

15 343320114242301 18.27 2 X V 448.2

17.97 2 R S 448.5 449.6 -1.1

18.06 2 R S 448.4

18.4 2 R S 448.1

16 343339114243001 18.62 2 S 448.8

18.63 2 S 448.8 449.6 -0.8

Table 2. Data for selected wells in the Chemehuevi area, California.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude and 

sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; Water-level

accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; X, affected by surface-water site; V, foreign matter; P, pumping; Water-level 

method: S, steel tape; V, calibrated electric tape; R, reported; Water-level elevation: Determined by difference between land-surface elevation at well and depth 

to water below land surface; Elevation of accounting surface: For all wells, based on average stage of Lake Havasu; Difference in elevation: Determined by 

subtracting elevation of accounting surface from water-level elevation at each well]
36 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

Table 3. Data for selected wells in the Mohave Mesa area, Arizona.

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude 

and sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; 

Water-level accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; T, nearby recently pumped; S, nearby pumping; Waterlevel method: S, steel tape; V, calibrated electric tape; R, reported; Water-level elevation: Determined by difference between land-surface elevation at well 

and depth to water below land surface; Elevation of accounting surface: Refer to description in text; Difference in elevation: Determined by subtracting 

elevation of accounting surface from water-level elevation at each well]

Map ID Site ID Latitude Longitude Land-net location

(Section-Township-Range)

Elevation of 

land surface

(feet above 

sea level)

Well depth

(feet below

land surface)

Water-level 

measurement

 date 

(year/month/day)

1 345810114314801 345810.42 1143147.92 SWSESES05 T18N R21W 860.1 20060927 

2 345812114340601 345812.35 1143405.83 NESWSES01 T18N R22W 573.2 260 19980409 

3 345815114322001 345814.59 1143219.88 NWSESWS05 T18N R21W 802.1 400 20060926 

4 345816114315401 345816.4 1143153.74 NESWSES05 T18N R21W 851.2 20060927 

20040115 

5 345817114321001 345816.8 1143209.96 NESESWS05 T18N R21W 820.1 20060926 

6 345829114314301 345829.42 1143143.42 NENESES05 T18N R21W 883.1 487 20060928 

883.1 20051207 

7 345848114315501 345848.41 1143154.88 SENWNES05 T18N R21W 865.9 537 20060927 

20051226 

8 345911114352401 345911.33 1143523.62 SENESWS35 T19N R22W 532.9 150 20060802 

9 345922114352301 345921.6 1143523.17 NENESWS35 T19N R22W 538.6 126 20060804 

10 345944114352801 345943.88 1143528.15 NWNENWS35 T19N R22W 538.9 20060718 

11 345948114354001 345947.57 1143540.32 NENWNWS35 T19N R22W 538.6 160 20060718 

12 350004114345501 350004.2 1143454.59 SENESES26 T19N R22W 569.3 120 20060615 

13 350023114352101 350023.42 1143521.24 NESENWS26 T19N R22W 561.2 120 20060614 

14 350030114353301 350029.96 1143533.48 SWNENWS26 T19N R22W 553.3 20060126 

553.3 20060126 

15 350031114354601 350030.68 1143545.57 SWNWNWS26 T19N R22W 545.2 100 20060125 

16 350034114353201 350033.64 1143531.94 SWNENWS26 T19N R22W 556.1 20060222 

17 350139114360401 350139.02 1143604.4 SWSESES15 T19N R22W 552.6 20060915 

18 350147114362001 350147.31 1143619.52 SWNWSES15 T19N R22W 545.6 108 20060912 

19 350148114355101 350146.69 1143533.62 NWSESWS14 T19N R22W 594 230 19690611 

19900626 

20060112 

20 350152114361401 350152.44 1143614.46 SWNWSES15 T19N R22W 549.6 125 20060913 

20020913 

21 350157114360801 350157.08 1143607.84 NENWSES15 T19N R22W 554.9 125 20060913 

22 350157114360802 350156.73 1143608.18 NENWSES15 T19N R22W 554.2 115 20060915 

23 350200114331201 350159.64 1143311.76 NWNWSWS18 T19N R21W 845.1 450 19980604 

24 350206114360701 350206.41 1143606.68 SESWNES15 T19N R22W 555.7 120 20060823 

25 350210114352401 350209.63 1143523.79 NESENWS14 T19N R22W 635.3 220 20060830 

635.3 20060830 

26 350220114352701 350220.46 1143526.94 NENENWS14 T19S R22W 630.6 185 20060810 

27 350618114360501 350617.08 1143605.92 SWNENES20 T20N R22W 588.1 390 19980604 

28 350618114360301 350619.38 1143601.43 SWNENES20 T20N R22W 602.9 19980604 

29 350649114340001 350649.35 1143357.89 SWSESES13 T20N R22W 714.2 340 19980529 

30 350649114344901 350649.52 1143447.52 NWNESES16 T20N R22W 701.0 600 19980529 

31 350728114330001 350728.35 1143300.33 NESWNES18 T20N R21W 830.8 450 19980528 

32 350758114323601 350757.68 1143236.38 SWNWSWS08 T20N R21W 860.6 900 19980603 

33 350833114314601 350832.92 1143145.96 SWSESES05 T20N R21W 1,121.4 1,212 19980528 

34 350951114331001 350952 1143310 NESENES31 T21N R21W 696.1 405 19980527 

35 351015114305901 351016 1143059 NWSWSWS27 T21N R21W 1,225.1 1,080 19980515 
Table 3 37

Map ID Site ID

Water level

(feet below 

land surface)

Water-level

accuracy

Water-level 

status

Water-level 

method

Water-level 

elevation

(feet above 

sea level)

Elevation of 

accounting 

surface 

(feet above 

sea level)

Difference in 

elevation

(feet)

1 345810114314801 391.55 2 V 468.6 470.8 -2.2

2 345812114340601 110.7 1 R 462.5 471.4 -8.9

3 345815114322001 339 2 V 463.1 471.0 -7.9

4 345816114315401 380.46 2 V 470.7 470.9 -.2

380 0 R

5 345817114321001 349.6 2 V 470.5 470.9 -.4

6 345829114314301 414.31 2 T V 468.8 471.1 -2.3

410 0 R

7 345848114315501 396.16 2 V 469.7 471.7 -2.0

411 0 R

8 345911114352401 71.41 2 V 461.5 472.8 -11.3

9 345922114352301 75.51 2 V 463.1 473.0 -9.9

10 345944114352801 75.64 2 V 463.3 473.4 -10.1

11 345948114354001 73.08 2 V 465.5 473.6 -8.1

12 350004114345501 102.9 2 R V 466.4 473.8 -7.4

13 350023114352101 95.85 2 R V 465.4 474.3 -8.9

14 350030114353301 87.89 2 S

87.9 2 S 465.4 474.5 -9.1

15 350031114354601 78.16 2 V 467.0 474.5 -7.5

16 350034114353201 89.48 2 V 466.6 474.5 -7.9

17 350139114360401 84.12 2 S V 468.5 476.2 -7.7

18 350147114362001 76.35 2 V 469.3 476.5 -7.2

19 350148114355101 123.5 2 S

122.49 2 V

125.45 2 V 468.6 476.5 -7.9

20 350152114361401 80.31 2 V 469.3 476.5 -7.2

78 0 R

21 350157114360801 85.34 2 R V 469.6 476.7 -7.1

22 350157114360802 85.34 2 R V 468.9 476.7 -7.8

23 350200114331201 379.06 2 V 466.0 476.8 -10.8

24 350206114360701 86.47 2 R V 469.2 476.7 -7.5

25 350210114352401 167.08 2 R S

167.1 2 R S 468.2 477.0 -8.8

26 350220114352701 160.98 2 V 469.6 477.2 -7.6

27 350618114360501 109.89 2 S 478.3 489.3 -11.0

28 350618114360301 122.25 2 V 480.7 490.6 -9.9

29 350649114340001 229.1 2 V 485.1 493.9 -8.8

30 350649114344901 215.58 2 V 485.4 494.4 -9.0

31 350728114330001 339.51 2 S 491.3 496.8 -5.5

32 350758114323601 373.31 2 V 487.3 498.1 -10.8

33 350833114314601 629.07 2 V 492.3 498.4 -6.1

34 350951114331001 199.18 2 V 497.0 501.6 -4.6

35 351015114305901 731.28 2 V 493.8 500.4 -6.6

Table 3. Data for selected wells in the Mohave Mesa area, Arizona.—Continued

[Site ID: 15-digit numeric identifier in U.S. Geological Survey National Water Information System (NWIS) database. Number is based on latitude-longitude 

and sequence number; Latitude and Longitude: Expressed in degrees, minutes, and decimal seconds; Land-net location: Refer to description in text; 

Water-level accuracy: 0, feet; 1, 0.1 foot; 2, 0.01 foot; Water-level status: R, recently pumped; T, nearby recently pumped; S, nearby pumping; Waterlevel method: S, steel tape; V, calibrated electric tape; R, reported; Water-level elevation: Determined by difference between land-surface elevation at well 

and depth to water below land surface; Elevation of accounting surface: Refer to description in text; Difference in elevation: Determined by subtracting 

elevation of accounting surface from water-level elevation at each well]
38 Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona

This page intentionally left blank.
Manuscript approved for publication, December 18, 2007

For more information concerning the research in this report, contact 

Director, Utah Water Science Center 

U.S. Geological Survey 

2329 W. Orton Circle

Salt Lake City, Utah 84119

http://ut.water.usgs.gov
Spangler and others—Geographic Information System Methods, Colorado River, Vidal and Chemehuevi, California, and Mohave Mesa, Arizona—Scientific Investigations Report 2007–5284