U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2009–3050

June 2009

Availability of Groundwater Data for California, Water Year 2008

Printed on recycled paper

INTRODUCTION

The U.S. Geological Survey, Water 

Resources, in cooperation with Federal, 

State, and local agencies, obtains a large 

amount of data pertaining to the 

groundwater resources of California each 

water year (October 1–September 30). 

These data constitute a valuable database 

for developing an improved understand‐

ing of the water resources of the State. 

This Fact Sheet serves as an index 

to groundwater data for water year 2008. 

The 2‐page report contains a map of 

California showing the number of wells 

(by county) with available water-level 

and water-quality data for water year 

2008 (fig. 1) and instructions for obtain‐

ing this and other groundwater informa‐

tion contained in the databases of the 

U.S. Geological Survey, California Water 

Science Center. 

From 1985 to 1993, data were 

published in the annual report “Water 

Resources Data for California, Volume 5. 

Ground-Water Data”; prior to 1985, the 

data were published in U.S. Geological 

Survey Water-Supply Papers.

HYDROLOGIC CONDITIONS

Because the geography and geology 

of California are so complex, 

groundwater conditions are difficult 

to summarize. Groundwater levels are 

affected by short- and long-term climatic 

conditions and also by groundwater 

withdrawals, irrigation returns, and other 

factors.

DATA COLLECTION

WATER-LEVEL MEASUREMENTS

Water-level measurements are made 

in many types of wells under varying 

conditions using standard methods and 

equipment to ensure that the measure‐

ments are consistently accurate and 

reliable. All water levels in the California 

database are given in feet with reference 

to land-surface datum.

WATER-QUALITY MEASUREMENTS

The quality of groundwater ordinar‐

ily changes slowly; therefore, a single 

annual sampling usually is sufficient to 

define groundwater quality in most set‐

tings. In special circumstances, such as 

studying the effects of artificial recharge, 

more frequent sampling may be done to 

identify the nature of rapid changes in 

groundwater quality.

WELL-NUMBERING SYSTEM

Wells and springs in California are 

assigned numbers according to their 

location in the rectangular system for the 

subdivision of public land. For example, 

in the number 005S012E22P001M (see 

well-numbering diagram), the first four 

characters indicate the township (T. 5 S.), 

and the next four characters indicate the 

range (R.12 E.); the two digits follow‐

ing the range indicate the section (sec. 

22); and the letter following the section 

indicates the 40-acre subdivision of the 

section. Within each 40-acre subdivision, 

the wells are numbered sequentially in 

the order in which they were invento‐

ried, as indicated by the last three digits. 

For springs, the first of these last three 

digits is assigned the letter ‘S’. The final 

letter indicates the baseline and merid‐

ian designation as follows: H, Humboldt; 

M, Mount Diablo; S, San Bernardino. 

This 15-digit number is called the Local 

Number or State Well Number.

DATA AVAILABILITY

Current and historical water data, 

including real-time data, for California 

and the United States may be accessed 

directly through the USGS National 

Water Information Website (NWISWeb) 

at: 

http://waterdata.usgs.gov/

 

For more information on how to obtain 

data, contact: 

Mary Ray, 619-225-6440 

(mray@usgs.gov)

or 

Tom Haltom, 916-278-3061

(tchaltom@usgs.gov).

A B C D 

E F G H 

K L M J 

N P Q R 

22 

005S012E22P001M 

1 2 3 4 5 6 

7 8 9 10 11 12 

16 17 18 15 14 13 

19 20 21 22 23 24 

30 29 28 27 26 25 

31 32 33 34 35 36 

MT DIABLO BASE LINE MT DIABLO MERIDIAN 

1 1 1 

2 

3 

4 

5 

6 

1 

2 11 12 13 

NORTH 

WEST EAST 

SOUTH 

TOWNSHIP GRID 

TOWNSHIP 5 SOUTH 

RANGE 12 EAST 

SECTION 22 

Well-numbering system.
For more information on water resources 

in California visit the USGS website at:

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

or contact:

Mary Ray (mray@usgs.gov)

Technical Information Specialist

U.S. Geological Survey California Water Science Center

San Diego Projects Office

4165 Spruance Road, Suite 200

San Diego, CA 92101

Figure 1. The number of wells for the 2008 water year for which 

data are available, by county.

Access this Fact Sheet and other U.S. Geological Survey 

Publications at 

http://pubs.usgs.gov/

Yolo

4/2

Ventura

1/1

Tuolumne

0/8

Madera

7/34 Fresno

28/11

Mariposa

0/5

Tulare

9/12

Trinity

Humboldt

Tehama

4/45

17/13 Sutter

Stanislaus

13/3

Solano

0/2

Siskiyou

Del

Norte

Sierra

Yuba

1/2

Shasta

3/21

Santa

 Cruz

0/4

Santa Clara

0/9

Santa

Barbara

393/112

San

Mateo

San

Luis

Obispo

22/26

San

Joaquin

42/26

San Francisco

San Diego

50/28

San Bernardino

1,073/204

San

Benito

0/10

Sacramento

9/17

Riverside

147/48

Plumas

0/5

Placer

3/7

11/5

Orange 

Nevada 

0/3

0/2

Sonoma

0/5 Napa

0/7

Marin

Monterey 0/4

Mono

26/4

Modoc

Merced

13/8

Los Angeles

172/85

Lassen

0/1

Lake 

Kings

3/0

Kern

95/48

Inyo

0/5

Imperial

67/20

Glenn

13/2

Mendocino

El Dorado

0/9

Contra

Costa

Colusa

4/1

Calaveras

0/1

Butte

6/3

Amador 0/2

Alameda

6/8

Alpine

0/2

NOTE: The number preceding the slash (/) indicates 

the number of wells with water-level data; the number 

following the slash indicates the number of wells 

with water-quality data.