CALIFORNIA

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EXPLANATION

Fault

Line of equal probability .

 Interval is 20 percent

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Modified from the original created by Southern California Earthquake Center

Garlock Fault

Fault

San

San

San

San Gabriel

Andreas Fault Zone

Jacinto

Andreas

Fault

Fault

Zone

Bakersfield

Barstow

Palmdale

San Bernardino

El Centro

MEXICO

San Diego

Oceanside

Santa Ana 

Los Angeles

Santa Barbara

Santa Maria

San Luis Obispo

Parkfield

Study area

Santa Rosa

 Island

Santa Catalina

 Island

PACIFIC OCEAN

UNITED STATES

The U.S. Geological Survey (USGS) has 

been mapping and studying California’s natural resources and hazards for more than 100 

years. In this time, the State population has 

grown from less than 1 million to more than 30 

million, which has increased demands on resources and exposed more people to natural 

hazards. Many population centers are in areas 

of natural hazards. Population growth, combined with development in arid and semiarid 

regions of the State, has stressed California’s 

water resources. USGS information is available to help people understand and deal with 

natural hazards and water-supply stresses.

Earthquakes

Although most major population centers in 

California are in seismically active areas, no 

earthquake in the past few decades has approached the maximum anticipated magnitudes. The principal earthquake hazard is the 

damage or collapse of buildings or of the infrastructure. The USGS, in cooperation with the 

California Department of Conservation’s Division of Mines and Geology (CDMG), the California Institute of Technology, and the Southern California Earthquake Center is collecting 

ground-motion data to produce regional riskassessment maps that provide estimates of the 

probability of significant ground movement 

(fig. 1). These maps are used by Federal, State, 

and local agencies as a basis for building codes 

and land-use zoning that can reduce loss of life 

and property.

In the San Francisco Bay region, USGS 

scientists are collaborating with the California 

Department of Transportation to improve the 

seismic safety of six bridges that cross San 

Francisco and San Pablo Bays. Deep core sediment samples collected beside the bridge 

foundations are being analyzed to determine 

the capability of the sediment to support the 

foundations during earthquake shaking. The 

USGS study uses geographic information system computer modeling to evaluate the spatial 

variation of sediment properties beneath these 

bridges.

Floods

Floods are a perennial concern for much of 

California, and flood forecasting is an essential 

part of flood management. The ability to 

predict flood frequency and magnitude depends on long-term, continuous records at 

many widespread sites. The USGS, in cooperation with Federal, State, and local water 

agencies, operates or reviews data for about 

1,000 surface-water stations throughout California. Data collected are used by those water 

agencies to design measurable, effective, and 

economically sound programs and practices 

for flood protection. Strategically located 

streamflow-gaging stations equipped with automatic recording instruments are connected 

to computerized flood-warning systems. Water 

levels, precipitation, and other data can be accessed by computer from anywhere.

Volcano Hazards

USGS scientists are closely monitoring 

California’s active and potentially active volcanos. Mount Shasta and Lassen Peak have 

been active historically and there are several 

geologically young volcanic systems, such as 

Medicine Lake Volcano in northern California 

and Long Valley Caldera on the eastern Sierra 

Nevada front. USGS scientists are updating 

hazards assessments of Lassen Peak, Mount 

Shasta, and Medicine Lake Volcanoes. Magma 

intrusion and seismic activity at Long Valley 

Caldera have been closely monitored by the 

USGS as part of the Volcano Hazards Program 

since 1978. Since May 1989, USGS scientists 

have detected and are studying the increased 

emission of carbon dioxide gas of volcanic origin in the southwestern part of the Caldera.

Index of Subjects

Earthquakes

Floods

Volcano Hazards

Landslides and Mudflows

San Francisco Bay/Delta System

Marine Wastes

National Marine Sanctuary

Water Quality

Water Supply

Saltwater Intrusion

Geologic Resources

Mining Byproducts

Sources Of Mercury 

Biological Resources

Resource Assessment

Sierra Nevada Ecosystem

Topographic Mapping

Earth Science Information Centers

Figure 1. Lines of equal probability, in percent, of earthquake-caused earth movement capable 

of significant damage in the next 30 years; these lines represent a measure of risk.

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

U.S. Geological Survey

Programs in California
USGS study area

USGS study site

EXPLANATION

San Francisco

Bay/Delta

Sacramento–

San Joaquin Delta

Antelope Valley

Salton Sea

Wolf Valley

Edwards Air Force Base

Oxnard Plain U.S. Marine

Corps Base Santa Ana Basin

Mojave River

Los Angeles

San Bernardino Basin

Santa Barbara

Iron Mountain Mine

Klamath Basin

Penn Mine

Yosemite CENTRAL VALLEY

Sacramento Basin

San Joaquin–Tulare Basin

Farallon

Islands

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NEVADA

Cache Creek

Monterey Bay

The world’s largest producing geothermal 

field, The Geysers near Santa Rosa, produces 

sufficient power to meet San Francisco’s 

electrical needs despite recent reductions in 

commercial generating capacity. The geothermal component of the Volcano Hazards Program includes studies at The Geysers.

Landslides and Mudflows

Landslides and mudflows are common in 

California because of active mountain-building processes, rock characteristics, earthquakes, and periodic intense storms. By using 

earthquake information and geologic data 

bases, USGS scientists, in cooperation with 

the CDMG and the private sector, have created a computer-generated landslide location 

map of the Los Angeles area. They are now 

working on landslide-hazard maps that show 

the slopes most likely to fail in earthquakes. 

The identification of areas that are likely to 

produce landslides in conjunction with earthquakes or severe storms enables the public, 

urban planners, and the private sector to 

address these conditions as part of any future 

development.

San Francisco Bay/Delta System

The Sacramento–San Joaquin Delta system (fig. 2) is a vital hydrologic link in California’s water supply, and it has been one of 

the most productive estuarine wetland systems on the West Coast. During the past 150 

years, the Bay/Delta system has been greatly 

modified by human activities. The Delta system is the habitat of two threatened fish species and several additional species of 

concern, and the perceived environmental 

consequences to them are constraining hydrologic use of the Delta as part of California’s 

water delivery system.

The USGS provides information for two 

related interagency programs, the CALFED 

Bay-Delta Program, which addresses longterm solutions to the Bay/Delta system’s 

problems, and the Interagency Ecological 

Program (IEP). The IEP is a cooperative 

study by nine agencies that has generated 

much knowledge about fish populations in the 

Bay/Delta system. The USGS provides to this 

program an improved understanding of the 

circulation and mixing of fresh and saline 

waters that affect water quality and fish reproduction and growth.

Additional USGS studies evaluate Delta 

island subsidence and discharges that affect 

drinking water quality in southern California, 

measure suspended sediment and contaminant movements and pesticide transport 

through the Delta, and investigate wetland 

functioning and dredge spoil suitability for 

wetland restoration. Results of these studies 

provide a better understanding of the physical, chemical, and biological factors that 

cause ecological and water-quality problems, 

and are used to reestablish functional tidal 

wetlands in the estuary.

Marine Wastes

Wastes generated by human activities have 

been relocated to the ocean floor off the California coast. Between 1946 and 1970, as many 

as 47,800 containers of low-level radioactive 

waste were dumped on the Continental Shelf, 

many west of the Gulf of the Farallons 

National Marine Sanctuary. The USGS, in 

cooperation with several Federal agencies, has 

developed computer-enhanced sidescan 

images useful for locating drums and other 

objects. Results of this work can be used by 

environmental, military, and fisheries-management agencies to manage waste disposal 

and to identify areas critical to fish populations.

The USGS, in cooperation with Federal 

and State agencies, has identified the distribution and character of effluent-affected marine 

sediment on the Continental Shelf south of 

Los Angeles and have modeled its calculated 

natural recovery during the next century. This 

information is used by Federal, State, and local agencies to develop and evaluate longterm management options for contaminated 

sediments.

National Marine Sanctuary

The Monterey Bay National Marine Sanctuary, south of San Francisco, is the largest 

marine sanctuary in the United States. Its 

15,000 square miles are home to a rich diversity of marine life and include Monterey Canyon, a submarine feature that rivals the Grand 

Canyon in topographic relief and complexity. 

The USGS, in cooperation with the National 

Oceanic and Atmospheric Administration and 

other Federal and State agencies, is studying 

the sanctuary to understand links among living resources, the physical environment, and 

human influences. USGS studies include detailed geologic mapping, and modeling sediment movement across the Continental Shelf 

and down the Canyon. The relations among 

fault lines, fluid seeps, and carbonate crusts 

are being discovered and are important to the 

distribution of clams on the ocean floor. A detailed understanding of these geologic processes will assist in the wise management of 

the Sanctuary. 

Water Quality

Historically, water quantity and distribution have been central issues in California because most water use is in semiarid areas. Because water quality has recently become a 

major concern, the USGS, in cooperation with 

State and local water agencies, is assessing 

the quantity and quality of California’s water, 

Figure 2. Selected U.S. Geological Survey water-resources study areas, California.
especially in the Central Valley, the San 

Francisco Bay/Delta system, and the rapidly 

growing urban areas of southern California.

The USGS studies water quality in the San 

Joaquin–Tulare, the Sacramento, and the 

Santa Ana River Basins for the National Water-Quality Assessment Program. These longterm studies of water quality trends are designed to provide a sound scientific understanding of the natural and human factors that 

affect water quality. They are conducted in cooperation with Federal, State, and local agencies and other interested parties that participate on advisory committees and provide 

historical and current information and guidance on the priorities for studies and reports.

Water Supply

Throughout southern California, local 

water supplies are limited, and much of the 

water is imported from northern California, 

the Colorado River, and Owens Valley. Aquifers provide storage for the imported and 

local water supplies. Increasingly, watermanagement agencies are concerned with 

making better use of existing and future supplies. The USGS is studying a comprehensive 

approach to integrated watershed management, which includes surface- and groundwater resources. The USGS, in cooperation 

with the Water Replenishment District of 

Southern California, is evaluating the effects 

of recharge on ground-water quality in the 

Los Angeles area. The results are being used 

by the District to develop water-quality criteria for artificial ground-water recharge that 

uses reclaimed wastewater and to identify 

specific characteristics of recharge sites that 

contribute to contaminant reduction.

In parts of San Bernardino and Riverside 

Counties, water-management agencies anticipate large increases in demand for water early 

in the next century. The USGS, in cooperation 

with these agencies, is engaged in studies that 

are designed to characterize hydrogeologic 

conditions in areas that appear to have good 

potential for water banking (recharging 

ground-water systems for future pumping) or 

where ground-water quality may be subject to 

degradation from land-use practices or other 

causes. 

The Mojave Desert region has one of the 

most rapidly growing populations in California. As a result, water is becoming more 

scarce, and ground-water resources are frequently pumped at rates that far exceed natural recharge. The USGS, in cooperation with 

the Mojave Water Agency, is investigating the 

surface- and ground-water relations along the 

Mojave River, which is the principal source 

of ground-water recharge. Study results are 

aiding water-management agencies in the 

efficient management of ground-water 

resources.

Saltwater Intrusion

Intensive ground-water pumping in coastal 

areas has contributed to aquifer saltwater intrusion. The USGS is investigating the potential for saltwater intrusion into coastal aquifers in Ventura and Santa Barbara Counties. 

USGS ground-water models are used with 

water-supply optimization techniques by State 

and local agencies to develop management 

strategies for controlling saltwater intrusion 

and accommodating water demands. Water 

managers are using the study results to modify recharge, pumping, and delivery practices.

Geologic Resources

The USGS, in cooperation with the 

CDMG, conducts geologic mapping activities 

throughout California for producing and disseminating geologic information to all levels 

of government, the private sector, and the general public. The USGS and the CDMG produce geologic maps at a scale of 1:100,000, 

thus improving on the statewide coverage at 

the 1:250,000 scale. These maps are being produced for areas that are of special interest; for 

example, various geologic hazards, specific 

properties, fault zones, and mineral resources. 

In addition, maps are being produced that provide three-dimensional representations of geologic structures, such as subsurface connections of parallel faults, or geologic changes, 

such as repeated volcanic eruptions.

Mining Byproducts

A new USGS project is focusing on reducing the environmental impact of mining 

through better byproduct recovery. The project 

goal is to provide comprehensive data on the 

existence and nature of useful substances in 

ores; the initial study sites are mines in California and Arizona. Better byproduct recovery 

will reduce the total volume of mine wastes 

and significantly lower their toxicity. This 

cleaner and cheaper way to mine can benefit 

the mineral industry and the environment.

Sources of Mercury

Elevated mercury concentrations in Cache 

Creek sediments have been a problem for 

many years. The Cache Creek watershed in 

the Coast Ranges, which is a tributary to the 

lower Sacramento River, has numerous mercury-depositing hot springs and abandoned 

mercury mines. Until recently, however, the 

primary sources and transport mechanisms 

had not been well identified. Studies by the 

USGS, in cooperation with the Central Valley 

Regional Water Resources Control Board and 

the Los Alamos National Laboratories, have 

identified hot springs in the Sulphur Creek 

drainage basin as a major mercury source. 

Abandoned mines are a secondary source in 

the basin. During most of the year, mercury is 

deposited primarily in fine-textured creek sediments within 0.5 mile of the sources, mercury concentrations can be as high as 195 

parts per million (compared with the average 

0.08 to 0.4 part per million for most rock 

types). During the first seasonal high streamflow, these sediments are transported down 

the drainage basin. This episodic nature of 

mercury transport is significant for Cache 

Creek watershed management and the evaluation of the fate of mercury originating in the 

area.

Biological Resources

On October 1, 1996, the National Biological Service joined the USGS as the Biological 

Resources Division. The USGS gathers information on threatened or endangered species 

throughout California; this information includes the habitat needs of the Central Valley’s 

giant garter snake, populations of the California sea otter and western burrowing owl, and 

salmon runs. The USGS, in cooperation with 

the Bureau of Land Management (BLM) and 

other land managers, also is studying the rare 

desert tortoise and the Mojave Desert. These 

studies provide technical information to help 

the recovery of the desert tortoise and for the 

better management of the Mojave Desert ecosystems. Additional studies focus on terrestrial 

and aquatic contaminant problems and on wetland restoration efforts in San Francisco Bay 

and the Klamath Basin.

Resource Assessment

The BLM is revising the Northern and 

Eastern Colorado Desert Coordinated Management Plan for 5.5 million acres in southeastern California. The most pressing management issue is implementing a recovery 

plan for the desert tortoise. Another 30 species of wildlife and plants also are at risk. 

Other concerns include biodiversity losses, 

the impact of decades of development along 

highways, expansion of recreation areas, and 

coordination among adjacent land-management agencies. 

The USGS has undertaken an assessment 

that includes studies of the environmental impact of mined and unmined mineral deposits, 

studies in support of mine remediation, and 

geochemical background and baseline studies. 

Hydrology and seismic hazards information 

also are included.
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EXPLANATION

Sierra Nevada Ecosystem

The Sierra Nevada Ecosystem Project is a 

congressionally mandated assessment to aid in 

developing of various policy choices for the 

future of the mountain range. The primary 

goals are a scientific review of mature forests, 

watersheds, and significant natural areas and 

an evaluation of the entire set of Sierra Nevada 

ecosystems that includes social, economic, 

and environmental components. USGS contributions to the project include information and 

expertise on mines, mineral resources, and 

mineral environmental issues, potential volcanic activities, and stream flows. USGS contributions for the final analysis include metal 

supply (undiscovered resources) and minerals 

hazards (acidic mine drainage, arsenic and 

mercury contamination in streams, asbestos, 

dust from open-pit mines, and cyanide leaks).

Topographic Mapping

Among the most popular and versatile 

products of the USGS are its 1:24,000-scale 

topographic maps that depict natural and cultural features of the landscape. California is 

covered by 3,289 maps at this scale. The 

USGS is collaborating with California’s 

Teale Data Center to reproduce these maps 

for computer use.

Today, scientists and engineers depend on 

computerized base maps for their research and 

analyses. Without the geographic context provided by these base maps, it would be impossible to understand the spatial patterns of natural 

and human activities. The USGS is working to 

ensure the availability of accurate digital cartographic data to facilitate studies in water, 

hazards, land, and resource management (fig. 

3).

The National Mapping Program in California has focused on those areas where data are 

not yet complete. The USGS has helped a consortium of Federal, State, and local agencies 

produce complete coverage of transportation, 

hydrography, boundaries, public land surveys, 

and elevation data for most of the Klamath and 

the Trinity River Basins. The USGS also is 

working with the U.S. Forest Service to produce digital orthophotoquads of all national 

forests in California and, through another program, is completing coverage of digital elevation data for the Mojave and the Lower Colorado Desert regions and the rest of southern 

California. 

Earth Science Information Centers

The USGS has an Earth Science Information Center (ESIC) in Menlo Park. In addition 

to supplying USGS reports, the ESIC 

searches data bases for aerial photographs, 

historical maps, and digital cartographic data. 

Topographic and national park maps for California, as well as other States, are available 

for sale over the counter, by mail, or FAX. 

Other State ESIC affiliates for USGS products are the CDMG in Sacramento and the 

Map and Imagery Laboratory at the University of California–Santa Barbara.

USGS state representative

Placer Hall, 6000 J Street

Sacramento, CA 95819-6129

(916) 278-3026

e-mail: dc_ca@usgs.gov

California District “Home Page”

http://water.wr.usgs.gov/

Additional earth science

information can be found by

accessing the USGS Home Page

on the World Wide Web at

http://www.usgs.gov/

For more information on

all USGS reports and products

(including maps, images,

and computerized data), call

1-800-USA-MAPS

The USGS provides maps,

reports, and information to help

others meet their needs to manage,

 develop, and protect America’s water,

energy, mineral, biological, and land

resources. We help find the natural

resources needed to build tomorrow,

and supply the scientific understanding needed to help minimize or mitigate the effects of natural hazards

and environmental damage caused

by natural and human activities. The

results of our efforts touch the daily

 life of almost every American.

U.S. Geological Survey

Fact Sheet FS–005–96

Figure 3. The extent of urban land use, decrease of tidal wetlands, and major 

earthquakes in the San Francisco Bay region, 1850–1990. Mapping was done by using 

historical USGS quadrangle maps and satellite images.

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