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USGS - science for a changing world

GMEG - Geology and Geophysics


Geologic Mapping

in the San Francisco Bay Region

On-line Geologic Maps and GIS Databases

The USGS makes regional geologic maps and on-line digital geologic map databases for the San Francisco Bay area.

Geologic maps show the age and distribution of geologic materials, the orientation of layered rocks, and the position of active and ancient faults.

In addition to helping understand how the landscape around us formed, geologic maps are used in the search for minerals and petroleum, the study of groundwater and groundwater pollution, and (especially in the San Francisco Bay area) the study of geologic hazards.

Geologic maps show the position of faults that might break in an earthquake and geologic materials that can magnify the amount of shaking felt during a quake.

Geologic maps can also show the location of geologic conditions susceptible to landslides.

The California Geological Survey and the USGS cooperate in the geologic mapping of the San Francisco Bay region. The California Geological Survey also uses the USGS geologic information to make regulatory maps showing the distribution of hazards in California.

To learn how to read a geologic map, like the one to the right, click here.

To see the USGS San Francisco Bay Region's digital geologic maps and databases on-line, click here.

Geology of the Cordelia and the northern part of the Benicia 7.5 minute quadrangles, California

Above: Geologic Map of the Cordelia and the northern part of the Benicia 7.5 minute quadrangles, California. The colors on the map represent different rock types. Cross-sections, rock unit descriptions, and index maps are included to interpret the geology and its impact on humans.

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