PROGRESS IN GEOLOGIC MAPPING AT THE CALIFORNIA GEOLOGICAL SURVEY

In California, almost all land-use planning and building decisions are made at the local level, but few local governments have the staff, funding, or expertise to interpret critical details of geologic hazards and resources from available geologic mapping. To accommodate this need, the California Geological Survey (CGS) prepares maps specifically for use in hazard and resource evaluation by local government. Those maps are derivatives of geologic maps and contain only the information needed by land-use planners and decision-makers.

CGS derives hazard or resource maps from geologic maps, so needs regionally consistent geologic maps to form the basis for analysis of a host of concerns in California, from seismic hazards to infrastructure engineering, environmental management, and groundwater issues. CGS aims to bring new and existing map information into a standardized cartographic format and release the new maps for public use in downloadable image and GIS file formats, as well as for viewing on an interactive Google Map platform.

Geologic mapping at CGS is partly supported by grants through the USGS STATEMAP program. Mapping projects are selected each year based on development pressures and geologic hazard potential with input from an independent advisory committee. Each year STATEMAP supports mapping of several 7.5’ quadrangles and compilation of existing mapping for a 30’ x 60’ quadrangle. CGS also prepares geologic maps for specific hazard mapping projects, such as the recent mapping of Quaternary deposits for evaluation of alluvial fan flood hazard. These maps can be combined with others, in this case with maps showing more detail of the bedrock, to develop complete geologic maps. Over the long term, CGS plans to complete 1:24,000-scale geologic mapping in urbanizing areas of the state and complete compilation of the 115 30’ x 60’ quadrangles that preserves the detail of the original mapping.

CGS can help other geologists get their work out to the public by providing GIS and cartographic support and publication. Examples include the Geologic Map of the North Lake Tahoe – Donner Pass Region, compiled by faculty and students of U.C. Santa Barbara, and mapping of four 30’ x 60’ quadrangles in northeastern California by T.L.T. Grose. New maps are announced on the CGS website as they are released.