GEOLOGIC MAPPING ACTIVITIES AT THE CALIFORNIA GEOLOGICAL SURVEY

Geologic maps are the necessary base for any study of geologic hazards or resources. The California Geological Survey (CGS) Geologic Mapping Program conducts original geologic mapping and compiles geologic maps by others to create a digital database of geologic map information in a standardized format and provide this data to the public. Regional geologic maps prepared by CGS provide a foundation upon which CGS builds a variety of derivative maps to identify and help mitigate potential geologic hazards.

Geologic mapping at CGS is partially supported by federal grants through the on-going USGS STATEMAP program. New geologic mapping projects are selected each year based on societal needs, with input from an independent geologic mapping advisory committee. Projects typically include new 1:24,000-scale geologic mapping of several 7.5’ quadrangles and compilation of mapped quadrangles into a 30’x60’ map sheet. Because geologic map unit boundaries may become boundaries of regulatory zones, new large-scale mapping must show the distribution of both bedrock and surficial deposits with consistent methods and standards. To provide timely access to new mapping, preliminary versions of the maps are posted to the CGS Preliminary Geologic Maps web page (http://www.conservation.ca.gov/cgs/rghm/rgm/Pages/preliminary_geologic_maps.aspx). When all aspects of the geologic mapping for a 30’x60’ quadrangle are compiled and reviewed, the map is published in CGS’s Regional Geologic Map series. While the final 30’x60’ compilations are printed as 1:100,000-scale maps, finer details of original 1:24,000-scale mapping are retained in the GIS database. Over the long term, CGS aims to perform new detailed geologic mapping for most urbanizing areas of the state and coordinate with the USGS to digitally compile the best available mapping covering all 115 30’ x 60’ quadrangles.

CGS continues to assist other geologists in getting their work out to the public by providing GIS and cartographic support, as well as a publication venue. Recently published examples are Map Sheet 61, Geologic Map of Part of Eastern Placer County, Northern Sierra Nevada by David Harwood and others, and Map Sheet 62, Geology of Ring Mountain and Tiburon Peninsula, Marin County by David Bero.  New maps are announced on the CGS website as they are released.