A MAP SYNTHESIS ENGINE FOR COMPILING MULTIPLE GEOLOGIC MAPS IN THE USGS GEOLOGIC MAP SCHEMA (GEMS): AN EXAMPLE USING CALIFORNIA’S STATEWIDE 1:250,000-SCALE GEOLOGIC ATLAS MAP SERIES

The USGS National Cooperative Geologic Mapping Program’s (NCGMP) National Geologic Synthesis (NGS) project developed a “map synthesis engine” for procedurally aggregating and synthesizing geologic maps based on the USGS Geologic Map Schema (GeMS). This system preserves the original interpretations of the published maps, while integrating them with a suite of taxonomic, searchable attributes and a consistent set of map units statewide. We applied this methodology to synthesize the California Geological Survey’s (CGS) existing 1:250,000-scale geologic map sheets into a new statewide representation of the state’s geology, and to demonstrate the ability to produce derivative map products from GeMS-compliant databases. Derivatives can be developed based on attributes recorded in the database, such as unit age, unit name, lithology, and fault characteristics.

Efforts to compile a statewide geologic map of California began in 1853 and have continued to the present day at various scales and amounts of detail. The 2010 Geologic Map of California published by the CGS is the most current representation of statewide geology for California, albeit at the relatively coarse scale of 1:750,000. However, in 1969 the CGS produced the Geologic Atlas of California, a series of twenty-seven 1:250,000-scale geologic map sheets covering the entire state with a consistent set of map units and harmonized geology across map borders. The CGS recently digitized these map sheets into separate GeMS-compliant geodatabases. The new datasets, standardized as they are to GeMS, proved to be ideal candidates to test the NGS map synthesis engine. The result of this effort provides opportunities to create increasingly detailed, modern representations of California’s geology.