PRELIMINARY QUATERNARY GEOLOGIC MAP OF THE UNITED STATES

The United States Geological Survey’s (USGS) National Geologic Synthesis (NGS) project is compiling previously published geologic maps from across the conterminous United States into an integrated database and creating four derivative map layers: Quaternary, Earth’s Surface, Bedrock and Precambrian. These layers accommodate different geologic mapping styles across the country, notably the dedicated Quaternary geologic maps in regions impacted by continental glaciers. Derivative maps are faithful to, and retain information from, their original sources. Source maps are composited to form a consistent map, to which is applied a set of synthesis units based on standard, searchable attributes (e.g., age, geologic material), resulting in a harmonized representation. This facilitates rapid assembly of derivative products while preserving published interpretations.

We present a Quaternary geologic map assembled from state and regional geologic maps spanning the conterminous United States. Source maps were converted into the National Cooperative Geologic Mapping Program’s (NCGMP) Geologic Map Schema (GeMS) format and vary in scale from 1:250,000 to 1:1,000,000. Contacts, faults, and other geologic features are consistently symbolized according to Federal Geographic Data Committee (FGDC) standards. Thousands of map units from around 50 individual maps were grouped into several dozen compilation units based on age and lithology. This map is the most detailed national depiction of Quaternary geology ever constructed, and it highlights regional patterns in erosional and depositional histories in unprecedented detail, particularly the role of continental glacial cycles in the last 2 million years. It also highlights where discrepancies still exist between maps.