GEOLOGIC MAP OF THE CONTERMINOUS UNITED STATES: QUATERNARY GEOLOGY

The USGS National Cooperative Geologic Mapping Program (NCGMP) was directed by Congress to create a new geologic map of the United States by “bring[ing] together detailed national and continental-resolution 2D and 3D information produced throughout the Survey and by federal and state partners” (House Report 116-100). To fulfill this goal we have created a database engine for synthesizing geologic maps (described in a companion poster) based on the Geologic Map Schema (GeMS) and used it to bring together geologic maps published by the USGS and State Geological Surveys and create derivative thematic geologic maps.

This Quaternary geology layer depicts Quaternary geologic units exposed at the earth’s surface over the entire conterminous United States, inclusive of everything from glacial deposits to lava flows. It includes all units that may, or are known to, span the Quaternary – Neogene boundary. In the glaciated region of the Midwest and Northeast, the map is a composite of 8 state geologic maps depicting Quaternary deposits and 30 USGS Quaternary Atlas Series maps depicting Quaternary deposits; Quaternary Atlas maps are used where modern state geologic maps are not available. In the West and parts of the Southeast, the map is a composite of Quaternary units from 19 state geologic maps depicting geology at the earth’s surface. Although this map attempts to depict the general character of Quaternary faulting in the western United States, it is not a substitute for maps of Quaternary faults.

About 1200 source map units from 57 maps are assigned to 68 synthesis map units, broadly grouped by age and deposit type, from the International Commission on Stratigraphy (ICS) timescale and GeMS Geomaterials fields, respectively. Synthesis map units are colored according to USGS guidelines in such that they are readable as a traditional geologic map. The locations of contacts and faults are unchanged from the original sources, but only those that bound synthesis units are solid; those within them are symbolized as “internal.” Numerous additional line and point features are included, mostly portraying glacial geomorphologic features such as eskers, drumlins, glacial striations, glacial termini, etc.