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, the NCGMP created a map synthesis engine (Johnstone and others, 2025) based on the Geologic Map Schema (GeMS) standard (NCGMP, 2020) and used it to bring together source geologic maps originally published by the USGS and State Geological Surveys. This thematic map layer was derived from this database using procedures described by Johnstone and others (2025) and is intended to serve as a legible national map of the nation; while it retains full descriptions of geologic units from source materials it does not include the full search functionality (described in Johnstone and others, 2025) that is facilitated by a true relational database. The Earth’s Surface Geology layer depicts geologic units exposed at the earth’s surface over the entire conterminous United States, inclusive of everything from Quaternary glacial deposits to Precambrian crystalline bedrock. In the West and Southeast, the map is a composite of 29 state geologic maps depicting geology at the earth’s surface. In the glaciated region of the Midwest and Northeast, the map is a composite of 21 state geologic maps depicting pre-Quaternary rocks (“bedrock”), 8 state geologic maps depicting Quaternary deposits, and 18 USGS Quaternary Atlas Series maps depicting Quaternary deposits; the Quaternary Atlas maps were used where modern state geologic maps were not available. Quaternary and pre-Quaternary maps were composited by replacing bedrock, residuum, and colluvium (as identified in the GeMS Geomaterials field) on Quaternary maps with the corresponding content from the underlying pre-Quaternary maps (including line and point features). The map is structured as a single GeMS database with three additional tables (also described in Johnstone and others, 2025); a Source_DescriptionOfMapunits table preserves all source inputs, a synthesis_to_source_units table relates aggregated national units to original map units, and a Symbol_Lookup table provides definitions of all FGDC geologic map symbol code values (U.S. Geological Survey, 2006) used for stylizing the map.