EFFORTS TOWARDS CONSISTENT AND COMPLETE BEDROCK AND SURFICIAL MAPS OF THE UNITED STATES

Geology in different parts of the United States has long been mapped with a different philosophy, arising from profound regional differences in geologic history and resulting outcrop patterns. In deformed areas of the west and along much of the coasts, Quaternary and older rocks are generally mapped together on one map, sometimes referred to as “surface” or “surficial” maps since they portray geologic materials exposed at the earth’s surface. These are not to be confused with “surficial materials” maps, which portray the character of unconsolidated materials at earth’s surface with less emphasis on geologic history. In the midcontinent, particularly the glaciated regions, Quaternary glacial deposits and much older sedimentary and crystalline bedrock are generally mapped on entirely separate map sheets. These different mapping approaches manifest as inconsistencies in national geologic maps such as the Reed et al. (2005) Geologic Map of North America, the King and Beikman (1974) Geologic Map of the Conterminous United States, and the more recent digital State Geologic Map Compilation (SGMC) (Horton et al., 2017). These maps preferentially show bedrock (pre-Quaternary rocks) in the midcontinent but include Quaternary deposits elsewhere, making them neither bedrock maps, surficial materials maps, or true surface maps. The USGS National Cooperative Geologic Mapping Program (NCGMP) has recently called for the development of new “seamless” national geologic maps and 3D models at multiple “resolutions.” Within these map layers and models, complete coverage of Quaternary geology is important for understanding active geologic processes and geologic hazards (e.g. landslides, liquefaction, etc.). Complete coverage of bedrock geology (inclusive of deposits older than Quaternary) is important for natural resources assessments (e.g. water, minerals, petroleum) and for projecting geologic units into the subsurface in the creation of 3D geologic models. This poster will showcase early efforts by the NCGMP’s National Geologic Synthesis (NGS) project to create consistent bedrock maps of large regions by integrating existing surface maps, shallow subsurface maps, and subsurface data (e.g. boreholes) to understand the map extent and geometry of bedrock units including in areas covered by Quaternary deposits.