Boundaries and Tags for Major Geologic Units in the United States

In addition to the polygons representing the areal extent of geologic units, it identifies boundaries of metamorphic provinces, major faults, calderas, impact structures, and the limits of continental glaciation. The data depict the geology of the bedrock that lies at or near the land surface, but not the distribution of surficial materials such as soils, alluvium, and glacial deposits.

The data are generalized from a compilation prepared for use in the Geologic Map of North America, to be published in hard copy by the Geological Society of America and released as a digital file by the U.S. Geological Survey. These data have been prepared with a degree of detail appropriate for viewing at a scale of 1:7,500,000. Because of the degree of generalization required (generalization based on compilation scale), the data are intended primarily for display and for regional and national analysis, rather than for more detailed analysis in specific areas.