Boundaries and Tags for Major Geologic Units in the United States

This data set contains boundaries and tags for major geologic units in the
conterminous 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. No
responsibility is assumed by the U.S. Geological Survey in the use of these
data.