From the site: "Major geologic units in the West Virginia region including 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.

Generalized geology shapefiles were downloaded from the National Atlas of the United States web site and clipped to an extent covering -76 to -84 degrees west longitude, 35 degrees 30 minutes to 42 degrees north latitude using a shape file that is included in the zip archive. Published April 2002. 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."