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A Tapestry of Time and Terrain: The Union of Two Maps - Geology and Topography
Information about the topography and geology of the continental United States. A digital map contains the description for each geologic feature with information for the eras in which it was formed. "Rock of Ages" is a timeline of each geologic era linked to the regions of the map. "Boundaries" shows two more maps: one with geomorphic, or physiographic, regions; the other with state boundaries. From the U.S. Geological Survey (USGS).
http://tapestry.usgs.gov/default.html

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