1. Geologic map database of the Washington DC area, featuring data from three 30 x 60 minute quadrangles, Frederick, Washington West, and Fredericksburg [electronic resource] Yale Public content 2002. 2002-09-20T15:50:12Z. 2005-05-18T17:47:38Z. Geological Survey (U.S.). U.S. Dept. of the Interior, U.S. Geological Survey. English. Public. Washington (D.C.) Region and Middle Atlantic States.