1. Geologic map of the Poolesville quadrangle, Frederick and Montgomery counties, Maryland, and Loudoun County, Virginia Yale Public content 1998. 2002-06-01T04:00:00Z. 2022-12-08T02:20:30Z. Geological Survey (U.S.). The Survey ; For sale by Information Services. English. Public. Maryland, Frederick County, Montgomery County, Virginia, and Loudoun County.