GEOLOGIC MAPS OF THE NATIONAL CAPITAL REGION FROM FEDMAP

New geologic maps in the National Capital Region, funded by the FEDMAP component of the USGS National Cooperative Geologic Mapping Program, are products resulting from mapping that occurred over the last decade. Printed publications include approximately 25 1:24,000-scale, 7.5-minute Geologic Quadrangle Maps and one 1:100,000-scale 30- by 60-minute quadrangle map. Geographic information systems and online publications containing ArcInfo and PDF formatted files include a composite of three 1:100,000-scale quadrangles and 5 1:24,000-scale maps. (http://geology.er.usgs.gov/eespteam/GISLab/Search/index.html). Our poster presentation portrays geologic maps at many scales, including 1:6,000 (Great Falls Park), 1:24,000 (Buckeystown, MD and VA 7.5-minute quadrangle), 1:50,000 (Loudoun County, VA), 1:100,000 (Frederick MD, VA, and WV, 30- by 60-minute quadrangle), and 1:500,000 (DC Database). The map area covers 5,679 sq. mi. within the Valley and Ridge, Blue Ridge, Piedmont, and Atlantic Coastal Plain Provinces. The maps depict 268 rock units that range in age from Mesoproterozoic gneiss (1153 ± 6 Ma in the Blue Ridge) to early Jurassic diabase (200 Ma in the Mesozoic basins of the Piedmont). In addition, 32 surficial units show the influence of fluvial and slope processes within the last million years. To date, specific applications of the data for land management decisions include: 1) A cost benefit analysis demonstrating a societal value of between $1.28 million to $3.50 million for siting a landfill and highway, 2) production of new soil maps, based exclusively on the geologic maps in 6 counties, for agricultural and development practices, 3) lithologic unit and fracture data for ground water studies of fractured bedrock aquifers in 7 counties, 4) definition of land use ordinances for foundations and septic systems in karst areas based on the distribution of carbonate conglomerate, 5) GIS for resource management in the region’s National Parks, and 6) infrastructure assessment for the identification of locations containing favorable aggregate.