Local DC-MD-VA Geology
Washington is centrally located in the middle of the North American Plate
✦ Screen shot of Earth showing crustal elevation, tectonic plates, and plate boundaries. Note that Washington sits near the locked (tectonically inactive) continent-ocean margin that marks the western rift margin for the opening of the Atlantic Ocean basin approximately 200 million years ago. (Original image from Tasa Graphic Arts, Inc.)
Washington sits at the edge of a long-ago assembled supercontinent
✦ Depiction of Archean through Neoproterozoic basement features of Precambrian North America (Laurentia). Significant terranes, orogenic belts, basins, rifts, and structural features are highlighted by individual colors. Original figure and parts of caption from Whitmeyer, S.J. and Karlstrom, K. (2007) Tectonic model for the Proterozoic growth of North America. http://doi.org/10.1130/GES00055.1, used with permission.
Physiographic provinces of Maryland and northern Virginia
✦ Map of the physiographic provinces of Maryland and Northern Virginia. From Southworth, S., Brezinski, D.K., Orndorff, R.K., Chirico, P.G., and Lagueux, K (2001) Digital Geologic Map and Database of the Chesapeake and Ohio Canal Hational Historical Park, District of Columbia,Virginia, Maryland, and West Virginia, USGS OFR 01-188.
✦ Simplified geologic cross section across the southern region (in northern Virginia) of the physiographic provinces map above. From northwest to southeast: west- vergent folded and faulted rocks of the Valley and Ridge (surf green), basement gneisses (stippled blue) and cover rocks (dark green) of the Blue Ridge, suspect terranes of the Piedmont (tan), Triassic basins (stippled green), and the Coastal Plain onlap in the eastern Piedmont (thin yellow band at the surface). Major structural features indicated: LCD—Lower Carbonate duplex; NMT—Little North Mountain thrust; MS—Massanutten synclinorium; BRF—Blue Ridge fault sys- tem; SM—Brookneal/Shores Mountain Run zone; SZ—Spotsylvania zone; HZ—Hylas zone; T—Taylorsville basin. Original figure and slightly modified caption from Whitmeyer, S. J., Bailey, C. M., & Spears, D. B. (2015). A billion years of deformation in the central Appalachians: Orogenic processes and products. In Tripping from the Fall Line: Field Excursions for the GSA Annual Meeting, Baltimore, 2015 (Vol. 40, pp. 11–33). Geological Society of America. http://doi.org/10.1130/2015.0040(02), used with permission.
State of geologic mapping at the 1:24,000 and greater scale around DC
See the index maps from the National Geologic Map Database to actively scroll and get geologic topographic basemaps for anyplace in the US.
Basemaps for the DC area can be found by clicking on the map above or here. *Note: This basemap series currently runs in Adobe Flashplayer which only runs on MacOs. It will in run on iOs (Apple iPhones and iPads). The USGS says that future updates will move off Flashplayer.
Geologic map of Washington, DC area
✦ Geologic Map of the District of Columbia and the proximal Potomac River. From Scott Southworth and Danielle Denenny (2006) Geologic Map of the National Parks in the National Capital Region, Washington, D.C., Virginia, Maryland, and West Virginia USGS OFR 2005-1331.
✦ Legend for geologic map above. From USGS OFR 2005-1331.