Geologic Provinces of the United States: Appalachian Highlands Gallery

Looking west from Loudoun Heights, Virginia.

Photo by Scott Southworth, USGS.

Looking west from Loudoun Heights, Virginia, to Harpers Ferry National Historical Park, West Virginia, at the confluence of the Shenandoah (left) and Potomac (right) Rivers. The low ridge just west of the terraced top of the town is underlain by the first Fossil-bearing (Lower Cambrian trilobites) metasandstone of the Paleozoic rock section. This is the boundary between the Blue Ridge province and the Great Valley of the Valley and Ridge province to the west. The resistant, quartz-rich metasedimentary rocks of the Blue Ridge underlie ridges as opposed to the calcite-rich carbonate rocks of the Great Valley that chemically dissolve to form a lowland. The famous water gap here provided a critical vantage point for the Civil War, made famous by John Browns raid on the armory. The armory was located here due to iron deposits, abundant lime, and water power.