Great Falls National Park on the Potomac River
October 29, 2007
The Great Falls on the Potomac River are located just west of Washington, D.C. Great Falls Park is located along the boundary between the Piedmont Plateau and the Atlantic Coastal Plain, in an area known as the fall zone. The rocks composing the Falls date from the late Precambrian (about 750 million years in age) and consist of resistant metamorphic rocks including schists, gneisses, metagraywackes, and metaconglomerates. These picturesque Falls formed when sea level dropped during the last Ice Age, essentially causing what's now the Potomac River to down cut its valley.
The Great Falls are actually a series of cascades and rapids along a two-thirds of a mile (1.2 km) stretch of the Potomac River. Here the river drops about 76 feet (23 m) over this distance. None of the individual falls exceeds a 20 foot (6 m) drop. The Potomac River narrows from nearly 1,000 feet (305 m), just above the falls, to between 60 ft (18 m) and 100 feet (30 m) wide as it rushes through Mather Gorge, a short distance below the falls. Great Falls display the steepest and most spectacular fall line rapids of any eastern river. Because the Falls presented a major obstacle to 18th century boat traffic, George Washington proposed the construction of the Patowmack Canal at Great Falls in 1784. The project required 16 years to complete. Photo taken on June 24, 2007 from the Maryland side of the Potomac River.