The C&O Canal's Geology: 184.5 Miles Across Three Provinces and the Fall Line

The Chesapeake and Ohio Canal exists because of a geological boundary. The Fall Line, where the soft rock of the Coastal Plain gives way to the hard metamorphic rock of the Piedmont, breaks the Potomac River into ridges, waterfalls and rapids for over 32 km (20 mi), from Theodore Roosevelt Island to Seneca Falls — with Great Falls at their heart. The canal was built to get boats around them.

The park

Chesapeake and Ohio Canal National Historical Park follows the 297 km (184.5 mi) canal along the Potomac between Washington, D.C., and Cumberland, Maryland. Built between 1828 and 1850 and inspired by George Washington's vision of an industrial corridor along the river, it mainly carried coal from western Maryland to the port of Georgetown.

• It crosses Allegany, Frederick, Montgomery and Washington counties in Maryland, borders five West Virginia counties, and reaches into Washington, D.C.
• The upper canal became a national monument on January 18, 1961, and the park was expanded and redesignated a national historical park on January 8, 1971.
• It protects the canal, more than 1,300 historic structures, the scenic 24 km (15 mi) Potomac Gorge, and archeological resources recording 13,000 years of people along the river.

A cross-section of the Appalachians

From east to west the canal crosses three physiographic provinces:

1. the Piedmont Plateau, whose resistant metamorphic rock begins at the Fall Line;
2. the Blue Ridge;
3. the Valley and Ridge.

The bedrock is a diverse set of formations from the Precambrian to the Mesozoic. Some of the oldest rocks along the canal are Mesoproterozoic metamorphic and meta-igneous rocks; the youngest are Jurassic diabase dikes around Harpers Ferry, West Virginia. The canal's route is a cross-section through the complex geology of the central Appalachians — and a way to see how building the canal shaped the region.

Limestone, dolomite and sandstone in the walls of Lock 33. Credit: NPS photo by Trista L. Thornberry-Ehrlich, Colorado State University.

Protected by law

• Fossils in national parks are protected under the Paleontological Resources Preservation Act of 2009.
• Caves are protected under the Federal Cave Resources Protection Act of 1988.
• Abandoned mineral lands can be valuable cultural resources and habitat, but many are dangerous and harm water and landscapes. Stay out and stay alive.

Where the detail lives

This summary comes from the NPS Geodiversity Atlas, drawn from the Geologic Resources Inventory, which produces geologic maps and reports for more than 270 natural resource parks. A Soil Resources Inventory has also been completed for the park, and the USGS has published a Geology of the Chesapeake and Ohio Canal. Everything is in the NPS DataStore.

Sources

Based on "NPS Geodiversity Atlas—Chesapeake and Ohio Canal National Historical Park, Washington D.C., Maryland, and West Virginia" from the National Park Service, a work of the United States government in the public domain.