Geologic Formations

For millions of years the power of the Potomac River shaped and reshaped the valley in which the C&O Canal NHP now lies. Rock formations exposed by the erosive force of the Potomac's flow provide a window into the continent's geologic past, a time when North America collided with continents that now lie across a vast ocean. Some of these rock formations were originally formed at the bottom of the sea. Fossils provide a record of this past. Read this brochure to learn more about the fossils of C&O Canal.


This naturally shaped landscape has attracted humans for thousands of years. Humans have in turn interacted with and reshaped this landscape. American Indians used the general west-east course of the Potomac River as a route through the Appalachian Mountains and constructed fish weirs in the river to trap fish. As the United States expanded westward, short canals, called skirting canals, were cut along the river's banks to "improve" the navigability of this route around naturally formed rocks and rapids.

The Chesapeake and Ohio Canal was envisioned as a continuous canal to further ease the movement of people and cargo along a course earlier carved by nature. The frequency of flooding along the Potomac along with the development of railroads eventually led to the demise of this idea to connect east and west through waterways. Today, many communities rely on the Potomac for public water and as a source of water for coal-fired electric plants. Therefore, low-head dams and water intake structures are some of the more recent additions that have reshaped the geologic landscape. With only one high dam, located many miles upstream from the western terminus of the canal, the same dynamic forces that shaped the Potomac Valley continue to ever-so-slowly reshape the land. This dynamic river system provides us today with the opportunity to marvel at our continent's geologic past, experience its scenic beauty, and reflect on how our daily choices will affect its future.

There are many geologic features and processes of interest at C&O Canal NHP, including the Great Falls of the Potomac, fossils, easy viewing of geologic rock layers along 184.5 miles of river drainage, and natural habitats such as bedrock terraces and river scourbars formed by the shifting sands of geology. The Potomac Gorge (the Gorge) is one of these areas. The Gorge is one of the most significant natural areas in the eastern United States. It extends for 15 miles along the Potomac River from Great Falls to Theodore Roosevelt Island, encompassing about 9,700 acres in Virginia, Maryland and the District of Columbia and incorporating sections of C&O Canal NHP and George Washington Memorial Parkway. Because of its unusual hydrogeology, the Gorge is one of the most biologically diverse areas for plant species in particular, serving as a meeting place for northern and southern species, midwestern and eastern species, and montane and coastal species. The site harbors more than 400 occurrences of over 200 rare species and communities, a major river system with numerous tributaries, noteworthy stands of upland forest, many seeps and springs harboring rare groundwater fauna, and abundant wetlands. The National Park Service is the principle landowner in the Gorge, however, The Nature Conservancy co-own Bear Island in the heart of the Gorge and has had long been interested in the extraordinary biological diversity of the site. The site is also renowned for its aesthetic, cultural and recreational values. Numerous vantage points of the river from both C&O Canal NHP and George Washington Memorial Parkway afford spectacular views of features like the Great Falls of the Potomac and the Potomac Palisades. The lush vegetation along the river screens out much of the sights and sounds of civilization, providing welcome tranquility in the midst of a densely populated urban area.

Contact the Park

Mailing Address:

1850 Dual Highway, Suite 100
Hagerstown, MD 21740


(301) 739-4200
This phone number is answered Monday-Friday from 8am-4pm.

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