As we celebrate Independence Day in the United States, our minds turn to our founding fathers. George Washington, Father of the Country and American Revolutionary War hero, was, in his youth, a draftsman, mapmaker, and land surveyor. During his lifetime, he was instrumental in the project to build a canal along the Potomac River.
Let’s take a look at that area’s history and geology!
Sharon Lyon
Editor, GeoLifestyle
Patowmack Canal History
John Bilous/Shutterstock.com
George Washington once envisioned a canal along the Potomac River to serve as a key route for westward expansion and trade.
Canal history: George Washington’s interest in a canal began during his youth when he surveyed Lord Fairfax’s western lands, traveling along the Potomac into the Ohio Valley.
Washington recognized natural challenges as major barriers to navigation—rapids, whirlpools, and especially Great Falls, where the river drops 75 feet in half a mile.
In 1774, Washington introduced a bill in Virginia’s House of Burgesses to build “skirting canals” around the Potomac’s worst obstacles. Maryland did not support the plan.
After the Revolutionary War, Washington succeeded in reviving the canal project. The Patowmack Canal Co. was chartered in 1785, and Washington was elected its first president.
Washington oversaw work on canal sections and locks, particularly the engineering marvel at Great Falls. The Patowmack Canal consisted of five canals designed to bypass rapids on the river. The project was completed in 1802, three years after Washington’s death.
The Patowmack Canal made 218 miles of the river navigable, but only under favorable conditions.
Second iteration: Twenty years later, Virginia and Maryland promoted the formation of a new company to build a continuous canal parallel to the river. The Chesapeake & Ohio (C&O) Canal Co. acquired the rights of the old Patowmack Canal Co.
On July 4, 1828, President John Quincy Adams broke ground on the C&O Canal at a celebratory event along the river near Little Falls.
The C&O Canal was designed to be more reliable than the Patowmack Canal, with lift locks to allow boats to traverse elevation changes, towpaths and mule teams to pull boats without entering the unpredictable Potomac, and dams to regulate water levels.
Crews completed the canal in 1850 after 22 years of construction, despite major obstacles such as rugged terrain, frequent flooding, financial difficulties, and competition from the expanding railroads.
By the mid-1870s, the railways took over freight transport, and the canal’s use declined. A major flood in 1924 caused extensive damage, leaving much of the canal in disrepair.
The bottom line: The C&O Canal operated for nearly 100 years and was a lifeline for communities along the Potomac. It allowed coal, lumber, and agricultural products to float on barges to market in Washington, D.C. Innovative features such as its locks, aqueducts, and culverts showcased 19th century American engineering.
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Faulted and tilted strata of the Wills Creek Shale, uphill from the C&O canal towpath, at Roundtop Hill, near Hancock, Maryland.
By the time the C&O canal reached Hancock, Maryland, it had crossed into the Valley and Ridge physiographic province.
These rocks are best exposed along the towpath at Roundtop Hill, five miles west of Lock 52 and the Tonoloway Aqueduct.
You can also bike or hike along the Western Maryland Rail Trail, located just uphill from the towpath, to view the rocks and structures more closely.
Geology: Roundtop Hill is located in the Cacapon Mountain anticlinorium, which plunges gently to the north.
The Silurian Bloomsburg Formation, dark red in color, consists of sandstones and shales deposited in a fluvial deltaic environment. The red color gives evidence of oxygen in the early Paleozoic atmosphere.
Lying unconformably above the Bloomsburg, the Wills Creek Shale is completely exposed at Roundtop Hill and dominates the section.
The Wills Creek is composed of gray mudstones, limestones, and sandstones.
The formations were folded and faulted during the Alleghenian Orogeny, the final mountain building event that formed the Appalachians.
The rocks have been folded into tight anticlines and synclines, cleaved along joint planes, and fractured by normal- and small-scale thrust faults.
You can also see mud cracks, ripple marks, and slickensides at the outcrops.
Round Top Cement Co: The argillaceous limestones in the Wills Creek Shale were mined for natural cement from 1863–1909. The ruins of the mill and remains of the kiln are still visible from the canal towpath.
An anticline, known as the Devil’s Eyebrow, was hollowed out to mine the limestone.
During the Civil War, the cement works were Hancock’s biggest employer. The water from the C&O canal was used to power the waterwheel and grind stones.
The cement was shipped as far as Washington, D.C., where it was used to construct the Capitol dome, the Washington Monument, and the Cabin John (now American Legion Memorial) Bridge.
The mill suffered numerous fires until a final blaze in 1903 shut it down. The discovery of stronger Portland cement also helped put it out of business.
Crack some geodes and start a collection, or paint rocks to create a rock garden
Great Falls is a series of majestic waterfalls and rapids along the Potomac River. The falls are located upriver from Washington, D.C., on the border of Maryland and Virginia.
National parks: There are two National parks along the river: Great Falls Park on the Virginia side and the Chesapeake and Ohio Canal National Historical Park, which runs from Georgetown, in Washington, D.C., to Cumberland, Maryland, along the historic C&O canal and its towpath.
Geology: Great Falls lies within the Piedmont physiographic province, just upriver from the Fall Line, the boundary between the hard rocks of the Piedmont and the softer sediments of the Atlantic Coastal Plain.
The underlying rocks are Precambrian-age schists, metagraywackes, granites, and quartzites. These rocks were metamorphosed, folded, and faulted during the three orogenies forming the Appalachian Mountains.
Igneous intrusions of granodiorite and lamprophyre occurred throughout the Paleozoic.
During the Triassic period, hot solutions migrating along parallel faults deposited thick veins of white quartz. Some of these veins carry small amounts of native gold, which was mined in the area from 1867 until 1941. Some of the buildings remain from goldmining operations on the Maryland side, but they are inaccessible.
Over millions of years, the Potomac River cut down into the hard bedrock, carving out the narrow Mather Gorge. Water erosion created plunge pools and narrow channels.
Jointed and fractured rock outcrops are visible in the gorge. Potholes can be seen along the canal towpath.
Stop by the Visitor Center to view the video presentation and explore exhibits about the canal, geology, flora, and fauna. There is an interactive children’s room for hands-on exploration.
Take a guided boat tour or canoe down a portion of the canal.
Stroll or bike down the towpath and view the canal locks.
For a strenuous hike, get up close and personal with the rocks on the Billy Goat Trail.
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