The National Park Service says it best:
At Great Falls, the Potomac River builds up speed and force as it falls over a series of steep, jagged rocks and flows through the narrow Mather Gorge. The Patowmack Canal offers a glimpse into the early history of this country. Great Falls Park has many opportunities to explore history and nature, all in a beautiful 800-acre park only 15 miles from the Nation’s Capital.
If you visit Washington, DC or live in the area, be sure to spend some time at the falls. You can see them from either the Maryland or the Virginia side. They are impressive year around and if you go to the Virginia side, you can hike and explore as well.
How did those guys get down into that water?