The Potomacfest logo depicts a petroglyph cut into the rock by Algonquin Indians about 1500 years ago in the rocks below the foot of Great Falls. The concentric shapes represent a fish coming toward you, with a vertical dorsal fin at the top and a face in the middle. It is thought that the petroglyph was put there to mark a good fishing hole. With the falls blocking upstream migration of shad, the fishing must have been great.