Harper's Ferry, West Virginia (39.32496 Lat, -77.73644 Long), sits at the confluence of the Potomac River and Shenandoah River, right upstream of where they flow east across two resistant ridges of rock. This double water gap marks the spot where the river exits the Valley & Ridge physiographic province and enters the Blue Ridge physiographic province. The stratigraphic column of the Blue Ridge is doubled by faulting, and the river has to trek twice over its most resistant layers. From Harper's Ferry, looking east, the two water gaps look like a gunsight.

Harper's Ferry is also one of the seminal locations of action that triggered the Civil War: it was here that John Brown made his raid on the armory. Here's an historical photo, looking over Harper's Ferry itself, east towards the rivers as they flow through the first gap: