The River continues east for 4 miles (6.4 km), passing through the White Horse Rapids, before reaching the second gap between the Short Hill Mountain to the south in Virginia and South Mountain to the north in Maryland.

U.S. Route 340 and the Baltimore and Ohio Railroad both pass through the Potomac Water Gap.

The history of the gap is inexorably tied to that of Harpers Ferry and the surrounding area.

In 1859, Robert E. Lee, was hastily sent in and while reportedly wearing civilian clothes, led a detachment of Marines which passed through the gap en route to Harpers Ferry to put down John Brown's raid.

During the American Civil War, the gap was used frequently by both Confederate and Union Armies to pass through the mountains and was the scene of fighting at the Battle of Harpers Ferry.