The James River flows through the mountains at this location, creating a water gap in the Blue Ridge, a type of formation characteristic of Appalachian geography. The Blue Ridge forms the eastern wall of the Appalachian Mountain system from northern Georgia to Pennsylvania. Historically, water gaps like this provided a gateway for westward expansion. Later, roads and highways were built across the Blue Ridge at many points, but rail and canal traffic still depend on these gaps. Over time, the river has cut more deeply into the mountain, exposing geologic formations more than 500 million years old. These rocks are mostly volcanic and sedimentary and have been severely folded in many places.