Castle Mountain is a forested ridge in Hampshire County, West Virginia, along the Cacapon River just south of its meeting with the North River at Forks of Cacapon. Running southwest to northeast and visible from Bloomery Pike, West Virginia Route 127, it is a prominent feature of the local landscape. Its name derives from Caudy's Castle, also called Castle Rock, a pillar-like rock outcrop at the mountain’s southern end overlooking the Cacapon River. Castle Run, which follows the ridge’s western flank to the North River, takes its name from that same outcrop.