Castle Mountain is a forested mountain ridge that lies along the Cacapon River south of its confluence with the North River at Forks of Cacapon in Hampshire County, West Virginia. The mountain is named for the Caudy's Castle (also known as Castle Rock) rock outcrop pillar that lies on its southern end overlooking the Cacapon River. Castle Run, which runs along its western flank into the North River, also takes its name from the outcrop.