South Mountain, northernmost section of the Blue Ridge in the Appalachian Mountains, extending southwestward for 65 miles (105 kilometers) from southern Pennsylvania to northern Virginia, United States. Quirauk Mountain (2,145 feet [654 meters]) in Maryland is the highest point. It is crossed by the Appalachian Trail (for hikers). The American Civil War Battle of South Mountain took place near Burkittsville, Maryland, on September 14, 1862.