South Mountain begins at the Potomac River as a low, narrow ridge, barely one mile wide and only 1,200 feet (370 m) above sea level at its crest. South of the Potomac River in Virginia, the ridge continues as Short Hill Mountain for about 12 miles (19 km) before subsiding near the town of Hillsboro. South Mountain in Maryland gradually grows higher and wider towards the north. Near the Pennsylvania border, the mountain merges with the hills of the parallel Catoctin Mountain range to the east and becomes more like a low mountain range than a single crest. North of U.S. Route 30 in Pennsylvania, the South Mountain highlands reach their greatest width, over 12 miles (19 km), and several summits top 2,000 feet (610 m). The mountain then turns more to the east and becomes a series of small rocky hills between Mount Holly Springs and the northeastern end of the mountain at Dillsburg, Pennsylvania.
The history of South Mountain defines the early history of western Maryland. It was viewed as a boundary to the Susquehannock (Conestoga) in their original treaty granting land to Maryland. In a 1732 letter to the colonial governor of Maryland, Togotolisa, (Captain Civility), chief of the Susquehannock people, warns against settlement in the valley beyond the mountain.[3] The first Euromerican land grant west of South Mountain by Maryland was William Park's "Park Hall" in 1731 near Crampton's Gap.[4] The earliest route of the Great Wagon Road crossed South Mountain by Fox's Gap on a course between Middletown and Sharpsburg.[5] Other important passes for migration and settlement were Turner's Gap near Boonsboro; Orr's Gap, used today by Interstate 70; and the course of "Cartledge's Old Road" generally following Maryland state route 77. Maryland finally gained clear title to the lands west of South Mountain in the 1744 Treaty of Lancaster.[6]
Following John Brown's Raid on Harpers Ferry in 1859, seven of the raiders escaped from their Kennedy Farm headquarters to Pennsylvania by following Elk ridge and South Mountain north. The escapees traveled by night and spent the days in cold camps among the densest thickets they could find along the remote ridge top.[7] They finally left the mountain near today's Caledonia State Park between Chambersburg and Gettysburg, Pennsylvania.
