 It junctions the Thomas Subdivision twice – near Keyser, West Virginia, and near Piedmont, West Virginia – and meets the Fairmont Subdivision near its west end at Grafton.At its west end, it continues as the Bridgeport Subdivision.The Mountain Subdivision's summit is at Altamont, Maryland, at the west end of the Seventeen Mile Grade; the grade's east end is at Piedmont, West Virginia.