The southern Great Valley is bounded on the east by the Blue Ridge physiographic province, which includes, from north to south, South Mountain in Pennsylvania and Maryland, the Blue Ridge of Virginia, Holston Mountain in Tennessee, and the Unaka Range and the Great Smoky Mountains of Tennessee and North Carolina. An important gap in these mountains occurs near Roanoke, Virginia. Other gaps of note in the Blue Ridge of Virginia, connecting the Piedmont region with the Great Valley, include Thornton Gap, Swift Run Gap, and Rockfish Gap.