Cross Mountain is the highest peak of Pennsylvania’s Bear Pond Mountains, a small Appalachian subrange along the Pennsylvania–Maryland border. With nearby Hearthstone Mountain in Maryland, it forms the rim of the Punchbowl, a large amphitheater-like landform shaped by erosion of weathered Ordovician shales at the center of a south-plunging anticline. Both mountains are made of the harder quartzite of the Silurian Tuscarora Formation, which stands prominently around the eroded basin. Cross Mountain also served during the Cold War as the location of Cannonball site 2, a microwave relay installation in a 103-foot tower; the station was deactivated in 1977, and summit access remains restricted.