This grouping of mountains straddle the Maryland and Pennsylvania border.

This feature was created by the weathered shales of the Ordovician age in the center of a south-plunging anticline, having been eroded to expose a large amphitheater like feature (punchbowl).

Cross and Hearthstone Mountain are made of hard resistant quartzite of the Tuscarora Formation of the Silurian age.

Cross Mountain is also the site of a deactivated microwave relay station, that was used during the Cold War.

Alan R. Geyer (1979) "Outstanding Geologic Features of Pennsylvania", Geological Survey of Pennsylvania Albert LaFrance, Secret Cold War Landscape, Presidential Emergency Facilities Microwave Radio Relay Station Site 2 - "Cannonball" atop Cross Mountain, near Shimpstown, PA., Cold War webring, last update June 12, 1999.