The Appalachian Mountain chain was formed starting around 420 million years ago with the collision of the North American craton and the Iapetus Ocean and culminating with the collision of the modern-day eastern seaboard of the then Euramerican continent with Africa, then Gondwana, about 290 million years ago forming the supercontinent Pangea. Since the collision event the mountains have been eroding from the break-up of Pangea and through sedimentation formed the coastal plains to the east and limestone plateaus to the west. The footprints of the mountains formed the ridge and valley geological region in which Penns Valley was formed through glacial and other activity.