The Hammersley Wild Area and Susquehannock State Forest are on the Allegheny Plateau, which was formed, along with the Appalachian Mountains in the Alleghenian orogeny, some 300 million years ago, when Gondwana (specifically what became Africa) and what became North America collided, forming Pangaea. Although the region appears mountainous, these are not true mountains: instead millions of years of erosion have made this a dissected plateau, causing the mountainous terrain seen today. The hardest of the ancient rocks are on top of the ridges, while the softer rocks eroded away, forming the valleys.