Next below these is the Mississippian Burgoon Sandstone, which is buff-colored with shale, coal, and conglomerate inclusions. Below this is the late Devonian and early Mississippian Huntley Mountain Formation, which is made of relatively soft grayish-red shale and olive-gray sandstone. The lowest and oldest layer is the red shale and siltstone of the Catskill Formation, some 375 million years old. This layer is relatively soft and easily eroded, which helped to form the Pine Creek Gorge. The source of Upper Pine Bottom Run is on Mauch Chunk rock, and the stream cuts deeper as it flows east to Pine Creek. In the park Upper Pine Bottom Run has cut through layers of Burgoon sandstone and Huntley Mountain rock, and downstream of the park to its mouth the deepest parts of the valleys are made of the Catskill Formation.