The exposed rocks in Bethel Park are mostly composed of sandstone, limestone, shale, and a few coal layers (Redstone, Waynesburg, Washington, etc.). The ages of the exposed rocks bracket the late Pennsylvanian epoch (Gzhelian age; approximately 303 million years ago) near the lowest elevations, and Early Permian period (Asselian age; approximately 297 million years ago) near the highest parts of the southern part of Bethel Park (e.g. Rocky Ridge). These sedimentary rocks were deposited as the sea level rose and fell along an ancient coastline (with the region alternating between delta, shallow lake, and shallow sea), and finally being uplifted with the formation of the Appalachian Mountains.