Formed over eons, the landscape of Petit Jean State Park reveals a story of stone, weather, and time. Much of its exceptional landscape results from earthen rock eroding and weathering at different rates. Hard Hartshorne Sandstone is slow to erode, and it composes the highlands and ridges at Palisades Overlook and across the canyon at CCC Overlook. Shale, quicker to erode, forms much of the mountain's lower-lying valleys. Hundreds of millions of years ago, what is now the top of Petit Jean Mountain was the floor of a valley. Water flowing along this valley carved away most of the earthen rock of today's upper and lower canyon. Shale landforms surrounding this ancient valley floor weathered away, while most of the harder Hartshorne Sandstone remained to become this elevation. The mountain's most dramatic drainage occurs at Cedar Falls, where mountain runoff arrives at the falls and cascades from its Hartshorne cap to the creek bed of softer shale. Millions of years of water carved the canyon deeper. Weathering is the breakdown of rocks and other natural materials on the earth's surface.