The caprock of the Pennyroyal Plateau in the Mammoth Cave region is are sandstone, shale, and conglomeratic beds of the Chester series (of latest Mississippian age. Starting about 330 million years years ago, an river delta system gradually prograded across the shallow sea basin that existed in the Kentucky region. This ancient river system, called the Michigan River, drained west and south from the northern Appalachian region into Pennsylvanian time and possibly longer. The result was the formation of massive and cross-bedded sandtone and shale beds across the top of the top of the older Mississippian-age limestones. As progressive erosion in the region, these Mississippian- and Pennsylvanian-age sandstones form the Dripping Springs Escarpment in the region, and forms the protective caprock for the cavern system in the Mammoth Cave region. This outcrop is near the Visitor Center along the trail to the Historic Cave Entrance.