Mammoth Cave

Mammoth Cave, in south central Kentucky across Edmonson, Hart and Barren counties, is the longest known cave system on Earth, with more than 426 miles of surveyed passageway as of 2025. The cave developed within thick Mississippian age limestone interbedded with dolomite, siltstone and shale, capped by a resistant sandstone layer called the Big Clifty Sandstone; acidic groundwater dissolved the limestone below while the caprock protected the passages from collapsing. The system began forming roughly 330 million years ago, with water reaching the Girkin limestone layer about ten million years ago and the cave's upper levels taking shape around 3.2 million years ago. People have explored Mammoth Cave for at least five thousand years, and the park preserves extensive Native American archaeological remains from that long history of use.