Mammoth Cave System is located about 160 km (100 miles) south of Louisville, Kentucky and about 56 km (35 miles) northeast of Bowling Green, Kentucky. Most of the cave lies within Mammoth Cave National Park, a World Heritage Site and a part of the United Nations program of International Biosphere Reserves. It is the longest cave in the world by a factor of 3, with about 631 km (392 miles) of surveyed passage. Mammoth Cave consists of active and abandoned conduits carrying water from the recharge area to the south to discharge as springs along the deeply incised Green River. Development of the cave has spanned a time period from the Pliocene to the present. The exceptional length has been preserved by the protective sandstone caprock. Mammoth Cave contains a variety of carbonate and sulfate minerals, the latter preserved by the dry environment beneath the caprock. Mammoth Cave also supports an exceptional biological diversity.