Mammoth Cave, located in Kentucky, is made up of limestone formations formed over the course of 100 million years. This network of underground passageways and natural caves is the largest in the world. More than 390 miles of these caves have been explored, mapped and surveyed. The caves are known for their vertical shafts and horizontal tunnels. Collectively, they demonstrate many facets of the evolutionary history of the Earth. There are also more than 200 caves in the park that are not connected to the larger cave or are fragments. The area was named Mammoth Cave because of the sheer vastness and complexity of its tunnels. The park protects not only the cave but also the hilly country above, as well as the Green River Valley. The flora and fauna with the cave is some of the most diverse cave-dwelling life in the world. Of the species that inhabits these caves, 14 are known to only exist in this area and 60 are endangered. When many people think of caves, they think of bats, and there are many different types of bats living within Mammoth Cave, including many that are endangered.