|Historic natural entrance to Carlsbad Caverns. The viewing area near the entrance is crowded on summer evenings when clouds of bats exit the cave. The caverns in the national park area (and throughout the Guadalupe Mountains region) formed in reef-tract limestones (the Capitan Reef complex) deposited in an ancient seaway system that covered the region during Permian Period (NPS, 2010b). The Permian Period extended from about 299 to 251 million years ago (GSA, 2009). The Capitan Reef complex is exposed throughout the southern Guadelupe Mountains in Texas and New Mexico.