About 250 million years ago, a shallow sea ringed by a vast, horseshoe-shaped limestone reef covered the area. This formation, called Capitan Reef, is found in southeastern New Mexico and western Texas and includes Guadalupe Mountains National Park, just southwest of Carlsbad Caverns National Park. Carlsbad Caverns National Park, area of the Chihuahuan Desert in southeastern New Mexico, U.S., near the base of the Guadalupe Mountains (a segment of the Sacramento Mountains). It was established in 1923 as a national monument, designated a national park in 1930, and proclaimed a UNESCO World Heritage site in 1995.