The Guadalupe Mountains are part of a mostly buried 400-mile-long U-shaped fossil reef complex, Capitan Reef, which extends through a large area of west Texas and southeastern New Mexico. The longest exposed stretch of Capitan Reef, 12 miles of which is in the park, extends from Guadalupe Mountains National Park northeast almost to the city of Carlsbad, New Mexico, a distance of almost 40 miles. This 260-million- to 270-million-year-old reef is one of the world’s finest examples of an ancient re