Carlsbad Caverns, located in the Guadalupe Mountains in southern New Mexico, is another popular U.S. cave system. Hundreds of thousands of years of erosion have created stunning, almost cartoon-like rock formations throughout the caverns. The estimated 120 limestone caves and surrounding 720 acres were designated Carlsbad Caverns National Park in 1930, and in 1995, the property was named a UNESCO World Heritage Site.