Jewel Cave National Monument, located in the Black Hills of South Dakota in the United States (U.S.), is the world's second longest cave. The cave isn't named for any actual jewels it possesses, but rather for the calcite spar crystals which glitter like jewels along the walls and ceilings. It spans roughly 150 miles (240 km), and is second only to Kentucky's Mammoth Cave National Park, also in the U.S., which more than doubles Jewel Cave National Monument with 367 charted miles (590 km). Jewel Cave was discovered in 1900, and U.S. President Theodore Roosevelt proclaimed it a national monument on February 7, 1908. It continues to operate as a tourist attraction under the U.S. National Parks Service, a division of the Department of the Interior.
Jewel Cave was discovered in 1900 by brothers Frank and Albert Michaud. Thinking the cave to be of some significance, the two filed a mining claim under the title of "Jewel Tunnel Lode." For a few years the Michaud brothers attempted to turn the cave into a tourist site, but eventually sold it off to the U.S. government for $750. The government continued efforts to bring tourists to Jewel Cave National Monument, while researchers continued to explore its passageways. In 1935, the Civilian Conservation Corps (CCC) used a $1500 budget from the government to set up new amenities for the public and the park service. A three-room cabin to be used by rangers was built, and comfort stations with working bathrooms were provided for tourists. The CCC also expanded the entrance to the cave.
Up until 1959, only two miles (3.2 km) of the cave had been discovered. By 1961, however, more than 15 miles (24 km) of cave passageways had been charted, thanks to an ambitious effort led by rock climbers Herb and Jann Conn, along with geologist Dwight Deal. Although the discovery was exciting, it presented problems. The newly charted passageways extended beyond the boundaries of the initial Jewel Cave National Monument and into U.S. Forest Service lands. This was solved by swapping land with the Forest Service, thereby extending the monument's boundaries. The National Park Service quickly set up a new visitor center, and began conducting new tour routes. Other features were also added over a five-and-a-half-year renovation period, such as an elevator, a parking lot and a maintenance area.
Even today, more than 45 percent of the cave's known passageways extend beyond the boundaries of Jewel Cave National Monument and into Black Hills National Forest. Based on the cave's airflow, researchers believe there is significantly more cave passageways yet to be discovered. Qualified volunteers continue to map out an average of 3 miles (4.8 km) of previously uncharted territory a year.
Jewel Cave National Monument is also host to a variety of surface hiking trails. There are 1,279 acres (5.17 square kilometers) of forest within the park to hike and explore. Guides offer tours within the cave as well as on surface trails. Some topics that tours focus on are birding and wildflowers. Tours on the surface are free, while tours within the cave are offered for a fee.