Jewel Cave National Monument

Jewel Cave National Monument, national monument proclaimed in 1908. Located in southwestern South Dakota, the monument preserves limestone caverns featuring a variety of calcite crystal formations. Jewel Cave was discovered in the early 20th century by brothers Frank and Albert Michaud, and extensively explored between 1959 and 1980 by the husband-and-wife team of Herb and Jan Conn. Jewel Cave has more than 160 km (100 mi) of passages and it is one of the most extensive caves in the world. Administered by the National Park Service. Area, 515 hectares (1,274 acres).