Jewel Cave National Monument in South Dakota protects Jewel Cave, discovered in 1900 by Frank and Albert Michaud after they noticed cold air from a canyon opening. Named for its calcite crystals, the cave became the first national monument created specifically to protect a cave when Theodore Roosevelt established it in 1908. Known for its glittering formations and its “breathing” airflow, Jewel Cave is a solutional limestone cave with more than 220 miles of mapped passages, making it among the longest caves in the world. Since 1959, exploration has greatly expanded knowledge of the system, which remains only partly known.

Photo: Wikipedia · Public domain

Photo: Wikipedia · Public domain

Photo: Wikipedia · Public domain

Custer, South Dakota · USA