Exploring the history of Jewel Cave
The attached interview above is from SDPB's daily public-affairs show, In the Moment.
In 1900, a small hole in the ground with cold air coming from it was discovered. Upon making this hole larger, a pair of brothers found several calcite crystals shining in the light.
Jewel Cave is 13 miles west of Custer. In 1908 President Theodore Roosevelt made this a national monument.