Jewel Cave: Crystal Walls in Limestone

Hidden in the hills west of Custer is a cave so large and so complex that scientists have been mapping it for over a century and are still finding new passages. Jewel Cave National Monument, proclaimed by President Theodore Roosevelt on February seventh, nineteen oh eight, contains the fifth longest cave in the world, with more than two hundred twenty miles of surveyed passages as of twenty twenty-five. The cave is carved through a limestone formation called the Pahasapa Limestone, laid down roughly three hundred fifty million years ago when this part of South Dakota lay beneath a shallow tropical sea.

Acidic groundwater slowly dissolved the limestone over millions of years, leaving behind the passages that explorers now navigate with headlamps and knee pads. The cave's name comes from its walls. Two brothers named Frank and Albert Michaud discovered the cave in nineteen hundred when they felt cold air blowing from a small hole in a canyon, enlarged the entrance with dynamite, and found a cavern whose ceilings and walls were covered in calcite crystals that glittered in their candlelight.

The crystals are a type of formation called dogtooth spar and nailhead spar, mineral growths that accumulated as mineral-laden water evaporated over millions of years. The Michaud brothers tried to make a business of the cave, and Roosevelt protected it as a national monument eight years after their discovery. Today rangers lead guided tours through the cave, and serious cavers can explore its deeper reaches on special wild cave tours.

The cave continues to grow, passage by passage, as new corridors are pushed open each season.