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Jewel Cave National Monument

Hidden beneath the Black Hills of South Dakota is the subterranean world of Jewel Cave National Monument, where countless crystal formations sparkle with the brilliance of gems.

When Jewel Cave National Monument was proclaimed in 1908, less than half a mile of cave had been discovered. Explorations in the past 40 years have revealed more than 135 miles of twisting and turning passages, making it the second-longest known cave in the world.

Jewel Cave National Monument
©National Park Service
Jewel Cave is the second-longest
known cave in the world.

The cave began forming millions of years ago as the Black Hills were being created. The forces that uplifted mountains also created faults in the earth. Beginning 30 to 50 million years ago, slightly acidic water seeping into these cracks and crevices dissolved the surrounding limestone and hollowed out the passages of Jewel Cave. When the water table lowered, caverns lined with a variety of formations remained. The process continues today, as water seeping into the cave alters its delicate formations.

Many of Jewel Cave's formations were formed as water trickling into the cave left behind tiny deposits of minerals. Formations called stalactites hang like icicles from the ceilings, while stalagmites reach up from the floors. Where they meet, columns and pillars divide the chambers. Water trickling down slanted ceilings created formations that look like draperies, some 30 feet long. Other formations are more mysterious. Hydromagnesite balloons -- tiny silver bubbles that are found in few other caves -- have yet to be explained.

The most abundant formations, and the ones for which Jewel Cave is named, are the jewellike crystals of calcite known as dogtooth spar and nailhead spar. Jewel Cave has the most extensive collection of calcite crystals known, coating nearly every chamber wall with layers six inches thick. Some are translucent, formed only of pure calcite. Others contain additional minerals and appear yellow, red, or opaque white. Individual crystals can be as tiny as a grain of rice or as large as a goose egg.

Though much of the cave is closed to the public because of its scientific value, several trails allow visitors to see the formations up close. The scenic tour leads through much-decorated rooms featuring sparkling calcite crystals and colorful stalactites, stalagmites, and draperies. The historic trail follows the paths of early cave explorers, and the formations are illuminated by old-style candle lanterns. A spelunking tour provides the chance to explore the wild, undeveloped portions of Jewel Cave.

Above ground is a ponderosa pine forest, home to whitetail deer, elk, marmots, golden eagles, and many other species. Hiking trails through the monument's two square miles allow visitors to sample the rugged hills, canyons, and prairies of the Black Hills.

Jewel Cave contains some of the world's most rare and unusual formations. Helictites, small formations made of calcite, twist and turn as though they were formed in a chamber without gravity. Another calcite formation, called popcorn, grows in small knobby clusters. Veins of calcite deposited in a crisscross pattern are called boxwork. Frostwork, needle-like formations of calcite or aragonite, are as delicate as blown glass.

Flowers, needles, spiders, and cottony beards of the mineral gypsum also decorate the cave. Underground sparklers called scintillites are composed of the reddish rock called chert coated with sparkling clear quartz crystals. These formations were unknown until discovered in Jewel Cave.

Jewel Cave National Monument Information
Address: 11149 U.S. Highway 16, Custer, SD
Phone: 605/673-2288
Hours of Operation:

  • Monument open year-round, but times of tours vary
  • visitor center is open from 8 a.m. to 4:30 p.m.


  • Tour fees range from $2 to $4
  • Spelunking tours range from $13.50 to $27
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Eric Peterson is a Denver-based freelance writer who has contributed to numerous guidebooks about the Western United States.