After we’d breakfasted on Monday morning, September 8, we drove the short distance from Elk Mountain Campground to the Wind Cave National Park visitor center. We were hoping to take the 9am Natural Entrance Tour, but we were too close to its starting time. Ranger Andrew sold us the final two tickets for the 9:45am tour. He informed us that there would be a group of middle schoolers on the tour with us, but it should be fine, since there had been others from the same large group on tours the day before without any problems.

As we waited the forty-five minutes for our tour, we watched the twenty-minute park introductory film and explored the exhibitions in the CCC-era visitor center. We also stopped by the bookstore.

A ranger announced over PA system that it was time for the 9:45 tour, so we made our way out of a lower-level door and along a path at the bottom of a shallow canyon to a meeting shelter. Once the entire group was there (about a dozen adults and maybe twenty-five middle schoolers), Ranger Madison took our tickets and introduced herself. She was originally from Wall, South Dakota and had begun her career with the Park Service at Badlands National Park.

She led us further down the canyon to a hole in the rock. This hole was the original, natural entrance to Wind Cave, where one of its many passages intersected the side of the canyon.

The first Euro-American to encounter the hole was pioneer Tom Bingham, who in 1881 came upon it while a gust of wind was rushing out. It was strong enough to blow off his hat, so he became curious about what was causing it.

We now know that the cave breathes as the barometric pressure in the cave adjusts to match the barometric pressure outside. Depending on whether a high or low pressure system is passing over the Black Hills, wind will alternately rush in or out of the cave. Wind speeds of 70mph have been clocked at the natural entrance.

On this particular morning, however, the pressure was balanced, and the air at the entrance was still.

The air pressure in the cave can be used to calculate the cave’s ultimate size. Currently, Wind Cave is the sixth longest in the world at over 140 miles of explored passages. The barometric pressure in the cave suggests, however, that the explored areas comprise only five percent of the cave’s total.

In 1890, the South Dakota Mining Company filed a claim on Wind Cave. The project manager was Jesse McDonald who explored the cave with his sons, Elmer and Alvin. Alvin, who spent many hours in his teenage years exploring the cave, left a detailed journal of his discoveries. His explorations and journal are all the more remarkable considering he died in 1893 at the age of twenty after contracting Typhoid Fever at the World’s Columbian Exhibition in Chicago.

Although they quickly discovered that there was no mining potential in the cave, the McDonalds were responsible for spreading the fame of Wind Cave, and in 1892 created a walk-in entrance near the natural entrance in order to begin giving caving tours.

It was this walk-in entrance through which Ranger Madison led us into Wind Cave.

Not only is Wind Cave among the longest caves in the world, it is also among the oldest. The cave began forming roughly 320 million years ago during the Paleozoic Era. The entire cave is located within the Pahasapa Limestone layer, which was laid down at the bottom of a vast shallow, sea. The oldest passages and rooms in the cave were created shortly after the limestone bedrock as hydrogen sulfide and sulfuric acid formed by the interactions between water and minerals dissolved the bedrock.

After the Pahasapa Limestone was deposited, sea level fell, allowing fresh water to seep into the cracks and fissures, some of which were exposed at the surface as sinkholes. Then sea levels rose again and anther layer of bedrock was deposited. The cave remained buried for the next 250 million years.

About 65 million years ago, the Black Hills were formed at the same time as the Rocky Mountains. Ancient granites in the center of the hills, which form Harney Peak, the Cathedral Spires, and Mount Rushmore were pushed up. The overlying limestones were eroded away, but a ring of Pahasapa Limestone surrounds the center of the hills. It is in this ring that both Wind Cave and Jewel Cave lie.

The tilting of the limestone into the foothills of the Black Hills caused the cave to drain and surface water erosion to enlarge and expand the passageways into the form of the cave we see today. Had the Black Hills not formed, pushing the cave toward the surface and eventually allowing for the erosion that would reveal the passage discovered by Tom Bingham, the cave would remain buried beneath the surface, completely unknown to anyone.

Ancient veins of calcite from compressed gypsum remain, harder than the surrounding limestone bedrock. The limestone eroded away, crumbling from between the calcite to create boxwork formations.

Ninety-five percent of the known boxwork formations on Earth are found in Wind Cave.

The Natural Entrance Tour lasts about an hour and fifteen minutes and covers half a mile from the walk-in entrance to an elevator that returns visitors to the surface. The tour path is dramatically lit to highlight interesting formations and features. Often Ranger Madison stopped the group in some of the larger rooms to explain some of the cave’s history and geology.

The teacher with the middle school students from Minnesota was excellent at handling the kids, asking them to allow the adults on the tour to go first each time we moved.

The trail along the tour’s path was paved, and occasionally metal staircases led us deeper underground. The tour itself passes right under the visitor center.

Ranger Madison, at one point, turned off the lights so that we could experience complete darkness. She also told us about the only person to have gotten lost in Wind Cave, a young woman who was part of a team working on their cave rescue certifications. She was found after two days and did not get certified, although everyone else on the team did.

Among the longest and oldest caves, Wind Cave is also the densest cave on Earth. All 140+ miles of passageways lie under one square mile of the surface.

Deep within the cave are a series of lakes first discovered by a caving team from Chicago in 1970. It was determined that he lakes are part of the water table, ultimately part of the massive Oglala Aquifer beneath the Great Plains.

All too soon we reached the end of the tour and returned via elevator to the surface into another CCC-era building a short walk from the visitor center.

Everything we’d just seen was beneath this part of the surface of the park.

In addition to the many interpretive installations at the visitor center, much of the information in the post comes from Ranger Madison’s tour and this book:

Wind Cave, An Ancient World Beneath the Hills by Arthur N. Palmer