South Dakota Sinkhole Reveals a Scary Surprise Under a Subdivision

One suburban neighborhood in South Dakota got the surprise of a lifetime.

About a dozen homes were evacuated after a sinkhole opened up. But the real surprise happened after people went inside.

Neighborhood Residents Evacuated After an Unusual Sinkhole Opened Up

Some residents of the Hideaway Hills development in Black Hawk, South Dakota were evacuated from their homes, after a massive sinkhole opened up.

The ground gave way on April 27th — right in someone’s front yard.

sinkhole that opened in a black hawk south dakota neighborhood
Paha Sapa Grotto via boredpanda

However, it looked a little different than your average sinkhole. In fact, it kind of looked like a cave.

A local caving group called Paha Sapa Grotto decided to take a look inside, and now the images are going viral.

The Paha Sapa Grotto is a subchapter of the National Speleological Society — a world leader in caving science, exploration, and conservation.

“When we heard about the sinkhole, we knew it was on a geological unit that could potentially have caves in it,” said Nick Anderson, a member of the caving group. “We also knew that county emergency management wouldn’t have much experience in this area, so we offered to help to determine the scope of the problem.”

So, working with emergency management officials, a group of cavers initially entered the sinkhole. The leader of the initial team was Adam Weaver, the Vice-Chairman of the Paha Sapa Grotto, and the Director of the National Speleological Society.

“When I got to the bottom,” Weaver said of the first assessment trip, “I could see 80 feet into a large cavity that was at that point under the street. I Stopped going forward because the sidewalk and street were bent down and cracked.”

The Cavers Discovered It Wasn’t a Cave – So What’s Under There?

abandoned mine under subdivision in south dakota
Paha Sapa Grotto via boredpanda

However, after emergency management brought in machinery to pull up the cracked and buckled concrete, they went back down.

That’s when they realized it wasn’t actually a cave. Instead, they had stumbled upon a mine.

“It was immediately obvious that it was a mine. There were a lot of drill holes and old mining debris,” Weaver said.

inside the mine under a subdivision in south dakota
Paha Sapa Grotto

He then sketched a quick map of what the team could see.

“I think that’s when the severity of the issue really set in with a lot of people,” he said.

The following evening, Weaver accompanied two teams of explorers equipped with survey gear, ready to map the mine. From what they could see, the mine was over 2,000 feet across and over 150 feet wide — sprawling directly under at least 12 homes in the subdivision.

map overlay showing the mine under Hideaway Hills subdivision
Paha Sapa Grotto

The full extent of the mine is still unknown, as some passages were collapsed, flooded, or too dangerous for the teams to enter.

As it turns out, the neighborhood was built on top of an abandoned gypsum mine from the 1920s.

Is That a Car?

The weirdest part? It appears as if the mine may have opened up at some point after it shut down. When the cavers took photos below the surface, there was a 1950s-era car down there.

car underground inside abandoned mine
Paha Sapa Grotto

In other words, someone knew this hazard was here.

The director of emergency management tried applying for grants to help the homeowners, but programs like FEMA said they were ineligible.

119 homeowners of the Hideaway Hills subdivision are now suing South Dakota, Meade County, and developers of the subdivision.

The complaint claims that the developers knew that the plat of land had been mined on its surface and underground.

They’re also going after title companies involved in sales of the homes, attorneys for previous owners, and real estate agents who sold the homes.