Christopher Pelczarski is a caver, and he’s seen a lot of underground passageways. But he’s never seen anything like the abandoned gypsum mine that was exposed by sinkholes this week in Black Hawk.
For one thing, he never expected to find a car down there.
“There was one place where there is actually literally a car coming out of a hole from the surface, an old car. It’s like a 1951 Ford,” Pelczarski said. “Yeah, it’s half sticking out of the ceiling, basically.”
He figures there used to be a scrapyard or garbage dump on the surface, and the car somehow sank down from there.
There are two sinkholes as large as 40 feet wide in the yards of a residential neighborhood of Black Hawk, just north of Rapid City. Local officials have evacuated at least a dozen homes.
Pelczarski is a member of a caving club called the Paha Sapa Grotto. Club members volunteered to explore the mine and use their expertise to measure and map it. Their efforts will help authorities pinpoint danger spots.
The cavers mapped 2,300 linear feet of passages, Pelczarski said. There were additional tunnels they couldn’t access because they were flooded or collapsed. Some of the tunnels were big – 12 feet high and 40 feet wide.
The ceiling at one place in the mine was 30 feet above their heads, indicating a potentially thin surface above.
“Being experienced at traveling underground, we were cautious to go in,” Pelczarski said, “but we recognized somebody needed to do this, and we’re the ones that have expertise in that area.”
Besides the car, the cavers also found old mining equipment.
“There are places you can see old rail-car tracks from the mining operation,” Pelczarski said. “There’s wood that’s just to the point where it looks like a piece of wood, but then you step on it and it just mushes like paper pulp.”
The mine apparently dates to the early 1900s. It’s unknown whether the neighborhood developers knew what was underground.
-Seth Tupper is SDPB's business and economic development reporter.