SinkholeOdds

Sinkhole risk in Niobrara County, WY: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock
15%
At or near the surface
15%
Buried under cover
0%

The next step for one property

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 397 of Niobrara County's 2,626 square miles on soluble rock, 397 of them with the rock at or near the surface. With about 2,301 residents (1 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 391 map points about 2.6 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Niobrara County

The nearest county rated sinkhole country is Fall River County, SD, about 49 miles east. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

What Niobrara County is built on

The largest mapped soluble unit here is the Pierre Shale (shale), Upper Cretaceous in age, covering about 10% of the county. Next is the Niobrara Formation at 2%.

10% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

The county also lies over the Powder River Basin, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Wyoming

Niobrara County ranks 8 of 23 in Wyoming for soluble rock at the surface, and sits above 72% of US counties on that measure.