SinkholeOdds

Sinkhole risk in Sheridan 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 386 of Sheridan County's 2,523 square miles on soluble rock, 386 of them with the rock at or near the surface. With about 32,978 residents (13 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 372 map points about 2.6 miles apart, so a pocket smaller than that can be missed or overstated.

Read next: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Sheridan County

The nearest county rated sinkhole country is Fall River County, SD, about 199 miles southeast. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Which formation it is

The largest mapped soluble unit here is the Madison Group and Darby Formation (TB, N) or Madison Group and Three Forks and Jefferson Formations (Y) (limestone), Upper Devonian-Upper Mississippian in age, covering about 6% of the county. Next is the Bighorn Dolomite at 3%.

1% 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

Sheridan County ranks 7 of 23 in Wyoming for soluble rock at the surface, and sits above 72% of US counties on that measure.