Sinkhole risk in Hot Springs 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: 18%
At or near the surface: 18%
Buried under cover: 0%

What this means before you buy

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 351 of Hot Springs County's 2,004 square miles on soluble rock, 351 of them with the rock at or near the surface. With about 4,625 residents (2 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 560 map points about 1.9 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 Hot Springs County

The nearest county rated sinkhole country is Fall River County, SD, about 249 miles east. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Washakie County, WY 40 mi east · 26% at surface
Fremont County, WY 47 mi south · 9% at surface
Big Horn County, WY 60 mi north · 25% at surface
Park County, WY 78 mi northwest · 1% at surface
Johnson County, WY 95 mi east · 15% at surface
Natrona County, WY 98 mi southeast · 8% at surface

What Hot Springs County is built on

The largest mapped soluble unit here is the Chugwater and Dinwoody Formations (mudstone), Lower Triassic-Upper Triassic in age, covering about 7% of the county. Next is the Bighorn Dolomite, Gallatin Limestone, and Gros Ventre Formation (TB), Bighorn Dolomite, Snowy Range Formation, Pilgrim Limestone, Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone (Y), Bighorn Dolomite, Gallatin Limestone, Gros Ve at 4%.

7% 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 Bighorn 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

Hot Springs County ranks 6 of 23 in Wyoming for soluble rock at the surface, and sits above 73% of US counties on that measure.