Sinkhole risk in Converse County, WY: Not karst, but voids possible

Not karst, but voids possible

No soluble bedrock; some pseudokarst (piping or lava-tube ground).

On soluble rock: under 1%
At or near the surface: under 1%
Buried under cover: 0%

What this means before you buy

Not true karst, but soil piping or lava tubes can still open voids - mention it to an inspector.

That works out to roughly 38 of Converse County's 4,255 square miles on soluble rock, 38 of them with the rock at or near the surface. With about 13,766 residents (3 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 347 map points about 3.5 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Converse County

The nearest county rated sinkhole country is Fall River County, SD, about 103 miles east. None of the 6 closest counties land in the same band, so Converse County stands out from its surroundings.

Niobrara County, WY 54 mi east · 15% at surface
Natrona County, WY 63 mi west · 8% at surface
Platte County, WY 66 mi southeast · 8% at surface
Weston County, WY 76 mi northeast · 14% at surface
Campbell County, WY 83 mi north · 0% at surface
Goshen County, WY 86 mi southeast · 1% at surface

Which formation it is

The largest mapped soluble unit here is the Casper Formation (sandstone), Upper and Middle Pennsylvanian-Permian in age, covering about under 1% of the county. Next is the Wells and Amsden Formations (TB), or Casper Formation and Madison Limestone (N, S) at under 1%.

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

Converse County ranks 20 of 23 in Wyoming for soluble rock at the surface, and sits above 55% of US counties on that measure.