Sinkhole risk in Natrona County, WY: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 8%
At or near the surface: 8%
Buried under cover: 0%

The next step for one property

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 433 of Natrona County's 5,341 square miles on soluble rock, 433 of them with the rock at or near the surface. With about 80,410 residents (15 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 382 map points about 3.7 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Natrona County

The nearest county rated sinkhole country is Fall River County, SD, about 165 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Converse County, WY 63 mi east · under 1% at surface
Johnson County, WY 74 mi north · 15% at surface
Washakie County, WY 77 mi northwest · 26% at surface
Carbon County, WY 88 mi south · 4% at surface
Fremont County, WY 93 mi west · 9% at surface
Hot Springs County, WY 98 mi northwest · 18% at surface

What Natrona County is built on

The largest mapped soluble unit here is the Chugwater and Goose Egg Formations (siltstone), Permian-Upper Triassic in age, covering about 2% of the county. Next is the Gallatin Limestone, Gros Ventre Formation and equivalents, and Flathead Sandstone (N) or Cambrian Rocks (S) at 1%.

3% 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 Wind 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

Natrona County ranks 14 of 23 in Wyoming for soluble rock at the surface, and sits above 66% of US counties on that measure.