Sinkhole risk in Sioux County, NE: 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: 13%
At or near the surface: 13%
Buried under cover: 0%

What to do about a house in Sioux County

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

That works out to roughly 267 of Sioux County's 2,067 square miles on soluble rock, 267 of them with the rock at or near the surface. With about 1,099 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 363 map points about 2.4 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Sioux County

The nearest county rated sinkhole country is Dawes County, NE, about 35 miles northeast, close enough that the same rock may run under the county line. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Dawes County, NE 35 mi northeast · 33% at surface
Box Butte County, NE 38 mi southeast · 0% at surface
Goshen County, WY 41 mi southwest · 1% at surface
Scotts Bluff County, NE 43 mi south · 0% at surface
Fall River County, SD 53 mi north · 37% at surface
Niobrara County, WY 55 mi northwest · 15% at surface

What Sioux County is built on

The largest mapped soluble unit here is the Pierre Shale (shale), Late Cretaceous in age, covering about 13% of the county.

13% 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 Northern Denver 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 Nebraska

Sioux County ranks 22 of 93 in Nebraska for soluble rock at the surface, and sits above 70% of US counties on that measure.