SinkholeOdds

Sinkhole risk in Dawes County, NE: Sinkhole country

Sinkhole country

Fast-dissolving gypsum or salt beds under a large part of the county.

On soluble rock
33%
At or near the surface
33%
Buried under cover
0%

What to do about a house in Dawes County

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

That works out to roughly 461 of Dawes County's 1,396 square miles on soluble rock, 461 of them with the rock at or near the surface. With about 8,003 residents (6 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 397 map points about 1.9 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Dawes County

The closest county with no soluble rock mapped is Box Butte County, NE, about 35 miles south. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

What Dawes County is built on

The largest mapped soluble unit here is the Pierre Shale (shale), Late Cretaceous in age, covering about 32% of the county. Next is the Niobrara Formation at under 1%.

32% 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

Dawes County ranks 12 of 93 in Nebraska for soluble rock at the surface, and sits above 81% of US counties on that measure.