SinkholeOdds

Sinkhole risk in Comanche County, KS: Sinkhole country

Sinkhole country

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

On soluble rock
39%
At or near the surface
39%
Buried under cover
0%

The next step for one property

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

That works out to roughly 307 of Comanche County's 788 square miles on soluble rock, 307 of them with the rock at or near the surface. With about 1,694 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 408 map points about 1.4 miles apart, so a pocket smaller than that can be missed or overstated.

Read next: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Comanche County

The closest county with no soluble rock mapped is Pratt County, KS, about 43 miles northeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Which formation it is

The largest mapped soluble unit here is the Nippewalla Group (siltstone), Late Permian- Custerian to Cimarronian in age, covering about 39% of the county. Next is the Guadalupia Series: Big Basin Formation, Day Creek Dolomite, and Whitehorse Formation at under 1%.

39% 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 Permian Basin, Anadarko Basin,Dalhart Basin, Palo Duro 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 Kansas

Comanche County ranks 36 of 105 in Kansas for soluble rock at the surface, and sits above 83% of US counties on that measure.