SinkholeOdds

Sinkhole risk in Harper County, KS: Sinkhole country

Sinkhole country

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

On soluble rock
31%
At or near the surface
31%
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 249 of Harper County's 801 square miles on soluble rock, 249 of them with the rock at or near the surface. With about 5,413 residents (7 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.

Two things to read before deciding: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Harper County

The closest county with no soluble rock mapped is Pratt County, KS, about 49 miles northwest. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

The rock underneath

The largest mapped soluble unit here is the Nippewalla Group (siltstone), Late Permian- Custerian to Cimarronian in age, covering about 27% of the county. Next is the Sumner Group at 5%.

31% 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

Harper County ranks 48 of 105 in Kansas for soluble rock at the surface, and sits above 80% of US counties on that measure.