SinkholeOdds

Sinkhole risk in Logan County, KS: 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
11%
At or near the surface
11%
Buried under cover
0%

What to do about a house in Logan County

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

That works out to roughly 113 of Logan County's 1,073 square miles on soluble rock, 113 of them with the rock at or near the surface. With about 2,694 residents (3 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 400 map points about 1.6 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 how these percentages are measured.

Counties around Logan County

The nearest county rated sinkhole country is Harlan County, NE, about 128 miles northeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

The rock underneath

The largest mapped soluble unit here is the Niobrara Chalk (shale), Late Cretaceous in age, covering about 5% of the county. Next is the Pierre Shale at 4%.

4% 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

Logan County ranks 71 of 105 in Kansas for soluble rock at the surface, and sits above 68% of US counties on that measure.