Sinkhole risk in Graham County, KS: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in 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 Graham County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 299 of Graham County's 899 square miles on soluble rock, 299 of them with the rock at or near the surface. With about 2,370 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 414 map points about 1.5 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 Graham County

The nearest county rated sinkhole country is Harlan County, NE, about 62 miles northeast. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Norton County, KS 30 mi north · 22% at surface
Rooks County, KS 30 mi east · 48% at surface
Trego County, KS 30 mi south · 57% at surface
Sheridan County, KS 30 mi west · 15% at surface
Phillips County, KS 41 mi northeast · 32% at surface
Decatur County, KS 43 mi northwest · 19% at surface

What Graham County is built on

The largest mapped soluble unit here is the Ogallala Formation (arkose), Miocene in age, covering about 24% of the county. Next is the Niobrara Chalk at 9%.

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

Graham County ranks 43 of 105 in Kansas for soluble rock at the surface, and sits above 81% of US counties on that measure.