Sinkhole risk in Thomas 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: 8%
At or near the surface: 8%
Buried under cover: 0%

What this means before you buy

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

That works out to roughly 84 of Thomas County's 1,075 square miles on soluble rock, 84 of them with the rock at or near the surface. With about 7,802 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 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 Thomas County

The nearest county rated sinkhole country is Harlan County, NE, about 106 miles northeast. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Rawlins County, KS 30 mi north · 24% at surface
Logan County, KS 31 mi south · 11% at surface
Sherman County, KS 34 mi west · 9% at surface
Sheridan County, KS 34 mi east · 15% at surface
Gove County, KS 44 mi southeast · 23% at surface
Decatur County, KS 44 mi northeast · 19% at surface

The rock underneath

The largest mapped soluble unit here is the Ogallala Formation (arkose), Miocene in age, covering about 8% of the county.

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

Thomas County ranks 74 of 105 in Kansas for soluble rock at the surface, and sits above 66% of US counties on that measure.