Sinkhole risk in Riley 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: 75%
At or near the surface: 73%
Buried under cover: 2%

The next step for one property

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 457 of Riley County's 610 square miles on soluble rock, 444 of them with the rock at or near the surface. With about 72,557 residents (119 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 607 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Riley County

The nearest county rated sinkhole country is Dickinson County, KS, about 37 miles southwest, close enough that the same rock may run under the county line. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Geary County, KS 20 mi south · 75% at surface
Pottawatomie County, KS 22 mi east · 6% at surface
Clay County, KS 24 mi west · 35% at surface
Marshall County, KS 36 mi north · 2% at surface
Wabaunsee County, KS 37 mi southeast · 65% at surface
Dickinson County, KS 37 mi southwest · 79% at surface

The rock underneath

The largest mapped soluble unit here is the Chase Group (shale), Early Permian - Gearyan in age, covering about 60% of the county. Next is the Council Grove Group at 10%.

4% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

Against the rest of Kansas

Riley County ranks 12 of 105 in Kansas for soluble rock at the surface, and sits above 93% of US counties on that measure.