Sinkhole risk in Washington 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: 28%
At or near the surface: 15%
Buried under cover: 13%

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 251 of Washington County's 895 square miles on soluble rock, 136 of them with the rock at or near the surface. With about 5,572 residents (6 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.

Worth reading for this county: why gypsum and salt move faster than limestone, and why the 13% under cover still counts.

Counties around Washington County

The nearest county rated sinkhole country is Dickinson County, KS, about 63 miles south. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Jefferson County, NE 28 mi north · 5% at surface
Republic County, KS 30 mi west · 19% at surface
Clay County, KS 30 mi south · 35% at surface
Marshall County, KS 31 mi east · 2% at surface
Cloud County, KS 35 mi southwest · 22% at surface
Thayer County, NE 38 mi northwest · 2% at surface

The rock underneath

The largest mapped soluble unit here is the Chase Group (shale), Early Permian - Gearyan in age, covering about 13% of the county. Next is the Sumner Group at 11%.

11% 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

Washington County ranks 65 of 105 in Kansas for soluble rock at the surface, and sits above 72% of US counties on that measure.