Sinkhole risk in Clinton County, IA: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 100%
At or near the surface: 1%
Buried under cover: 99%

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 695 of Clinton County's 695 square miles on soluble rock, 10 of them with the rock at or near the surface. With about 46,015 residents (66 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 352 map points about 1.4 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 99% under cover still counts, and the signs to look for and how an inspection works.

Counties around Clinton County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 36 miles northeast, close enough that the same rock may run under the county line. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Scott County, IA 18 mi south · under 1% at surface
Jackson County, IA 19 mi north · 33% at surface
Rock Island County, IL 30 mi south · 0% at surface
Cedar County, IA 32 mi west · 0% at surface
Carroll County, IL 34 mi east · 11% at surface
Whiteside County, IL 34 mi east · under 1% at surface

The rock underneath

The largest mapped soluble unit here is the Niagaran Series (dolostone (dolomite)), Middle Silurian in age, covering about 87% of the county. Next is the Alexandrian Series at 7%.

Against the rest of Iowa

Clinton County ranks 11 of 99 in Iowa for soluble rock at the surface, and sits above 56% of US counties on that measure.