Sinkhole risk in Clayton County, IA: Sinkhole country

Sinkhole country

Soluble rock at or near the surface across much of the county.

On soluble rock: 97%
At or near the surface: 54%
Buried under cover: 43%

What this means before you buy

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

That works out to roughly 752 of Clayton County's 778 square miles on soluble rock, 418 of them with the rock at or near the surface. With about 16,931 residents (22 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 298 map points about 1.6 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 43% under cover still counts, and the signs to look for and how an inspection works.

Counties around Clayton County

The closest county with no soluble rock mapped is Juneau County, WI, about 97 miles northeast. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Delaware County, IA 26 mi south · 5% at surface
Fayette County, IA 26 mi west · 19% at surface
Allamakee County, IA 30 mi north · 25% at surface
Grant County, WI 32 mi east · 84% at surface
Crawford County, WI 34 mi northeast · 71% at surface
Dubuque County, IA 35 mi southeast · 34% at surface

The rock underneath

The largest mapped soluble unit here is the Galena-Decorah-Platteville Formations (dolostone (dolomite)), Middle Ordovician-Mohawkian Series in age, covering about 43% of the county. Next is the Maquoketa Formation at 32%.

Against the rest of Iowa

Clayton County ranks 1 of 99 in Iowa for soluble rock at the surface, and sits above 88% of US counties on that measure.