Sinkhole risk in Allamakee 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: 61%
At or near the surface: 25%
Buried under cover: 36%

What this means before you buy

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 392 of Allamakee County's 639 square miles on soluble rock, 161 of them with the rock at or near the surface. With about 14,184 residents (22 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 321 map points about 1.4 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 36% under cover still counts, and the signs to look for and how an inspection works.

Counties around Allamakee County

The nearest county rated sinkhole country is Crawford County, WI, about 23 miles east, 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.

Crawford County, WI 23 mi east · 71% at surface
Winneshiek County, IA 24 mi west · 18% at surface
Houston County, MN 28 mi north · 28% at surface
Clayton County, IA 30 mi south · 54% at surface
Vernon County, WI 36 mi northeast · 63% at surface
Fayette County, IA 37 mi southwest · 19% at surface

Which formation it is

The largest mapped soluble unit here is the Galena-Decorah-Platteville Formations (dolostone (dolomite)), Middle Ordovician-Mohawkian Series in age, covering about 31% of the county. Next is the Prairie du Chien Formation at 28%.

Against the rest of Iowa

Allamakee County ranks 4 of 99 in Iowa for soluble rock at the surface, and sits above 77% of US counties on that measure.