Sinkhole risk in Grant County, WI: Sinkhole country

Sinkhole country

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

On soluble rock: 91%
At or near the surface: 84%
Buried under cover: 6%

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 1,041 of Grant County's 1,148 square miles on soluble rock, 969 of them with the rock at or near the surface. With about 52,330 residents (46 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 257 map points about 2.1 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Grant County

The closest county with no soluble rock mapped is Juneau County, WI, about 79 miles north. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Crawford County, WI 28 mi northwest · 71% at surface
Dubuque County, IA 30 mi south · 34% at surface
Iowa County, WI 30 mi east · 77% at surface
Clayton County, IA 32 mi west · 54% at surface
Lafayette County, WI 32 mi southeast · 91% at surface
Richland County, WI 37 mi north · 41% at surface

Which formation it is

The largest mapped soluble unit here is the Sinnipee Group (dolostone (dolomite)), Ordovician in age, covering about 49% of the county. Next is the Ancell Group at 26%.

Against the rest of Wisconsin

Grant County ranks 2 of 72 in Wisconsin for soluble rock at the surface, and sits above 95% of US counties on that measure.