Sinkhole risk in Winnebago County, IA: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 95%
At or near the surface: 0%
Buried under cover: 95%

What to do about a house in Winnebago County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 380 of Winnebago County's 400 square miles on soluble rock. With about 10,383 residents (26 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 392 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Winnebago County

The nearest county rated sinkhole country is Clayton County, IA, about 128 miles east. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Hancock County, IA 21 mi south · 0% at surface
Faribault County, MN 23 mi northwest · 0% at surface
Worth County, IA 25 mi east · 0% at surface
Kossuth County, IA 26 mi southwest · 0% at surface
Freeborn County, MN 28 mi northeast · 0% at surface
Cerro Gordo County, IA 32 mi southeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Cedar Valley Limestone (limestone), Middle Dovonian in age, covering about 56% of the county. Next is the Maquoketa Formation at 27%.

Against the rest of Iowa

Winnebago County ranks 96 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.