Sinkhole risk in Iowa 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: 98%
At or near the surface: 0%
Buried under cover: 98%

What this means before you buy

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

That works out to roughly 576 of Iowa County's 586 square miles on soluble rock. With about 16,423 residents (28 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 391 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 98% under cover still counts, and how these percentages are measured.

Counties around Iowa County

The nearest county rated sinkhole country is Clayton County, IA, about 88 miles northeast. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Poweshiek County, IA 24 mi west · 0% at surface
Johnson County, IA 24 mi east · 0% at surface
Keokuk County, IA 25 mi south · 0% at surface
Benton County, IA 28 mi north · 0% at surface
Washington County, IA 30 mi southeast · 0% at surface
Linn County, IA 36 mi northeast · 0% at surface

What Iowa County is built on

The largest mapped soluble unit here is the Yellow Spring Group (shale), Late Devonian in age, covering about 48% of the county. Next is the Lime Creek Formation at 35%.

Against the rest of Iowa

Iowa County ranks 53 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.