Sinkhole risk in Benton 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 this means before you buy

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

That works out to roughly 678 of Benton County's 716 square miles on soluble rock. With about 25,799 residents (36 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 399 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 95% under cover still counts, and how these percentages are measured.

Counties around Benton County

The nearest county rated sinkhole country is Clayton County, IA, about 64 miles northeast. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Linn County, IA 24 mi east · 0% at surface
Tama County, IA 24 mi west · 0% at surface
Iowa County, IA 28 mi south · 0% at surface
Buchanan County, IA 28 mi northeast · 0% at surface
Black Hawk County, IA 29 mi northwest · 0% at surface
Poweshiek County, IA 37 mi southwest · 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 69% of the county. Next is the Lime Creek Formation at 22%.

Against the rest of Iowa

Benton County ranks 18 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.