Sinkhole risk in Mills 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: 86%
At or near the surface: 0%
Buried under cover: 86%

The next step for one property

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

That works out to roughly 378 of Mills County's 437 square miles on soluble rock. With about 14,717 residents (34 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 394 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 86% under cover still counts, and how these percentages are measured.

Counties around Mills County

The nearest county rated sinkhole country is Johnson County, KS, about 154 miles south. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Fremont County, IA 20 mi south · 0% at surface
Pottawattamie County, IA 22 mi north · 0% at surface
Montgomery County, IA 24 mi east · 0% at surface
Sarpy County, NE 26 mi west · 0% at surface
Cass County, NE 29 mi west · 0% at surface
Page County, IA 32 mi southeast · 0% at surface

What Mills County is built on

The largest mapped soluble unit here is the Shawnee Group (limestone), Late Pennsylvanian-Virgil Series in age, covering about 65% of the county. Next is the Kansas City Group at 11%.

Against the rest of Iowa

Mills County ranks 67 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.