Sinkhole risk in Iron County, MO: Sinkhole country

Sinkhole country

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

On soluble rock: 79%
At or near the surface: 79%
Buried under cover: 0%

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 434 of Iron County's 550 square miles on soluble rock, 434 of them with the rock at or near the surface. With about 9,420 residents (17 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 515 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Iron County

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

St. Francois County, MO 18 mi northeast · 71% at surface
Madison County, MO 22 mi southeast · 67% at surface
Reynolds County, MO 23 mi southwest · 98% at surface
Washington County, MO 24 mi northwest · 96% at surface
Ste. Genevieve County, MO 34 mi northeast · 76% at surface
Wayne County, MO 38 mi south · 95% at surface

What Iron County is built on

The largest mapped soluble unit here is the Eminence Dolomite, Potosi Dolomite (dolostone (dolomite)), Late Cambrian-Croixian Series in age, covering about 58% of the county. Next is the Elvins Group- (Including Derby-Doerun Dolomite, Davis Formation), Bonneterre Dolomite at 18%.

Against the rest of Missouri

Iron County ranks 46 of 115 in Missouri for soluble rock at the surface, and sits above 94% of US counties on that measure.