Sinkhole risk in Madison County, MO: Sinkhole country

Sinkhole country

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

On soluble rock: 67%
At or near the surface: 67%
Buried under cover: 0%

The next step for one property

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

That works out to roughly 329 of Madison County's 494 square miles on soluble rock, 329 of them with the rock at or near the surface. With about 12,852 residents (26 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 395 map points about 1.1 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 Madison County

The closest county with no soluble rock mapped is Perry County, IL, about 68 miles northeast. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Bollinger County, MO 21 mi southeast · 91% at surface
Iron County, MO 22 mi northwest · 79% at surface
St. Francois County, MO 24 mi north · 71% at surface
Wayne County, MO 26 mi south · 95% at surface
Ste. Genevieve County, MO 30 mi north · 76% at surface
Perry County, MO 34 mi northeast · 86% at surface

Which formation it is

The largest mapped soluble unit here is the Eminence Dolomite, Potosi Dolomite (dolostone (dolomite)), Late Cambrian-Croixian Series in age, covering about 52% of the county. Next is the Elvins Group- (Including Derby-Doerun Dolomite, Davis Formation), Bonneterre Dolomite at 12%.

Against the rest of Missouri

Madison County ranks 53 of 115 in Missouri for soluble rock at the surface, and sits above 92% of US counties on that measure.