Sinkhole risk in St. Francois County, MO: Sinkhole country

Sinkhole country

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

On soluble rock: 71%
At or near the surface: 71%
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 319 of St. Francois County's 452 square miles on soluble rock, 319 of them with the rock at or near the surface. With about 67,503 residents (149 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 533 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around St. Francois County

The closest county with no soluble rock mapped is Perry County, IL, about 63 miles east. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Iron County, MO 18 mi southwest · 79% at surface
Ste. Genevieve County, MO 18 mi east · 76% at surface
Madison County, MO 24 mi south · 67% at surface
Washington County, MO 25 mi west · 96% at surface
Jefferson County, MO 31 mi north · 98% at surface
Monroe County, IL 36 mi northeast · 6% at surface

Which formation it is

The largest mapped soluble unit here is the Elvins Group- (Including Derby-Doerun Dolomite, Davis Formation), Bonneterre Dolomite (dolostone (dolomite)), Late Cambrian-Croixian Series in age, covering about 41% of the county. Next is the Eminence Dolomite, Potosi Dolomite at 26%.

Against the rest of Missouri

St. Francois County ranks 52 of 115 in Missouri for soluble rock at the surface, and sits above 93% of US counties on that measure.