Sinkhole risk in St. Clair County, MO: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 43%
At or near the surface: 43%
Buried under cover: 0%

The next step for one property

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 288 of St. Clair County's 675 square miles on soluble rock, 288 of them with the rock at or near the surface. With about 9,848 residents (15 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 336 map points about 1.4 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 St. Clair County

The nearest county rated sinkhole country is Cedar County, MO, about 22 miles south, close enough that the same rock may run under the county line. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Cedar County, MO 22 mi south · 54% at surface
Henry County, MO 24 mi north · 18% at surface
Hickory County, MO 26 mi east · 92% at surface
Benton County, MO 32 mi northeast · 89% at surface
Vernon County, MO 34 mi southwest · 9% at surface
Bates County, MO 34 mi northwest · 45% at surface

The rock underneath

The largest mapped soluble unit here is the Osagean Series (limestone), Early Mississippian-Osagean Series in age, covering about 20% of the county. Next is the Smithville Dolomite, Powell Dolomite, Cotter Dolomite, Jefferson City Dolomite at 11%.

Against the rest of Missouri

St. Clair County ranks 60 of 115 in Missouri for soluble rock at the surface, and sits above 85% of US counties on that measure.