SinkholeOdds

Sinkhole risk in St. Louis city, MO: Pockets of it

Pockets of it

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

On soluble rock
66%
At or near the surface
47%
Buried under cover
20%

What this means before you buy

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 41 of St. Louis city's 62 square miles on soluble rock, 29 of them with the rock at or near the surface. With about 279,695 residents (4,532 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 474 map points about 0.4 miles apart, so a pocket smaller than that can be missed or overstated.

Read next: why gypsum and salt move faster than limestone, and why the 20% under cover still counts.

Counties around St. Louis city

The nearest county rated sinkhole country is St. Louis County, MO, about 11 miles west, close enough that the same rock may run under the county line. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

What St. Louis city is built on

The largest mapped soluble unit here is the Meramecian Series (limestone), Late Mississippian-Meramecian Series in age, covering about 53% of the county. Next is the Marmaton Group at 11%.

The county also lies over the Illinois Basin, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Missouri

St. Louis city ranks 57 of 115 in Missouri for soluble rock at the surface, and sits above 86% of US counties on that measure.