SinkholeOdds

Sinkhole risk in Randolph County, IL: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock
38%
At or near the surface
under 1%
Buried under cover
37%

What to do about a house in Randolph County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 217 of Randolph County's 575 square miles on soluble rock, 5 of them with the rock at or near the surface. With about 29,903 residents (52 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 251 map points about 1.5 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 37% under cover still counts.

Counties around Randolph County

The nearest county rated sinkhole country is Ste. Genevieve County, MO, about 22 miles southwest, 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 Randolph County is built on

The largest mapped soluble unit here is the Lower Chesterian (Glen Dean - Renault) Series (limestone), Mississippian in age, covering about 30% of the county. Next is the Upper Valmeyeran (Aux Vases, Ste. Genevieve, St. Louis) Series at 4%.

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 Illinois

Randolph County ranks 22 of 102 in Illinois for soluble rock at the surface, and sits above 54% of US counties on that measure.