SinkholeOdds

Sinkhole risk in Greene 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
48%
At or near the surface
0%
Buried under cover
48%

What this means before you buy

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

That works out to roughly 263 of Greene County's 543 square miles on soluble rock. With about 11,417 residents (21 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 310 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and why the 48% under cover still counts.

Counties around Greene County

The nearest county rated sinkhole country is Calhoun County, IL, about 20 miles southwest, close enough that the same rock may run under the county line. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Which formation it is

The largest mapped soluble unit here is the Lower Valmeyeran (Keokuk-Sedalia) Series (limestone), Mississippian in age, covering about 28% of the county. Next is the Middle Valmeyeran (Salem, Warsaw, Borden, Springville; includes thin Mvl and Mk in south and east) Series 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 Illinois

Greene County ranks 53 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.