SinkholeOdds

Sinkhole risk in Jefferson County, IA: 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 209 of Jefferson County's 436 square miles on soluble rock. With about 15,781 residents (36 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 392 map points about 1.1 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 Jefferson County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 130 miles northeast. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

The rock underneath

The largest mapped soluble unit here is the Meramec Series (limestone), Late Mississippian in age, covering about 43% of the county. Next is the Osage Series at 5%.

The county also lies over the Forest City 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 Iowa

Jefferson County ranks 55 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.