Sinkhole risk in Lee 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: 92%
At or near the surface: 2%
Buried under cover: 91%

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 478 of Lee County's 518 square miles on soluble rock, 9 of them with the rock at or near the surface. With about 32,376 residents (63 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 570 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and why the 91% under cover still counts.

Counties around Lee County

The nearest county rated sinkhole country is Calhoun County, IL, about 111 miles southeast. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Clark County, MO 21 mi southwest · 0% at surface
Hancock County, IL 23 mi southeast · 0% at surface
Henry County, IA 24 mi north · 0% at surface
Des Moines County, IA 24 mi northeast · 3% at surface
Van Buren County, IA 26 mi west · 0% at surface
Henderson County, IL 30 mi northeast · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Meramec Series (limestone), Late Mississippian in age, covering about 34% of the county. Next is the Osage Series at 32%.

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

Lee County ranks 10 of 99 in Iowa for soluble rock at the surface, and sits above 57% of US counties on that measure.