SinkholeOdds

Sinkhole risk in Marion 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
9%
At or near the surface
0%
Buried under cover
9%

The next step for one property

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

That works out to roughly 48 of Marion County's 554 square miles on soluble rock. With about 34,048 residents (61 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 391 map points about 1.2 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 9% under cover still counts.

Counties around Marion County

The nearest county rated sinkhole country is Clayton County, IA, about 138 miles northeast. 5 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 8% of the county. Next is the Marmaton Group at under 1%.

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

Marion County ranks 65 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.