SinkholeOdds

Sinkhole risk in Audubon 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
31%
At or near the surface
0%
Buried under cover
31%

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 137 of Audubon County's 443 square miles on soluble rock. With about 5,562 residents (13 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 356 map points about 1.1 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 31% under cover still counts.

Counties around Audubon County

The nearest county rated sinkhole country is Knox County, NE, about 167 miles northwest. 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 Marmaton Group (shale), Middle Pennsylvanian-Des Moines Series in age, covering about 24% of the county. Next is the Kansas City Group at 7%.

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

Audubon County ranks 17 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.