SinkholeOdds

Sinkhole risk in Cass 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
28%
At or near the surface
0%
Buried under cover
28%

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 159 of Cass County's 564 square miles on soluble rock. With about 13,024 residents (23 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 391 map points about 1.2 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 28% under cover still counts.

Counties around Cass County

The nearest county rated sinkhole country is Jackson County, MO, about 164 miles south. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Which formation it is

The largest mapped soluble unit here is the Shawnee Group (limestone), Late Pennsylvanian-Virgil Series in age, covering about 14% of the county. Next is the Kansas City Group at 9%.

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

Cass County ranks 27 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.