SinkholeOdds

Sinkhole risk in Hamilton 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
55%
At or near the surface
0%
Buried under cover
55%

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 318 of Hamilton County's 577 square miles on soluble rock. With about 14,856 residents (26 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 376 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 55% under cover still counts.

Counties around Hamilton County

The nearest county rated sinkhole country is Clayton County, IA, about 125 miles east. 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 33% of the county. Next is the Kinderhook Series at 22%.

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

Hamilton County ranks 46 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.