SinkholeOdds

Sinkhole risk in Calhoun County, MI: 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%

What to do about a house in Calhoun County

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

That works out to roughly 64 of Calhoun County's 706 square miles on soluble rock. With about 133,785 residents (189 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 390 map points about 1.3 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 Calhoun County

The nearest county rated sinkhole country is Barry County, MI, about 28 miles northwest, close enough that the same rock may run under the county line. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

The rock underneath

The largest mapped soluble unit here is the Bayport Limestone (limestone), Mississippian in age, covering about 5% of the county. Next is the Michigan Formation at 4%.

4% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

The county also lies over the Michigan Basin; Ohio Basin; Appalachian 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 Michigan

Calhoun County ranks 23 of 83 in Michigan for soluble rock at the surface, and sits above 0% of US counties on that measure.