SinkholeOdds

Sinkhole risk in Crawford County, MI: Sinkhole country

Sinkhole country

Fast-dissolving gypsum or salt beds under a large part of the county.

On soluble rock
34%
At or near the surface
0%
Buried under cover
34%

What this means before you buy

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

That works out to roughly 191 of Crawford County's 556 square miles on soluble rock. With about 13,599 residents (24 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.

Two things to read before deciding: why gypsum and salt move faster than limestone, and why the 34% under cover still counts.

Counties around Crawford County

The closest county with no soluble rock mapped is Clare County, MI, about 49 miles south. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

What Crawford County is built on

The largest mapped soluble unit here is the Michigan Formation (black shale), Mississippian in age, covering about 34% of the county.

34% 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

Crawford County ranks 28 of 83 in Michigan for soluble rock at the surface, and sits above 0% of US counties on that measure.