SinkholeOdds

Sinkhole risk in Tuscola County, MI: Sinkhole country

Sinkhole country

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

On soluble rock
39%
At or near the surface
0%
Buried under cover
39%

What to do about a house in Tuscola County

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

That works out to roughly 316 of Tuscola County's 805 square miles on soluble rock. With about 52,757 residents (66 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 300 map points about 1.6 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 39% under cover still counts.

Counties around Tuscola County

The closest county with no soluble rock mapped is Bay County, MI, about 31 miles northwest. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

What Tuscola County is built on

The largest mapped soluble unit here is the Michigan Formation (black shale), Mississippian in age, covering about 35% of the county. Next is the Bayport Limestone at 5%.

35% 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

Tuscola County ranks 79 of 83 in Michigan for soluble rock at the surface, and sits above 0% of US counties on that measure.