SinkholeOdds

Sinkhole risk in Genesee County, MI: Sinkhole country

Sinkhole country

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

On soluble rock
38%
At or near the surface
0%
Buried under cover
38%

What to do about a house in Genesee County

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

That works out to roughly 243 of Genesee County's 637 square miles on soluble rock. With about 402,279 residents (632 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 359 map points about 1.3 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 38% under cover still counts.

Counties around Genesee County

The closest county with no soluble rock mapped is Saginaw County, MI, about 28 miles northwest. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Which formation it is

The largest mapped soluble unit here is the Michigan Formation (black shale), Mississippian in age, covering about 37% of the county. Next is the Bayport Limestone at under 1%.

37% 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

Genesee County ranks 33 of 83 in Michigan for soluble rock at the surface, and sits above 0% of US counties on that measure.