Sinkhole risk in Sanilac 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: 7%
At or near the surface: 0%
Buried under cover: 7%

The next step for one property

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

That works out to roughly 68 of Sanilac County's 963 square miles on soluble rock. With about 40,293 residents (42 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 339 map points about 1.7 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Sanilac County

The nearest county rated sinkhole country is Lapeer County, MI, about 38 miles southwest, close enough that the same rock may run under the county line. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Huron County, MI 33 mi north · 0% at surface
St. Clair County, MI 36 mi south · under 1% at surface
Lapeer County, MI 38 mi southwest · 0% at surface
Tuscola County, MI 40 mi west · 0% at surface
Macomb County, MI 55 mi south · 0% at surface
Genesee County, MI 61 mi southwest · 0% at surface

What Sanilac County is built on

The largest mapped soluble unit here is the Bedford Shale (shale), Upper Devonian in age, covering about 4% of the county. Next is the Michigan Formation at 3%.

3% 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

Sanilac County ranks 77 of 83 in Michigan for soluble rock at the surface, and sits above 0% of US counties on that measure.