Sinkhole risk in Washington County, WI: 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: 100%
At or near the surface: 0%
Buried under cover: 100%

What to do about a house in Washington County

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

That works out to roughly 431 of Washington County's 431 square miles on soluble rock. With about 138,727 residents (322 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 380 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 100% under cover still counts, and how these percentages are measured.

Counties around Washington County

The nearest county rated sinkhole country is Oceana County, MI, about 90 miles east. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Ozaukee County, WI 21 mi east · 0% at surface
Dodge County, WI 24 mi west · 0% at surface
Waukesha County, WI 26 mi south · 0% at surface
Fond du Lac County, WI 28 mi northwest · 0% at surface
Sheboygan County, WI 35 mi northeast · 0% at surface
Jefferson County, WI 38 mi southwest · 3% at surface

Which formation it is

The largest mapped soluble unit here is the Silurian, undivided (dolostone (dolomite)), Silurian in age, covering about 78% of the county. Next is the Maquoketa Formation at 21%.

Against the rest of Wisconsin

Washington County ranks 68 of 72 in Wisconsin for soluble rock at the surface, and sits above 0% of US counties on that measure.