Sinkhole risk in Washington County, MN: 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: 69%
At or near the surface: 0%
Buried under cover: 69%

What this means before you buy

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

That works out to roughly 267 of Washington County's 385 square miles on soluble rock. With about 283,960 residents (738 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 335 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 69% under cover still counts, and how these percentages are measured.

Counties around Washington County

The nearest county rated sinkhole country is Vernon County, WI, about 143 miles southeast. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Ramsey County, MN 10 mi west · 0% at surface
St. Croix County, WI 22 mi east · 1% at surface
Anoka County, MN 24 mi northwest · 0% at surface
Dakota County, MN 27 mi south · 0% at surface
Hennepin County, MN 29 mi west · 0% at surface
Pierce County, WI 31 mi southeast · 35% at surface

What Washington County is built on

The largest mapped soluble unit here is the Lower Ordovician rocks, undivided (dolostone (dolomite)), Lower Ordovician in age, covering about 40% of the county. Next is the Middle Ordovician rocks, undivided at 29%.

Against the rest of Minnesota

Washington County ranks 83 of 87 in Minnesota for soluble rock at the surface, and sits above 0% of US counties on that measure.