Sinkhole risk in Columbia 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: 24%
At or near the surface: under 1%
Buried under cover: 24%

What to do about a house in Columbia County

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

That works out to roughly 186 of Columbia County's 766 square miles on soluble rock, 2 of them with the rock at or near the surface. With about 58,113 residents (76 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 333 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 24% under cover still counts, and how these percentages are measured.

Counties around Columbia County

The nearest county rated sinkhole country is Iowa County, WI, about 52 miles southwest. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Marquette County, WI 25 mi north · 0% at surface
Green Lake County, WI 28 mi northeast · 0% at surface
Dane County, WI 28 mi south · 19% at surface
Sauk County, WI 31 mi west · 16% at surface
Dodge County, WI 32 mi east · 0% at surface
Adams County, WI 41 mi northwest · 0% at surface

What Columbia County is built on

The largest mapped soluble unit here is the Prairie du Chien Group (shale), Lower Ordovician in age, covering about 20% of the county. Next is the Ancell Group at 3%.

Against the rest of Wisconsin

Columbia County ranks 22 of 72 in Wisconsin for soluble rock at the surface, and sits above 51% of US counties on that measure.