Sinkhole risk in Fillmore County, MN: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 95%
At or near the surface: 26%
Buried under cover: 68%

The next step for one property

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 815 of Fillmore County's 861 square miles on soluble rock, 227 of them with the rock at or near the surface. With about 21,502 residents (25 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 406 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 68% under cover still counts, and the signs to look for and how an inspection works.

Counties around Fillmore County

The nearest county rated sinkhole country is Vernon County, WI, about 64 miles east. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Howard County, IA 25 mi southwest · 5% at surface
Winona County, MN 26 mi northeast · 27% at surface
Olmsted County, MN 27 mi northwest · 6% at surface
Winneshiek County, IA 29 mi southeast · 18% at surface
Houston County, MN 30 mi east · 28% at surface
Mower County, MN 33 mi west · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Upper and Middle Ordovician rocks, undivided (limestone), Late and Middle Ordovician in age, covering about 40% of the county. Next is the Lower Ordovician rocks, undivided at 34%.

Against the rest of Minnesota

Fillmore County ranks 3 of 87 in Minnesota for soluble rock at the surface, and sits above 78% of US counties on that measure.