Sinkhole risk in Jackson County, IA: Pockets of it

Pockets of it

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

On soluble rock: 99%
At or near the surface: 33%
Buried under cover: 66%

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 630 of Jackson County's 636 square miles on soluble rock, 209 of them with the rock at or near the surface. With about 19,390 residents (30 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 286 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 66% under cover still counts, and the signs to look for and how an inspection works.

Counties around Jackson County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 23 miles northeast, close enough that the same rock may run under the county line. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Clinton County, IA 19 mi south · 1% at surface
Jo Daviess County, IL 23 mi northeast · 58% at surface
Dubuque County, IA 26 mi northwest · 34% at surface
Jones County, IA 28 mi west · 1% at surface
Carroll County, IL 34 mi east · 11% at surface
Scott County, IA 36 mi south · under 1% at surface

The rock underneath

The largest mapped soluble unit here is the Niagaran Series (dolostone (dolomite)), Middle Silurian in age, covering about 71% of the county. Next is the Maquoketa Formation at 15%.

Against the rest of Iowa

Jackson County ranks 3 of 99 in Iowa for soluble rock at the surface, and sits above 81% of US counties on that measure.