Sinkhole risk in Dubuque 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: 34%
Buried under cover: 66%

What to do about a house in Dubuque County

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 604 of Dubuque County's 608 square miles on soluble rock, 206 of them with the rock at or near the surface. With about 99,242 residents (163 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 281 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Dubuque County

The nearest county rated sinkhole country is Grant County, WI, about 30 miles north, close enough that the same rock may run under the county line. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Delaware County, IA 25 mi west · 5% at surface
Jackson County, IA 26 mi southeast · 33% at surface
Jones County, IA 26 mi southwest · 1% at surface
Grant County, WI 30 mi north · 84% at surface
Clayton County, IA 35 mi northwest · 54% at surface
Jo Daviess County, IL 35 mi east · 58% at surface

Which formation it is

The largest mapped soluble unit here is the Niagaran Series (dolostone (dolomite)), Middle Silurian in age, covering about 44% of the county. Next is the Alexandrian Series at 22%.

Against the rest of Iowa

Dubuque County ranks 2 of 99 in Iowa for soluble rock at the surface, and sits above 81% of US counties on that measure.