Sinkhole risk in Delaware 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: 100%
At or near the surface: 5%
Buried under cover: 95%

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 578 of Delaware County's 578 square miles on soluble rock, 28 of them with the rock at or near the surface. With about 17,609 residents (30 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 391 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Delaware County

The nearest county rated sinkhole country is Clayton County, IA, about 26 miles north, 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.

Buchanan County, IA 24 mi west · 0% at surface
Dubuque County, IA 25 mi east · 34% at surface
Clayton County, IA 26 mi north · 54% at surface
Jones County, IA 27 mi southeast · 1% at surface
Linn County, IA 30 mi southwest · 0% at surface
Fayette County, IA 36 mi northwest · 19% at surface

The rock underneath

The largest mapped soluble unit here is the Niagaran Series (dolostone (dolomite)), Middle Silurian in age, covering about 78% of the county. Next is the Alexandrian Series at 12%.

Against the rest of Iowa

Delaware County ranks 8 of 99 in Iowa for soluble rock at the surface, and sits above 63% of US counties on that measure.