Sinkhole risk in Linn 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: 0%
Buried under cover: 100%

What to do about a house in Linn 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 717 of Linn County's 717 square miles on soluble rock. With about 231,762 residents (323 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 399 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 100% under cover still counts, and the signs to look for and how an inspection works.

Counties around Linn County

The nearest county rated sinkhole country is Clayton County, IA, about 55 miles north. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Benton County, IA 24 mi west · 0% at surface
Jones County, IA 25 mi east · 1% at surface
Johnson County, IA 28 mi south · 0% at surface
Delaware County, IA 30 mi northeast · 5% at surface
Buchanan County, IA 30 mi northwest · 0% at surface
Cedar County, IA 32 mi southeast · 0% at surface

What Linn County is built on

The largest mapped soluble unit here is the Niagaran Series (dolostone (dolomite)), Middle Silurian in age, covering about 39% of the county. Next is the Wapsipinicon Formation at 39%.

Against the rest of Iowa

Linn County ranks 59 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.