Sinkhole risk in Fremont County, IA: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 99%
At or near the surface: 0%
Buried under cover: 99%

The next step for one property

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 504 of Fremont County's 511 square miles on soluble rock. With about 6,494 residents (13 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 351 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 99% under cover still counts, and how these percentages are measured.

Counties around Fremont County

The nearest county rated sinkhole country is Johnson County, KS, about 135 miles south. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Mills County, IA 20 mi north · 0% at surface
Atchison County, MO 23 mi south · 0% at surface
Page County, IA 24 mi east · 0% at surface
Nemaha County, NE 28 mi southwest · 0% at surface
Otoe County, NE 29 mi west · 0% at surface
Montgomery County, IA 30 mi northeast · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Wabaunsee Group (shale), Late Pennsylvanian-Virgil Series in age, covering about 68% of the county. Next is the Shawnee Group at 29%.

Against the rest of Iowa

Fremont County ranks 42 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.