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

What this means before you buy

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

That works out to roughly 473 of Howard County's 473 square miles on soluble rock, 25 of them with the rock at or near the surface. With about 9,360 residents (20 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 416 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Howard County

The nearest county rated sinkhole country is Clayton County, IA, about 62 miles southeast. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Chickasaw County, IA 21 mi south · 0% at surface
Mitchell County, IA 23 mi west · 0% at surface
Winneshiek County, IA 24 mi east · 18% at surface
Fillmore County, MN 25 mi northeast · 26% at surface
Mower County, MN 30 mi northwest · 0% at surface
Floyd County, IA 32 mi southwest · 0% at surface

What Howard County is built on

The largest mapped soluble unit here is the Cedar Valley Limestone (limestone), Middle Dovonian in age, covering about 98% of the county. Next is the Maquoketa Formation at 1%.

Against the rest of Iowa

Howard County ranks 7 of 99 in Iowa for soluble rock at the surface, and sits above 63% of US counties on that measure.