Sinkhole risk in Bon Homme County, SD: 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: 50%
At or near the surface: under 1%
Buried under cover: 50%

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 283 of Bon Homme County's 564 square miles on soluble rock, 2 of them with the rock at or near the surface. With about 7,071 residents (13 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 328 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 50% under cover still counts, and how these percentages are measured.

Counties around Bon Homme County

The nearest county rated sinkhole country is Knox County, NE, about 24 miles south, close enough that the same rock may run under the county line. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Knox County, NE 24 mi south · 22% at surface
Yankton County, SD 25 mi east · 0% at surface
Hutchinson County, SD 25 mi north · 0% at surface
Douglas County, SD 37 mi northwest · 0% at surface
Charles Mix County, SD 39 mi northwest · 3% at surface
Cedar County, NE 41 mi southeast · 0% at surface

What Bon Homme County is built on

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 50% of the county.

Against the rest of South Dakota

Bon Homme County ranks 13 of 66 in South Dakota for soluble rock at the surface, and sits above 51% of US counties on that measure.