Sinkhole risk in Brule 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: 8%
At or near the surface: under 1%
Buried under cover: 8%

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 68 of Brule County's 817 square miles on soluble rock, 5 of them with the rock at or near the surface. With about 5,261 residents (6 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 336 map points about 1.6 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 8% under cover still counts, and how these percentages are measured.

Counties around Brule County

The nearest county rated sinkhole country is Boyd County, NE, about 60 miles south. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Buffalo County, SD 22 mi north · 3% at surface
Aurora County, SD 26 mi east · 0% at surface
Jerauld County, SD 33 mi northeast · 0% at surface
Gregory County, SD 39 mi south · 17% at surface
Lyman County, SD 39 mi west · 0% at surface
Douglas County, SD 44 mi southeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 8% of the county.

Against the rest of South Dakota

Brule County ranks 12 of 66 in South Dakota for soluble rock at the surface, and sits above 53% of US counties on that measure.