Sinkhole risk in Brown 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: 10%
At or near the surface: 0%
Buried under cover: 10%

What to do about a house in Brown County

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

That works out to roughly 163 of Brown County's 1,713 square miles on soluble rock. With about 37,495 residents (22 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 399 map points about 2.1 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 10% under cover still counts, and how these percentages are measured.

Counties around Brown County

The nearest county rated sinkhole country is Boyd County, NE, about 187 miles south. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Dickey County, ND 36 mi north · 0% at surface
Marshall County, SD 39 mi east · 0% at surface
Day County, SD 41 mi southeast · 0% at surface
Edmunds County, SD 43 mi west · 0% at surface
McPherson County, SD 44 mi west · 0% at surface
Spink County, SD 46 mi south · 0% at surface

What Brown County is built on

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 10% of the county.

Against the rest of South Dakota

Brown County ranks 18 of 66 in South Dakota for soluble rock at the surface, and sits above 0% of US counties on that measure.