Sinkhole risk in Sanborn 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: 82%
At or near the surface: 0%
Buried under cover: 82%

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 465 of Sanborn County's 569 square miles on soluble rock. With about 2,392 residents (4 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 408 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 82% under cover still counts, and how these percentages are measured.

Counties around Sanborn County

The nearest county rated sinkhole country is Boyd County, NE, about 85 miles southwest. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Davison County, SD 24 mi south · 0% at surface
Miner County, SD 24 mi east · 0% at surface
Jerauld County, SD 27 mi west · 0% at surface
Hanson County, SD 28 mi southeast · 0% at surface
Beadle County, SD 29 mi north · 0% at surface
Aurora County, SD 32 mi southwest · 0% at surface

What Sanborn County is built on

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 82% of the county.

Against the rest of South Dakota

Sanborn County ranks 57 of 66 in South Dakota for soluble rock at the surface, and sits above 0% of US counties on that measure.