Sinkhole risk in Yankton 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: 25%
At or near the surface: 0%
Buried under cover: 25%

What to do about a house in Yankton County

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

That works out to roughly 132 of Yankton County's 521 square miles on soluble rock. With about 23,509 residents (45 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 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 25% under cover still counts, and how these percentages are measured.

Counties around Yankton County

The nearest county rated sinkhole country is Knox County, NE, about 36 miles southwest, 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.

Clay County, SD 22 mi east · 0% at surface
Turner County, SD 24 mi northeast · 0% at surface
Bon Homme County, SD 25 mi west · under 1% at surface
Cedar County, NE 29 mi south · 0% at surface
Hutchinson County, SD 29 mi northwest · 0% at surface
Knox County, NE 36 mi southwest · 22% at surface

What Yankton County is built on

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 25% of the county.

Against the rest of South Dakota

Yankton County ranks 65 of 66 in South Dakota for soluble rock at the surface, and sits above 0% of US counties on that measure.