Sinkhole risk in Clay 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: 21%
At or near the surface: 0%
Buried under cover: 21%

What to do about a house in Clay County

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

That works out to roughly 84 of Clay County's 412 square miles on soluble rock. With about 15,245 residents (37 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 352 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Clay County

The nearest county rated sinkhole country is Knox County, NE, about 50 miles southwest. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Union County, SD 18 mi east · 0% at surface
Yankton County, SD 22 mi west · 0% at surface
Cedar County, NE 26 mi southwest · 0% at surface
Lincoln County, SD 28 mi northeast · 0% at surface
Turner County, SD 28 mi north · 0% at surface
Dixon County, NE 30 mi south · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 20% of the county. Next is the Greenhorn Limestone and Graneros Shale at under 1%.

Against the rest of South Dakota

Clay County ranks 21 of 66 in South Dakota for soluble rock at the surface, and sits above 0% of US counties on that measure.