Sinkhole risk in Marshall 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: 6%
At or near the surface: 0%
Buried under cover: 6%

What this means before you buy

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

That works out to roughly 50 of Marshall County's 838 square miles on soluble rock. With about 4,395 residents (5 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 369 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 6% under cover still counts, and how these percentages are measured.

Counties around Marshall County

The nearest county rated sinkhole country is Boyd County, NE, about 205 miles south. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Sargent County, ND 26 mi north · 0% at surface
Day County, SD 26 mi south · 0% at surface
Roberts County, SD 32 mi east · 0% at surface
Brown County, SD 39 mi west · 0% at surface
Richland County, ND 48 mi northeast · 0% at surface
Ransom County, ND 49 mi north · under 1% at surface

What Marshall County is built on

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 6% of the county.

Against the rest of South Dakota

Marshall County ranks 49 of 66 in South Dakota for soluble rock at the surface, and sits above 0% of US counties on that measure.