SinkholeOdds

Sinkhole risk in Butte 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
6%
Buried under cover
0%

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 142 of Butte County's 2,250 square miles on soluble rock, 142 of them with the rock at or near the surface. With about 10,891 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 368 map points about 2.5 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Butte County

The nearest county rated sinkhole country is Fall River County, SD, about 116 miles south. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Which formation it is

The largest mapped soluble unit here is the Belle Fourche Shale (shale), Late Cretaceous in age, covering about 3% of the county. Next is the Greenhorn Formation at 2%.

The county also lies over the Williston Basin, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of South Dakota

Butte County ranks 6 of 66 in South Dakota for soluble rock at the surface, and sits above 64% of US counties on that measure.