SinkholeOdds

Sinkhole risk in Tripp 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
3%
At or near the surface
3%
Buried under cover
0%

What to do about a house in Tripp County

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

That works out to roughly 55 of Tripp County's 1,612 square miles on soluble rock, 55 of them with the rock at or near the surface. With about 5,717 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 353 map points about 2.1 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Tripp County

The nearest county rated sinkhole country is Boyd County, NE, about 64 miles southeast. 1 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 Pierre Shale (shale), Late Cretaceous in age, covering about 3% of the county.

3% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

Against the rest of South Dakota

Tripp County ranks 8 of 66 in South Dakota for soluble rock at the surface, and sits above 60% of US counties on that measure.