Sinkhole risk in Lemhi County, ID: 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: 12%
At or near the surface: 12%
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 561 of Lemhi County's 4,564 square miles on soluble rock, 561 of them with the rock at or near the surface. With about 8,397 residents (2 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 465 map points about 3.1 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Lemhi County

The nearest county rated sinkhole country is Emery County, UT, about 440 miles southeast. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Custer County, ID 49 mi south · 15% at surface
Beaverhead County, MT 51 mi east · 10% at surface
Ravalli County, MT 80 mi north · 5% at surface
Valley County, ID 85 mi west · 1% at surface
Clark County, ID 87 mi southeast · 14% at surface
Deer Lodge County, MT 88 mi northeast · 10% at surface

Which formation it is

The largest mapped soluble unit here is the Quartzite and marble; Middle Proterozoic Hoodoo Quartzite; southern Belt province (quartzite), Middle Proterozoic in age, covering about 5% of the county. Next is the Limestone, shale, siltstone, chert, and conglomerate; Mississippian western turbiditic flysch to eastern shallow-water carbonates; east-central Idaho at 3%.

Against the rest of Idaho

Lemhi County ranks 12 of 44 in Idaho for soluble rock at the surface, and sits above 69% of US counties on that measure.