Sinkhole risk in Ravalli County, MT: 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: 5%
At or near the surface: 5%
Buried under cover: 0%

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 110 of Ravalli County's 2,391 square miles on soluble rock, 110 of them with the rock at or near the surface. With about 48,187 residents (20 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 592 map points about 2.0 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Ravalli County

The nearest county rated sinkhole country is Emery County, UT, about 518 miles south. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Granite County, MT 39 mi northeast · 17% at surface
Deer Lodge County, MT 46 mi east · 10% at surface
Missoula County, MT 66 mi north · 12% at surface
Idaho County, ID 67 mi west · under 1% at surface
Silver Bow County, MT 71 mi east · 10% at surface
Powell County, MT 77 mi northeast · 13% at surface

Which formation it is

The largest mapped soluble unit here is the Newland limestone (carbonate), Middle-Proterozoic in age, covering about 4% of the county. Next is the Piegan group at under 1%.

Against the rest of Montana

Ravalli County ranks 28 of 56 in Montana for soluble rock at the surface, and sits above 62% of US counties on that measure.