Sinkhole risk in Lake 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: 15%
At or near the surface: 15%
Buried under cover: 0%

What to do about a house in Lake County

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

That works out to roughly 219 of Lake County's 1,491 square miles on soluble rock, 219 of them with the rock at or near the surface. With about 33,403 residents (22 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 597 map points about 1.6 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Lake County

The nearest county rated sinkhole country is Fall River County, SD, about 596 miles southeast. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Missoula County, MT 43 mi south · 12% at surface
Flathead County, MT 45 mi north · 25% at surface
Sanders County, MT 52 mi west · 20% at surface
Mineral County, MT 59 mi southwest · 37% at surface
Powell County, MT 77 mi southeast · 13% at surface
Teton County, MT 85 mi east · 9% at surface

Which formation it is

The largest mapped soluble unit here is the Piegan group (carbonate), Middle-Proterozoic in age, covering about 15% of the county.

Against the rest of Montana

Lake County ranks 12 of 56 in Montana for soluble rock at the surface, and sits above 71% of US counties on that measure.