Sinkhole risk in Sanders County, MT: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 20%
At or near the surface: 20%
Buried under cover: 0%

What this means before you buy

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 558 of Sanders County's 2,760 square miles on soluble rock, 558 of them with the rock at or near the surface. With about 13,895 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 416 map points about 2.6 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Sanders County

The nearest county rated sinkhole country is Emery County, UT, about 644 miles south. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Shoshone County, ID 43 mi southwest · under 1% at surface
Mineral County, MT 44 mi south · 37% at surface
Lake County, MT 52 mi east · 15% at surface
Lincoln County, MT 57 mi north · 29% at surface
Flathead County, MT 64 mi northeast · 25% at surface
Kootenai County, ID 71 mi west · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Wallace formation (meta-argillite), Middle-Proterozoic in age, covering about 20% of the county. Next is the Piegan group at under 1%.

Against the rest of Montana

Sanders County ranks 8 of 56 in Montana for soluble rock at the surface, and sits above 74% of US counties on that measure.