Sinkhole risk in Powell 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: 13%
At or near the surface: 13%
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 293 of Powell County's 2,326 square miles on soluble rock, 293 of them with the rock at or near the surface. With about 7,120 residents (3 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 468 map points about 2.2 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Powell County

The nearest county rated sinkhole country is Fall River County, SD, about 523 miles southeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Lewis and Clark County, MT 32 mi northeast · 25% at surface
Granite County, MT 39 mi southwest · 17% at surface
Missoula County, MT 47 mi west · 12% at surface
Deer Lodge County, MT 53 mi south · 10% at surface
Jefferson County, MT 65 mi southeast · 6% at surface
Silver Bow County, MT 67 mi south · 10% at surface

The rock underneath

The largest mapped soluble unit here is the Piegan group (carbonate), Middle-Proterozoic in age, covering about 3% of the county. Next is the Cambrian, undifferentiated at 3%.

Against the rest of Montana

Powell County ranks 13 of 56 in Montana for soluble rock at the surface, and sits above 70% of US counties on that measure.