Sinkhole risk in Park 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: 6%
At or near the surface: 6%
Buried under cover: 0%

What to do about a house in Park County

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

That works out to roughly 163 of Park County's 2,802 square miles on soluble rock, 163 of them with the rock at or near the surface. With about 18,074 residents (6 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 584 map points about 2.2 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Park County

The nearest county rated sinkhole country is Fall River County, SD, about 380 miles east. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Gallatin County, MT 31 mi west · 18% at surface
Sweet Grass County, MT 37 mi northeast · 3% at surface
Stillwater County, MT 57 mi east · under 1% at surface
Madison County, MT 68 mi west · 9% at surface
Carbon County, MT 75 mi east · 12% at surface
Broadwater County, MT 76 mi northwest · 27% at surface

The rock underneath

The largest mapped soluble unit here is the Cambrian, undifferentiated (carbonate), Cambrian in age, covering about 4% of the county. Next is the Mississippian, undifferentiated at 1%.

The county also lies over the Crazy Mountains Basin, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Montana

Park County ranks 24 of 56 in Montana for soluble rock at the surface, and sits above 64% of US counties on that measure.