Sinkhole risk in Silver Bow 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: 10%
At or near the surface: 10%
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 68 of Silver Bow County's 718 square miles on soluble rock, 68 of them with the rock at or near the surface. With about 36,134 residents (50 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 441 map points about 1.3 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 Silver Bow County

The nearest county rated sinkhole country is Emery County, UT, about 486 miles south. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Deer Lodge County, MT 27 mi northwest · 10% at surface
Jefferson County, MT 33 mi northeast · 6% at surface
Granite County, MT 50 mi northwest · 17% at surface
Madison County, MT 53 mi southeast · 9% at surface
Beaverhead County, MT 54 mi south · 10% at surface
Broadwater County, MT 63 mi northeast · 27% at surface

Which formation it is

The largest mapped soluble unit here is the Mississippian, undifferentiated (carbonate), Mississippian in age, covering about 3% of the county. Next is the Devonian, undifferentiated at 2%.

Against the rest of Montana

Silver Bow County ranks 20 of 56 in Montana for soluble rock at the surface, and sits above 68% of US counties on that measure.