Sinkhole risk in Jefferson 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%

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 94 of Jefferson County's 1,657 square miles on soluble rock, 94 of them with the rock at or near the surface. With about 13,304 residents (8 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 263 map points about 2.5 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 Jefferson County

The nearest county rated sinkhole country is Fall River County, SD, about 465 miles east. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Broadwater County, MT 30 mi northeast · 27% at surface
Silver Bow County, MT 33 mi southwest · 10% at surface
Deer Lodge County, MT 52 mi west · 10% at surface
Madison County, MT 56 mi south · 9% at surface
Gallatin County, MT 60 mi southeast · 18% at surface
Meagher County, MT 63 mi northeast · 49% at surface

The rock underneath

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

Against the rest of Montana

Jefferson County ranks 25 of 56 in Montana for soluble rock at the surface, and sits above 64% of US counties on that measure.