Sinkhole risk in Gallatin 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: 18%
At or near the surface: 18%
Buried under cover: 0%

The next step for one property

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 469 of Gallatin County's 2,605 square miles on soluble rock, 469 of them with the rock at or near the surface. With about 126,984 residents (49 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 444 map points about 2.4 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Gallatin County

The nearest county rated sinkhole country is Fall River County, SD, about 410 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Park County, MT 31 mi east · 6% at surface
Madison County, MT 39 mi west · 9% at surface
Broadwater County, MT 58 mi north · 27% at surface
Jefferson County, MT 60 mi northwest · 6% at surface
Sweet Grass County, MT 62 mi east · 3% at surface
Meagher County, MT 75 mi north · 49% at surface

What Gallatin County is built on

The largest mapped soluble unit here is the Mississippian, undifferentiated (carbonate), Mississippian in age, covering about 6% of the county. Next is the Jurassic, undifferentiated at 5%.

5% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

Against the rest of Montana

Gallatin County ranks 10 of 56 in Montana for soluble rock at the surface, and sits above 73% of US counties on that measure.