Sinkhole risk in Madison 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
- 9%
- At or near the surface
- 9%
- Buried under cover
- 0%
What to do about a house in Madison County
Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.
That works out to roughly 337 of Madison County's 3,588 square miles on soluble rock, 337 of them with the rock at or near the surface. With about 9,753 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 276 map points about 3.6 miles apart, so a pocket smaller than that can be missed or overstated.
Read next: how these percentages are measured, and the warning signs that apply anywhere.
Counties around Madison County
The nearest county rated sinkhole country is Fall River County, SD, about 440 miles east. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.
- Gallatin County, MT 39 mi east · 18% at surface
- Beaverhead County, MT 49 mi west · 10% at surface
- Silver Bow County, MT 53 mi northwest · 10% at surface
- Jefferson County, MT 56 mi north · 6% at surface
- Park County, MT 68 mi east · 6% at surface
- Broadwater County, MT 72 mi north · 27% at surface
Which formation it is
The largest mapped soluble unit here is the Mississippian, undifferentiated (carbonate), Mississippian in age, covering about 5% of the county. Next is the Cambrian, undifferentiated at 2%.
Against the rest of Montana
Madison County ranks 21 of 56 in Montana for soluble rock at the surface, and sits above 67% of US counties on that measure.
- Meagher County 49%
- Mineral County 37%
- Judith Basin County 33%
- Lincoln County 29%
- Broadwater County 27%