SinkholeOdds

Sinkhole risk in Montrose County, CO: 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
1%
At or near the surface
1%
Buried under cover
0%

What this means before you buy

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

That works out to roughly 22 of Montrose County's 2,241 square miles on soluble rock, 22 of them with the rock at or near the surface. With about 44,806 residents (20 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 309 map points about 2.7 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Montrose County

The nearest county rated sinkhole country is Emery County, UT, about 139 miles west. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Which formation it is

The largest mapped soluble unit here is the Morrison Fm and Wanakah Fm (Junction Creek Sandstone Member at or near top; Pony Express Limestone Member at base) (mudstone), Jurassic in age, covering about under 1% of the county. Next is the Hermosa Fm at under 1%.

1% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

The county also lies over the Paradox 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 Colorado

Montrose County ranks 31 of 64 in Colorado for soluble rock at the surface, and sits above 55% of US counties on that measure.