SinkholeOdds

Sinkhole risk in Pitkin 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
5%
At or near the surface
5%
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 49 of Pitkin County's 971 square miles on soluble rock, 49 of them with the rock at or near the surface. With about 16,643 residents (17 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 258 map points about 1.9 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Pitkin County

The nearest county rated sinkhole country is Emery County, UT, about 204 miles west. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

The rock underneath

The largest mapped soluble unit here is the Eagle Valley Fm (siltstone), Pennsylvanian in age, covering about 2% of the county. Next is the Leadville Limestone, Williams Canyon Limestone , Manitou Limestone, and Sawatch Quartzite at 2%.

3% 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 Eagle Valley 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

Pitkin County ranks 17 of 64 in Colorado for soluble rock at the surface, and sits above 63% of US counties on that measure.