Sinkhole risk in Fremont 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: 12%
At or near the surface: 12%
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 179 of Fremont County's 1,534 square miles on soluble rock, 179 of them with the rock at or near the surface. With about 50,093 residents (33 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 351 map points about 2.1 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 Fremont County

The nearest county rated sinkhole country is Emery County, UT, about 288 miles west. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Custer County, CO 25 mi south · under 1% at surface
Teller County, CO 31 mi northeast · under 1% at surface
Park County, CO 48 mi north · 13% at surface
Chaffee County, CO 51 mi west · 4% at surface
Saguache County, CO 53 mi southwest · 1% at surface
Pueblo County, CO 55 mi east · 45% at surface

Which formation it is

The largest mapped soluble unit here is the Niobrara Fm (shale), Cretaceous in age, covering about 4% of the county. Next is the One or more Ordovician fms at 3%.

1% 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 Colorado

Fremont County ranks 11 of 64 in Colorado for soluble rock at the surface, and sits above 69% of US counties on that measure.