Sinkhole risk in Larimer 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: 9%
At or near the surface: 9%
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 221 of Larimer County's 2,596 square miles on soluble rock, 221 of them with the rock at or near the surface. With about 374,574 residents (144 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 305 map points about 2.9 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 Larimer County

The nearest county rated sinkhole country is Dawes County, NE, about 187 miles northeast. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Boulder County, CO 39 mi south · 4% at surface
Jackson County, CO 44 mi west · 4% at surface
Grand County, CO 50 mi southwest · 6% at surface
Broomfield County, CO 54 mi southeast · 0% at surface
Gilpin County, CO 55 mi south · 0% at surface
Weld County, CO 58 mi east · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Ingleside Fm and Fountain Fm (sandstone), Permian-Pennsylvanian in age, covering about 4% of the county. Next is the Jelm, Lykins, Lyons, and Satanka Fms 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.

Against the rest of Colorado

Larimer County ranks 12 of 64 in Colorado for soluble rock at the surface, and sits above 66% of US counties on that measure.