Sinkhole risk in Napa County, CA: 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: 2%
At or near the surface: 2%
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 13 of Napa County's 752 square miles on soluble rock, 13 of them with the rock at or near the surface. With about 132,727 residents (177 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 536 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Napa County

The nearest county rated sinkhole country is Emery County, UT, about 626 miles east. None of the 6 closest counties land in the same band, so Napa County stands out from its surroundings.

Yolo County, CA 26 mi northeast · 0% at surface
Solano County, CA 27 mi southeast · 0% at surface
Sonoma County, CA 32 mi west · 0% at surface
Marin County, CA 39 mi southwest · 0% at surface
Contra Costa County, CA 45 mi southeast · 0% at surface
Colusa County, CA 47 mi north · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Franciscan melange (melange), Jurassic to Cretaceous in age, covering about under 1% of the county. Next is the Jurassic marine rocks, unit 2 (Coast Ranges) at under 1%.

Against the rest of California

Napa County ranks 15 of 58 in California for soluble rock at the surface, and sits above 57% of US counties on that measure.