Sinkhole risk in Santa Clara 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: 4%
At or near the surface: 4%
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 54 of Santa Clara County's 1,291 square miles on soluble rock, 54 of them with the rock at or near the surface. With about 1,926,325 residents (1,492 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 613 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Santa Clara County

The nearest county rated sinkhole country is Emery County, UT, about 609 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Santa Cruz County, CA 23 mi southwest · 3% at surface
Alameda County, CA 32 mi northwest · 0% at surface
San Mateo County, CA 40 mi west · 1% at surface
Stanislaus County, CA 44 mi northeast · 0% at surface
Contra Costa County, CA 50 mi north · 0% at surface
Merced County, CA 53 mi east · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Franciscan Complex, unit 1 (sandstone), Jurassic to Cretaceous in age, covering about 4% of the county.

Against the rest of California

Santa Clara County ranks 7 of 58 in California for soluble rock at the surface, and sits above 62% of US counties on that measure.