Sinkhole risk in Santa Cruz 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: 3%
At or near the surface: 3%
Buried under cover: 0%

What to do about a house in Santa Cruz County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 15 of Santa Cruz County's 445 square miles on soluble rock, 15 of them with the rock at or near the surface. With about 262,406 residents (590 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 378 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Santa Cruz County

The nearest county rated sinkhole country is Emery County, UT, about 629 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Santa Clara County, CA 23 mi northeast · 4% at surface
San Mateo County, CA 34 mi northwest · 1% at surface
Alameda County, CA 44 mi north · 0% at surface
San Benito County, CA 58 mi southeast · 0% at surface
Contra Costa County, CA 63 mi north · 0% at surface
Monterey County, CA 66 mi southeast · under 1% at surface

The rock underneath

The largest mapped soluble unit here is the Schist of various types and ages, unit 6 (Santa Cruz Mountains) (schist), Paleozoic or Mesozoic in age, covering about 2% of the county. Next is the Oligocene nonmarine rocks, unit 2 (Central and Southern California) at 1%.

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 California

Santa Cruz County ranks 8 of 58 in California for soluble rock at the surface, and sits above 60% of US counties on that measure.