Sinkhole risk in Ventura 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: 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 168 of Ventura County's 1,841 square miles on soluble rock, 168 of them with the rock at or near the surface. With about 835,427 residents (454 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 309 map points about 2.4 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 Ventura County

The nearest county rated sinkhole country is Emery County, UT, about 566 miles northeast. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Los Angeles County, CA 51 mi east · 1% at surface
Santa Barbara County, CA 53 mi west · 3% at surface
Kern County, CA 72 mi north · under 1% at surface
Orange County, CA 91 mi southeast · 6% at surface
San Luis Obispo County, CA 103 mi northwest · under 1% at surface
Kings County, CA 125 mi north · 0% at surface

What Ventura County is built on

The largest mapped soluble unit here is the Oligocene nonmarine rocks, unit 2 (Central and Southern California) (sandstone), middle Eocene to early Miocene in age, covering about 9% of the county.

9% 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

Ventura County ranks 3 of 58 in California for soluble rock at the surface, and sits above 67% of US counties on that measure.