Sinkhole risk in San Mateo 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
- 1%
- At or near the surface
- 1%
- Buried under cover
- 0%
What to do about a house in San Mateo County
Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.
That works out to roughly 5 of San Mateo County's 449 square miles on soluble rock, 5 of them with the rock at or near the surface. With about 742,893 residents (1,656 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 482 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.
Read next: how these percentages are measured, and the warning signs that apply anywhere.
Counties around San Mateo County
The nearest county rated sinkhole country is Emery County, UT, about 642 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.
- Alameda County, CA 30 mi northeast · 0% at surface
- Santa Cruz County, CA 34 mi southeast · 3% at surface
- Santa Clara County, CA 40 mi east · 4% at surface
- Contra Costa County, CA 42 mi northeast · 0% at surface
- San Francisco County, CA 42 mi northwest · 0% at surface
- Marin County, CA 49 mi northwest · 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 1% of the county.
Against the rest of California
San Mateo County ranks 17 of 58 in California for soluble rock at the surface, and sits above 56% of US counties on that measure.
- Trinity County 25%
- Inyo County 17%
- Ventura County 9%
- Shasta County 9%
- Siskiyou County 9%