County regional graticules for California.
Note: Calaveras County is almost exactly 1 degree wide - it's easternmost point is about -121.02, and westernmost point is about -121.99.
 Contra Costa
 Del Norte
Note: due to surveying errors, the California/Oregon state boundary is not exactly at Latitude 42, and there is technically a tiny sliver of Grants Pass, Oregon inside Del Norte County. This sliver is less than 150 meters wide at its greatest extent.
 El Dorado
That bit of Tehachapi, California is small, and at the ridgeline of the Sierra Nevada mountains. Good luck!
The part of Lake County in the Bodega Bay graticule is very, very small.
 Los Angeles
Editor's note: San Clemente Island will probably have to be achieved by boat as the island itself is owned by the US Navy, regardless Wikipedia says it is Los Angeles County so you must succeed in this graticule to claim the LA regional achievement. Please refer to the San Clemente Island Website for information and exclusion zones. Please read and understand SCI Safety Zone Procedures before approaching the island.
Note: The bits of land within Marin County in the Bodega Bay and Farallon Islands graticules are really, really tiny. They're reachable, but the odds of a hashpoint falling in them is low.
 San Bernardino
 San Diego
 San Francisco
Good luck with the Farralon Islands graticule. The Farallon Islands are part of a National Wildlife Refuge, with access restricted to the public. The rest of the graticule is either water, or part of Marin County, or not in any county.
 San Joaquin
 San Luis Obispo
 San Mateo
 Santa Barbara
 Santa Clara
 Santa Cruz