Statewide: Any concealed (upon the person, ready for use) fixed blade knife is a felony,(no fixed blade neck knives). No statewide wide blade length limit on folders. Key to note the plastic knives(Cold Steel Zytel tanto, Busse Stealth hawk, etc.)are also a felony. No autos over two-inch blade lenght. No Balisongs, kubotons(unless keys are attached), Collasipble batons, clubs, billies, throwing stars, etc.... etc.... etc....
The Catch 22 in Kali is that many cities have their own knife laws, that do focus on such things as folder blade lenght. The joke in Southern Kal People's Republic is that you can put a four-inch folder in your pocket, drive 20 miles on the Freeway; and go in and out of local code violation 6 times.
The City of San Francisco currently has no folder lenght limit. Uncertain about the other cities of the Bay Area. Best bet for low hassle factor is a folder with a 2.78" blade.(this is not to say that 4" or more is illegal, is't not; just a lower hassle magnet) Enforcement is real spotty as well, since not even the Cops can keep up with the jumble of laws.
If you get over to Oakland, Look up Triple Aught Design.