Hey OP, I actually live in California and have been carrying knives for years. Yes a 4 inch blade is over legal limit. I believe 3-3.5 inch is the limit. Personally I've carried up to about 3.75 inch blades. The current one I carry is just a smidge over 3.5 inch assisted opening Kershaw. I have shown it to cops and most like it never said anything about it. One said it might be over the limit but unless I did something to piss him off probably wouldn't think twice about it. My other I carry is a 3 inch Kershaw assisted as well and that one I know has no legal issues. If you're that worried about getting in trouble with a knife. I'd say you're pretty safe with a 3 inch folder
My pistols, however, I always kept by me.