StealthCamping is legal in California as long as you leave-no-trace, only use unimproved and non-posted land, and you are sure to leave immediately when asked. You must be sure to not interfere with any business that happens on the land.
You cannot use any of the wood or produce (602.a, 602.b, 602.c), you cannot dig (602.d, 602.e), you cannot remove anything, you cannot damage anything (602.f), you cannot enter shellfish raising areas (602.g), you cannot enter posted land used for farm animals (602.h), you cannot open fences (602.i), you cannot build a fire if the land is posted (602.j), you cannot interfere or obstruct any business (602.k), you cannot use any cultivated, fenced, or posted lands (602.l), you must leave when asked (602.l.1), you cannot use a firearm (602.l.3), you cannot enter and occupy any structures (602.m).
You can stealth camp if the area is unimproved, unfenced, non-posted, and you have not been asked to leave.
You should verify this with your own research including laws and codes at the city, township, and county levels.