Cal. Fish & Game Code § 2016

It is unlawful to enter any lands under cultivation or enclosed by a fence, belonging to, or occupied by, another, or to enter any uncultivated or unenclosed lands, including lands temporarily inundated by waters flowing outside the established banks of a river, stream, slough, or other waterway, where signs forbidding trespass or hunting, or both, are displayed at intervals not less than three to the mile along all exterior boundaries and at all roads and trails entering those lands, for the purpose of discharging any firearm or taking or destroying any mammal or bird, including any waterfowl, on those lands without having first obtained written permission from the owner, or his or her agent, or the person in lawful possession of, those lands. Signs may be of any size and wording that will fairly advise persons about to enter the land that the use of the land is so restricted.