California Code, Penal Code - PEN § 596

Every person who, without the consent of the owner, wilfully administers poison to any animal, the property of another, or exposes any poisonous substance, with the intent that the same shall be taken or swallowed by any such animal, is guilty of a misdemeanor.

However, the provisions of this section shall not apply in the case of a person who exposes poisonous substances upon premises or property owned or controlled by him for the purpose of controlling or destroying predatory animals or livestock-killing dogs and if, prior to or during the placing out of such poisonous substances, he shall have posted upon the property conspicuous signs located at intervals of distance not greater than one-third of a mile apart, and in any case not less than three such signs having words with letters at least one inch high reading “Warning--Poisoned bait placed out on these premises,” which signs shall be kept in place until the poisonous substances have been removed. Whenever such signs have been conspicuously located upon the property or premises owned or controlled by him as hereinabove provided, such person shall not be charged with any civil liability to another party in the event that any domestic animal belonging to such party becomes injured or killed by trespassing or partaking of the poisonous substance or substances so placed.