California Code, Civil Code - CIV § 2080

Any person who finds a thing lost is not bound to take charge of it, unless the person is otherwise required to do so by contract or law, but when the person does take charge of it he or she is thenceforward a depositary for the owner, with the rights and obligations of a depositary for hire.  Any person or any public or private entity that finds and takes possession of any money, goods, things in action, or other personal property, or saves any domestic animal from harm, neglect, drowning, or starvation, shall, within a reasonable time, inform the owner, if known, and make restitution without compensation, except a reasonable charge for saving and taking care of the property.  Any person who takes possession of a live domestic animal shall provide for humane treatment of the animal.