Where does it say its illegal to spend cash you found on a public lot like walmart or even on the street ?
CA CIVIL § 2080 - 2082
§ 2080. Duties of finder
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.
§ 2080.1. Delivery to police or sheriff; affidavit; charges
(a) If the owner is unknown or has not claimed the property, the person saving or finding the property shall, if the property is of the value of one hundred dollars ($100) or more, within a reasonable time turn the property over to the police department of the city or city and county, if found therein, or to the sheriff's department of the county if found outside of city limits, and shall make an affidavit, stating when and where he or she found or saved the property, particularly describing it.