Cal. Civ. Code § 1631

Every person in this State who sells machinery used or to be used for mining purposes shall, at the time of sale, give to the buyer a bill of sale for the machinery. The seller shall keep a written record of the sale, giving the date thereof, describing the machinery, and showing the name and address of the buyer, and the buyer, if in this State, shall keep a record of his purchase, giving the name and address of the seller, describing the machinery, and showing the date of the purchase.