Cal. Health & Safety Code § 8628

An affidavit by any person having knowledge of the facts setting forth the fact of the death of one joint tenant and establishing the identity of the surviving joint tenants named in the deed to any plot, when filed with the cemetery authority operating the cemetery in which the plot is located, is complete authorization to the cemetery authority to permit the use of the unoccupied portion of the plot in accordance with the directions of the surviving joint tenants or their successors in interest.