Cal. Rev. & Tax. Code § 6453

For purposes of the sales tax, the return shall show the gross receipts of the seller during the preceding reporting period and, in the case of a person who is liable for the sales tax and is not a seller, the gross receipts of such person for the period in which the liability was incurred. For purposes of the use tax, in case of a return filed by a retailer, the return shall show the total sales price of the property sold by him or her, the storage, use, or consumption of which property became subject to the use tax during the preceding reporting period; in case of a return filed by a purchaser, except as provided in Section 6452.1, the return shall show the total sales price of the property purchased by him or her, the storage, use, or consumption of which became subject to the use tax during the preceding reporting period.

The return shall also show the amount of the taxes for the period covered by the return and any other information which the board deems necessary for the proper administration of this part.