Cal. Pub. Util. Code § 794

The commission may, after notice, and hearing if requested within 15 days after receipt of notice, prescribe by order the accounts in which particular outlays and receipts shall be entered, charged, or credited. Where the commission has prescribed the forms of accounts, records, or memoranda to be kept by any public utility for any of its business, it is unlawful for such public utility to keep any accounts, records, or memoranda for such business other than those so prescribed, or those prescribed by or under the authority of any other state or of the United States, except such accounts, records, or memoranda as are explanatory of and supplemental to those prescribed by the commission.