California Code, Government Code - GOV § 11425.50

(a) The decision shall be in writing and shall include a statement of the factual and legal basis for the decision.

(b) The statement of the factual basis for the decision may be in the language of, or by reference to, the pleadings. If the statement is no more than mere repetition or paraphrase of the relevant statute or regulation, the statement shall be accompanied by a concise and explicit statement of the underlying facts of record that support the decision. If the factual basis for the decision includes a determination based substantially on the credibility of a witness, the statement shall identify any specific evidence of the observed demeanor, manner, or attitude of the witness that supports the determination, and on judicial review the court shall give great weight to the determination to the extent the determination identifies the observed demeanor, manner, or attitude of the witness that supports it.

(c) The statement of the factual basis for the decision shall be based exclusively on the evidence of record in the proceeding and on matters officially noticed in the proceeding. The presiding officer's experience, technical competence, and specialized knowledge may be used in evaluating evidence.

(d) Nothing in this section limits the information that may be contained in the decision, including a summary of evidence relied on.

(e) A penalty may not be based on a guideline, criterion, bulletin, manual, instruction, order, standard of general application or other rule subject to Chapter 3.5 (commencing with Section 11340) unless it has been adopted as a regulation pursuant to Chapter 3.5 (commencing with Section 11340).