California Code, Government Code - GOV § 11512

(a) Every hearing in a contested case shall be presided over by an administrative law judge.  The agency itself shall determine whether the administrative law judge is to hear the case alone or whether the agency itself is to hear the case with the administrative law judge.

(b) When the agency itself hears the case, the administrative law judge shall preside at the hearing, rule on the admission and exclusion of evidence, and advise the agency on matters of law; the agency itself shall exercise all other powers relating to the conduct of the hearing but may delegate any or all of them to the administrative law judge.  When the administrative law judge alone hears a case, the judge shall exercise all powers relating to the conduct of the hearing.  A ruling of the administrative law judge admitting or excluding evidence is subject to review in the same manner and to the same extent as the administrative law judge's proposed decision in the proceeding.

(c) An administrative law judge or agency member shall voluntarily disqualify themselves and withdraw from any case in which there are grounds for disqualification, including disqualification under Section 11425.40.  The parties may waive the disqualification by a writing that recites the grounds for disqualification.  A waiver is effective only when signed by all parties, accepted by the administrative law judge or agency member, and included in the record.  Any party may request the disqualification of any administrative law judge or agency member by filing an affidavit, prior to the taking of evidence at a hearing, stating with particularity the grounds upon which it is claimed that the administrative law judge or agency member is disqualified.  Where the request concerns an agency member, the issue shall be determined by the other members of the agency.  Where the request concerns the administrative law judge, the issue shall be determined by the agency itself if the agency itself hears the case with the administrative law judge, otherwise the issue shall be determined by the administrative law judge.  No agency member shall withdraw voluntarily or be subject to disqualification if their disqualification would prevent the existence of a quorum qualified to act in the particular case, except that a substitute qualified to act may be appointed by the appointing authority.

(d) The proceedings at the hearing shall be reported by a stenographic reporter.  However, upon the consent of all the parties, or if a stenographic reporter is unavailable and upon finding of good cause by the administrative law judge, the proceedings may be recorded electronically.

(e) Whenever, after the agency itself has commenced to hear the case with an administrative law judge presiding, a quorum no longer exists, the administrative law judge who is presiding shall complete the hearing as if sitting alone and shall render a proposed decision in accordance with subdivision (b) of Section 11517.