California Code, Government Code - GOV § 11513

(a) Oral evidence shall be taken only on oath or affirmation.

(b) Each party shall have these rights:  to call and examine witnesses,  1 to introduce exhibits;  to cross-examine opposing witnesses on any matter relevant to the issues even though that matter was not covered in the direct examination;  to impeach any witness regardless of which party first called him or her to testify;  and to rebut the evidence against him or her.  If respondent does not testify in his or her own behalf he or she may be called and examined as if under cross-examination.

(c) The hearing need not be conducted according to technical rules relating to evidence and witnesses, except as hereinafter provided.  Any relevant evidence shall be admitted if it is the sort of evidence on which responsible persons are accustomed to rely in the conduct of serious affairs, regardless of the existence of any common law or statutory rule which might make improper the admission of the evidence over objection in civil actions.

(d) Hearsay evidence may be used for the purpose of supplementing or explaining other evidence but over timely objection shall not be sufficient in itself to support a finding unless it would be admissible over objection in civil actions.  An objection is timely if made before submission of the case or on reconsideration.

(e) The rules of privilege shall be effective to the extent that they are otherwise required by statute to be recognized at the hearing.

(f) The presiding officer has discretion to exclude evidence if its probative value is substantially outweighed by the probability that its admission will necessitate undue consumption of time.