California Code, Welfare and Institutions Code - WIC § 5270.20

(a) For a person to be certified under this article, a second notice of certification shall be signed by the professional person in charge of the facility providing intensive treatment to the person and by either a physician who shall, if possible, be a board-qualified psychiatrist, or a licensed psychologist who has a doctoral degree in psychology and at least five years of postgraduate experience in the diagnosis and treatment of emotional and mental disorders. The physician or psychologist who signs shall have participated in the evaluation and finding referred to in subdivision (a) of Section 5270.15.

(b) If the professional person in charge is the physician who performed the medical evaluation and finding, or a psychologist, the second person to sign may be another physician or psychologist unless one is not available, in which case a social worker, licensed marriage and family therapist, licensed professional clinical counselor, or registered nurse who participated in the evaluation and finding shall sign the notice of certification.