California Code, Welfare and Institutions Code - WIC § 4021

(a) When the department has reason to believe that a person held in custody as having a mental health disorder is wrongfully deprived of his or her liberty, or is cruelly or negligently treated, or that inadequate provision is made for the skillful medical care, proper supervision, and safekeeping of that person, it may ascertain the facts. It may issue compulsory process for the attendance of witnesses and the production of papers, and may exercise the powers conferred upon a referee in a superior court. It may make such orders for the care and treatment of such person as it deems proper.

(b) Whenever the department undertakes an investigation into the general management and administration of an establishment or place of detention for persons with mental health disorders, it may give notice of that investigation to the Attorney General, who shall appear personally or by deputy, to examine witnesses in attendance and to assist the department in the exercise of the powers conferred upon it in this code.