Cal. Welf. and Inst. Code § 4428
When complaint is made to the department regarding the officers or management of any hospital or institution for the developmentally disabled, or regarding the management of any person detained therein or regarding any person held in custody, the department may, before making an examination regarding such complaint, require it to be made in writing and sworn to before an officer authorized to administer oaths. On receipt of such a complaint, sworn to if so required, the department shall direct that a copy of the complaint be served on the authorities of the hospital or institution or the person against whom complaint is made, together with notice of the time and place of the investigation, as the department directs.
Ca. Welf. and Inst. Code § 4428