Cal. Welfare and Institutions Code § 6004

The superintendent or person in charge of the county psychiatric hospital may receive, care for, or treat in the hospital any person who voluntarily makes a written application to the superintendent or person in charge thereof for admission into the hospital for care, treatment, or observation, and who is a suitable person for care, treatment, or observation, and who in the case of an adult person is in such condition of mind, at the time of making application for admission, as to render him competent to make such application. In the case of a minor person, the application shall be made by his parents, or by the parent, guardian, or other person entitled to his custody. A conservatee, with a conservator of the person, or person and estate, appointed under Chapter 3 (commencing with Section 5350) of Part 1 of Division 5, with the right as specified by court order under Section 5358 to place his conservatee, may be admitted upon written application by his conservator.