CA Prob Code Section 3203

A petition may be filed by any of the following:

(a)

The patient.

(b)

The patient’s spouse.

(c)

A relative or friend of the patient, or other interested person, including the patient’s agent under a power of attorney for health care.

(d)

The patient’s physician.

(e)

A person acting on behalf of the health care institution in which the patient is located if the patient is in a health care institution.

(f)

The public guardian or other county officer designated by the board of supervisors of the county in which the patient is located or resides or is temporarily living.