Cal. PROB § 4675

(a) If an individual is a patient in a skilled nursing facility when a written advance health care directive is executed, the advance directive is not effective unless a patient advocate or ombudsman, as may be designated by the Department of Aging for this purpose pursuant to any other applicable provision of law, signs the advance directive as a witness, either as one of two witnesses or in addition to notarization. The patient advocate or ombudsman shall declare that he or she is serving as a witness as required by this subdivision. It is the intent of this subdivision to recognize that some patients in skilled nursing facilities are insulated from a voluntary decisionmaking role, by virtue of the custodial nature of their care, so as to require special assurance that they are capable of willfully and voluntarily executing an advance directive.

(b) A witness who is a patient advocate or ombudsman may rely on the representations of the administrators or staff of the skilled nursing facility, or of family members, as convincing evidence of the identity of the patient if the patient advocate or ombudsman believes that the representations provide a reasonable basis for determining the identity of the patient.