Cal. Probate Code § 4405

(a) A statutory form power of attorney under this part that limits the power to take effect upon the occurrence of a specified event or contingency, including, but not limited to, the incapacity of the principal, may contain a provision designating one or more persons who, by a written declaration under penalty of perjury, have the power to determine conclusively that the specified event or contingency has occurred. (b) A statutory form power of attorney that contains the provision described in subdivision (a) becomes effective when the person or persons designated in the power of attorney execute a written declaration under penalty of perjury that the specified event or contingency has occurred, and any person may act in reliance on the written declaration without liability to the principal or to any other person, regardless whether the specified event or contingency has actually occurred. (c) The provision described in subdivision (a) may be included in the “Special Instructions” portion of the form set forth in Section 4401. (d) Subdivisions (a) and (b) do not provide the exclusive method by which a statutory form power of attorney under this part may be limited to take effect upon the occurrence of a specified event or contingency.