Cal. PROB § 4207

(a) An attorney-in-fact may resign by any of the following means: (1) If the principal is competent, by giving notice to the principal. (2) If a conservator has been appointed, by giving notice to the conservator. (3) On written agreement of a successor who is designated in the power of attorney or pursuant to the terms of the power of attorney to serve as attorney-in-fact. (4) Pursuant to a court order. (b) This section is not subject to limitation in the power of attorney.