California Code, Probate Code - PROB § 15660

(a) If the trust has no trustee or if the trust instrument requires a vacancy in the office of a cotrustee to be filled, the vacancy shall be filled as provided in this section.

(b) If the trust instrument provides a practical method of appointing a trustee or names the person to fill the vacancy, the vacancy shall be filled as provided in the trust instrument.

(c) If the vacancy in the office of trustee is not filled as provided in subdivision (b), the vacancy may be filled by a trust company that has agreed to accept the trust on agreement of all adult beneficiaries who are receiving or are entitled to receive income under the trust or to receive a distribution of principal if the trust were terminated at the time the agreement is made.  If a beneficiary has a conservator, the conservator may agree to the successor trustee on behalf of the conservatee without obtaining court approval.  Without limiting the power of the beneficiary to agree to the successor trustee, if the beneficiary has designated an attorney in fact who has the power under the power of attorney to agree to the successor trustee, the attorney in fact may agree to the successor trustee.

(d) If the vacancy in the office of trustee is not filled as provided in subdivision (b) or (c), on petition of any interested person or any person named as trustee in the trust instrument, the court may, in its discretion, appoint a trustee to fill the vacancy.  If the trust provides for more than one trustee, the court may, in its discretion, appoint the original number or any lesser number of trustees.  In selecting a trustee, the court shall give consideration to any nomination by the beneficiaries who are 14 years of age or older.