California Code, Probate Code - PROB § 17304

(a) At any time after final distribution of the decedent's estate, a trust described in Section 17300 may be transferred to a different county in this state as provided in this section.

(b) The petition for transfer shall set forth all of the following:

(c) If, after hearing, it appears to the court that the transfer of jurisdiction to the county designated in the petition or to any other county in this state will be in the best interests of the estate, or that economical and convenient administration of the trust will be facilitated by the transfer, the court shall make an order transferring jurisdiction over the trust. Upon such order, the court clerk shall certify a copy of the order of transfer to the clerk of the court to which jurisdiction is transferred, together with copies of the instrument creating the trust, the decree of distribution, and any other documents or matters of record the court determines by order to be necessary to define the powers and duties of the trustee, or otherwise to be necessary in connection with further administration of the trust.

(d) The court to which jurisdiction is transferred may from time to time require by order the filing of certified copies of additional papers or matters of record from the court in which the decedent's estate was administered as are required.

(e) Upon the filing of a certified copy of the order of transfer, together with supporting documents, the court to which jurisdiction is transferred has the same jurisdiction over the trust as the court in which the decedent's estate was administered but for the transfer.