California Code, Probate Code - PROB § 15301

(a) Except as provided in subdivision (b) and in Sections 15304 to 15307, inclusive, if the trust instrument provides that a beneficiary's interest in principal is not subject to voluntary or involuntary transfer, the beneficiary's interest in principal may not be transferred and is not subject to enforcement of a money judgment until paid to the beneficiary.

(b) After an amount of principal has become due and payable to the beneficiary under the trust instrument, upon petition to the court under Section 709.010 of the Code of Civil Procedure by a judgment creditor, the court may make an order directing the trustee to satisfy the money judgment out of that principal amount.  The court in its discretion may issue an order directing the trustee to satisfy all or part of the judgment out of that principal amount.