California Code, Probate Code - PROB § 16064

(a) To the extent the trust instrument waives the account, except that no waiver described in subdivision (e) of Section 16062 shall be valid or enforceable.  Regardless of a waiver of accounting in the trust instrument, upon a showing that it is reasonably likely that a material breach of the trust has occurred, the court may compel the trustee to account.

(b) As to a beneficiary who has waived in writing the right to an account.  A waiver of rights under this subdivision may be withdrawn in writing at any time as to accounts for transactions occurring after the date of the written withdrawal.  Regardless of a waiver of accounting by a beneficiary, upon a showing that is reasonably likely that a material breach of the trust has occurred, the court may compel the trustee to account.

(c) In any of the circumstances set forth in Section 16069.