California Code, Revenue and Taxation Code - RTC § 17745

(a) If, for any reason, the taxes imposed on income of a trust which is taxable to the trust because the fiduciary or beneficiary is a resident of this state are not paid when due and remain unpaid when that income is distributable to the beneficiary, or in case the income is distributable to the beneficiary before the taxes are due, if the taxes are not paid when due, such income shall be taxable to the beneficiary when distributable to him except that in the case of a nonresident beneficiary such income shall be taxable only to the extent it is derived from sources within this state.

(b) If no taxes have been paid on the current or accumulated income of the trust because the resident beneficiary's interest in the trust was contingent such income shall be taxable to the beneficiary when distributed or distributable to him or her.

(c) The tax on that income which is taxable to the beneficiary under subdivisions (a) or (b) is a tax on the receipt of that income distributed or on the constructive receipt of that distributable income. For purposes of this section income accumulated by a trust continues to be income even though the trust provides that the income (ordinary or capital) shall become a part of the corpus.

(d) The tax attributable to the inclusion of that income in the gross income of that beneficiary for the year that income is distributed or distributable under subdivision (b) shall be the aggregate of the taxes which would have been attributable to that income had it been included in the gross income of that beneficiary ratably for the year of distribution and the five preceding taxable years, or for the period that the trust accumulated or acquired income for that contingent beneficiary, whichever period is the shorter.

(e) In the event that a person is a resident beneficiary during the period of accumulation, and leaves this state within 12 months prior to the date of distribution of accumulated income and returns to the state within 12 months after distribution, it shall be presumed that the beneficiary continued to be a resident of this state throughout the time of distribution.

(f) The Franchise Tax Board shall prescribe such regulations as it deems necessary for the application of this section.