California Code, Probate Code - PROB § 16365

(a) A tax required to be paid by a fiduciary that is based on receipts allocated to income shall be paid from income.

(b) A tax required to be paid by a fiduciary that is based on receipts allocated to principal shall be paid from principal, even if the tax is called an income tax by the taxing authority.

(c) Subject to subdivision (d) and Sections 16363, 16364, and 16366, a tax required to be paid by a fiduciary on a share of an entity's taxable income in an accounting period shall be paid from the following:

(d) After applying subdivisions (a) to (c), inclusive, a fiduciary shall adjust income or principal receipts, to the extent the taxes the fiduciary pays are reduced because of a deduction for a payment made to a beneficiary.