Cal. Prob. Code § 16364

(a) If a fiduciary makes or expects to make a principal disbursement described in subdivision (b), the fiduciary may transfer an appropriate amount from income to principal in one or more accounting periods to reimburse principal or provide a reserve for future principal disbursements.
(b) To the extent a fiduciary has not been, and does not expect to be, reimbursed by a third party, principal disbursements to which subdivision (a) applies include all of the following:
1. (1) An amount chargeable to income but paid from principal because income is not sufficient.
2. (2) The cost of an improvement to principal, whether a change to an existing asset or the construction of a new asset, including a special assessment.
3. (3) A disbursement made to prepare property for rental, including tenant allowances, leasehold improvements, and commissions.
4. (4) A periodic payment on an obligation secured by a principal asset, to the extent the amount transferred from income to principal for depreciation is less than the periodic payment.
5. (5) A disbursement described in subdivision (a) of Section 16361.
(c) If an asset whose ownership gives rise to a principal disbursement becomes subject to a successive interest after an income interest ends, the fiduciary may continue to make transfers under subdivision (a).