Cal. Gov. Code § 16304.1
Disbursements in liquidation of encumbrances may be made before or during the two years following the last day an appropriation is available for encumbrance, except in the case of a fund made up of federal funds. Disbursements in liquidation of encumbrances may be made before or during the four years following the last day an appropriation of federal funds is available for encumbrance. Whenever, during either liquidation period, the Department of Finance determines the purpose for which the appropriation was made is completed and a portion of the appropriation is deemed not necessary, that portion shall, upon order of the Department of Finance, revert to and become a part of the fund from which the appropriation was made. Upon the expiration of two years, or four years in the case of a fund made up of federal funds, following the last day of the period of its availability for encumbrance, the balance in any appropriation shall revert to and become a part of the fund from which the appropriation was made. After reversion, any unpaid encumbrance against the appropriation may be paid from any current appropriations available for the same purposes.
To the extent that an appropriation is exempt from limitations as to periods of availability under Section 16304, it shall not be subject to the provisions of this section.
Ca. Gov. Code § 16304.1