Ed. Code, § 16104

Any portion of an apportionment paid to a school district under this chapter shall be available for expenditure by its governing board for not less than one year nor more than three years, as the board shall determine, after the date on which the warrant covering that portion of the apportionment was issued by the Controller, provided that no limitation on expenditure shall be applicable with respect to any items the payment or reimbursement of which is required to be made by special resolution pursuant to Section 16057, whether the special resolution is adopted prior or subsequent to the termination of the period of availability herein specified. For the purposes of this chapter, an apportionment shall be deemed to be expended at the time and to the extent that the amount thereof on deposit in the county treasury has been encumbered by the creation of a valid obligation on the part of the school district. Upon the expiration of its period of availability, the unencumbered balance of any apportionment made under this chapter shall become due and payable to the State of California; and the governing board of the school district and the county treasurer shall pay the amount of the unencumbered balance to the Treasurer, out of the funds, and in the manner specified in Section 16100 of this code. The payment shall, on order of the Controller, be deposited in the State School Building Aid Fund in the State Treasury, to be reapportioned by the board.

It shall be the duty of the governing body and county treasurer to make the payments to the Treasurer as provided in this section, and it shall be the duty of the Controller to enforce the collection on behalf of the state, provided that notwithstanding the above duties shall not be deemed to exist with respect to any amount heretofore or hereafter due the state occasioned by the termination of the period of availability of expenditure provided by this section where the period of availability of expenditure for the items representing the amount is subsequently made inapplicable by the adoption of a special resolution pursuant to Section 16057.