Cal. Pub. Cont. Code § 21566

The board, in advertising for bids and in letting contracts as provided in Section 21565, may require that all articles furnished to the district pursuant to such contracts be manufactured, produced, or fabricated in the United States or its territories, and may prohibit the use in, or employment in connection with, the carrying out of such contracts by the contractor or any subcontractor, of all machinery or materials except those which have been manufactured, produced, or fabricated in the United States or its territories, if they are determined by the board to be available.