Pub. Contract Code, § 21341

(a) All contracts for the construction of any unit of work, except as provided in this article, estimated to cost in excess of five thousand dollars ($5,000) shall be let to the lowest responsible bidder. The board shall advertise by three insertions in a daily newspaper of general circulation or two insertions in a weekly newspaper of general circulation published by the agency inviting sealed proposals for the construction of the work before any contract is made, and may let by contract separately any part of the work. The board shall require the successful bidder to file with the board good and sufficient bonds to be approved by the board conditioned upon the faithful performance of the contract and upon the payment of the claims for labor and material, the bonds to contain the terms and conditions set forth in Title 3 (commencing with Section 9000) of Part 6 of Division 4 of the Civil Code, and to be subject to the provisions of that title. The board shall also have the right to reject any bid, in which case the board may advertise for new bids. In the event no proposals are received pursuant to advertisement or where the estimated cost of the work does not exceed five thousand dollars ($5,000), or where the work consists of emergency work, the board, by unanimous vote of all members present, may, without advertising for bids, have the work done by force account. In case of an emergency, if notice for bids to let contracts will not be given, the board shall comply with Chapter 2.5 (commencing with Section 22050). The agency may purchase in the open market, without advertisement for bids, materials and supplies for use in any work either under contract or by force account.

(b) The provisions of this section have no application to a contract entered into with the United States under the authority of Section 59 of Chapter 1512 of the Statutes of 1957, or to a contract authorized by a vote of the electorate of the agency.