Cal. Pub. Cont. Code § 20201

Every complete project for new construction or project for any alteration, maintenance, or repair, if the costs of materials, supplies and labor exceed fifteen thousand dollars ($15,000), shall be let to the lowest responsible bidder. The board shall adopt plans and specifications, strain sheets, and working details and shall advertise for bids for the project in accordance with the plans and specifications so adopted. Notice inviting bids for all projects shall be published in a newspaper in the district at least one week prior to the time specified for receiving bids.