Cal. Pub. Contract Code § 21042
The district may prescribe methods for the construction of works and for the letting of contracts for any of the following purposes:
When work is not to be done by the district itself by force account, and the amount involved is forty thousand dollars ($40,000), or more, any contract for the doing of the works shall be made by the district with the lowest and best bidder after the publication pursuant to Section 6061 of the Government Code in a newspaper of general circulation published within the district, of a notice calling for bids and fixing a period during which bids will be received, which shall be not less than 10 days after the publication of the notice. The district may reject any and all of the bids presented and may readvertise in its discretion. After rejecting bids, or if no bids are received, the district may determine and declare that in its opinion, based on estimates submitted by the engineer for the district, any work may be performed better or more economically by the district with its own employees, or after hiring additional employees. After the adoption of a resolution to this effect by at least seven affirmative votes of the directors of the district, the district may proceed to have that work done in the manner stated and without further observance of the provisions of this section.
Ca. Pub. Cont. Code § 21042