Cal. Pub. Contract Code § 20951
After adopting a plan for such conduits, drains, pumping plants, watergates, and other works which are provided for in this act, the board of directors shall give notice by publication thereof not less than 10 days as required in Section 6062a of the Government Code, in one newspaper published in each of the counties composing the district (provided, a newspaper is published therein) and in such other newspapers as they may deem advisable, calling for bids for the construction of such work, or of any portion thereof; if less than the whole work is advertised, then the portion so advertised must be particularly described in such notice. Said notice shall set forth that plans and specifications can be seen at the office of the board, and that the board will receive sealed proposals therefor, and that the contract will be let to the lowest responsible bidder, stating the time and place for opening said proposals, which, at the time and place appointed shall be opened in public; and as soon as convenient thereafter the board shall let said work, whether in portions or as a whole, to the lowest responsible bidder; or they may reject any or all bids and readvertise for proposals, or may proceed to construct the work under their own superintendence. Contracts for the purchase of material shall be awarded, or the board may reject any or all bids, and may readvertise for proposals. Any person or persons to whom a contract may be awarded shall enter into a bond, with good and sufficient sureties, to be approved by the board, payable to said district for its use for 50 percent of the amount of the contract price, conditioned for the faithful performance of the contract. The work shall be done under the direction and to the satisfaction of the engineer, and be approved by the board.
Contracts under this section calling for an expenditure of less than three thousand five hundred dollars ($3,500) may be let without bid.
Ca. Pub. Cont. Code § 20951