California Code, Public Contract Code - PCC § 21002

The notice inviting sealed proposals or bids shall be published by at least two insertions in the newspaper or newspapers designated in the resolution of intention, and (though it need not be simultaneously) a copy or copies of the same shall be posted and kept posted for five days, at or near the chamber door of the board of supervisors.  All proposals or bids shall be accompanied by a check, payable to the county, certified by a responsible bank in an amount not less than 10 percent of the aggregate of the proposal or bid, or by a bond in such amount running to the county, signed by the bidder, with two sureties qualifying before an officer competent to administer oaths, each in said amount over and above all statutory exemptions, or executed by some bonding company acceptable to said board of supervisors.  Said proposals or bids shall be delivered to the clerk of said board.