Cal. Pub. Cont. Code § 20538

All of the bonds shall be executed by the bidder and by a corporate surety duly authorized to do business as such under the laws of the State of California. Each bond shall be in an amount not less than 50 percent of the aggregate contract price. The contract shall not be executed on behalf of the district until all the contract bonds are approved by the president of the board of directors and the district engineer.