Cal. Gov. Code § 26443

The board may fix terms and conditions for the sale or other disposition of any authorized issue of bonds. The board may sell bonds at less than their par or face value but no bond may be sold at a price below the par or face value thereof which would result in a sale price yielding to the purchaser an average of more than six (6) percent per annum, payable semiannually, according to standard tables of bond values.