Cal. Pub. Util. Code § 130543

The proceeds of any bonds issued for the additional purpose of paying all or any part of the cost of constructing and acquiring additions, improvements, extensions, or enlargements of a project may be invested and reinvested by the commission or its trustee in obligations of, or guaranteed by, the United States of America, or in certificates of deposit or time deposits secured by obligations of, or guaranteed by, the United States of America, maturing not later than the time or times when the proceeds will be needed for the purpose of paying all or any part of the cost. The interest, income, and profits, if any, earned or realized on the investment may be applied to the payment of all or any part of the cost or may be used by the commission in any lawful manner.