Cal. Health & Safety Code § 51372

Refunding bonds issued as provided in Section 51371 may be sold, or exchanged for outstanding bonds issued under this part and, if sold, the proceeds thereof may be applied, in addition to any other authorized purposes, to the purchase, redemption, or payment of such outstanding bonds. Pending the application of the proceeds of any such refunding bonds, with any other available moneys, (1) to the payment of the principal, accrued interest, and any redemption premium on the bonds being refunded, (2) to the payment of any interest on such refunding bonds, or (3) to any expenses incurred in connection with such refunding, such proceeds may be invested in such obligations as are permitted under the bond resolution authorizing the issuance of refunding bonds.