Cal. Pub. Util. Code § 22906

The proceeds of the bond tax shall be paid into the treasury of the principal county to the credit of the district interest and sinking fund and shall be used only for the payment of the principal and interest on the bonds. The treasurer of the principal county shall pay the principal and interest on the bonds upon the warrant of the auditor of the principal county out of this fund. The county auditor shall cancel and retain the bonds and coupons when he draws his warrants on the treasurer in favor of the owners.