Cal. Health and Safety Code § 4801

(1) An issue of bonds is hereby defined to be the aggregate principal amount of all of the bonds authorized to be issued in accordance with a proposal submitted to and approved by the electors of the district, but no indebtedness will be deemed to have been contracted until bonds shall have been sold and delivered and then only to the extent of the principal amount of bonds so sold and delivered. (2) The board of directors of any district issuing any bonds heretofore or hereafter authorized may, in its discretion, divide the aggregate principal amount of such issue into two or more divisions or series and fix different dates for the bonds of each separate division or series. In the event any authorized issue is divided into two or more divisions or series, the bonds of each division or series may be made payable at such time or times as may be fixed by the legislative body of the district separate and distinct from the time or times the payment of bonds of any other division or series of the same issue.