Streets and Highways Code § 6440

After the street superintendent files his list of unpaid assessments with the treasurer, the principal of each unpaid assessment shall thereafter become due and payable to the treasurer in equal annual payments on each October 15th succeeding the September 1st following the date of the bonds until fully paid. The number of annual payments shall correspond to the number of serial payments to be made on the principal of the bonds issued to represent the unpaid assessment.