Streets and Highways Code § 8206

All bonds shall be payable in lawful money of the United States at the office of the county treasurer of the county, and shall bear interest at a rate not to exceed 6 percent per annum, which shall be payable semiannually. Not less than one-thirtieth part of the total issue of bonds shall be payable each year, commencing not more than five years after the date of the bond issue.