California Code, Streets and Highways Code - SHC § 25348

The treasurer of the district shall, prior to the fifteenth day of August in each year, transmit to the board of supervisors of each county within the district a statement of the total sum to be collected within that county during the fiscal year in behalf of the district.  It shall be the duty of the board of supervisors of each county in the district, and of the other proper fiscal officers thereof, to cause the amount so certified by the district treasurer to be collected from the taxable property within the county and the total amount of such collections shall be transmitted to and deposited with the district treasurer not later than the first day of each month following the date of their collection.