California Code, Education Code - EDC § 15260

In case of a district lying in two or more counties, the assessor of each of the counties in which the district lies, shall annually as soon as the county assessments have been equalized by the State Board of Equalization, certify to the board of supervisors of each of the counties in which any portion of the district is situated, the assessed value of all taxable property in the county situated in the school district or community college district.  The tax shall be levied according to the ratio which the assessed value of the property in the district in any county bears to the total assessed value of the property in the district.  Each board of supervisors shall levy upon the property of the district and within its own county the rate of tax that will be sufficient to raise not less than the amount needed to pay the interest and any portion of the principal of the bonds that is to become due during the year.