California Code, Streets and Highways Code - SHC § 5852

If a part only of the district is so included within one city and the remaining part of the district is so included within one or more other cities, so that no portion of the district remains within unincorporated territory of the county, the district shall continue in existence for all purposes until a copy of a joint resolution adopted by all of the cities requesting dissolution of the district is filed with the board of supervisors whereupon the district shall be dissolved.  The proportionate part of such funds shall be paid to the treasurer of each such city as the assessed valuation of the real property of the portion of the district included therein bore, before being so included, to the total assessed valuation of the real property of the district, and such funds shall be administered by the legislative bodies of such cities for the benefit of the district.  Any one city may withdraw its territory from the district in the manner provided by Section 5853.