If any portion of the unincorporated area of the county is annexed to a member city, that city shall assume the service obligation of the county for that area. If any portion of the unincorporated area of the county becomes incorporated, the incorporating city shall assume the service obligations of the county for that area.
Source:
Section 107007, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=PUC§ionNum=107007..