SHC §989: (a) (1) Upon the incorporation of a city or upon the annexation of territory to a city, all right, title, and interest of the county, including the underlying fee where owned by the county, in and to

(a) (1) Upon the incorporation of a city or upon the annexation of territory to a city, all right, title, and interest of the county, including the underlying fee where owned by the county, in and to any county highway within the territory involved, which had been accepted into the county road system pursuant to Section 941 shall vest in the city and shall thereupon constitute a city street. (2) All right, title, and interest of a county in and to any county highway included within territory heretofore incorporated as a city or annexed to a city is hereby determined to have vested in the city as a city street. (b) Subdivision (a) does not apply to a road or highway which had been accepted into the county road system pursuant to Section 941 after the date of the first signature on a petition for annexation or incorporation, the adoption of a resolution of application by an affected local agency, or a date mutually agreed upon by the city and county. (c) Nothing in subdivision (a) requires a city to improve the affected road or highway to city standards.