Chapter 2. City Streets As Part Of The State And County Highway Systems of California Streets And Highways Code >> Division 2.5. >> Chapter 2.

Any city may, by ordinance or resolution, permit the use of its streets and highways by the board of supervisors of the county, for the purpose of constructing and maintaining thereon any highway or boulevard, as part of a county system of roads within any portion of its incorporated limits.

The legislative body of any city may establish the grades of those portions of any county highway lying within the city boundaries.

No city shall change the grade of any portion of a state or county highway where such grade has been established prior to the incorporation of the city, without first obtaining the written consent of the State or county authorities, as the case may be.