California Code, Streets and Highways Code - SHC § 114

(a) When the commission or other public entity has allocated any funds for the construction, improvement, or maintenance of any portion of a state highway within a city or a county, the department may enter into a cooperative agreement with the city or the county or other public entity for the performance of the work by the department or by the city or the county or other public entity, or for the apportionment of the expense of the work between the department and the city or the county or other public entity.

(b) The department shall enter into a cooperative agreement with a city, county, or other public entity to perform professional and technical project development services, if the department determines that the city, county, or other public entity in which the project is located has qualified and available staff to perform the necessary project services.