2005 California Streets and Highways Code Sections 1710-1712 Article 4. Cooperation Between Cities and Counties

1710.  A city and a county may agree that the city shall construct,
repair and maintain designated county highways or portions thereof
within the unincorporated territory of the county, the cost thereof
to be paid by the county to the city.
1711.  A county and a city may agree that the county shall
construct, repair or maintain designated county highways, or portions
thereof, within the unincorporated territory of the county, the cost
thereof to be paid in whole or in part by the city to the county.
1712.  (a) A county and a city or cities may join in the acquisition
of rights-of-way, construction, maintenance, improvement, or repair
of bicycle routes or paths, or portions thereof, located within or
without the city or cities.
   (b) The cost or expense thereof shall be apportioned among the
county and the city or cities as the legislative bodies thereof
determine by agreement.
   (c) The authority and responsibility for the acquisition and work
shall vest in the county or in the city or cities, or in both, as
provided in the agreement apportioning the cost or expense thereof.