It includes routes defined by the California State Legislature but never built, as well as routes entirely relinquished to local governments.

It also includes the routes that were decommissioned during the 1964 state highway renumbering.

Each U.S. Route in California is maintained by the California Department of Transportation (Caltrans) and is assigned a Route (officially State Highway Route[2][3]) number in the Streets and Highways Code (Sections 300-635).

California still uses a version of the 1961 U.S. Route shield, featuring a simplified cutout shield containing only the outer border, "U S," and the route marker.

All other U.S. states adopted the 1971 version of the marker, consisting of a white shield outline on a black square background.