The route spurs out of U.S. Route 97 in Weed while carrying Business Loop 5 from that intersection to Interstate 5. It was once part of U.S. Route 99. At a distance of 0.7 miles (1.1 km), it is the shortest signed California state highway. For many years the route was hidden, but was signed in 2005 in anticipation of a complete redesign - reconstruction of Weed Boulevard. Previously, the only visual proof of the route was the bridge ID that was spraypainted on the base of the Interstate 5 overpass, i.e. "265 overcrossing".
Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. R reflects a realignment in the route since then. The entire route is in Weed, Siskiyou County.