SR 1 signs first went up after California decided to number its highways, in 1934. The section for Humboldt, Mendocino, Sonoma, Marin, San Francisco, San Mateo, Santa Cruz, Monterey, San Luis Obispo and Santa Barbara counties was posted as SR 1, that section of the road known Route 56 (Las Cruces to Fernbridge). For Ventura, Los Angeles and Orange counties, Route 60 (San Juan Capistrano to the Oxnard area) became SR 3, and a few SR 3 signs were actually posted. The SR 3 signs were replaced by US 101 Alt. shields by 1936, as the road was built out; this change also allowed the extension of US 66 to end at another U.S. Route, in Santa Monica.