The precursor to the Santa Ana Freeway between Los Angeles and Anaheim was U.S. Route 101 Bypass from the early 1940s to the mid-1950s, when it became part of US 101.

[1][2] At the urging of local businesses and groups, a proposal was submitted to AASHO to move US 101 back to El Camino Real, which was approved in 1938 alongside the creation of US 101 Bypass for the Bayshore Highway.

Its southernmost section between US 101 near Scotia to the north end of the Eel River Bridge is legally defined as an unsigned California State Route 283.

It is a former alignment of US 101, bypassed in 1964 when a new bridge opened across Youngs Bay; the business designation for the old route was approved by AASHO in 1965.

[9] The Oregon State Highway Commission originally requested the designation of U.S. Route 101 Alternate, which was rejected.