Before the construction of US 101, it was part of the main highway between Los Angeles and Santa Barbara.

The only current remnants of that routing are at the mileage signs for westbound State Route 150, which have the control city as Santa Barbara west of Santa Paula, even though SR 150 currently ends 12 miles (19 km) east of the city.

A portion of the route between Santa Paula and Ojai was closed indefinitely by a landslide in February 2024 following a significant rain storm.

[6][7] Cleanup and the reopening of the section from Stonegate Road in Santa Paula to Steckel Park, north of the city, was delayed due to the risk of triggering additional slides that could damage nearby homes or utility lines.

[8] Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage.