The west segment of SR 90 begins at Lincoln Boulevard (State Route 1) in the Del Rey district of Los Angeles.

The east segment begins at the intersection of Imperial Highway and Beach Boulevard (State Route 39) in La Habra.

It heads east and southeast on Imperial Highway, ending at State Route 91 about 1⁄4 mile (400 m) after crossing the Santa Ana River from Yorba Linda into Anaheim.

[2] However, the same state law that authorized relinquishment required the city to "maintain signs directing motorists to the continuation of Route 90".

[2] By the 1960s, community opposition had reduced it to what is effectively a minor spur of I-405 to Marina Del Rey[9] (derisively dubbed the "Slauson Cutoff" by comedian Johnny Carson).

Strong opposition, the acquisition of surrounding properties, and potentially infringing on a public park along Admiralty, which contains a section of the Marvin Braude Bike Trail killed the proposal.

The freeway extension also allows Route 90 drivers to avoid a traffic signal at Alla Road (just west of Culver Boulevard.).

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.