The southern section begins as Decker Canyon Road near Trancas in Malibu, where SR 23 intersects with the Pacific Coast Highway (State Route 1), or "PCH."

This portion provides numerous vistas of the Santa Monica Mountains and the Pacific Ocean during the daytime, but extreme caution is advised, especially as the road nears PCH.

Philip Taylor Kramer, bassist with the rock band Iron Butterfly from 1974–1977, allegedly committed suicide by driving his van over the side along this route.

Along its steep and winding path through the Santa Monica Mountains as an increasingly tight and twisting canyon road until its intersection with Potrero Road, SR 23 becomes Westlake Boulevard, where it departs Los Angeles County for Ventura County and heads roughly two miles northeast through the Westlake section of Thousand Oaks, a developed residential community.

The middle section is a major route for traffic headed between Thousand Oaks and Moorpark.

The road in Fillmore actually continues past Route 126 up to the foot of the Los Padres National Forest.

[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.