California Code, Streets and Highways Code - SHC § 390

(a) Route 90 is from Route 1 northwest of the Los Angeles International Airport to Route 91 in Santa Ana Canyon passing near La Habra, except for the portion within the city limits of Yorba Linda.

(b) The relinquished former portion of Route 90 within the City of Yorba Linda is not a state highway and is not eligible for adoption under Section 81.

(c) The City of Yorba Linda shall ensure the continuity of traffic flow on the relinquished former portion of Route 90, including any traffic signal progression.

(d) For the relinquished former portion of Route 90, the City of Yorba Linda shall maintain signs directing motorists to the continuation of Route 90.