California Code, Streets and Highways Code - SHC § 366

(a) Route 66 is from:

(b) The relinquished former portions of Route 66 within the city limits of the Cities of Claremont, Fontana, Rancho Cucamonga, Rialto, and Upland are not state highways and are not eligible for adoption under Section 81. For the portions of Route 66 relinquished under this section, the Cities of Claremont, Fontana, Rancho Cucamonga, Rialto, and Upland shall maintain within their respective jurisdictions signs directing motorists to the continuation of Route 66 and shall ensure the continuity of traffic flow on the relinquished portions of Route 66, including any traffic signal progression.