It provided premium extra fare service from Chicago to San Francisco when introduced in 1936 with a running time of 39 hours and 45 minutes each way.

[1][2] Under an order of the War Production Board, no new head-end or passenger cars of any type (other than "military sleepers") were built and delivered to US railroads from mid 1942 until late 1945.

[3] On October 1, 1946, service was increased to thrice weekly departures from both Chicago and San Francisco made every Tuesday, Thursday and Saturday evening.

Amtrak retained the name for the thrice-weekly Denver–San Francisco/Oakland portion of the run until June 1972, when the entire Chicago-San Francisco/Oakland route became daily again as the San Francisco Zephyr.

[9] Amtrak replaced its service between Chicago and San Francisco/Oakland on July 16, 1983 with its current daily train, the California Zephyr, when a portion of the route was moved from Union Pacific tracks in Wyoming to those of the Denver and Rio Grande Western Railroad in Colorado.

During the effort to reach the train, the railroad's snow-clearing equipment and snow-blowing rotary plows became frozen to the tracks near Emigrant Gap.

Hundreds of workers and volunteers, including escaped German POW Georg Gaertner, rescued stranded passengers by clearing nearby Route 40 to reach the train.

[22] The new City consist had 60 compartments, drawing rooms, bedrooms, and "roomettes" instead of the regular nine for a larger variety of sleeping accommodations to choose from than on any train in America.

Union Pacific itself has a dome lounge car used on excursion and executive trains which carries the City of San Francisco name.