San Francisco Zephyr, 1970s.

Between May 1971 and  June 1972, the Chicago-San Francisco/Oakland route was covered by two trains: the daily Denver Zephyr (Chicago-Denver) and the thrice-weekly City of San Francisco (Denver-San Francisco/Oakland). In mid-1972, the route became daily and was rebranded the San Francisco Zephyr.  Eleven years later, the service was restored to its historic route through Colorado's Rocky Mountains; in celebration, it was renamed the California Zephyr.

In this image, the train is led by SDP40F locomotive No. 629, wearing the Amtrak Phase I paint scheme introduced in 1972. The first locomotive built expressly for Amtrak, the SDP40F was a six axle diesel-electric unit that sported a 3,000 horsepower engine. It was built in 1973 and 1974 by the General Motors Electro-Motive Division. Since many passenger rail cars were still heated via steam, the SDP40F included two steam generators and a water tank. Within a decade, most of these locomotives were replaced with F40PH models that could operate more easily with the new and refurbished fleet of all-electric passenger cars.