The Rio Grande Zephyr was a remnant of the former California Zephyr?, covering only the Rio Grande's portion of the route. The California Zephyr, operated jointly by the Chicago, Burlington & Quincy, the Denver & Rio Grande Western, and the Western Pacific, had made its last through run on 22-Mar-1970. After that run, the Western Pacific no longer participated in the train's operation. The Burlington continued operating their portion from Chicago, IL, to Denver, CO, as the "California Service". The Rio Grande created the Rio Grande Zephyr and extended it from Salt Lake City to Ogden, UT. This linked the Burlington's train at Denver, CO, and allowed passengers to continue westward on the Southern Pacific and Union Pacific trains at Ogden.

Nearly every other railroad turned over their passenger operations to the newly-created Amtrak on 1-May-1971. Even the Rio Grande had considered joining, but shortly before Amtrak was set to take over, opted to continue operating their own trains. The reasoning behind this decision was purely financial.

Part of joining Amtrak was paying a sum equal to what it lost on passenger operations in an average year, as well as negotiating ongoing payments equal to the incremental cost of running passenger trains. Cost sharing for regular maintenance and upgrades was not allowed - only incremental cost of wear/tear on the track by Amtrak's trains, etc. Amtrak and the D&RGW could not come to terms on a contract, and at that point the Rio Grande apparently calculated that the costs of running the RGZ would be less than what they'd have to pay Amtrak.

Amtrak launched its version of the old California Zephyr? on day one - 1-May-1971 - and called it the San Francisco Zephyr. The train would use the old Burlington Route into Denver, CO, and then turn north and travel to Salt Lake City, UT, via the Union Pacific's Wyoming mainline (known as the Overland Route). West of Salt Lake, the train would not follow the traditional CZ route via the Western Pacific, but rather the Southern Pacific.

For just slightly over thirteen years, the Rio Grande Zephyr made tri-weekly trips between Denver and Salt Lake City. Equipment was largely left-overs from the California Zephyr?, heavy on dome cars and with sleepers converted back into coaches, as the RGZ easily made the run as a day trip. The tri-weekly schedule took only six days (one day each way for three trips), and always excluded Wednesday. Hence, the train is often associated with the motto, "Never on Wednesdays".

On 14-Apr-1983, the last full run of the Rio Grande Zephyr would be completed. The westbound RGZ passed Thistle, UT, at 2030h, and shortly afterwards, the line was severed by the Thistle Mudslide. The train, like all other end-to-end Rio Grande traffic, returned to Denver via Wyoming, detouring over the Union Pacific. Afterwards, the RGZ trainset would continue making a handful of runs to Grand Junction, but Rio Grande passenger operations were winding down. On 24-Apr-1983, the Rio Grande ran its last Rio Grande Zephyr, and at last relented and joined Amtrak.

It would be nearly three months before Amtrak began using the traditional route. With the train renamed the California Zephyr? again, the first eastbound originated from Chicago on 15-Jul-1983, and passed the site that killed its predecessor - Thistle, UT - the following day, on 16-Jul-1983.