u/wazardthewizard

Yes, this is quite literally just a Union Pacific menu with the Amtrak logo stamped in two places on the interior. Amtrak in 1971 was a strange Frankenstein's Monster of an operation.

Interestingly, this menu says it is for the 'Traveler's Rest', a specific pattern of lounge/dinette car formerly used by the Northern Pacific and Great Northern; not Union Pacific, as this menu might otherwise suggest. After their acquisition by Amtrak, these cars were usually used on the San Francisco Zephyr, but not always.

Important to note is that Traveler's Rests were not full-service dining cars. As you might be able to tell from the relative lack of menu variety, their galley only had access to a small griddle and steam tables. These cars were much better suited to their role as lounge cars. Full dining car menus from the same year were of largely identical design, but with more variety.

Credit to trainlover at streamlinermemories.info for the menu and context, and to Howard Fogg for the original cover painting.

Credit to Trainlover at streamlinermemories.info for the menu.

This menu was in use before air conditioning became standard in passenger trains, but during the transition to refrigeration/machine-made ice. At least your food's cold.

Credit to Trainlover at streamlinermemories.info for the menu.

The San Diegan was only roughly a 2.5 to 3 hour trip between Los Angeles and San Diego, meaning that, as far as I can tell, a full dining car was never part of the consist. Instead, food service at this point in time was provided in a 'Lunch Counter Tavern/Diner' car, which had a counter with swivel seats where a light or full meal could be eaten, just without all the pomp and circumstance.

Nowadays, the modern equivalent of this train (The Pacific Surfliner) only has a counter-service cafe car with premade food and beverages, albeit with some table seating to eat at.
The concept of intermediate meal service similar to the San Diegan's setup was briefly experimented with in cafe cars on the San Joaquins and Capitol Corridor trains at some point in either the 90s or 2000s, but proved to be unpopular with modern passengers.

Credit to Trainlover at streamlinermemories.info for the menu and date range.