There is virtually NO similarity between the equipment used now and that of the original California Zephyr, other than they both use stainless steel. The original equipment was single level with dome cars and a round end observation. It was built by the Budd Company. The current equipment is double decked Superliner, made by Pullman-Standard (Superliner I - 1979-80) and Bombardier (Superliner II 1992). Even the fluting pattern is very different.
There is really no continuity of history in the equipment. The original California Zephyr was discontinued by the WP in March 1970, over a year before Amtrak. BN and D&RGW continued "California Service" on a different schedule,using the original equipment, continuing on to Ogden where there was cross-platform transfer to SP's City of San Francisco. After Amtrak, D&RGW elected not to join Amtrak and ran their own Denver-Salt Lake City train, the Rio Grande Zephyr, using their CZ cars. Amtrak ran the "San Francisco Zephyr" at first basically with the SP/UP City of San Francisco equipment Day 1, and shortly transitioning to the "rainbow" period of cars from a variety of railroads, which were ultimately standardized into Amtrak livery. This continued until roughly 1980 when the San Francisco Zephyr was re-equipped with the then new Superliners. In April 1983, D&RGW finally joined Amtrak and discontinued the Rio Grande Zephyr. Amtrak renamed the San Francisco Zephyr to California Zephyr, a name which had been out of use at that point for 13 years when they re-routed over the old CZ D&RGW routing (the name change happened immediately, notwithstanding that they didn't physically re-route immediately due to the huge Thistle landslide, which had cut the D&RGW). The last remnant of the original CZ was the Rio Grande Zephyr.
In terms of equipment, the lineage is really SP City of San Francisco - Amtrak San Francisco Zephyr - Amtrak California Zephyr. That was the continuously operating service.
The current routing is the same as the original CZ from Chicago to Weso, NV just east of Winnemucca, NV. At that point, the Amtrak CZ follow the SP line over Donner Pass instead of the old WP through Feather River Canyon.