Here is more about the Atchison, Topeka and Santa Fe Railway’s Super Chief, which operated between Chicago and Los Angeles between 1937 and 1971, when Santa Fe passenger service was taken over by Amtrak. Santa Fe licensed the name “Super Chief” to Amtrak, but withdrew their permission to use the name in 1974 due to the decline in quality of service under the grey shroud of socialism.
The Super Chief made the run in 36 hours and 49 minutes, for an average speed end-to-end of 60 miles per hour and peak speed of 100 miles per hour.
Here is a 1948 advertisement for the Super Chief.