The Post Office cancelled all railroad mail contracts in September, 1967

In the 19th century, the railroads and the RPO cars replaced the Pony Express. In the 20th century, the airlines and the Interstate highways replaced the railroads.

Loosing the mail to the airlines and Interstate highways was the "nail in the coffin" for passenger trains. Notice how long the Santa Fe's Grand Canyon is in the 1966-67 photos.

Marty Bernard shared a Roger Puta photo
 ATSF 30C (F3A) with The Grand Canyon stopping at Chillicothe, Illinois to pick up passengers and train orders on October 7, 1966.

Marty Bernard shared a Roger Puta photoATSF 46, I assume it's 46L, a F7A with Train 23, The Grand Canyon, arrives at Joliet, Illinois Union Station on October 16, 1966. Note the semaphore signals.

Marty Bernard shared a Roger Puta photoATSF 306 (F7A) with Train 2, The San Francisco Chief, at Clovis, NM (note the great length of the train) on August 27, 1967.
Ginger Dawgg This is where the Los Angeles-Dallas sleeper was cut off. That car had a logistically complex routing: It was on the Grand Canyon from L.A. to Winslow, the San Francisco Chief from there to Clovis, The California Special from there to Brownwood, The Angelo from there to Ft. Worth, and an unnamed train from there to Dallas. It was a slower schedule but attempted to compete with a SP-T&P routing via El Paso. A Richmond-Houston sleeper was also removed here.Marty Bernard It's an ABBBA consist.Steve Rippeteau The old F units were becoming un-reliable so they added more units.

Then notice how short the Grand Canyon is in the 1968 photos. Amtrak was formed just a couple of years later so that the railroads no longer had to loose money on passenger trains.

Marty Bernard shared a Roger Puta photo ATSF 45C (F7A) with Train 23, The Grand Canyon, departing Dearborn Station, Chicago, IL on February 19, 1968. Notice that the double slip switch in front of 45C has movable frogs moved by pneumatic switch machines. The pipe from the compressor can be seen running along between the tracks.
Tom Casey It's such a short train because this is after the loss of mail contracts and the ICC denied Santa Fe's request to discontinue this train completely.Michael Bruchas No diner?
Steve Rippeteau BYOB and your dinner. I think later the ATSF did run a lunch counter car? It ran this short consist until Amtrak took over 5/1/71.

Marty Bernard shared a Roger Puta photo ATSF 32L (F3A) with Train 23, The Grand Canyon, with only 1 baggage car and 2 chair cars leaving Dearborn Station, Chicago, IL on February 6, 1968. Look at the Board of Trade Building out in the open and no Sears Tower.

Marty Bernard shared a Roger Puta photoATSF 344 (F7A) with Train 16, The Texas Chief, ready to depart Union Station in Houston, TX on June 7, 1969.
Jim Dubrow The rails look rusty and overgrown with weeds.Steve Rippeteau Weeds and rusty rail was common even on the ATSF in that era. Company officials were rewarded and promoted for deferred maintenance and tearing out tracks.

Update:

Carl Venzke posted
Robert Petit The RPO, or oiling the journal brass?Carl Venzke I was thinking more about the RPO.Eric Risse The demise of handling mail via passenger trains had a lot to do with the demise of passenger rail in the USA and the creation of Amtrak.Carl Venzke Found this Eric. You are exactly right " In September 1967 the POD cancelled all "mail by rail" contracts, electing to move all First Class mail via air and other classes by road (truck) transport. This announcement had a devastating effect on passenger train revenues; the Santa Fe, for example, lost $35 million (US) in annual business, and led directly to the ending of many passenger rail routes. After 113 years of railway post office operation, the last surviving railway post office running on rails between New York and Washington, D.C. was discontinued on June 30, 1977." Sad

Illinois Railway Museum posted three photos with the comment: "Check out some photos from our Railway Post Office Days event last weekend. There will be more great photography opportunities tomorrow on Chicago Day!"

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Railway Mail Service Library Foundation posted
RPO Days return to the Illinois Railway Museum in Union, Illinois, on June 5th and 6th (Saturday and Sunday). During the event, catching mail on the fly will be demonstrated using Chicago, Burlington, and Quincy baggage/RPO 1923. Visitors also will be able to visit the 30 foot RPO apartment. Former RPO Clerks have been invited to visit and participate. For information about IRM, it’s hours, and admission information, go to www.IRM.org . The RMSLF will not be attending this year, but hopefully others can. RMSLF shared