Where else would I expect an observation lounge to be, you might ask. But until I found this wonderful picture on the “other” Streamliner Memories blog (streamlinermemories.info, whereas I’m at .com), I wasn’t sure these cars had ever been run on the end of the train. By April 1959, the first time I saw the COSL, and ever thereafter, they were run mid-train, behind the diner. The interior of the car is shown in the City of St. Louis brochure posted below, and in that interior picture it’s obviously being run on the end.
The cars were added to the Cities of LA, Portland, and St. Louis in 1955, so they ran on the end of trains at most four years. Competitor Santa Fe dropped its observation cars around the same time.