Chicago & North Western fully streamlined its 400 in 1939, but the postmark on this postcard showing the train crossing the Mississippi on the Stone Arch Bridge is dated 1949. The bridge itself was built by the Great Northern Railway, but obviously other railroads used it.
This picture of the Olympian Hiawatha being pulled by an Erie-built Diesel probably dates from 1947, when the train began operating.
The image on the postcard is identical to one on the cover of the brochure below about the train–except the image on the brochure shows a second train going the other direction. This shows off the Sky Top car. Although the Sky Top cars survived a lot longer than the Erie-built locomotives, for some reason they were deemed less important advertising for the train.