Each year from at least 1926 to 1941, GN and its partner railroads, NP and Burlington, produced a thick booklet, such as this one from 1937, describing escorted tours to destinations along their lines. This is a small brochure from Great Northern that focuses on a few of the tours that followed its routes.
Click image to download a 2.4-MB PDF of this brochure.
The brochure is undated but it has the 1936 Rocky logo so it must have been issued sometime after that. It says that one of the tours left Chicago on Saturday, June 19, and the only year between 1936 and 1941 that June 19 fell on a Saturday was 1937. So I presume this is from that year.