Postcards and other memorabilia can sometimes be dated merely by the use of a particular slogan. In this case, “air-conditioned” means the card was probably issued in 1935 or 1936; in 1937 the slogan was changed to “completely air-conditioned.”
The first card shows one of NP’s A-2 locomotives, that is, the third class of 4-8-4 locomotives built for the railway. (The first class was A, then A-1.) The 77-inch drivers dwarf the little boy, but the 16-foot-tall, 110-foot-long locomotive would dwarf just about anyone. I’ve seen other postcards with the same photo in black-and-white, but this one is printed in green on both sides.
This card identifies Red Cloud as “Sioux,” but today the proper term is “Oglala Lakota.” Unfortunately, the card doesn’t give the name of the artist.
The last two cards show paintings of cowboys. Northern Pacific evidently issued a series of such cards in the air-conditioned era; several more are illustrated in a book titled Railroad Postcards of Yellowstone. Again, the cards fail to name the artist.