Guess what? I found an admittedly very loose connection to the above poster!
Leslie asked from when it may be, which set me off to google.
I found
this page on Wikimedia saying it's from ca. 1937 and was a work done for the
WPA under the New Deal.
And this, which is of course the Riverton post office mural, is also a New Deal piece of art (from 1942).
Ta-da!
ETA: Oh my, once you start googling, you can really get lost!
Slightly OT:
Did you know that Ennis and Jack had a second job as excavators?
Down in Kemmerer, WY. Near Sage, where Ennis came from.
Mural in the post office of Kemmerer, WYSorry for the OT.