This menu is undated, but the prices are similar to other menus from about 1950. I previously posted a 1948 menu with this photo on the cover from the New York Public Library; this one is from my own collection.
In tiny print where the date code is sometimes located is written, “11-12 1ST. EW 9-8.” Trains 11 & 12 were the west- and eastbound Idahoan, between Chicago and Portland, which had inconvenient, late-night bus connections to Sun Valley. Connections to the City of Portland and Portland Rose were both in daylight, so most rail travelers going to Sun Valley would chose one of those trains. Train 9 was paired with train 10 and I can’t find a train 8 during this time period, so the “9-8” in the code must refer to something else.