These postcards depict Sun Valley in the winter. Most are undated though all but one appear to be post-war. Since UP sold Sun Valley in 1964, it is likely that none are after that year.
The back of this card has the “overland” logo, so it is from before World War II. It also is one-half of a perforated dual card.
This one has a linen finish so, while it is after the war, it is probably from the early 1950s at the latest. We know from other cards that UP distributed linen cards as late as the mid-1950s.
Another card with a linen finish.
The back of this card says “Place two cent stamp here.” Two cent stamps were required from 1951 to 1958, so the card was issued sometime during that period.
This card doesn’t say how much of a stamp to use, and it looks recent, so I’m guessing it is from after 1958.
This one is also probably from after 1958.