These postcards were all issued by Union Pacific to advertise its trains to various national parks. As usual, click images to download PDFs of the postcards, most of which are under 400 KB in size.
Here’s another linen postcard from Yellowstone Park.
A postcard from the same era showing the Grand Canyon.
Finally, a card from the chrome era, meaning it is almost certainly post-war and probably from the 1960s.