Mid-century Christmas letter from Richland

During the recent sorting and pruning of old family ephemera I came across this homemade Christmas letter from some family friends who lived in "Richland" and said of it, "This is the town that 'Sam' built." 

That would be Richland, Washington. The area that became Richland was acquired by U.S. Army in 1943, built up by "Uncle Sam" and turned into a fully closed, secretive community — it didn't appear on maps! — in which many people worked on the Manhattan Project, though few people knew that's what they were actually doing. The veil of secrecy wasn't lifted until after the mid-1945 atomic bombings of Hiroshima and Nagasaki, the surrender of Japan and the end of World War II.

Of course there were other cities that Uncle Sam built, such as Oak Ridge, Tennessee.

I'm going to guess this Christmas letter, with its nifty illustrations, dates to sometime between 1948 and 1952.