Wow! That's great identification of a unique structure in the Colorado Rockies.
With that information in hand, I was able to find a later postcard (circa 1957 based on the Chevy Wagon in the picture) that shows the structure a decade or so later:

What neither of these postcards mention, though, is that the structure was known as "Crest House" and was constructed in 1940 and 1941, which fits into the date of the original RPPC posting.
Sadly, it is now in ruins, having been destroyed by fire in 1979:
From Wiki:
Quote:
On September 1, 1979, while refilling a propane tank, an employee of an Evergreen propane company failed to secure a safety valve, igniting a fire. While the Idaho Springs volunteer fire department responded quickly, efforts to contain the fire were hampered by high winds and a lack of water. Fortunately, all the occupants were evacuated safely.
Most of the steel, glass, and wood timbers, paneling, and flooring was destroyed in the fire, leaving only the cast concrete walls and outer stonework. The U.S. Forest service received a $450,000 settlement from the propane company for the loss. This was deemed insufficient to cover the estimated $2 million in restoration costs, so the funds were used to rehabilitate the ruins into an observation platform.
http://en.wikipedia.org/wiki/Crest_HouseWhat's left of it today:

Still, some terrific panoramic views from the location:
