Thanks to everyone who entered the 50s Western Matte Painting Contest. Unfortunately, there was no winner.
The image (seen below) was from Rails Into Laramie (1954), a good Universal-International Western directed by Jesse Hibbs. As is typical of films from this period, there is no credit of any kind for the matte work.
If you get a chance to see Rails Into Laramie, I recommend it. James H. Griffith, one of my favorite character actors, has a good-sized part — and John Payne was on a real roll in the mid-50s.
Of all the entries I received, John Knight came closest. He was pretty sure it was a Universal-International picture.