I lived at Essex for a few years in the mid-1980s and was able to document first hand daily operations in Marias Pass. I literally have hundreds of Marias Pass images from Whitefish to Browning. Each gallery is in somewhat alphabetical order.
These web pages are a sampling of many photographs in my publications. Here are the books that feature Marias Pass:
The Great Northern Railway in Marias Pass
Snowsheds and Train Orders - Marias Pass Operations 1950s thru 1980s
Running Extra Anthology - 1999 to 2002
Glacier National Park - Great Northern Railway - Fred Kiser Artographs 1909-1912