Great photo, Kurt!! I've never seen this one before.
I'm with Chris, location looks to be lower Chalk Creek, I would have guessed near Cascade.
The details in the photo are fabulous:
I'd guess the time to be 1886-1887, certainly after the 1885 UP system renumbering. The lead locomotive is one of the 1883 Cooke 2-8-0s, the second locomotive likely is too.
Notice the first two freight cars. The boxcar is one of the UP built 1882-1883 27' boxcars (identified by the square shaped poling pockets on the sides at the lower corners). The reefer is one of the big 27' Tiffany cars built by St. Charles, that has the same square poling pockets. Not completely sure, but the two coal cars look to be the two classes of 27' coals, the 300 series with the tall side sills and the 400 series with the higher coal boards
The listing doesn't credit the photographer, but it has the feeling of an M.E. Chase photo. He photographed South Park freight trains at Romley and Hancock in 1888, so it could be the same year.
Jim Courtney
Poulsbo, WA