Coker,
It's a UP standard cast in 1877. It was actually a hallmark of the South Baker yards and is rumored to have been in service from the early days of the Sumpter Valley. There were many Union Pacific stands on the line, some dating back as far as 1869. There are photographs that show eight or more of them piled up in by the engine house when they upgrading. Other railroads were represented as well with these attractive pieces of iron. I have the parts from an 1880 Utah Central stand, and Smitty has a beautifully restored Colorado Central from I believe 1871. There is also a complete and good condition Union Pacific 1877 out in a collection as well. There are also a couple more out in the woods.
Thanks, Taylor