Photo taken by John Russell
License: Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND)
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BH Photo #316113
The above link gives an original location for this truss bridge. Based on the other two remaining trusses, it is safe to assume that this one was probably built around 1901. I also believe that several other bridges in this area of Butte were built using secondhand material.
This one sure appears to be a reused Union Pacific span. It is a standard design on the UP system: