I checked the grade profile--there's no branch there. My guess is either the wye (which is/was actually east of Rifle) or that's the siding/main.
It's been a while since I took the picture but I want to say that it is one of the new spurs west of Rifle that was installed to deliver supplies to one of the new oil field yards. They seem to have a lot of rail traffic these days delivering chemicals in covered hoppers and their is a lot of flat cars and gondolas that arrive daily with drilling pipe. Ben