It might be S wye, but I agree with Steve, I think the ph. line ran on the opposite side of the track as the tank. There are two other possibilties that seems likely to me which are McCoy tank or Carrol. At McCoy the ground should drop off on the far side of the track into a creek bottom and it appears to do so, but at McCoy I think a substantial hill should be in the background behind the trees. It may be however that hill is not high enough to show up in the photo. Also at McCoy there is a hill substantial rise in the ground accros from the tank as I recall, so the photo may not be McCoy. At Carol there is a little space on the near side of the track across from the water tank that may have had a spur at one time. There is a a farily steep hill across from the tank that would behind the photographer.
Also, the more I think about it Taylor may be right about the 70lb rail on BWP. I think that is actually what the joint bars were that I found on the Curry line as I remember thinking we could use these and joked with my wife about loading them in her day pack. Needless to say they were left in the woods.