After posting this photo I received an email from a friend who has first hand knowledge of Tres Piedras and the tank.
The text went:
"Your photo of the Tres Piedras water tank really brought back memories for me. I can remember as a kid of ten or eleven years of age having climbed up the tank ladder to look down inside the tank through the hatch in the roof. I was with some other boys. The tank was full of water at the time and it had a few dead birds floating around in it, otherwise it was uneventful. Our mothers would have killed us if they had known where we were.
The Tres Piedras elementary school was behind the camera (that building is no longer a school) so I passed that tank often going to school. I attended through the seventh grade. We then moved to Santa Fe after that. I am now eighty years of age so you can do the math.
You will note in the photo that the wooden trestle over the arroyo that runs through TP has already been removed but the fact that the tank ladder is still standing tells me this photo was taken not very long after the abandonment of the Chili line. I do not believe the ladder lasted very long. Note the ball ornament is missing from the top of the roof also.
The RR r/w north from the tank made a large curve clockwise around behind the water tank and disappeared in the right side of the photograph. It then curved back to the left and headed for San Antone mtn. There was a wye just north of TP.
The other buildings in TP are pretty much the same as I remember them at the time we moved away."