I took these shots on the fly from the raft with my wife's small waterproof digital. Wish I had my camera with a better lens, but it wouldn't have survived the class III rapids!

Thanks to Ed Brown who informed me that this sidepin arrangement is used to detect rockfall or landslides along the track.

Ed says, "Falling debris would break the wires, thereby opening the circuit, and setting off an alarm back at the depot or dispatch. From there they could signal trains to slow down, stop or at least be very observant of the track conditions ahead."