Semaphore Signal at Goat Canyon - One of the two bridge signals (one at each end) that let train crews know that the large wooden trestle at Goat Canyon was intact and passable.
The idea was that if the trestle were to catch fire, or be impassible, a worker would activate the signal changing it from clear, to a stop indication.
The signals on both ends appear to be electric (the wires) and there was once a telegraph line with poles running from Jacumba to Dos Cabezas, so the power to activate and light the signals presumably was carried on that pole line.