Exactly, the Shannon RR was the upper line, built circa 1910, the lower line was the Coronado Ry which was owned by the Arizona Copper Company. This was the subject of a lawsuit, don't know the results but the rock wall and fill were replaced by a trestle. I have one of the photo exhibits from the lawsuit, dated about 1920 which is close to when the Shannon was absorbed by the ACCo.
BTW, the Shannon had two of the five locos that were sister engines to the DRGW C-25. They also we the first to use steel our cars on the 3 foot lines in the area.
Mike Conder