Terry, I think your guess is likely correct. When I have more time, I cold post the ROW map for that area. Boulder Gorge Siding was just down stream from where the road to the dam takes off. One can see evidence of the siding in the park area along the river where the rest stop is. Maps show a spur from the siding to the edge of the river at the upper end. One can tell there once was a bridge from the spur to the flat along the river and tie mounds are evident across the river. The bridge and track across the river are however not shown on any SVRy maps that I have seen suggesting they were put in by private owners such as Shockley and McMurren owners of the mill that was apparently over there in the early days. That said, the area where the track was on the other side is withing the ROW ownership of SVRy per the ROW maps. There is a neat early photo of SVRy 1st #4 at the Boulder Gorge water tank with stock cars stored on the track across the river. The connection with Stoddard's Black Mtn. logging system was called Mason, so I doubt that is related.