While in Silverton last week I was able to hike another mile or so of the lower grade. It is shown on the map in violet below the 550 highway symbol. I also hiked along the Chattanooga loop and found the bathtub complete with standpipe and valve. A second bathtub is also in the vicinity but lying on its side. Up on the pass I explored some of the structures and will add photos to the map as time permits.
Silverton RR map