Greetings:
It looks like you have identified the right of way rather well. According to the map in
The Western Railroader issue on the Iron Mountain Ry. (Vol. 27, No. 1, January, 1964, Issue No. 288), the loop was just about where your red line ends on the upper end of the line. The photographer was standing close to where your line ends. The track looped around to the right from that place, and then continued up to the mine on the lower of the large "white" lines that go uphill from that place.
On the TerraServer web site, the USGS map for this area shows the right of way as a Jeep road.
The lower end of the line was in an area that seems to have been re-graded, making it hard to figure out where the track ran. However, it followed that creek down to the main line on the west side of the Sacramento River. According to the above-mentioned map, the line ran from the SP connection through Keswick a little ways up the creek, and there was what I can only describe as a switchback to get the trains headed up the hill.
Tom Armstrong