Hey Steve, I think the dam was built about 1964. Somebody correct me.
Just for kick and gigles I spent some hours a few years ago working out a new route on USGS Topo maps. My route follows the original out of S Baker untill just after you enter the Bowen Vly. Just after the old ROW crosses the first road turning to the right, the new route leaves the start of the long tangent and crosses the highway at a long diagonal. Right after the highway is crossed the new line begins a steady 3% climb reaching it's highest point over near Old Auburn. At this point the grade is basically flat all the way to Union Crk. On my route a large high curving trestle is required to get across California Gulch. Another small but fairly long trestle is required just above highway 7 to cross above Union Crk Rd and Union Crk. Just after this trestle the line drops to a crossin of Hwy 7 into Union Crk Campground to tie into the Union Crk. Extension which is already plotted. I tried to work out curves with a compas to put the max curve around 16deg. I drew my map such that their was no elevation gain in the curves, so in reality the overall grade would be a little less and the route would be approximate. I tried working out a route with around 2% on the maps, but ended up in steep terrain in the cliffs N of old Auburn Rd. overlooking the Powder River. Kinda fun to dream about this sort of thing. Given enough money it could be done....