As far as I know it from Cheney to the Snake it's the S P+S, but since some of the RRs went out of business and the tracks were merged for those still in business it's hard to tell, even if you "look it up", as "official" records are often wrong as the trail from Fish Lake to Cheney is listed officially as being Union Pacific. I saw lots of SP+S but NEVER any UP on the track at Fish Lake, but the trail by my house is on U.P. The Lines "switch" somewhere between Marshall and Fish Lake, probably very near Fish Lake as the lines are MUCH closer there.