The Sierra are home to many unusual Railroad features, due to the grades required to cross. Off Hwy 70 east of Quincy, Ca are one of these. I hiked the railroad tracks to locate a continuous loop like a corkscrew, in which the train if long enough, crosses over itself. this enables to train to make the grade more gradual. I was lucky enough to catch one in pictures. If you would like to see an aerial view: http://en.wikipedia.org/wiki/Williams_Loop