Palisade Canyon, Nevada

Along the Humboldt River on the original US transcontinental route. The route of the Western Pacific (Feather River route) also comes thru this canyon (it's on the other side), and in fact parallels the transcontinental route for 100 miles or so. Of course, it's all Union Pacific now, but even back before the railroads had merged there was a joint operating agreement along the parallel tracks, such that one side was westbound and the other eastbound.