A freight train of Central Oregon & Pacific descending towards California. The upper part of the valley is narrow and steep, forcing a grade of 3.3%. Direction of the valley is a rather straight north to north-east, most of the sharp curves are short and not really necessary. Since even today's Amtrak won't exceed 35 mph on this kind of grade, due to the weight of the trains, it is understandable that the track builders of 1887 didn't invest any additional money into avoiding sharp curves.
© Larry Tuttle, used with permission. Larry provides lots of information about the Siskiyou line on his own website. There are more photos of trains crossing the Siskiyou pass at the original location of this photo.