Southern Pacific's Sierra Crossing John R. Signor 8½x11 - Hardbound, 290 pages, 492 illustrations, maps, profiles, bibliography, and index. This volume presents all you ever wanted to know about Southern Pacific's rail passage over California's Donner Pass. At the summit, over 90 feet of snow falls annually. Everything about the Sierra crossing was monumental: the grade, the locomotives required to lift the trains over the Sierra, the helper locomotives, the tonnage handled, and those unique snowsheds that protected the tracks from the record snowfall and rock slides.