When finished in 1926 the two lane Rainbow Bridge, "eliminated for all time the terrors of the Donner grade". The U.S. Forest Service contracted the bridge, in part for transport of lumber. The bridge had a grade and a compound curve, making it a unique engineering feat for the time, and it reduced the maximum grade over the pass from 18% to 7%.
All images copyright © 2014 F.W. Vollmer and may not be used without permission.