The Tehachapi Loop is a railway line through the Tehachapi Mountains in south central California, connecting the San Joaquin Valley to Los Angeles via the Antelope Valley. In its day it was hailed as one of the greatest engineering feats and is the world’s busiest single-track railway line. The particular loop shown is such a tight turn and the trains are so large that the engine at the front actually passes over the rest of the train. Prety cool. More pictures and information over on wikipedia.