The Williams Loop is a rail spiral located on the Union Pacific Railroad's (originally Western Pacific Railroad's) Feather River Route through the Sierra Nevada mountains in northeastern California, connecting the Sacramento Valley to Salt Lake City via the Feather River canyons. Located approximately five miles east of East Quincy, the loop is used to gain elevation on the WP's eastward climb to its summit at Beckwourth Pass while maintaining the railroad's overall 1.0 percent (compensated) grade, the least steep of any grade on a transcontinental railroad.