UP 1957 (SD40N) brings a short cut of cars through the refineries in Commerce City, Colorado.

UP 1957 (SD40N) and UP 1640 work sorting a cut of cars in the Union Pacific's North Yard in Denver, Colorado.

UP 1957 (SD40N) gets ready to pull a string of freight cars out of the ladder for sorting in the North Yard in Denver, Colorado.

Union Pacific heavy and light power populate the UP's North Yard in Denver, Colorado.

UP 1957 (SD40N) works the Union Pacific's North Yard in Denver, Colorado.

UP 1957 (SD40N) works the North Yard in Denver, Colorado.

UP 1957 (SD40N) shuffles a load of coal in the North Yard in Denver, Colorado.

UP 1957 (SD40N) works the North Yard in Denver, Colorado.

UP 1957 (SD40N) sorts a cut of cars in the Union Pacific's North Yard in Denver, Colorado.

A wide-angle view of the Union Pacific's North Yard catches a variety of light power that are working the ladders and sorting cars.

UP 1957 (SD40N) leans on the tack at the North Yard in Denver, Colorado.

UP 1957 (SD40N) sorts cars in the Union Pacific's North Yard in Denver, Colorado.

The first light of the morning finds UP 1957 (SD40N) positioning to shuffle cars at the North Yard in Denver, Colorado.

UP 1957 (SD40N) runs with open doors in the Union Pacific's North Yard in Denver, Colorado.

The doors are open on a hot day as UP 1957 (SD40N) heads for the barn after a day of sorting cars.