UP 1640 (SD40N) moves through the BNSF's Denver Yard after dropping off a cut of cars.

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.

UP 1826 SD40N get ready to sort a string of cuts in the bathroom.

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

The remote operator of UP 1957 (SD40N) catches a ride back to the barn after a day of sorting cars in the North Yard.

UP 1817 (SD40N) heads deeper into the North Yard in Denver, Colorado to sort train cars.

UP 1817 (SD40N) gets repositioned in the North Yard in Denver, Colorado.

UP 1957 (SD40N) moves south in the North Yard as the Amtrak's Winter Park Express Ski Train heads north.

Snow clouds are moving in as UP 1957 (SD40N) works the North Yard in the evening sun.

UP 1826 (SD40N) moves with two other light power units through the North Yard in Denver, Colorado.

UP 1997 (SD40N) holds station in the Union Pacific's North Yard in Denver, Colorado.

UP 1845 (SD40N) makes a run into the large Union Pacific yard at Cheyenne, Wyoming.

A variety of Union Pacific motors spotted in the North Yard in Denver, Colorado.

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