A pair of Union Pacific SD40N motors wait their turn in the North Yard for a chance to sort freight cars.

The Armour Yellow of the Union Pacific motors stand out in the snow as they sit in the North Yard in Denver, Colorado.

A pair of Union Pacific SD40N's sit in the snow at the North Yard in Denver, Colorado.

UP Heavies sit at the servicing islands while other light power get ready for the call to action.

Sunrise in the Union Pacific's North Yard finds a stranger in a strange land, as a BNSF motor gets fuel and sand and the service island.

UP 1997 (SD40N) joins other light power waiting in the Union Pacific's North Yard in Denver, Colorado.

UP 1826 (SD40N) works a cut of cars in the North Yard in Denver, Colorado.

UP 1837 (SD40N) sorts cars into the ladders at the Union Pacific's North Yard in Denver, Colorado.

UP 1980 (SD40N) works the local in Brighton on the Greeley Sub.

A SD40N (1598) repositions in the Union Pacific's North Yard in Denver, Colorado.

UP 1598 (SD40N) heads towards the services islands for fuel as a line of SD70Ms occupy the other track.

The yard is busy on this day as UP 1817 (SD40N) moves a cut of cars for sorting into the Union Pacific's North Yard in Denver, Colorado.

UP 1640 (SD40N) joins a variety of UP power at the servicing island in the North Yard.

UP 1359 GP40-2 works the intermodal facility in Denver, Colorado.

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