UP 1507 (GP40M) passes the Union Pacific's operations building at the North Yard in Denver, Colorado.

Light snow falls on UP 1507 (SD40N) as it drops off a gondola at a recycling facility in Littleton, Colorado.

Snow is falling as UP 1507 (SD40N) crosses Santa Fe Drive in Englewood, Colorado, taking with it a gondola and a bay window caboose.

UP 1507 (GP40M) moves through the Union Pacific's North Yard in Denver, Colorado.

UP 1507 (GP40M) heads to the BNSF yard in Denver, Colorado with a cut of freight cards from the Union Pacific's North Yard.

UP 1507 (GP40M) brings a freight into the BNSF yard in downtown Denver, Colorado.

UP 1507 (GP40M) leads a freight towards the BNSF yard in Denver, Colorado.

UP 1507 (GP40M) is entering the BNSF's Denver Yard with a cut of freight cars and will head back to the UP North Yard after dropping off the cars.

UP 1507 (GP40M) moves a cut of cars early in the morning in the Union Pacific's North Yard in Denver, Colorado.

A wide-angle view of the Union Pacific's North Yard in Denver, Colorado shows the fuel and sand service islands on the left, the ready tracks in the middle (with a former Southern Pacific GP40M - ... (more)

UP 1507 (GP40M) sorts cars in the North Yard in Denver, Colorado.

UP 1507 (GP40M) sits waiting in the Union Pacific's North Yard for its turn to sort cars.

Snow and subfreezing temperatures blanket the Union Pacific's North Yard in Denver, Colorado.

UP 1507 (ex Southern Pacific GP40M built in 1969) joins other light power in the Union Pacific's North Yard in Denver, Colorado.

The majority of power in the Denver North Yard on this day is light units, including UP 1507 (GP40M).