Light power dominates the Union Pacific North Yard in Denver, Colorado.

Its' Throwback Thursday at the BNSF engine servicing facility as 1656 (SD40-2) waits for service or assignment.

UP Y625 (GP15-1) sports a unique shark-mouth pilot blade as it sits in the Union Pacific's North Yard in Denver, Colorado.

UP 1980 (GP38N) waits in the Union Pacific's North Yard in Denver, Colorado for service at the fuel islands.

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.

BNSF light and heavy power line up for servicing at the engine facility in Denver, Colorado

Long shadows in the early minutes of sunrise creep across the Union Pacific's North Yard as UP 845 (GP38-2) gets a early start sorting cars.

The California Zephyr runs through fog and freezing sleet in the Union Pacific's North Yard as it leaves Denver, Colorado for the Rocky Mountains.

Steam 20 in the steam.

Polar Express , Lantern

Engine 20 with its firebox visible rolls on down the track.

Engine 20 being put away for the night..

UP 6417 (AC4400CW) waits in the North Yard for a new crew before heading south through Denver, Colorado on the Joint Line.

UP 6417 (AC4400CW) runs through the Union Pacific's North Yard in Denver, Colorado.