Under threatening skies, UP 8669 (SD70ACe) repositions at the Union Pacific's North Yard in Denver, Colorado.

UP 8669 (SD70ACe) moves a cut of heavies into the North Yard in Denver, Colorado.

The Denver Rock Island Railroad's #1083 (SW1500) pics up an oil can from a customer in Denver, Colorado.

BNSF 6293 (ES44AC) leads an oil can train towards Denver, Colorado on the Brush Sub.

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

Union Pacific Big Boy #4014 (4-8-8-4) gets ready to leave the UP's North Yard in Denver, Colorado and will heads back to home base in Cheyenne, Wyoming.

BNSF 2371 (GP38-2) runs over the South Platte River as it moves through Denver, Colorado.

BNSF 2692 (GP39-3) has been serviced and will soon head to the Denver Yard to sort cars.

BNSF 2371 (GP38-2) in the Heritage II paint scheme works the bowl in the yard in downtown Denver, Colorado.

A pair of light and heavy units get ready to head into the Yard in Denver, Colorado.

BNSF 2371 (GP38-2) in a Heritage II paint scheme with the wagon wheel on the nose, works the yard in downtown Denver, Colorado.

A group of Union Pacific heavies get ready to lash up to a long oil can train which will soon get the green to head west on the Moffat Tunnel Sub.

UP 1640 (SD40N) and mate have the yard to themselves as they work on sorting freight cars into the ladders of the North Yard in Denver, Colorado.

UP 1357 (former Denver & Rio Grande Western GP40-2) waits in the yard for orders to shuffle freight cars.

BNSF 1720 (SD40-2) and yard mate have just received a new load of fuel and sand at the BNSF engine facility in downtown Denver, Colorado.