Even with a combined 5,300 horsepower, UPY 681 (GP15-1) and UP 2278 (SD60M) strain to pull a string of freight cars out of the 36th Street Yard.

It's gondola sorting day at the UP North Yard.

UPY 613 has just pushed back a tank car into the North Yard.

UPY 681 - 33 years old and making smoke while making money

UPY 681 struggles to pull a stick of cars out of the 36th Street Yard as a coal train enters the yard in the background

Synchronized freight car shuffling is about to get into full swing at the 36th Street Yard as a couple of GP15-1's (UPY 681 and 570) jockey for position.

A trio of Geeps were waiting in the 36th Street Yard for an assignment. The colorful maroon Helms Financial HLCX schemes really stand out.

UPY 681 huddles with the other North Yard workers against the sub-freezing temperatures until they receive their orders.

UPY 681 (GP15-1) and GMTX 2135 (GP38-2) sit on a siding in the 36th Street Yard waiting for orders.

UPY 681 (GP15-1) and GATX partner finish dropping off a load of freight cars and get ready to head back to the 36th Street Yard.

UPY 681 makes smoke pulling some cars out of the 36th Street Yard in Denver

UPY 681 (GP15-1) lashes up to three other workhorses in the 36th Street Yard to wait for the next assignment. Pretty soon the new RTD Light Rail line will run along this stretch, making shots fro... (more)

UPY 681 (GP15-1) sits among mates in the Union Pacific North Yard in Denver waiting for service and assignments.

A variety of power sits in the 36th Street UP yard on a mild December day. GATX 2679 (GP38), UPY 586(GP15-1), Y681 (GP15-1) and UP 8568 (SD70ACe) wait their turn to shuffle cars.