Union Pacific UPY 577 has maintenance work done on Track 2 in the Diesel House at the railroad’s former Rio Grande Burnham Shops in Denver, Colorado, on December 8, 2015.

UPY 577 (GP15-1) works the UP's North Yard in Denver, Colorado.

UPY 577 (A 45 year old former Missouri Pacific GP15-1) puts some muscle into moving a cut of cars in the Union Pacific's North Yard in Denver, Colorado.

UPY 577 (GP15-1) is sorting a cut of cars into the ladder of the North Yard in Denver, Colorado.

UPY 577 (GP15-1) has just released a wood car into the ladder in the Union Pacific's North Yard in Denver, Colorado. The crew will lash up to another string of cars and repeat the process.

The sorting of engines in the UP's North Yard in Denver is fun to watch. The remote engineers pull a long line of freight cars from a receiving track and then give brief spurts of power as they s... (more)

The UP and BNSF operate side by side at the UP's North Yard in Denver.

UPY 577 strains to pull a cut of cars in the UP's North Yard in Denver.

The remote operators reposition UPY 577 (GP15-1) in the 36th Street Yard.

Two pairs of Geeps work the 36th Street Yard in Denver. Both UPY 577 (GP15-1) and UP 703 (GP38-2) are former Missouri Pacific engines.

Geeps dominate the 36th Street Yard in Denver

UPY 577 (GP5-1) pulls hard on a string of freight in the 36th Street Yard

UPY 577 holds station in the 36th Street Yard while the 'Train to the Plane' commuter train that runs from downtown Denver to Denver International Airport arrives at the adjacent station.

Its a busy day in the 36th Street Yard as the Geeps sort freight.

It is late in the evening and sun has almost set on the UP's 36th Street Yard as the remote engineer of UPY 577 (GP15-1) brings out with one more string to sort.