UP 1957 (SD40N) sorts cars in the Union Pacific's North Yard in Denver, Colorado.

UP 801 (GP38-2) waits for the call to action to sort cars in the Union Pacific's North Yard in Denver, Colorado.

UP 688 (GP38-2) strains to pull a cut of cars out of the North Yard for sorting.

A Union Pacific and a Kansas City Southern motor visit the BNSF engine servicing facility in Denver, Colorado.

The operations building in the Union Pacific's North Yard in Denver, Colorado has a commanding view of the massive yard.

Otto's trusty 1935 Ford sedan is visible to the left of UP 966A. Finding a clean and shiny EMD F3 set was a great way to start off the new year of 1948. Otto Perry photo, from my collection.

MOW equipment joins other BNSF motors in the engine servicing facility in Denver, Colorado.

Union Pacific train number 111, the City of Denver, is seen leaving Denver on its first westbound run, with ten cars at 35 MPH, on June 19th 1936. Otto Perry photo, from my collection.

An Executive Grinstein SD70MAC waits for service at the BNSF engine serving facility in Denver, Colorado.

The California Zephyr runs towards Denver's Union Station, passing through the Union Pacific's North Yard.

A red caboose sits with firefighting tank cars at the BNSF engine servicing facility in Denver, Colorado. Perhaps the BNSF is anticipating an active wildfire season, which is likely given the rec... (more)

BNSF 1729 (SD40-2) is sorting a cut of cars in the Denver Yard while a RTD communter rail train passes by in the background.

BNSF 1789 (SD40-2) waits for servicing at the BNSF engine facility in Denver, Colorado.

BNSF 5859 (ES44AC) leaves the Denver Yard as other power sit idle on the ready tracks.

BNSF 1789 (SD40-2) is framed by the RTD Commuter Rail Line as it pulls a cut of cars out of the Denver Yard for sorting.