Kansas City Southern #4709 (ES44AC) leads a train south on the Joint Line, which parallels Interstate 25 between Castle Rock and Larkspur, Colorado.

An optical illusion makes it appear as though the Union Pacific oil train is running up an extra steep grade at Rocky, Colorado.

Light snow is falling in the valley of Crescent, Colorado as UP 7104 (AC4400CW) leads an oil can train south on the Moffat Tunnel Sub.

The hills are frosted with snow as the Winter Park Express Ski Train runs through Coal Creek Canyon, Colorado.

Amtrak engine #158 (P42DC) leads the California Zephyr through the trees in Coal Creek Canyon, Colorado.

BNSF 9214 (SD70ACe) muscles the Denver to Provo train through Rocky, Colorado on the Moffat Tunnel Sub.

BNSF 1532 (GP28-2) climbs out of the bowl at the huge yard in downtown Denver, Colorado.

Amtrak heritage engine #160 (P42DC) leads the California Zephyr through Arvada, Colorado.

The California Zephyr rounds the corner at Plainview, Colorado and will enter Tunnel #1, the first of 29 tunnels leading to the Moffat Tunnel at Tolland.

The California Zephyr runs through the S Curve at Coal Creek Canyon as it begins the climb up to Tunnel #1.

The California Zephyr runs through Keenesburg, Colorado at sunrise. The golden glow of the morning sun skips across the snow along the track and glints off the stainless-steel skin of the passeng... (more)

With only minutes of evening sunlight left, UP 5567 (AC4400CW-CTE) and four other UP motors head for the servicing island in the North Yard after being separated from the coal train in the upper l... (more)

The Boulder Flatirons loom big in the background as UP 8435 (SD70ACe) leads a loaded coal train through Plainview, Colorado on the Moffat Tunnel Sub.

It's Throwback Sunday at the BNSF engine servicing facility, with two former Santa Fe Warbonnets and a Cascade Green Burlington Northern SD40-2 waiting for service or orders.

A BNSF oil can train led by #6339 (ES44AC) rounds the corner after exiting Tunnel #1 at Plainview, Colorado.