Union Pacific MRODV (Roper Yard in Salt Lake City to Denver) freight passes a coal train in the siding at Rocky, Colorado, as it departs for Denver on April 29, 2001.

The California Zephyr rounds Big Ten Curve as it heads to Denver.

UP 6720 (former Chicago & Northwestern AC4400CW) pulls a coal train through Rocky, Colorado. In the background is the National Wind Technology Center at the National Renewable Energy Laboratory i... (more)

AMTK 74 (P42DC) pulls the California Zephyr around the tight radius of Big Ten Curve. The row of trees you see are lined up against a row of hidden loaded coal cars, which have been placed there ... (more)

Union Pacific’s West local out of Denver climbs Rocky Spur at Rocky, Colorado, on January 18, 2001. Powering the local is a trio of Rio Grande GP40-2s—Nos. 3121, 3100 and 3111. Below is EMD SD... (more)

The California Zephyr makes the turn at Big Ten Curve. With the angle of the low sun the lead unit almost looks like it's about to time travel ala Back to the Future.

BNSF 8159 (ES44C4) runs downhill to the bottom of Big Ten Curve.

A long BNSF freight makes the turn at the bottom of the Big Ten Curve and heads towards Arvada, Colorado.

UP 6720 (a former Chicago & North Western AC4400CW) leads an empty coal train as it climbs Ten Mile Curve, which will lead them to Coal Creek Canyon and the first of many tunnels as they head into... (more)

A westbound Union Pacific manifest freight climbs the mesa where Big 10 Curve is located on the climb up the front Range of Colorado’s Rocky Mountains on the afternoon of June 20, 2018. The head... (more)

Rounding Big 10 Curve west of Rocky, Colorado, is a westbound Union Pacific manifest freight with lone DPU GE AC4400CW No. 6216 shoving hard on the rear on the afternoon of June 20, 2018. In the b... (more)

California Zephyr's AMTK 43 makes the turn leading to the Big Ten Curve.

Under threatening skies, AMTK 837 leads the California Zephyr through Big Ten Curve. After traveling through Rocky and Arvada it will soon pull into Denver's Union Station before eventually headi... (more)

Looking more like a roller coaster ride than an Amtrak train, the California Zephyr reaches the bottom of the hill west of Arvada and will soon enter Big Ten Curve to begin the climb up to the Roc... (more)

The California Zephyr runs down the hill from Arvada to Rocky, Colorado, passing the spur that at one time led trains to the Rocky Flats Nuclear Weapons Plant. The facility produced plutonium tr... (more)