A westbound coal train skirts the Colorado River, approaching tunnel 39 on a chilly fall morning.

A lone rafter floats down the Colorado River as a westbound BNSF manifest freight rumbles through Tunnel’s 39 and 40 in Little Gore Canyon west of Azure, Colorado, on the afternoon of August 4, ... (more)

Westbound Union Pacific MNYRO is approaching Tunnel 39 and Little Gore Canyon west of Azure, Colorado, on the morning of August 3, 2014.

Tunnel 40—all 63 feet
Amtrak No. 6, the eastbound California Zephyr, curves along the Colorado River through Tunnel 40 in Little Gore Canyon west of Azure, Colorado, on August 21, 201... (more)

Passing through Tunnel 40 along the Colorado River, an eastbound Union Pacific coal train traverses Little Gore Canyon east of Azure, Colorado, on August 21, 2014.

About to enter Tunnel 39 and Little Gore Canyon, Amtrak No. 5, the westbound California Zephyr, is west of Azure, Colorado, along the Colorado River on August 20, 2014.

An eastbound Union Pacific coal train rumbles along the Colorado River through Little Gore Canyon east of Azure, Colorado, on August 21, 2014.

Union Pacific MRONY (manifest Roper Yard in Salt Lake City to North Yard in Denver) freight approaches Tunnel 39 in Little Gore Canyon west of Azure, Colorado, on a beautiful, August 20, 2014.

Stainless steel smile
Amtrak No. 5, the westbound California Zephyr, curves into a smile as seen from high above Tunnel 40 in Little Gore Canyon west of Azure, Colorado, on August 21, 2... (more)

An eastbound BNSF manifest exits Tunnel 40 on the UP Moffat Subdivision near Azure, Colorado.

Amtrak No. 5, the westbound California Zephyr, has just exited 294-foot Tunnel 39 and is now threading 63-foot Tunnel 40 in the heart of Little Gore Canyon between Azure and Radium, Colorado, on t... (more)

After a quiet morning on the Moffat Sub, an eastbound coal train skirts the Colorado River, passing through Tunnel 40 in this rugged stretch of railroad.

An eastbound Union Pacific coal load is rumbling through Little Gore Canyon west of Azure, Colorado, on June 6, 2013. The train is threading short 63-foot Tunnel 40 in the distance, and is about t... (more)

An eastbound Union Pacific coal load has just exited Little Gore Canyon along the Colorado River west of Azure, Colorado, on June 6, 2013. The lead locomotives are in the distance snaking their wa... (more)

An eastbound Union Pacific coal train rattles through Little Gore Canyon east of Azure, Colorado, on June 6, 2013. The train is threading 63-foot Tunnel 40, the shortest tunnel on UP’s Moffat Tu... (more)