An eastbound Union Pacific empty ore train winds around Arnold Loop at Clifside, Nevada, on March 6, 2012. The train is heading downgrade into the lower part of the loop while traversing Silver Zo... (more)

A westbound Union Pacific oil train climbs Silver Zone Pass at Clifside, Nevada, on March 6, 2012. The train is approaching Arnold Loop and in a few minutes will traveling the opposite direction o... (more)

At dawn, a westbound BNSF manifest freight climbs around Arnold Loop, near Clifside, Nevada, on March 6, 2012. On the lower right just visible going through a rock cut is a lone SD70MAC helping ou... (more)

As dawn arrives on March 6, 2012, a Union Pacific grain train grinds around Arnold Loop, Nevada, pulled by two GE AC4400CWs.

The DPU of the westbound Union Pacific grain train pushes the tonnage around Arnold Loop as dawn colors the eastern sky before sunrise near Clifside, Nevada, on March 6, 2012.

A Union Pacific unit tank train climbs Silver Zone Pass through Arnold Loop at Clifside, Nevada, on March 6, 2012.

An eastbound Union Pacific empty ore train encircles Arnold Loop at Clifside, Nevada, on March 6, 2012. The lead locomotives are traversing the lower part of the loop, and Pilot Peak looms above.

A BNSF westbound freight climbs through Arnold Loop, near Clifside, Nevada, on the morning of March 6, 2012. Helping out on the rear of the train below is a lone SD70MAC DPU.

An eastbound empty Union Pacific export ore train bound for Cedar City, Utah, traverses Arnold Loop on Silver Zone Pass near Clifside, Nevada, on March 6, 2012.