From the Summit Tunnel, a remnant of the heroic effort to build the Transcontinental Railroad in the 1860s.

Chinese laborers drilled the hole from top left. It was filled with blasting powder and a cord leading to a fuse. A flashlight replicates the explosion.

The hole at right center appears to be from another blast. Flat marks across the center may be from chisel work. The tunnel goes through granite, some of the hardest rock in the world.

This one project took 8,000 workers, most of them Chinese, three-years to complete. It was the longest tunnel in the world at the time, @1650 ft (@500 m).