What are some of the dangers the workers encountered when carving out the tunnels in the Sierra Nevada Mountains?

Feb 21, 2012 · what sort of dangers do you think were encountered? Off the top of my head ... attacks by hostiles, diseases in the camps, storms ... dust, snow, tornadoes, etc ..., working with explosives, cave-ins while digging tunnels, avalanches, flash floods, unloading material, sabotage.