The winter of 1867 came bitter and merciless to the Chinese men that tunneled through the transcontinental railroad’s most formidable section, a nearly 1,700-foot stretch of granite at the Donner Summit in California’s Sierra Nevada Mountains. The men, immigrants from subtropical Guangdong, had never before known snow, let alone the relentless blizzards of the kind that, just 20 years before, forced the Donner party into cannibalism a few miles away. The laborers, who worked around-the-clock to drill the tunnels by hand, were no strangers to suffering. Starvation, however, was one…