Cement Ridge in Sierra Nevada, with Old Man Mountain in the distance. [Photo provided to China Daily]

The Chinese workers set a record for laying 10 miles and 56 feet (16 km) of track in 12 hours and were considered indispensable by their foremen.

As California Governor Leland Stanford reported to congress in 1865, "Without them (Chinese workers), it would be impossible to complete the western portion of this great national enterprise, within the time required by the Acts of Congress."

Desperate for work to support their families, Chinese workers left their towns and villages in Guangdong province, which were then blighted by poverty and unrest, and boarded ships bound for California.

Historians estimate that at any one time as many as 10,000 to 15,000 Chinese laborers were working on construction of the railroad between 1865 and 1869.

The hardest and most hazardous sections of the railroad route included the construction of tunnels at high elevations through the mountains of the Sierra Nevada range.