Final answer:
Construction workers, including Chinese immigrants, Irish and African American laborers, played a valuable role in building the first transcontinental railroad by working in the Union Pacific and Central Pacific work camps. These camps paid workers based on the amount of track they built each day, with incentives for reaching certain milestones.
Step-by-step explanation:
The group that proved to be a valuable addition to the effort of building the first transcontinental railroad were the construction workers who migrated to America from China and Europe. These workers, including Chinese immigrants, Irish and African American laborers, Anglo homesteaders, failed mining prospectors, and orphans, worked in the Union Pacific and Central Pacific work camps. These camps were melting pots and paid workers based on the amount of track they built each day, with time-and-a-half bonuses as incentives for reaching certain milestones.