In an interview before her speech, Yu told NBC News she knew this was the moment.

“It’s sort of like the completion of an arc,” she said. “And I know I have this huge responsibility weighing on me to get it right.”

For Chinese American advocates, the railroad’s 150th anniversary has been a chance to write the Chinese laborers and their heroic contributions back into the annals of history.

“The railroad they built or helped to build unified the country,” said Russell Low, 66, whose great-grandfather and great-grandfather’s brother worked for the Central Pacific. “It made us one nation for the very first time — socially, psychologically, economically — and that is important. But the lasting impact is the people.”

A RAILROAD IS BUILT

The Union Pacific and Central Pacific both broke ground on the first transcontinental railroad in 1863.

Connecting with existing eastern lines, the Union Pacific built west from Council Bluffs, Iowa (bordering Omaha), relying on workers who included Civil War vets and East Coast immigrants. Many of them were Irish, though none were Chinese.

Pushing east out of Sacramento, California, the Central Pacific had a labor force that was predominantly Chinese. Many were contracted migrants who arrived on ships from China.

Acts of Congress provided both companies with land grants and financing.

Facing a labor shortage, the Central Pacific hired Chinese living in California as an experiment in 1865. Once it exhausted that pool of laborers who had arrived in the early 1850s to work in mining and other sectors of the West, the railroad began recruiting directly from China, mostly from Guangdong province in the south.

By February 1867, around 90 percent of the Central Pacific workforce was Chinese, according to the Chinese Railroad Workers in North America Project at Stanford University. The rest were of European American descent, mostly Irish.

At its highest point, between 10,000 and 15,000 Chinese were working on the Central Pacific, with perhaps as many as 20,000 in total over time.

An estimated 10,000 to 12,000 Irish also helped build the railroad. Smaller numbers of Mormons, Civil War vets, blacks and other nationalities, including Italians and Germans, were employed as well.

Hundreds, possibly more than a thousand, Chinese died during the line’s construction.

Their hard work and industriousness won over the Central Pacific’s top brass, including railroad president Leland Stanford, whose anti-Chinese views were central to his campaign for California governor.

Still, despite their accomplishments, the Chinese laborers have often been reduced to blurbs in American history classes and textbooks, a point that advocates and educators have been working to change.

“These stories...are American stories,” Low said. “They’re not Chinese American stories. They’re stories that belong to you, to all of us.”

RECLAIMING A PLACE IN HISTORY

At Promontory Summit, a secluded expanse around 5,000 feet above sea level where the tracks met, Friday's celebration kicked off with a lion dance, a Chinese tradition to bring good luck and to get rid of evil.

Transportation Secretary Elaine L. Chao also spoke about the contributions of the Chinese railroad workers.