The labor required to build the Transcontinental Railroad was extensive. The main laborers, the ones who laid the track, did back-straining work for days on end, for not necessarily high wages, in sometimes brutal conditions. This massive transportation construction project also required an entire network of support, including medical staff, cooks, and proprietors of provisions stores and living areas.

Irish immigrants were the primary early builders of the Central Pacific Railroad. Management of the initial railroad work was not very inspirational, and pay was not exactly high; as a result, many Irish workers walked off the job. To fill the gap, Central Pacific turned to Chinese immigrants, who were traveling across the Pacific Ocean in increasing numbers, 40,000 in the 1850s alone. Many of these Chinese immigrants had come to California for the Gold Rush and had stayed.

Chinese workers continued to fill the Central Pacific ranks; by 1868, they numbered about 12,000, or 80 percent of the entire workforce. Their Central Pacific bosses found the Chinese workers to be punctual and amenable to the hardest of tasks. Despite racial harassment, Chinese laborers worked hard. They were paid a maximum of $30 a month and often lived in the underground tunnels they were constructing, some of which collapsed onto the workers. (More than 1,000 Chinese workers died in rail-related accidents.) By contrast, Irish workers got $35 a month, and living space.

Railroad workers, whatever their country of origin, lived in makeshift camps right alongside the railroad line. An exception to this was in the mountains, when workers sheltered at night in wooden bunkhouses (which were exactly weather-proof but still offered protection from the worst of the mountain weather).

For food and drink, the Chinese workers drank lukewarm tea, which was boiled in the morning to remove bacteria and then dispensed throughout the day. They also ate a combination of dried food brought out from San Francisco and freshly prepared food from pigs and chickens kept onsite. By contrast, Irish workers got by on company-provided boiled beef and potatoes, mostly, and drink of both water and alcohol.

Track construction through mountainous terrain was painstaking. Some days, crews managed little more than several feet of track. Tunnels through hills and mountains were especially time-consuming. The advent of dynamite, invented in 1867 by Alfred Nobel, helped somewhat in this regard. In all, Central Pacific crews built 15 tunnels along the route. The longest tunnel, called the Summit, ran 1,659 feet.

Despite the initial segregation and distrust, Irish and Chinese laborers worked together more and more as the miles of track piled up. As the route wound further eastward and into flatter land, rail crew bosses pushed their workers to go faster. On April 28, 1868, a crew laid 10 miles of track in one day. The distrust also eased because the number of Chinese workers easily outstripped the number of Irish and American workers. By the time that the railroad was finished, the workforce was 90 percent Chinese.

Construction was especially slow going in the mountains. The route wound through a low pass, but the route still went through the Sierra Nevada Mountains. To keep work going through the winter, workers built dozens of miles of huge wooden show sheds to cover the tracks; as a result, avalanches and snow drifts blew over the wooden "roofs" and didn't cover the tracks or the workers laying them down underneath.

The Central Pacific construction was well under way before the Union Pacific work got started. Union Pacific bosses didn't have the benefit of the vast numbers of Chinese workers laboring away for the western part of the rail network. In fact, labor in the middle of the country was in short supply. By the end of 1865, the miles of track laid stood at 40.

The following year, however, construction began in earnest, as new waves of Irish immigrants and a huge influx of Civil War veterans showed up in pursuit of work and, more importantly, money paid for that work. Also laying track for Union Pacific were many members of the Mormon Church. As out west, Union Pacific workers formed an assembly line, laying rails and track, wielding hammers, driving spikes, and then repeating the sequence. The average amount of construction for one day was two miles.

Sanitation was a prime concern with Union Pacific workers. Diets were regular, consisting mainly of beef and bread and coffee. Water-borne illnesses were rampant, as were squalid conditions in the close quarters of the working camps.

Native Americans harassed construction of the eastern railroad. Livestock rustling was common, as were raids, burnings, and even scalpings. An 1866 massacre of troops at Fort Philip Kearny in Wyoming did little to dispel rail workers' fears of continued reprisals for pushing the rail line through lands once lived in by Native Americans.

Also plaguing Union Pacific efforts was the activity of its vice president, Thomas C. Durant. Later disgraced in the Credit Mobilier scandal, Durant made a habit of manipulating railroad finances to put money into his own pocket. The federal law authorizing payment of the railroad paid by the mile, and Durant took full advantage, choosing a meandering route that, in many instances, went across land he himself owned.

Despite all of these challenges, the railroad was completed. The two railroads met at Promontory Summit, in Utah, on May 10, 1869, and drove in the Golden Spike, symbolizing the completion of the biggest step in a coast-to-coast railway. Along the way, Central Pacific had laid 690 miles of track and Union Pacific had laid 1,087 miles of track.