In 1869, the presidents of the Union Pacific and Central Pacific railroads meet in Promontory, Utah. They had come to Utah to drive a ceremonial last spike into a rail line that connected their railroads. This made transcontinental railroad travel possible for the first time in U.S. history.

The First Transcontinental Railroad (originally called the "Pacific Railroad" and later the "Overland Route") was a 1,907 mile (3,069 km) contiguous railroad line constructed in the U.S. between 1863 and 1869 west of the Mississippi and Missouri Rivers to connect the Pacific coast at San Francisco Bay with the existing eastern U.S. rail network at Council Bluffs, Iowa.

This specific railroad revolutionized the settlement and economy of the American West by bringing the western states and territories firmly and profitably into the "Union" and making goods and transportation much quicker, cheaper, and more flexible from coast to coast.

More Info: en.wikipedia.org