The Union Pacific Railroad, along with the Central Pacific, formed the first transcontinental railroad, which significantly opened the West, including parts of the Rockies, to settlement and commerce.

The construction of the transcontinental railroad, primarily the Union Pacific heading west from Omaha, Nebraska, and the Central Pacific heading east from Sacramento, California, played a crucial role in opening the West, including the Rocky Mountain region, to increased settlement. Completed in 1869, this railroad provided a much faster and more reliable means of transportation compared to previous methods, facilitating westward migration, trade, and resource extraction in the Rockies. While the other railroads operated in the West, the Union Pacific's role in the transcontinental railroad was most significant for opening the Rockies.