Before 1860, railroad lines in the United States generally reached as far west as the Mississippi River. Although there were a few exceptions, such as the Hannibal and St. Joseph Railroad (completed in 1859) that extended slightly beyond the Missouri River, the vast majority of the country's rail network was concentrated in the eastern states. The lack of infrastructure and the challenges of crossing the Rockies and Sierra Nevada mountains made westward railroad expansion challenging, and it wasn't until the completion of the Transcontinental Railroad in 1869 that a continuous rail line connected the East and West coasts of the United States.