How did new methods of travel affect population movement in the US in the 19th century?

There is one huge improvement in travel that affected the rise of the US population in the areas west of the Mississippi River. This was the success and relative low cost of locomotive powered train travel. Steam powered trains were connected from the rails begun in California and those begun from the eastern part of the USA. Before trains to the west, the only two ways to travel from the East to the West was by covered wagons or taking a long sea voyage from say New York City, around the horn of South America and landing in either San Francisco or Los Angeles.