Between 1800 and 1870, nearly half a million Americans set out across the frontier on the many trails that led westward. Using the Santa Fe Trail, the Oregon-California Trail, the Mormon Trail, or one of the many other trails, these trappers, traders, farmers, and families set out on a journey of discovery. For many the western frontier represented the opportunity of a lifetime: a chance to take control of their lives, to strike it rich, to make their own rules, or to claim their own land. Lured by promises—of gold, of lucrative trade, or of fertile farmland—pioneers endured weeks and even months of arduous travel in order to reach their destination and build the communities that defined the American West. The trails they blazed helped pave the way for the civilizing of the West.

The pioneers who journeyed west in the middle of the...