Until the Mexican-American War (1846–48) only a few Americans—explorers, soldiers, trappers, sheep drivers—visited Arizona. In 1851 the U.S. Army Corps of Engineers sent several expeditions into Arizona to find a suitable route on which to build a wagon road to California. To protect travelers, miners, and other settlers from Native Americans, the U.S. government began to locate army posts at key sites. In 1883 workers completed the Atchison, Topeka and Santa Fe Railway across northern Arizona, thereby linking St. Louis, Missouri, with California; that same year the Southern Pacific Railroad completed a line from New Orleans to Los Angeles by way of Tucson and Yuma.
