By the 1840's, the fur trade had declined, and virtually the only whites to set foot in Utah were pioneers on their way west. Settlement began in 1847 when a vanguard of 148 Mormons, led by Brigham Young, followed the pioneer trails into the mountain valleys of Utah. They made their first settlement at the site of present-day Salt Lake City. The Mormons had been driven out of their previous home, Nauvoo, Illinois, and were seeking a remote area to practice their religion and avoid persecution. Here, in the valley of the Great Salt Lake, they planned to establish God's earthly kingdom, their Zion.

The advance party immediately began to plow and irrigate the desert land, preparing for the arrival of additional Mormons. In 1848 swarms of crickets threatened to destroy the first crops. However, large flocks of California gulls appeared, devoured the crickets, and saved the crops. During the first four years of settlement, nearly 12,000 Mormons came to Utah. Mormon communities were established in the mountain valleys north and south-southwest of Salt Lake City. Settlements included Ogden, Logan, Provo, Fillmore, and Cedar City.