Driven from their homes in Missouri and Illinois by political and religious prejudice, the Mormons began a historic fifteen hundred mile trek from Nauvoo to the Rocky Mountains on February 4, 1846, after church leaders had determined as early as September 9, 1845, to found their Zion in the valley of the Great Salt Lake, a move said to have been prophesied by Joseph Smith four years earlier. The four hundred mile crossing of Iowa in 1846 was the most trying part of the exodus because of intense cold and cholera, and these hardships, together with the furnishing of five hundred volunteers in the Mormon Battalion for the war against Mexico, forced a temporary halt on the Missouri River, where Winter Quarters was established at the present site of Florence, Nebraska. From there, on April 7, 1847, a pioneer company left for the Rocky Mountains with 143 men, 3 women, 2 children, 72 wagons, 93 horses, 66 oxen, 52 mules, 19 cows, and 17 dogs; seventeen additional members of the Crow and Therlkill families with three wagons joined at Fort Laramie, and six members of the Mormon Battalion joined at the crossing of the Green River, making 171 people who entered Great Salt Lake Valley on July 22-24, 1847. The company reached Fort Laramie on June 1, South Pass on June 27, and Fort Bridger on July 7; on July 13, Orson Pratt was directed to take 23 wagons and 42 men ahead to determine where the Reed-Donner trail crossed the mountains, and two days later his company found the trail running southwest for fifteen miles from the present site of Henefer, Utah, then turning west over the mountains. Following this route, Orson Pratt and John Brown ascended Big Mountain and on July 19 saw the Great Salt Lake for the first time; two days later Pratt and Erastus Snow went from the foot of Little Mountain down Emigration Canyon, climbed a hill near the entrance to the valley, and rejoiced at the extensive scene before them. On the morning of July 22, nine horsemen headed by Orson Pratt and George A. Smith rode into the valley to locate a place to plant crops that same day, while Willard Richards led a train of sixty wagons into the valley and made a temporary encampment seven and one-half miles southwest of the canyon mouth; early the next morning a permanent encampment was made two miles farther north on the banks of the South Fork of City Creek, and the waters of City Creek were turned onto the hard-baked soil, inaugurating the system of modern scientific irrigation in America. Brigham Young, delayed by serious illness with mountain fever, entered the valley on July 24 with the remaining fifteen wagons, and Wilford Woodruff recalled that as Young surveyed the country from his carriage he said, “this is the right place. Drive on.” The arrival was later associated not only with the Mormon pioneers but also with the roles of Spanish Catholic fathers, trappers and fur traders, official government explorers, and California immigrants in the successful founding of an empire in “the top of the mountains.”