Fleeing religious and political hostility and persecution, many members of The Church of Jesus Christ of Latter-day Saints abruptly left their homes in Nauvoo, Illinois, in February 1846 and traveled 265 agonizing miles in four months before exhaustion, poor provisions, and heavy spring rains that turned southern Iowa into axle-deep mud forced them to winter near the Missouri River. In the spring of 1847, after resting and preparing more carefully, 143 men, three women, and two boys set out across Nebraska for the new Zion on the western slopes of the Rocky Mountains, following a rough trace made by earlier explorers, fur traders, and missionaries and beginning a route later used by thousands of other Mormons and Forty-niners. These first pioneers established ferries, campsites, bridges, and supply depots along the way, and as they moved slowly up the north bank of the Platte River they looked eagerly for Chimney Rock, the most famous landmark on the Great Platte River Road. When they reached a point opposite it on May 26, 1847, the landmark marked the psychological halfway point of their journey to the Valley of the Great Salt Lake and gave them a chance to test the mileage on John C. Fremont's 1844 map. Orson Pratt took astronomical observations of their location and estimated the chimney's height at 260 feet from base to summit, about 100 feet short of its probable height in the 1840s.