During the mid-1800s, more than 500,000 pioneers journeyed west along trails that began in Missouri, crossed the plains, and entered Wyoming along the North Platte River. Travel grew harder in Wyoming as the terrain shifted from open plains to a rugged, arid landscape, and the journey by wagon or on foot often took four to six months and brought danger, accidents, disease, and shortages that killed many emigrants. The California Trail, used from 1841 to 1868, drew large numbers west after the discovery of gold in California, including more than 30,000 Forty-Niners in 1849, and followed the Oregon Trail through southern Wyoming to Fort Bridger before turning southwest. The Oregon Trail, used from 1843 to 1868, carried people seeking fur, missionary work, and farmland, while the Mormon Pioneer Trail, used from 1846 to 1868, carried Brigham Young and 148 followers from Nauvoo, Illinois, across Nebraska and southern Wyoming to near the Great Salt Lake in Utah, with more than 70,000 Mormons making the journey over the next 20 years. Although westward migration by wagon trains declined after the transcontinental railroad was completed in 1869, the trails continued in use by local travelers, ranchers herding stock, and the military. In Wyoming, some of the best-preserved evidence of this passage is found in four-foot-deep wagon ruts cut into a sandstone ridge, where thousands of travelers passed through winding, rocky ground and camped just west of this point rather than risk fording the swift and dangerous North Platte River.