A massive Mormon exodus swells the ranks of the emigrants to some 4000 pioneers, though it's an off year for the Oregon Trail side of the Platte River as cholera strikes Independence. Council Bluffs and St. Joseph replace Independence as the leading jumping-off points. The discovery of gold in California draws off more than three-quarters of the male population of Oregon, but most return before the arrival of the 49ers the following year. 1849 Word of the gold strike at Sutter's Mill turns the trail into a superhighway as 30,000 emigrants, most of whom are California-bound, race west. Overland parties come from as far away as the east coast.
Cholera spreads west along the Trail, helped by damp weather.
Some 55,000 emigrants make this the banner year on the trail, but cholera runs rampant, killing thousands. 1851 Word of the cholera epidemic spreads, discouraging many and holding traffic down to about 10,000 souls. Most emigrants start out for California but news of the Donation Land Act causes many to change their minds mid-route and opt for Oregon, instead. From 1851 to 1855, nearly half of those who would claim land in Oregon under the Donation Land Act leave the United States and head west. Half leave from St. Joe and half from Omaha, and half head to California and half to Oregon.