<P> The cause of cholera, ingesting the Vibrio cholerae bacterium from contaminated water, and the best treatment for cholera infections were unknown in this era . Literally hundreds of travelers on the combined California, Oregon, and Mormon Trails succumbed to cholera in the 1849 - 1855 time period . Most were buried in unmarked graves in Kansas, Nebraska, and Wyoming . </P> <P> A branch of the Oregon Trail crossed the very northeast corner of Colorado if they followed the South Platte River to one of its last crossings . This branch of the trail passed through present - day Julesburg, Colorado before entering Wyoming . Later settlers to much of what became the state of Colorado followed the Platte and South Platte rivers into their settlements there . </P> <P> After crossing the South Platte River the Oregon Trail follows the North Platte River out of Nebraska into Wyoming . Fort Laramie, at the junction of the Laramie River and the North Platte River, was a major stopping point . Fort Laramie was a former fur trading outpost originally named Fort John that was purchased in 1848 by the U.S. Army to protect travelers on the trails . It was the last army outposts till travelers reached the coast . </P> <P> After crossing the South Platte the trail continues up the North Platte River, crossing many small swift flowing creeks . As the North Platte veers to the south the trail crosses the North Platte to the Sweetwater River valley which heads almost due west . Independence Rock is located on the Sweetwater River . The Sweetwater would have to be crossed up to nine times before the trail crosses over the Continental Divide at South Pass, Wyoming . From South Pass the trail continues southwest crossing Big Sandy Creek (about 10 feet (3.0 m) wide and 1 foot (0.30 m) deep) before hitting the Green River . Three to five ferries were in use on the Green during peak travel periods . The swift and treacherous Green River, which eventually empties into the Colorado River, was usually at high water in July and August, and it was a dangerous crossing . After crossing the Green the main trail continues on in an approximate southwest direction until it encounters the Blacks Fork of the Green River and Fort Bridger, Wyoming . From Fort Bridger the Mormon Trail continued southwest following the upgraded Hastings Cutoff through the Wasatch Mountains . From Fort Bridger, the main trail, comprising several variants, veered northwest over the Bear River Divide and descended to the Bear River Valley . The trail turned north following the Bear River past the terminus of the Sublette - Greenwood Cutoff at Smiths Fork and on to the Thomas Fork Valley at the present Wyoming - Idaho border . </P>

Which river did the emigrants not follow on the oregon trail