<P> Overall it is estimated that over 400,000 pioneers used the Oregon Trail and its three primary offshoots, the California, Bozeman, and Mormon Trails . The trail was still in use during the Civil War, but traffic declined after 1855 when the Panama Railroad across the Isthmus of Panama was completed . Paddle wheel steamships and sailing ships, often heavily subsidized to carry the mail, provided rapid transport to and from the east coast and New Orleans, Louisiana, to and from Panama to ports in California and Oregon . </P> <P> Over the years many ferries were established to help get across the many rivers on the path of the Oregon Trail . Multiple ferries were established on the Missouri River, Kansas River, Little Blue River, Elkhorn River, Loup River, Platte River, South Platte River, North Platte River, Laramie River, Green River, Bear River, two crossings of the Snake River, John Day River, Deschutes River, Columbia River, as well as many other smaller streams . During peak immigration periods several ferries on any given river often competed for pioneer dollars . These ferries significantly increased speed and safety for Oregon Trail travelers . They increased the cost of traveling the trail by roughly $30.00 per wagon but increased the speed of the transit from about 160--170 days in 1843 to 120--140 days in 1860 . Ferries also helped prevent death by drowning at river crossings . </P> <P> In April 1859, an expedition of U.S. Army Corps of Topographical Engineers led by Captain James H. Simpson left Camp Floyd (Utah) to establish an army supply route across the Great Basin to the eastern slope of the Sierras . Upon return in early August, Simpson reported that he had surveyed the Central Overland Route from Camp Floyd (Utah) to Genoa, Nevada . This route went through central Nevada (roughly where U.S. Route 50 goes today) and was about 280 miles shorter than the' standard' Humboldt River California trail route . </P> <P> The Army improved the trail for use by wagons and stagecoaches in 1859 and 1860 . Starting in 1860, the American Civil War closed the heavily subsidized Butterfield Overland Mail stage Southern Route through the deserts of the American Southwest . </P>

Who led a team that explored and mapped the oregon trail