The Oregon Trail was one of the main overland migration settler routes on the North American continent, leading from locations on the Missouri River to the open Oregon Territory. The eastern half of the trail was also used by emigrants on the California Trail, Bozeman Trail, and Mormon Trail which used much of the same shared trail routes before turning off to their separate final destinations. To complete the journey in one season most travelers left in April to May—as soon as grass was growing enough to support their teams and the trails dried out enough to support their wagons. To meet their constant needs for water, grazing grass, and wood/sod fuel for campfires the trail followed various large perennial rivers and streams across the continent. In addition the network of trails required a minimum of fixes and road grading work to be made passable for wagons. People using the trail traveled in wagons, pack trains, on horseback, walked, and by boat/raft to establish new farms, homestead lives, and businesses in the new Oregon Territory. This new territory in the early 19th century was initially jointly governed by both the United States and England.
The four-to six-month journey spanned over half the U.S. continent as the wagon trail proceeded about 2,000 miles west through wild territories and land that would later become six U.S. states: these are Missouri, Kansas, Nebraska, Wyoming, Idaho, and Oregon. Extensions of the Oregon Trail were the main arteries that led settlers into six more soon to be settled states: Colorado, Utah, Nevada, California, Montana and Washington. Between 1841 and 1869 the Oregon Trail was used by many settlers, farmers, miners, and business men migrating to the open Pacific Northwest of what is now the North-western United States. Once the transcontinental railroad was completed in 1869, the use of this hard trail by long distance travelers rapidly diminished as the safe and fast railroad traffic replaced most need for it. By 1883 the Northern Pacific Railroad had reached Portland, Oregon and most of the reason for the once important trail disappeared. Now modern paved roads are built over or near most of the Oregon Trail as local travelers traveled to the now developed cities and towns originally established along the Oregon Trail.
Source: Wikipedia