I think the answer is fairly obvious - water. Water was essential for drinking, cooking, cleaning, bathing, and livestock, but much of the area these trails covered are very dry.
Oregon Trail
The Oregon trail was a 2000 mile long string of rivers and national land marks.
Travelers leaving Fort Hall could follow the Oregon Trail, which led to Oregon City, Oregon, or the California Trail, which led to Sacramento, California.
Missouri yellowstone des chutes big horn
the Colorado Rockies, and rivers
A scow was used cross the rivers.
The Oregon Trail no longer exists. Paved roads run close to the route taken by The Oregon Trail. So it is possible to drive a route similar to that taken by The Oregon Trail. It would not be safe to try to follow the exact route of The Oregon Trail.
the weather, fearce Natives, rivers, disease ect
The Oregon trail never was modernized. Some parts of the freeway system do follow some of the trail. The current freeway system began in the 1950's.
The trails were the Oregon trail and the California trail the California trail led to California and the Oregon trail led to Missouri.
The trails were the Oregon trail and the California trail the California trail led to California and the Oregon trail led to Missouri.
The trails were the Oregon trail and the California trail the California trail led to California and the Oregon trail led to Missouri.