The highest point on this trail was the South Pass. After this the trail led down to the Green River, a tributary of the Columbia (and which flowed into the Pacific).
Fort Bridger was on this stretch, and it was the place the Mormon Trail went south to Utah.
Crossing the Green River and then the Snake River was a great challenge as western rivers are in deep canyons and flow far faster.
Many crossed at Fort Boise, before making the final run to the Columbia.