From Missoula the TransAm Trail turns southward, following the footsteps of Lewis and Clark through the Bitterroot Valley. It then crosses a succession of passes, one over the Continental Divide, to Dillon, the heart of Montana's sheep country. The Big Hole Battlefield National Monument is along the way. The route continues through the Alder Gulch into Virginia City, site of the state's first great gold strike. Section 4 ends at West Yellowstone, gateway to Yellowstone National Park.

More information about this route is available here.