Oregon Trail marker in the Oregon Trail Reserve in east Boise. Wagons were lowered through natural breaks in the volcanic rim rocks here. The route along the Snake River plain was dry and hot for the wagoners. They could often see the Snake River flowing beneath them in deep canyons but they couldn’t get to it in their wagons. Once they pulled within sight of where modern Boise is located breaks like this allowed them to get down to the more accessible Boise River.