why the Nez Perce, a mountain tribe, and not aboriginals closer to the Pacific coast?Yes, why them, who had no contact with the Spanish? ;') The tribes moved around, though, so it's tough to point to points of origin.
See my post #35 for speculations. Many tribes were expert horse thieves -- a constant complaint in early Western journals -- so horses got around pretty quickly. I suspect the Nez Perce got horses from the Blackfoot, Gros Ventre, Shoshone, Flatheads or other plains Indians.
Reminds me of the story of the chickens. As it is told, chickens were not indigenous to the Americas, and were brought by the Spanish (we always forget about the Portuguese cod fishermen, but let that pass).
At any rate, everywhere the Spanish went, they found chickens, so assumed that chickens were native to the Americas, but in fact, they were stolen and thus disseminated before the Spanish came to the area.
I have no idea whether this is a true story or not.