I've noticed this here, but oftentimes, we assume that the American Indians groups were where they were when the white man met/fought them OTL, as opposed to independent potentials? American Indian history is rich in possibility as to how tribes could've migrated, who might've fought the white man, etc. Look at the Kiowas, for instance--they were once a Puebloan people, but they evolved into a Plains Indian group. Who else might've done that? The historical record suggests quite a few groups could have that didn't, simply because other groups did it first.
That's not even getting into alternate agriculture amongst the Indians, where different tribes might dominate and the whole thing turned upside down.
I say this because if you open up a history book on the Plains Indians, you can basically launch a million scenarios. Like what if the Cheyenne Indians don't want to become horse nomads? It's wrapped up in their mythology that they accepted the consequences of becoming like the Comanche when their god Maheo effectively offered them that chance. But what if their leaders refused to? It could easily be a different story in American Indian relations--the US will fight the Cheyenne in their homeland in Eastern South Dakota/Western Minnesota, instead of in Colorado, which will have huge influence on Colorado's settlemnt--no Sand Creek massacre for one, John Chivington's career isn't marred by his act of utter idiocy, etc. The Cheyenne's Maheo story, which is very telling in Plains Indian history, would not exist, but perhaps an analogue might, where the Cheyenne choose to stay where they are and keep to their traditional lifestyle. But barring alternate agriculture, that probably means another American Indian group might be fulfilling the role the Cheyenne did OTL. Which in turn might have butterflies on groups like the Sioux and such.