http://www.aaanativearts.com/Native_American_map.jpg

Looks like the "big groups" (if I'm reading it right) west of the Mississippi are:
Sioux, Pawnee, Apache, Blackfoot, Crow, Cheyenne, Shoshone, Ute, Navajo, Apache, Paiute

That would seem correct.

Thanks for the info. I'll try to update native civs in either the next patch or the one following it, or the next big version.

For 0.3 I'm going to add these in and remove the non-area-appropriate native civs.

So if anyone has leader (or city name) suggestions (or art, I guess), please post them here or elsewhere.