Also keep in mind that over the years, North American Indians were forced to give up, not only their language, but their spiritual beliefs as well.
Standard Christianity seemed to decimate almost everything the Natives held dear. If you refused to convert, you were murdered.
I once asked my father about books regarding our Choctaw history. He said that there weren't many sources of written information because so many of the tribes were forced to abandon their beautiful heritage. Therefore, much of the history was simply handed down from generation to generation in ceremony and private conversation as apposed to being physically documented.
I truly hope that a treasure trove of information does exist out there somewhere. It would be tragic if such wondrous knowledge was just gone forever.