Black Elk Speaks, but in what Genre?

I really don't have much to say on this book, because, to be quite honest, it confuses me as to what genre it fits into.
Part of me wants to label it as an autobiography, biography, or a memoir but that feels far too simplistic.
I think Neihardt did his own interpretation a great deal on what Black Elk was saying and that sort of idea speaks more of the author than the subject. It's well worth noting that this book is by John Neihardt as opposed to being by Black Elk. So that eliminates autobiography from the genres.
However, that still leaves biography and memoir.
Biography, again, doesn't work because it's far too focused on other factors outside of Black Elk's life, Black Elk even goes so far as to say something like "I am going to tell you the story of my life...and if it were only the story of my life I think I would not tell it." (pg 1). And it's narrated by other people too much to be a simple biography because oftentimes, the other speakers don't reference Black Elk but things within his life.
This is also the reasoning I use to eliminate memoir from the list-plus, it's far too overarching to be a memoir, this is a large span of time.
What then, if there is a label to be imposed, should Black Elk Speaks be called? I could take the English major route and say that "the genre encompasses many bases and you can't define something into one clean and neat label. The world doesn't work that way, art and literature means something different to everyone." (The English major in me believes this wholeheartedly, but also realizes this is something other majors may call... a cop-out...)
So, if I were to give a broad sweeping label to this, I'd go with religious/prophetic work. It's filled with iconography, Black Elk sees the future of his tribe within these gorgeous (and surprisingly universal) symbols. He continues to be haunted by his visions until he chooses to do something about it.
In a close second, I'd call this an ethnography. It's a character study of a tribe of people. Unfortunately, it's during a time of transition, so you're watching a culture, if not in decline, then in adaptation, and to my mind, this isn't the same thing as a purely ethnographic piece.
Neither of these fits are perfect, which makes me reluctant to label, but if forced, I'll respond with religious work or ethnography. (If there were a way to merge both into a nice little name, I would...religiography? Ethelgious? I'll work on it).
Regardless of the problems with genre, the relevance of Black Elk Speaks within the realm of the American Conversation program remains unaffected because it crosses those boundaries. On the one hand, Black Elk Speaks focuses upon these same apocalyptic themes that created the North American culture which I was raised in (Midwestern Suburbanite of European descent) and it deals with the loss of democracy within a tribe and how a change in culture and the definitions of the "average American" and with that, who gets the right to a say within a democracy.
I realize this post followed a stream of consciousness randomosity without any of the ultimate insight, so let me cut myself by saying, that although I don't have a lot to say about Black Elk Speaks, he definitely has a lot to say on the subject.