I was going to say it was a good luck symbol of fertility until I remembered that Native Americans may not have been properly equipped to see a sperm cell, even a fat one.
Ok, sorry, odd sense of humor over here.
That is a super cool piece though, I'd love to have something like that for my 'what the hell was this used for' rack.
pure speculation...Maybe it was used to mash up like indigo or some kind of dye then they could tilt it and the liquid would pour out the little spout there. Thats my best guess haha. Awesome find!
I live near Cherokee Co. I know the director of the local museum there and I'll see if they know what it is. If you find out through native artifacts keep us informed