I'm have a pretty simplistic understanding about Navajo and Hopi cultures (and the Zuni, who are not far south of the Navajo reservation in New Mexico) but from what some people explained to me, both the Hopi and the Navajo claim the Anasazi to be their elders. It is the one thing the Hopi and the Navajo seem to agree about. I certainly couldn't talk about dates or timelines, but the differentiation of religious beliefs could be a really interesting idea as to why there are so many different groups of people so geographically close to each other with threads of shared tradition, yet with such a great deal of in-fighting.

(But in thinking about it, I don't remember how close the languages are - I think maybe there is a big difference)