"Aztlan isn't just about the Chicano movement of the 1960's. It's been a mythical place of fiction for hundreds of years. It wasn't until the 1960s that some people started using the term to describe a new homeland for Mexican nationals.
In fact, the mythical land of Aztlan never really had an agreed-upon location."
The idea of the southwestern US being Atzlan was adopted by the Chicano movement at their convention in the '60s when a poet read his piece to only inspire them in their struggle for recognition/rights. He never intended it for the use that it is now. I heard this from him first hand on a great video about the Chicano movement titled "Chicano". It is well worth everyone's time.
Additionally, when Montezuma was asked about the location, he stated that it was a fictional place. Atzlan, by-the-way, refers to an island.