They are all over. Start with looking for Nahuatl language on Wikipedia.
Mexico is filled with Indian tribes, Aztec related tribes are still there. 1.5 million still speak Aztec/Nahuatl but many more of the same stock speak Spanish.
Mexicans have more Indian blood then European. The upper class is mostly white.
If you go back 30 to 40 thousand years, all Indians of North, Central and South America originally came from their Central Asian ancestors in Kazakhstan. Those Kazakhstanians are also the ancestors of all Europeans. They migrated to Kazakhstan from the Middle East after leaving Africa. At least according to 'The History of Man' PBS program (there source data was DNA analysis from male blood samples). So we will all end up looking like Central Asian Kazakhstanians after the DNA bloodlines get mixed back together through globalization.