Did you know the Anasazi people who built the cliff dwellings were actually Vikings? It's true. After the last ice age when all the ice melted the sea levels were much higher and the canyons in which the Anasazi built their villages were full of water. The Vikings were in an age of exploration and sailed up the river from the ocean. The 'cliff dwellings' were actually riverside settlements with a similar layout to the Viking base in Newfoundland. When sea levels began to receed around 1000 AD life in the settlements became harder and harder, and the Vikings finally abandoned both the 'cliff dwellings' and Newfoundland, giving up their North American presence by 1300 AD.
The word Anasazi means 'northern,' while the word Viking means 'overseas exploration.' It's clear to anyone looking at pictures of their buildings that they are radically different from other 'native' structures, but contemporary polictical correctness in American culture would never conceed that some groups of 'natives' may actually have come from somewhere else, especially not from Europe. Evidence that some west coast 'native' tribes may have sailed from China and Japan and even the well-documented Viking settlements in Newfoundland are constantly argued against by those with an interest in maintaining the image of America's 'native people' as culturally and historically unique and independent, but the facts are there.
References:
http://www.crystalinks.com/anasazi.html
http://en.wikipedia.org/wiki/Viking
http://en.wikipedia.org/wiki/Indigenous_peoples_of_the_Americas