What is the name of this creature from the mythology of the North American Southwest?

I'm trying to remember the name of a creature I learned about years back in a mythology class in high school. It was a fairy-like spirit, associated with creation, or at least with helping early man to survive. They came from the mythology of a culture in the North American Southwest, and were depicted in rock art. I am about 80% sure that the name started with a "y", but I could be wrong. I think they were depicted with bright colo(u)rs, like yellow, and I know that they had weirdly-shaped heads--square and triangular. Ringing any bells? Thanks in advance.