What Happened to the Anasazi?

As a resident of the western United States I've had the opportunity to visit some of the pueblos of the Anasazi Indians. The first site I ever visited was in southern Utah.
One of the most enduring mysteries of the ancient America's is what happened to the Anasazi people who built dwelling places much like homes and apartments within ancient caves. Many of these Anasazi dwellings are found in southern Utah and southwestern Colorado. As well as New Mexico and northern Arizona.
These people seem to have vanished from off the face of the earth, leading to many crazy ideas from the idea that there was a huge war that wiped them out to the idea that aliens or interdimensional beings took them away. Although there are many theories on this subject (some less believable or more outlandish than others) the most likely theory is that many of their numbers died out because of drought, famine, and overall lack of resources to sustain a growing population within their societies. There is even some evidence that they were driven out by other Native American people. Some may be members of the Zuni, Hopi, Navajo, and possibly even the Ute tribes of today.
It is alarming, however, that such a large ancient population suddenly declined. Was it merely famine and drought that starved many of them to death and forced them to migrate from their communities or something more?
As archaeology uncovers more facts, hopefully we can piece together more evidence as to the circumstances that led to their disappearance. Even so, tourists will continue to visit these places to be awed and inspired by this great ancient mystery.

For more on the Anasazi there's a book I own that I recommend called House of Rain by Craig Childs. It's an excellent read on the subject.