10. Mystery of the Anasazi
　　As the tourists prepare to depart Spruce Tree House, one asks Qumawunu the question that's on everyone's mind: Why, after having invested so much work in this place, did the ancestral Pueblo people leave it all behind?
　　The park ranger's answer sounds well-rehearsed: "We can come up with so many thoughts about why they moved in and why they moved out. But no one really knows for sure."
　　But it's a mystery that is finally beginning to unravel.
　　But while Crow Canyon has brought professional archaeology to the masses, it has yet to dismantle the biggest misconception about Mesa Verde's prehistory: that the ancestral Pueblo people simply vanished.
　　"I don't think we really ever thought that they just vanished into thin air," says Kuckelman. "I think the real enigma of the ancestral Pueblo people in the Mesa Verde region is, ŒWhy did they leave?'"
　　The ancestral Pueblo people didn't have a written language; no one left behind a detailed account of their last days in the Mesa Verde region. But Kuckelman believes that if she looks hard enough at places like Goodman Point Pueblo, she can find this story written on the walls-and on the floors and in the trash heaps.
　　There's a partially excavated kiva, a subterranean dwelling near the northwest corner, that could hold part of the story. Standing over it, Kuckelman lifts the plywood covering that will protect the underground chamber over the winter and peers into the darkness. When this kiva was first excavated last summer, workers discovered prehistoric ash in the hearth and a rabbit skeleton nearby. Kuckelman thinks those findings may be the remains of one of the last meals ever eaten in the village.
　　She believes that when researchers dissolve the ash in liquid and analyze what remains, they'll find markedly little evidence of maize, compared to the amount of maize refuse in rubbish pits around the village. This isn't a wild guess. Kuckelman and her co-workers noticed the pattern when they ran similar tests at a nearby contemporary ruin, Sand Canyon Pueblo. These findings helped Kuckelman piece together a new theory about the ancestral Pueblo's departure, a theory she hopes to bolster with evidence from Goodman Point Pueblo and other excavations.
　　Kuckelman believes that as more and more people settled in the Mesa Verde region in the thirteenth century, they overwhelmed wild food sources in the area, such as deer and wild plants. As a result, they became increasingly dependent on maize crops-not just for food, but for feed for domesticated turkeys-as evidenced by the ubiquity of maize in refuse pits, essentially time capsules of the villagers' eating habits and customs. But then something wiped out their ability to cultivate their crops, as indicated by the limited maize remains in hearths. The rabbit skeleton may also be a clue, suggesting that turkey populations may have died out and forced these people to fall back on small wild game. This could mean that Kuckelman has found more than just evidence of the last meals ever eaten by the ancestral Pueblo people in the Mesa Verde region; she's found a possible impetus for their leaving: to search out new means of sustenance.
　　"The folks in this area had become very, very dependent on crops, like maize, and wild turkeys. Ultimately, I think that system backfired and collapsed on them," she says.
　　But why did the system backfire? Why did the entire population collapse? For a while, archaeologists thought they had the single answer: a great drought.
　　This idea was born from ancient wooden beams found in Mesa Verde ruins, beams whose tree rings captured the exact date and climate conditions of the prehistoric time period. Andrew E. Douglass, the father of tree-ring dating, studied these beams and, in a 1929 National Geographic article evocatively titled "The Secret of the Southwest Solved by Talkative Tree-rings," announced that he'd cleared up the mystery of the prehistoric migration. The beams, he wrote, showed evidence of a massive drought in the region from 1276 to 1299. Drought can be apocalyptic in the Mesa Verde region-soil turns to powder, trees hold less moisture than kiln-dried wood-and this one, it seemed, had led to a mass exodus.
　　Scholars are skeptical of single-factor explanations. Could one drought, no matter how devastating, be enough to depopulate an entire region? But for decades, no one had the hard evidence to challenge the drought theory. "Interpretations were kind of all over the board," says Kuckelman. That changed seventeen years ago, thanks to the work of a Ph.D. student named Carla Van West.