This is an ancient site known as Montezuma's Well, which is actually a collapsed caldera fed by an underground spring. The Sinaqua people who lived here over a thousand years ago created an aquaduct system that allowed them to grow crops in the Sonoran Desert. They disappeared sometime in the 1400s and no one knows why or where they went. If you click on the photo to get the large version, you'll be able to see a couple of the cliff dwellings above the large tree. For perspective, you can also make out some people on the cliff just to the left of the largest dwelling. Near Rimrock, Arizona. May, 2007.