ADAM PRESSES ON into the mouth of the canyon, where the ghostly cottonwoods are just beginning to turn yellow. After a mile or so, I feel a sense of imminent claustrophobia, the sheer rock faces climbing higher with every bend. We're cruising on the sand floor, moving at a good, jittery clip. The nearby Thunderbird Lodge has a small fleet of World War II–era open-air troop-transport trucks, called "shake-and-bakes," touring the canyon today, and there are other 4x4s prowling the flats. Until we all veer off into various side passages, the bucking procession has something of a Mad Max feel.

In many places, the sandstone is streaked with brown stains—called desert patina—that curl like a wizard's long fingers down the massive sculpted walls. There is a convoluted chemical explanation for these streaks, but I like Adam's explanation better. "That's Changing Woman's Hair," he says, a reference to the Navajo matriarch goddess, who changes her appearance with the seasons and presumably leaves her hair all over the place.

Early on, Adam conducts a seminar on nomenclature. The Navajo are not properly Navajo, he reminds me; they're Diné, which simply means "the People." ("Navajo" is a Spanish corruption of a Pueblo word meaning "People of the Great Planted Fields.") Similarly, the preferred term for the Anasazi, those prehistoric druids of the Southwest, is now "Ancestral Puebloans," because "Anasazi," a Navajo name often translated as "Ancient Enemies," gives offense to the Hopi and other current-day Pueblo descendants. There are dozens of other lexical do's and don'ts, all rooted in the basic problem that so many different cultures have intersected here at various times, and all of them have been somewhat at loggerheads, if not plunged in outright warfare, with one another. You can't open your mouth without saying something that's either nonsensical or just plain pisses someone off.

Adam doesn't seem to care much about any of this naming business, actually. "You can call me Butthead if you like," he says. Nonetheless, in due time, my Indian name develops. "You ask a lot of questions," Adam says, and so, perhaps inevitably, I become Many Questions.

About eight miles in, we hit our first serious patch of quicksand. You have to be extremely wary driving in Canyon de Chelly—its famous sloughs are deep enough in places to swallow an entire car.

"If you get stuck here," Adam says, "AAA won't come and pull you out." Like sunken wrecks in the Caribbean, there are lost relics buried all over the place: tractors, ATVs, even a couple of those Thunderbird shake-and-bakes. Canyon de Chelly's greedy quicksand has been known to mire a packhorse so deeply that it has to be pulled out with a winch. Not infrequently, the animal breaks a leg in the trauma and has to be put down.

The difficulty of driving in the canyon is yet another reason why guides are required. Adam has spent much of his life mastering the technique: steady gas but not too fast, a rhythmic dance of the wheel in the rough spots, never under any circumstances tapping the brake. He's got just the right touch, and with a few skittery fishtails, we wallow on through.

We push a few more miles into the main branch and round a corner. There, looming before us, is one of the most fabled landmarks in all of Navajo country: Spider Rock, an 800-foot-tall pinnacle erupting from the floor of the canyon. The Navajo say that a great goddess, Spider Woman, lives atop this fantastical spire. Spider Woman is the wise but cryptic old crone who gave the Navajo the gift of weaving.

At the same time, Spider Woman is something of a bogeywoman for Navajo kids. "Grandma used to warn me when I was being mischievous," Adam says. "She'd say, 'Spider Woman is going to come and get you. She boils and eats bad little kids.' Look up there—see those white banded streaks on top? Those are the bones of disobedient children, bleaching the rocks."

Although he wears a faint smile, Adam says all this in a perfectly inscrutable tone that suggests he believes it—or at least doesn't rule it out. It's always best to adopt a respectful demeanor, Adam says, and keep your voice down. "Who knows? She might be listening."