FOUR CORNERS – The question is not: Why did the Anasazi disappear? (The answer to that one, of course, is still a swirl of conjecture.)

The question should be: Why were they there in Chaco Canyon in the first place? And what is the meaning of the monumental architecture they left behind?

That’s what we talked about with Zebulon Miracle on a recent one-day “taste” of the vast complex of ceremonial and astronomical sites in Chaco Canyon, a shallow sandstone wash that lies 20 rough dirt miles from the middle of nowhere, off Highway 550 between Farmington and Cuba, N.M.

Miracle is the curator of anthropology at the Museum of Western Colorado in Grand Junction, and an admitted nut for astroarcheology. The first place he took us was the Fajada Butte Overlook. We couldn’t hike out to the 400-foot-high sandstone layer cake because of the site’s fragile nature, but Miracle described the astonishing Anasazi calendar wedged inside a cluster of rocks at the top.

Ancestral Puebloan astronomers (ancestral Puebloans is the term scientists and Park Service people want to use now, because, Miracle told us, Anasazi in the Navajo language is a “vulgar” term for thief) carved a spiral in the blank rock of one wall. Only a sliver of sunlight enters the cavity each day. On the summer solstice, sometime in late June, the light shaft strikes through the center of the spiral. On the winter solstice, it grazes precisely down the outside edge. Equinox dates, like the one we just had on September 23, line up with a second, smaller spiral.

A solar calendar makes a lot of sense, of course, for timing the planting of your beans and squash. And for marking annual celebrations. But the sun is relatively simple; its position on the horizon is the same for a fixed date year after year.

The moon, on the other hand – “Oh, swear not by the inconstant moon,” Juliet said to Romeo. The moon’s position on the horizon is much trickier to figure out. The cycle takes nearly 19 years, Miracle told us, to go from minor standstill to major standstill. (I’d never heard the terms, but I had always been baffled by the moon’s varying path above my house, sometimes wildly different from week to week.)

Did the Anasazi (Miracle still prefers the simpler term) figure out the moon, too? His evidence came from the ruin at Chetro Ketl, one of our next stops. It is one of the huge, D-shaped great houses, second only in size to Pueblo Bonito, with hundreds of rooms and dozens of kivas, including a great kiva that could seat hundreds around its stone circumference.

The straight line in Pueblo Bonito’s massive “D” runs exactly east west. (The Anasazi had their cardinal directions down, too.) Lots of features in Chaco line up with each other, even ones miles away and up on top of the mesas, along nearly perfect north-south or east-west axes.

But the back wall at Chetro Ketl points north of east at about 67 degrees, very close to the compass point at lunar minor standstill.

Did he know for sure that this design was intentional? No, Miracle said. Not at all. In fact, he sometimes felt that archeologists had overreached during the 1980s and 90s, when connections between astronomy and ancient structures seemed to appear everywhere. No, he said. “We just don’t know. We do know that knowledge was power, and architecture was knowledge. These structures were planned and built over 400 years, starting in about 800 A.D. Maybe Chaco was a spiritual center, like Mecca, and people came on pilgrimages.”

There is some evidence of cannibalism here, he said. Pretty brutal stuff. Was that a way of sending a message to non-believers? A way, through fear, to keep satellite communities in line? “We just don’t know. Religion or defense, that’s our fallback. If you don’t understand something you’ve found, the answer is religion or defense.”

Miracle embraces the mysteries of the place, all the tantalizing clues. He doesn’t believe in miracles (he’s a scientist). Although at lunch, when a member of our group brought up the possibility that the great houses might have been built by aliens, he politely didn’t dismiss the idea out of hand.

He wanted to know why, just as we did. Why here, where there is essentially no water, little game, scarce fuel – and so distant from the tall forests the Chacoans needed for ceilings and roof beams? (It is estimated, Miracle said, that they cut, peeled, dried and carried a quarter-million logs from forests as far as to 60 miles away, in the San Juans to the north, the Chuskas to the west and the Jemez to the east. They had no horses, no beasts of burden.)

Why all this intense effort in this place? Why the moon? And, yes, why was it all abandoned, quite suddenly, around the year 1200? Miracle Miracle doesn’t pretend to know the answers. Religion or defense, he said again, smiling.

On the van-rattling washboard ride back to civilization, I couldn’t get that mantra out of my head. Why do we sophisticated moderns do what we do? The answer doesn’t seem ancient at all.