It is said that the First People climbed into the daylight of the Earth from the underworld. According to one version of the Hopi creation myth, a bird, the tiny shrike, found an opening at the top of the underworld, and the chipmunk made a plant grow up to it so that the First People could climb out. They arose into sunshine, coming up in the Grand Canyon and wandering about in search of the place described to them by the Earth's guardian spirit, where they might live in peace.

Earlier this fall I took a hike across a desert in Arizona, a two-day walk that linked ruins of places built and abandoned in that search.

I flew into Flagstaff, a small town in northern Arizona beneath the forested San Francisco Peaks. Seen from the air, the peaks are not exactly plural. Some ancient eruption blew the mountain's top away, and the peaks that remain are jagged points around the rim of the resulting crater. Around the big mountain are the anthill-like mounds of small, round volcanoes. The big peak caps a huge trunk of magma rising from the depths of the Earth; the smaller peaks cap branches of that vent.

These volcanoes sit like a big island and its archipelago in the sea of the high desert, which spreads away in all four directions, magnificently gouged a hundred miles to the north by the Grand Canyon. Rectilinear Flagstaff hugs the southern slope of the big peak like a ship at harbor.

The San Francisco Peaks are sacred to the Hopi, and once I was in Flagstaff -- called "Flag" by the natives -- I thought I could see why. Besides their austere and commanding isolation, the peaks above town are the green of ponderosa pines, and bless the place with the promise of water. The slopes allow Flagstaff to appear less precarious than other desert towns, Las Vegas, for instance, which in its stark Martian landscape seems like so much dry circuitry, artificial and impossible.

Beseeching water from the gods was one prime function of Hopi ritual, and it was to these green peaks that they turned to ask for it. The Hopis say that the katsinas, the messengers of the gods, descend and depart from these mountains, which in summer may be capped by the only clouds in the sky.

It was dark and cold when I left Flagstaff the next morning. I turned the heater up as I drove the 35 miles north toward Wupatki National Monument, skirting around the mountain and descending out of the pine forests into stunted pinyon and junipers growing on cindery ridges, then into the desert proper, even the scrub trees giving way to the scant brush of the dry country. Salt bush, rabbit brush, sage, Mormon tea, all bright with the first brief rains of the season, covered the pale limestone plain. Out the windshield lay miles and miles of Painted Desert.

Out there, the astonishing and ancient geological forces in the Earth were not just apparent, they were gorgeously so. There the vertical layers in the earth rise to the plain along a vast diagonal, and have been sheared off at the surface by the forces of erosion, so that they appear in cross-section, as bands upon the landscape, of white or red, yellow or pink rock.

The pueblo ruins at Wupatki National Monument lie at the edge of this desert, along the fault line between the zone of red Moenkopi shale, which has worn off the uplands here, and the white-yellow Kaibab limestone. The shale can look as delicate in its layers as Greek pastry, and tends to break off at perpendicular angles, into perfect flagstones, which the people who arrived here about 900 years ago stacked into the walls that the dry climate has preserved for centuries.

Anthropologists call these ancestors of the Hopi the Sinagua, naming them for their seeming ability to live without water. They may have come into the Wupatki Basin when volcanic eruptions in the winter of 1065 (the date precise from tree-rings) drove them out of the higher country to the south. These eruptions had an unlooked-for benefit as well -- the cinder tended to mulch the soil in the desert, helping it retain moisture and slightly lengthening the growing season, and making refuge in the desert more tolerable.

The Sinaguan people made a life for themselves in the basin for a century or two before abandoning it, and leaving their ruins. The reasons for their leaving remain mysterious. Perhaps another subtle alteration in the climate deprived them of the thin margin they needed for survival here; perhaps they were besieged by enemies -- the later buildings here seem more fortified in their construction. Or perhaps the Wupatki Basin was simply not The Place.

So at Wupatki -- which means "tall house" in Hopi -- they left their houses and their kivas, chambers for religious and social gatherings that bore an opening in the wall near the floor -- a sipapu, symbolic of the opening through which the first people climbed out of the underworld. The Wupatki pueblo also contains an amphitheater about 50 feet in diameter and a masonry ball court, like those in Mexico. (The Hopi language is distantly related to the Aztec.)

There were a dozen in our hiking party, including a couple in their fifties from Massachusetts, a pair of Northern Arizona University English instructors in their twenties, and a Japanese biochemist whose two passions in life, he said, were covered bridges and petroglyphs. He spent every vacation photographing one or the other, he said. He would shoot perhaps 500 pictures on this hike.

After a brief bumping ride in the back of a pick-up, we shouldered our burdens and started into the desert with our guide, himself a Hopi. We set out along the fault line -- red shale beneath our feet, the white limestone rising just few years to the west. The shale made better walking, our guide said: The limestock tended to break into basketball-sized cubes, which was harder on the ankles.

The shale was as thin, brittle and red as flowerpot shards. It clinked and snapped beneath our boots. In the ravines, where some rare water had run once, we walked on black sand, volcanic cinder washed down from the hills. In the summer, said our guide, the cinder in the washes held and intensified the heat, and you couldn't walk there. But as we crunched along in the morning sun, it was still cool.

The Sinagua people built their homes on mesas of Moenkopi shale, on top of the hills of loose stone or talus, but beneath the tabletop of harder rock. The lip provided a natural shelter, which they enclosed with walls. On top of the mesas stood other, more fortified structures.

Our goal was the most elaborate of these mesa forts, called Crack-in-Rock after the narrow vertical opening that provides the only access to the upper fort.

We passed perhaps a dozen similar sites on our way to Crack-in-Rock. Around many, we found a litter of pottery fragments and stone tools -- blades and scrapers and arrowheads. The red and white pot shards bore parallel zigzags and other designs. It was Hopi tradition to break pots upon leaving a place; that way, some fragment would always remain to mark the site.

I found a black rock with one rounded edge smooth from long polishing and a fingergrip cut into one side. It seemed like a grinding stone, and fit perfectly into my hand. The person who used it -- almost a thousand years ago -- was right-handed, I realized.

Our guide reminded us to take care to put everything back where we found it. "Don't you hate it when a when a piece of the puzzle is missing?" he said.

By afternoon we were pouring sweat and guzzling water; I'd already gone through two of the eight quarts I'd hauled in. We came into an area of mesas lined up one after another, like aircraft carriers in port. Beneath one, we dropped our gear in a wash -- our campsite -- and climbed the mesa unencumbered. This was Crack-in-Rock mesa.

Carved on the solid walls above us were hundreds of signs a millennium old: lines of men or spirits like paper dolls, mazes and spirals, sun-bursts, tools, birds and animals. One depicted copulating coyotes, another a baby being born, a third the flute player of the Hopi pantheon, Cocopelli. Some of the carvings seemed playful, others ghostly, others like diagrams or maps.

Many of these petroglyphs, our guide told us, were territorial marks, signs of the various clans among the tribe: a vertical zigzag for the snake clan, a geometric checkerboard pattern for the corn clan. He himself was of the fire clan, he said.

We climbed through the crack in the rock -- a steep, S-shaped channel, a chimney, really, only a foot or two wide -- and emerged on top of the mesa.

Up there the Sinaguans had built a complex structure of red shale bricks, the walls knitted at the corners, the low doorways fitted with shelves on which our hands fell naturally as we entered.

One room had probably been a granary, another a kiva, with its spirit hole near the floor. A series of loopholes was set into one exterior wall, each opening offering a particular vantage on the distant plain.

The cliffs were sheer beyond the walls; below, to the east, lay our little camp. Beyond that were the dry valley of the Little Colorado, the pink mesas of the Painted Desert and, far off, towers of rock distinct on the horizon -- 50 miles away in Navajo Territory.

The sun went down fast behind the bluff to the west, and suddenly it was cold. We climbed down off the mesa in a landscape already dark under a blue sky, and made dinner as the stars came out.

We ate under the swath of the Milky Way, then built a campfire. With its light on our faces and the broad darkness beyond, our guide told us the story of the Emergence of the Ancient Ones. In the morning we woke to the distant howls of coyotes greeting the dawn, and found the peaks in the direction of Flagstaff dusted with snow.

Jim Paul's book "Catapult: Harry and I Build a Seige Weapon" will be released by Villard Books in April.