That experience was a mind-blower, even though at that time the only construction the artist had finished was the leveling of the crater rim. So 11 years later I really wanted to see how Turrell was coming along in his stubborn resolve to turn an extinct volcano on the southwestern edge of the Painted Desert east of Flagstaff into a celestial observatory.

This time, I went along with a small group of collectors from the Museum of Modern Art's contemporary arts council. The council had set up this three-day trip to Arizona specifically to visit the Crater. It was a last chance. Roden Crater is not yet open to the public, and Turrell's assistant told us that May was a cut-off date for having more visitors to the site. Those site tours eat up a lot of time and energy, and the artist and his team needs to work undistracted on the construction still to be done.

My 1990 visit had made me a dedicated believer in Turrell's genius, in the scale and depth of his vision. Only Christo, whose fugitive installations aim to change social consciousness about art and landscape, and whose cultural background could hardly be more diametrically opposite, formulates projects comparable in scale and intellectual complexity to the vision that has driven the Roden Crater project. Christo's process radicalizes consciousness of the political process through art and theatrically transforms his sites temporarily into spectacles of astonishing beauty. And Christo's works are for crowds. It's the classic difference between the European social impulse and the American conviction that the individual is at his most genuine outside society.

Turrell's work, as he himself repeatedly has said, is always for "one person at a time." His medium is light itself in space. "My material is light and it is responsive to your seeing," he has said. Since his earliest days as an artist in Ocean Park, Ca., Turrell has been consistently fascinated with using light as a conduit to enlarged perception of our own senses and of the cosmos.

Roden Crater is a natural cinder volcano that Turrell managed to locate and then acquire after flying over the American West for seven months. (The detailed history of his search is documented on the artists' web site, www.rodencrater.org.) "My airplane is my studio," Turrell used to say.

Though the crater is not a monument in any historical or traditional sense, it will "harness the drama of light, landscape and celestial events; disturbing and wakening our subjective understanding of the universe." A monument to perception, it will activate people's awareness not only of light, but also of the passage of time and the way the earth moves in space.

In 1990, Turrell had just begun to level off the elliptical edge of the crater. He drove us out there in his big beat-up pickup truck. This time, I got there in a Hummer (rented out by a local catering and adventure travel outfit in Flagstaff). On Friday, May 4, we got to Flagstaff around noon where we hooked up with Turrell's chief assistant, artist Michael Bolt, and drivers with three Hummers that would transport the group on the hour-long drive out to the Crater.

Acquiring the Crater property was difficult. (Dia Foundation helped him and it is still helping.) But keeping it pristine has been even harder. Since I was last there, the Western version of suburban sprawl has sped across the flat, semi-arid land toward what had been the very isolated location of the site. As a result, Turrell has taken steps to preserve the landscape around the Crater as well as the Crater itself, in part by becoming a cattle rancher. He now lives on a ranch near the Crater, and through annually renewable grazing leases and through outright land acquisition, controls some 150 square miles around the site. So Turrell has become an embattled preserver of the vast landscape in ways he probably never anticipated back when he began the project.

The temperature was around 40 degrees Fahrenheit. Hail was falling in Flagstaff and hard rain spit down intermittently as we climbed up through the one nearly completed sky tunnel to a sky chamber and the Crater's bowl. For most of the afternoon, high gray clouds scudding in layers, and shifting ribbons of rain obscured the Painted Desert and most of the sunlight. But the magnificence of the view remains, a vast panorama visible from the lip of the Crater -- it is 75 stories tall -- or from the huge windows of the just-completed overnight shelter on the side of the mountain.

The crater is still $12 million and many months away from its final form. In fact, the ongoing construction makes the site seem much tamer than it was 11 years ago. Climbing up through the still-raw concrete of the North Tunnel toward what looked like a circular opening to the sky was not unlike climbing around in a big construction site. We imagined what it will be like when the moon beams down the tunnel, once every 18 years, and reflects off the white plinths of stone at the bottom the shaft as a 10-foot tall glowing disk in the middle of nocturnal darkness.

Turrell and his crew have had to adapt the original plans and negotiate with federal and state ADA regulators to solve the problems of required handicapped access, probably sacrificing a certain structural purity. But the payoff came when we arrived at the huge sky chamber at the top of the tunnel.

It's actually not ideal to see the Crater with a group, even a small group. It's too distracting. A group talks too much and our group -- a hothouse bunch -- didn't much like the dark tunnels they had to feel their way through, thus diminishing the sense of spiritual calm required to best experience what Turrell is all about.

But when we got outside and into the bottom of crater bowl we found the four concrete viewing platforms had nearly been finished and everyone (who could) lay down on them -- head outward toward the crater -- and gazed upward, hoping to see the celestial vaulting effect as the sky wonderfully changes into a blue or gray solid above. When this happens, you feel dizzy and amazed. And your gut tells that your perception of the world been altered permanently. There are profound spiritual and metaphysical aspects to this grand manipulation of light and space that will be much clearer when Roden Crater is no longer a construction site.

Italian collector Count Giuseppe Panza called Roden Crater "the Sistine Chapel of America." And hardly any other contemporary work provides anything as powerful as the experiences produced by a visit there. But "James Turrell: Infinite Light," an exhibition mounted at the Scottsdale Museum of Contemporary Art, at least served to give the regional public a solid introduction to Turrell's work. Turrell may be world-famous, but he's not well known in Arizona, and this show was the first major museum exhibition of his work in the state. The Scottsdale MCA is a new facility established in a former movie theater complex in a rather creative example of contemporary adaptive reuse.

The show, which closed June 3, 2001, included a half-dozen scale models, plus photographs and maps that provided a detailed history as well as a dramatic overview of the development of the Roden Crater project. It also included five of the artist's room-size light works. The most amazing piece in the Scottsdale exhibition was one of Turrell's Space-Division pieces, a series he began creating in 1976. The Scottsdale example was a walk-in raised room containing a sky-blue Ganzfield (a uniform visual field used in perceptual experiments). Once inside, you were blanketed in what seemed to be a beautiful thick blue fog and you'd swear the light had material substance. When finally, after several minutes, you turned around and faced the opening of the room, what was a white wall at the outset now appeared to be an intense yellow. The rods and cones of your eyes were reacting to the blue and so you saw yellow instead of white (When you approached the entrance to the space, the wall gradually turned white again.) Such an intense visual and physical experience became particularly exhilarating because it was free of objects -- it was an experience not only of pure perception but one that generated intense feelings of euphoria and delight.

Similar things happen when you spend enough time in one of Turrell's "Skyspaces." The new Scottsdale "Skyspace," now installed at the museum, is the artist's first permanent public work to be installed in Arizona. Elliptical, pure white, and faced with opalescent plaster in which bits of seashells have been embedded, the Scottsdale chamber, its ceiling open to the sky, could hardly be simpler. Yet if you sit there at sunset and watch the light gradually change, you can see the phenomenon of celestial vaulting, and, as the colors shift from gray and blue to an ever-darker blue, and finally, and onward to velvet black, you realize with awe that you are watching the rotation of the earth through space. It's trippy to say the least.

Also there was one of Turrell's "perceptual cells, called "GasWorks," a spherical device that allowed one person at a time to immerse him or herself in an intense panoply of changing colored light (sort of the reverse of a sensory deprivation chamber). At the museum people were waiting in line for 30 minutes or more to get inside the sphere -- I was too impatient to join the queue. But as white-coated attendants opened up the MRI-like platform upon which the intrepid viewers would repose themselves for the 20-minute-long perception-expanding experience, I did glimpse an intense blue light filling the interior -- part of a changing sequence of intense Ganzfield light emitted inside the sphere.

Fans of Turrell's work find it difficult to understand why one of America's greatest living artists has to struggle to raise the funds needed to complete Roden Crater, when collectors regularly assemble at New York auctions to throw millions at more modest works by Jeff Koons, Bruce Nauman and other celebrities of the marketplace? Similarly, one wonders why the major New York museums seem inclined to marginalize Turrell's accomplishment. The last major retrospective he's had here was at the Whitney Museum in the early 1980s.

Still, New Yorkers can take in two permanent installations by Turrell at P.S. 1 in Long Island City. And Turrell won't let anything stop him. When money ran out to build the base for the Statue of Liberty, fundraisers launched a drive to get the children of America to send in their pennies. They did and the money was raised. Perhaps we should do the same for Roden Crater.