Smithson built the spiral out of black basalt rocks taken from the shore and arranged them to a height just above the surface of the water so people could walk on the earthwork as if on a pier.

He was one of a number of artists in the 1960s and early '70s who chose to build site-specific pieces outdoors in the West, far from the commercialism of art galleries. Holt, also an earthwork artist, built a piece called "Sun Tunnels" near the abandoned town of Lucin, Utah, in a remote area near the Nevada border. Smithson in particular was intrigued by the idea of entropy, the inevitable disintegration of all objects in nature. But there is no definitive record of how he felt about the disintegration of his own artworks.

Just before his death he hinted at his beliefs in an interview with Moira Roth, chairwoman of the art department at Mills College in Oakland, Calif. The complete text of the interview is to be printed in the catalog accompanying a Smithson retrospective opening in September at the Museum of Contemporary Art in Los Angeles. (It will travel to the Dallas Museum of Art and the Whitney Museum of American Art in New York in 2005.)

In the interview, he said "Spiral Jetty" was strong enough to take care of itself, adding, "Because it's 80 percent rock, it won't erode completely." Later in the conversation, he said he planned for his pieces to be permanent and seemed to say he wanted them preserved. Holt said she agreed with that interpretation.

Finding a contractor willing to build a giant artwork in such a remote spot was a challenge. Many Utah contractors were suspicious of a New York artist who wore black leather pants in the middle of summer, said Bob Phillips, the contractor from Ogden who finally signed on to help Smithson move rocks into the lake.

"Man, his ideas sounded really strange," Phillips said. "I'd never heard about anything like earth art before."

Phillips and another worker used two dump trucks, a tractor and a large front-loader to move 6,650 tons of rock and earth from the shore into the water. At 1,500 feet long, the giant spiral is large enough to be seen in photographs taken from space.

Phillips said Smithson had a precise vision for the project and supervised every step, making sure individual rocks fell in the right spots.