Flop hats, padre brims, Indiana Jones fedoras and indefinable sun-fending headgear bobbed on the heads of some 100 geologists and soil scientists as they gathered on the dry mountainside around the grand old man of the Desert Project, Lee Gile. Tall, slight, dressed in white with his head draped in a kerchief, Gile delivered his sermon on the mount.

Gesturing to a marked hole in front of him, he recalled the day, 40 years before, when he first explored beneath the surface.

"I put a shovel in and ... I'll never forget ... all that clay. Well, that was quite a day!"

It was a eureka moment only a geomorphologist could fully appreciate, but this crowd did.

On the mile-long hike between the site and the bus, the crowd patter had a flavor all its own. A geologist scanned the bluffs and got a laugh from his colleagues by saying, "This is really old. It's the ancestral Mississippi!" When asked how he was, a geothermal expert replied, "Still in hot water."

More serious shop talk revolved around cleaning up lead from con-taminated sites or declaring rivers in Cretaceous sediment "impaired" because they don't look like Eastern rivers.

The group parted to let Gile and his driver through in a car. "Reminds me of the queen going by waving to the crowd," a walking scientist said, acknowledging Gile's exalted status as one of the first men to understand desert soils.

In the 1960s, as a Soil Conserva- tion Service scientist, Gile advised Berkeley geologist Richard Hay, who was helping Richard Leakey define the origins of man in Olduvai Gorge in Africa. Strict ideas about newer soil layers always being above older ones were being challenged by the Desert Project, which showed how down-cutting and backfilling in river valleys confounded the layering process.

Desert explorers: Lee Gile speaks into the microphone about a eureka moment.

This spring's group was on a Mecca-like pilgrimage. They had come to Las Cruces from as far away as London, representing 14 universities, six government agencies and eight consulting firms, to be at the birthplace of so much of the knowledge that defined their fields.

"This has been a great week," said Missy Eppes, a geology graduate student from the University of New Mexico, who contacted NMSU organizers for a chance to work on the May 2000 tour. "You hear so much about the Desert Project," she said. "So many methods we take for granted were developed over 40 years here."

Her elders agreed. Don Johnson, professor of geography from the University of Illinois, considers the project a treasure. "New Mexico State University and scientists of this area are really fortunate to have the Desert Project here for study."

Johnson worked on an early guidebook for the project in 1966 and met Guy Smith, the federal scientist who started four major projects in North Carolina, Iowa, Oregon and New Mexico to define, classify and understand soils. "I didn't know who he was, but I noticed that whenever he so much as cleared his throat, everyone shut up, he commanded so much respect."

The projects were the first major studies of soil that didn't have an immediate agricultural application. This was particularly so for the Desert Project, where intensive study started during the International Geophysical Year of 1957, when the United States, fueled by Cold War fears, put its muscle behind science.

Desert explorers: Pilgrims mull the soil profile in the hole Lee Gile dug 40 years earlier. Another pilgrim practices the touchy-feely art of soil science by caressing a moistened sample (below).

For the next 15 years, the project literally put much of the southern New Mexico desert under a microscope. Johnson said New Mexico's project has stood the test of time better than the other three, confirming NMSU soils professor Curtis Monger's claim that the Desert Project is the crown jewel of the government's major soil classification studies.

The 400-square-mile area surrounding Las Cruces was selected because it was a microcosm of characteristics found in arid lands that make up about one-third of Earth's land surface-a major river valley, mountains, alluvial plains and other topographical features.

"This region in southern New Mexico had everything they wanted," Monger said. "It had soils that were very young and soils that were ancient, millions of years old."

Geologist John Hawley joined soil scientists on the project in 1962. At the time, the only geology course at nearby NMSU was taught by famed astronomer Clyde Tombaugh. It was the project that brought geology to NMSU, Hawley said.

The lucky few who worked the project got to conduct studies that will likely never be duplicated. "You couldn't do research like this today," Hawley said. He and project colleagues dug some 1,000 holes and trenches, most of which have long ago been filled and seeded over with native grasses. Such digging would be difficult at best with current permitting procedures.

Their own digging wasn't enough, though. The researchers were opportunists, following pipeline trenches and peering into holes dug for power poles to get more glimpses of what lay below. At a time when few instruments were available for analysis, the group learned to find ways to get the data they needed.

The project challenged the assumption that calcium deposits in desert soils were artifacts of old water tables that left us with impenetrable caliche layers and other calcium carbonate features. Project scientists proved that the calcium deposits arrived from above, not below. Bob Grossman, in charge of analysis, came up with the dust trap-a tray filled with marbles on a pedestal left in the open from February to May. The results showed that calcic deposits were blown into and rained into the desert soils, explaining why we get white deposits on our windows that are so hard to clean.

Understanding how calcium reacts with carbon dioxide to form calcium carbonate in the soil begs questions related to global warming. Could significant amounts of carbon dioxide from the atmosphere be trapped through the process? Conversely, could carbon dioxide be released from the soil under the influence of acid rain?

The project confirmed the fragility of desert soils and their vulnerability to desertification from both long-term climatic phenomenon and short-term drought and human activity. But the project also showed how soil could be used to map past climate changes and suggest what changes are in store for the planet.

Roy Shlemon, a consultant from California on the tour, has used the knowledge from the project to evaluate the stability of locations for major dams, nuclear power plants and other projects. In his opinion, no other project has integrated knowledge and made it available on the scale of the Desert Project. "It was true multidisciplinary work," he said, adding that it should be just the beginning.

"There is an incredible demand for knowledge about arid lands and what makes it so powerful is that it can be extrapolated around the world. We need to show the practicalities of this stuff for technology transfer."

Shlemon thinks an arid lands center should include not only geologists and soil scientists, but also social scientists, lawyers and public officials. "The potential is there for an international desert studies institute." And if first impressions mean anything, Shlemon said there is no better place than clean, friendly Las Cruces, which happens to be located at the center of the incomparable Desert Project.