Even the minimalist approach requires substantial work, and it's difficult to round up money and skilled craftspeople. Concerned about the deterioration of ruins, national park preservation workers in New Mexico and Arizona began a grassroots campaign in the mid-1990s to get more support. "The Navajo and Hispanic guys in New Mexico got to talking, saying, 'When we're gone, there's no more like us,' " Yubeta recalls. The "Vanishing Treasures" campaign started receiving congressional funding in 1998 to assist preservation in 45 "earthen resource parks," including four mission ruins, in seven Western states and Texas. These parks compete for a share of $1 million each year. That's small change compared to other federal programs but noticeable on the ground: Vanishing Treasures funded more than 60 new preservation efforts in its first 10 years and still covers the work done by Moss.

But the workshops and campaigns have not succeeded in recruiting young people to the cause. Yubeta has spoken to students at Hispanic college conferences, but even those with a cultural connection to the missions want the "computers, three-piece suits and money" that come with more  fashionable -- and lucrative -- professions. He worries that much of the preservation work might end up going to recent college graduates who majored in historic preservation, rather than to talented masons. "They'll be great architects but they'll never touch the mud" -- unless they attend workshops or get other hands-on experience.

Yubeta, who recently retired, spent 25 years holding entropy in check. He and his crew traveled around the Southwest working on ruins on Park Service and other federal land, using traditional materials like adobe and lime to repair and stabilize the sites. Often the work involves triage, as crews do emergency repairs. Comic and gregarious, Yubeta is widely regarded as the region's foremost expert on adobe preservation. "It's just dirt," he says modestly. "I understand dirt. It's very simple, very forgiving."

Yubeta picked up some of his knowledge when his Hispanic relatives taught him how to repair his grandmother's adobe house. But Yubeta's Apache mother was not so keen on preservation. "When I came to work at the Park Service ... my mom really balked," says Yubeta. She scolded him for forgetting that everything must grow old and die; in her view, preserving a decaying building goes against the natural order of things. Some feel that's especially true of the missions because of what they symbolize.

The biggest churches, with their European architecture, can look absurdly out of place in the desert, looming over mesquite and prickly pear cactus. They are also relics of the colonization of tribes, including the Tohono O'odham's ancestors. Dale Brenneman, assistant curator of documentary history at the Arizona State Museum, points out that the Spaniards may have forced the Natives to labor on these buildings. The missionaries -- and the soldiers that accompanied them -- had a permanent impact on the locals.

"To us (people of European descent), the missions evoke something romantic," Brenneman says. "To the Tohono O'odham, they might represent something different: domination, extermination."

But Austin Nuñez, chairman of the San Xavier district of the Tohono O'odham nation, says that most hard feelings about what the missions represent have faded. "Now, it's just a given," says Nuñez. "From a spiritual standpoint, 80 percent of this community is practicing Catholic." (Many still practice traditional beliefs as well.) "The church binds families together," Nuñez says. "It's good."