One of the liveliest mission churches, San Xavier del Bac -- nicknamed "the White Dove of the Desert" -- stands on the Tohono O'odham Reservation on Tucson's southern fringe. At a Sunday Mass, Tohono O'odham, Mexican-American and Anglo patrons pack the wooden pews, their choruses of "Thanks be to God" echoing in the vaulted domes, as a bearded Franciscan friar leads the congregation in prayer. This is no re-enactment, and San Xavier is not a national park. Since its construction in the late 1700s, San Xavier has been an active Catholic church, hosting baptisms, funerals, weddings and quinceañeras (elaborate 15th-birthday celebrations for Hispanic girls).

On any given day, tourists wander around the church and visit the tiny museum and gift shop. An adjacent smoky candlelit chapel is dedicated to St. Francis, and Tohono O'odham sell fry bread in ocotillo-roofed lean-tos.

Four generations of the Morales family have tended San Xavier, supervised since 1989 by historic preservation architect Bob Vint. There is very little missing plaster, and the inside walls are covered with colorful murals that gleam brightly after careful cleaning by European specialists. Statues of saints are tucked into niches, and the walls are so heavily decorated with gold and silver leaf that they resemble the Vatican. Outside the church, Vint points out blue barrels that hold slaked lime (calcium oxide), explaining how the limestone is heated, pulverized and mixed with water to achieve a good plaster. The preservation crew, at least half of whom are Tohono O'odham, boils prickly-pear cactus pads and presses out a natural glue they add to the lime plaster. The cactus glue helps the plaster flow smoothly, adhere well and cure without cracks.

When Vint started working here, the Morales family was still using synthetic materials. Vint's mentor in Mexico City recommended a switch to traditional materials. So the crew stripped layers of cement and latex paint off the church, scraping the walls down to the original adobe brick. Then they applied lime plaster, bright white and smooth to the touch. The work is funded by the Patronato San Xavier foundation. And the Tohono O'odham are proud of it, or at least accept it, say Nuñez and Vint.

Caring for a functioning church is different than caring for ruins, says Vint. "We're preserving it on into the future because it still has a life, so we're renewing it. ... The guts of it are old, it just has a new skin." The skin -- the lime plaster -- will last a couple hundred years with proper maintenance, he says proudly, sliding his hand across the wall.

But recently, the reconstruction has been struggling. Owing to a budget crisis, this year the state withdrew a $150,000 grant, which would have helped complete the unfinished left tower. Two workers were laid off and the rest of the crew now works a four-day week. The slower pace means that the east tower (still under a cement casing) will deteriorate further and ultimately cost more to repair.

Near downtown Tucson, dust devils swirl on roughly 15 bulldozed acres at the base of Sentinel Peak. The vacant lot is occupied by a single square adobe wall. You'd never guess that this was the site of the city's humble beginnings, where Franciscan friars built the Mission San Agustín in the O'odham village of Chuk-shun around 1800. The historic buildings are long gone, and the city of Tucson destroyed the remains of the old mission in the 1950s. For a while the site was even used as a landfill.

The reconstructed adobe wall, built to surround a reconstruction of the mission gardens, is the first phase of the planned Tucson Origins Heritage Park. If completed, the complex will eventually include a brand-new Mission San Agustín, with a reconstructed chapel, convento and walled orchard as well as a re-creation of Native American settlements.

Archaeologists recently found evidence here of settlement and maize cultivation dating back 4,100 years. They also found North America's earliest known irrigation canals and the Southwest's oldest known pottery, according to Jonathan Mabry, Tucson's historic preservation officer. The site also holds artifacts from Chinese tenant farmers, remains of mission-era Native American pithouses and the foundations of a 19th-century brick factory. "With the archaeological findings from this project, Tucson can arguably claim to be the oldest continually inhabited place in the U.S.," says Mabry. "There's no other place that lays claim to that deep of a history."

But the mission reconstruction might not ever be finished. The work has stagnated for a decade, and not just because of the money problems of its parent entity, the ambitious Rio Nuevo downtown revitalization project approved by voters in 1999. It's also caught up in the philosophical argument over the meaning of historical preservation.

People like R. Brooks Jeffery, coordinator of preservation studies at the University of Arizona, see this reconstruction as an assault on history, not an homage to it. Jeffery, who's also involved in the Missions Initiative efforts around the Southwest, says the contextual relationship between the Santa Cruz River, Tucson's old presidio (the original walled fort) and Mission San Agustín has been lost due to urban development. The historical place "has been completely desecrated," he says. Furthermore, he argues that it will be close to impossible to recreate a historically accurate building using modern materials and without any existing physical remains or documentary evidence of how the mission was built. To people in Jeffery's camp, new structures would dishonor the existing missions that Missions Initiative is working so hard to help maintain.

Vint, at the San Xavier Mission, also strongly opposes the reconstruction. "We have a real, intact 18th-century building (at San Xavier). If people want to go back in time, they can come here and walk inside this intact architectural space." Vint calls Tucson's reconstruction "a waste of money and a falsification of history."

Supporters include the Friends of Tucson's Birthplace, a nascent group that is collecting donations just to cover the mission gardens. The garden wall and gates are finished, and the Friends group is launching a fund-raising effort to pay for water and electricity. They would like to start planting by March 2011; meanwhile, a joint city-state effort is planned to plant 100 "(Father) Kino Heritage trees" next year, grown from cuttings of very old trees -- direct descendants of the Old World fruit trees brought here by the Spanish missionaries.

Diana Hadley, former director of Ethnohistorical Research at the Arizona State Museum, envisions the downtown park as a living history museum for newcomers as well as longtime Tucson residents. "There's no hands-on instruction of our history here," Hadley says. The park would be an "unparalleled teaching tool." She acknowledges that the reconstruction would not be totally accurate but believes that people would "still get the wonderful feeling of what a mission was really like ... (understanding) that the mission wasn't just the church but rather a Native American village with a Spanish settlement laid on top."

Tumacácori's Don Garate shares Hadley's reasoning: "Tucson doesn't know its history, especially its Spanish history. Like all big cities, it's buried its history and built stuff over the top of it."

Unfortunately, the general public is not exactly clamoring for historical missions in any condition. None of the missions attract the throngs of visitors that charismatic natural recreation parks like Yellowstone or Yosemite do. Tumacácori attracts only 40,000 or so visitors each year -- one of the lowest totals in the national park system. Mission supporters hope to draw more visitors in the future, but they also believe, as Moss says, "You can't measure resources by the amount of people that visit. (The missions have) a larger meaning."

That notion seems to be shared by everyone involved. Despite his skepticism about Tucson's fumbling reconstruction of the downtown mission, Jeffery says the importance of preservation work in general lies in cultural identity -- in the feeling of connection to a specific place. "The next generation is one of placelessness -- we're already a very transient society. This is about what makes this place unique."

Ariana Brocious, a former High Country News intern, is a native of Tucson. Don Garate passed away on Sept. 21, 2010.

This story was funded with reader donations to the High Country News Research Fund.