The late James Michener once wrote a novel called THE SOURCE, which told the story of a single piece of land in Israel. The metaphor of the story was an archeological dig: the reader went back in time, as if removing layer after layer of soil, uncovering a different story with each stratum. I could never finish the book, to tell the truth: The writing was dry, and the book was a bit of a doorstop. Still, I admired the conceit that any given piece of ground had a good story to tell, or indeed many stories. A San Francisco-based nonprofit homebuilder, Mercy Charities Housing California, recently discovered the decidedly mixed joys of working on a piece of land that had many stories to tell. The case in point was the former Notre Dame High School, a building in San Francisco's Mission District, which the nonprofit converted last year into 66 units of low-income housing. While the homebuilder was not exactly bargaining for a major archaeological find, Mercy Charities found itself in the position of sponsoring a dig for antiquities at the same time that it was coping with the complexities of adapting an old, non-residential building into housing. Now known as Notre Dame Plaza, the former school is a local landmark in San Francisco's tough but gentrifying Mission District. The site is across the street from the Mission San Francisco de Assisi, popularly known as Mission Dolores, which dates from the 1780s. In the 1860s, the church gave the site to the Sisters of Notre Dame, who built a convent on the site, and later expanded it into a school in the following decades. Although the building survived the 1906 earthquake, city officials dynamited the school to prevent the spread of fire that was ravaging the city immediately after the quake. The present building, a broad-shouldered structure with a mansard roof, was built on the foundation of the earlier building in 1907, and operated as a school until the early 1980s. The idea to convert the old school into low-income housing came from the Sisters of Notre Dame themselves in the 1980s, but the idea was slow to catch. "In the early stages, everyone in the city thought it was crazy. I thought it was crazy," said Barbara Gualco, who later became project manager. Cost was an obvious concern: Converting the old school into housing meant partitioning the old classrooms into separate apartments, and Gualco acknowledged that adaptive reuse would cost only a little less than new construction. Eventually, however, the nonprofit became convinced that the project was feasible, and work began in 1996. Financially, Notre Dame Plaza is unusual among low-income housing projects in California, because it makes use of neither redevelopment housing set-aside money nor historic-preservation tax credits. HUD's Section 202 Program provided $6.12 million in both construction and permanent financing. (The project applied three times for the federal funding before getting a thumb's up from the feds). A second HUD grant, this time a Rental Project Rental Assistance Contract, provided $5 million in rental subsidies over 20 years. Residents pay no more than 30% of their income in rent. One resident is paying $150 in a district where comparable market-rate units are going for as much as $1,000. Additionally, the Mayor's Office of Housing provided a deferred loan of $4.74 million, which was funded by the city's "bed tax" on hotel rooms. "One of the joys of doing business in San Francisco is that the city has a huge commitment to housing," Gualco said. Although the project is not technically historic preservation, the building is a designated landmark, and the State Office of Historic Preservation took an active interest in both the building and the archaeological importance of the site. The state agency made an agreement with HUD to excavate portions of the site during rehab. Eventually, the church-based nonprofit spent about $100,000 of its construction budget on archaeology. The dig, as it turned out, was unexpectedly productive. The site yielded plentiful artifacts of the mission and the Spanish occupation of California, particularly the little-documented lives of Native Americans who lived and worked at the missions. Prior to the padres, a band of Chutchui Indians had lived on the spot. Archaeologists found glass tools dating back to the 18th Century, which demonstrated that the Spanish had forced the Native Americans to abandon their traditional stone tools and adopt European-style implements of iron and glass. Researchers also discovered a stone-and-adobe wall, identical to the walls of the original mission. By the early 19th Century, several thousand Native Americans from several tribes lived on the site. After the secularization of the mission in 1833, however, the community quickly disbanded, and the Mission area became a sort of Gold Rush-era urban entertainment zone: A bear-and-bull baiting ring stood on the current site of the Notre Dame Plaza, before the nuns and their students arrived. Archaeology and construction are not a natural mix, and the potential for conflict is great. In this case, however, the contractor and the archaeologists were mutually cooperative: the contractor re-arranged his construction schedule to accommodate the archaeologists. Construction ended about a year ago, and in April, the state historic-preservation agency nominated Notre Dame Plaza for the National Trust/HUD Secretary's Award for Excellence in Historic Preservation. Luckily, most affordable housing projects do not bear the weight of history as intimately as Notre Dame Plaza. Still, it is pleasing to think that the project was the vehicle that allowed the earth to speak, as it were, and divulge some ancient secrets. More to the point, perhaps, the old convent school has provided affordable housing in a city with rapidly rising rents and a high housing deficit. And this old building, which has seen disaster and prosperity and decline, will now be around to witness another century of stories in the historic core of San Francisco.