Radar reveals San Francisco's buried Presidio SAN FRANCISCO State-of-the-art tools let archaeologists map original Spanish settlements in city

Sandra Massey examines artifacts unearthed during a week-long scientific dig on the Main Post of the Presidio in San Francisco, Calif., on Friday, Sept. 19, 2008. Sandra Massey examines artifacts unearthed during a week-long scientific dig on the Main Post of the Presidio in San Francisco, Calif., on Friday, Sept. 19, 2008. Photo: Paul Chinn, The Chronicle Photo: Paul Chinn, The Chronicle Image 1 of / 5 Caption Close Radar reveals San Francisco's buried Presidio 1 / 5 Back to Gallery

Archaeologists are using cutting-edge technology - including ground radar and laser scanning - to uncover vanished walls and dwellings of the original Spanish Presidio of San Francisco, one of the two oldest European settlements in the Bay Area.

The other is Mission Dolores, several miles away. Both were founded by Spanish missionaries and colonists in 1776, just weeks before the United States declared independence.

The present mission church was built in 1791, but the Presidio's original buildings have crumbled away, and the extent of the fort's original walls and outbuildings is a mystery.

The remains of some adobe walls in the former Army Officers Club date back to the 1790s, but the date of their construction is uncertain. "We don't know exactly how old this building is, to tell you the truth," said Eric Blind, an archaeologist with the Presidio Archaeological Lab.

The Officers Club, which was extensively remodeled in the 1930s, was on one side of a four-sided fort that when it was new marked the frontier of the Spanish empire, the edge of European power on the west coast of North America.

Under Pershing Square

There are written accounts, pictures and drawings of the fort dating from the late 18th century, but the real El Presidio of Spanish times lies under a couple of streets, a parking lot and lawn that rings Pershing Square, where the main flagpole marks the center of the Presidio as it was in U.S. Army days.

Archaeologists have been digging for years into the Presidio's past and have come up with more than 80,000 artifacts, buttons, bones, pieces of foundation, crockery - all the remains of 220 years of military occupation.

But only 2 percent of the original Presidio has been dug up to date. "It's still unexcavated and unknown," Blind said.

The archaeologists have figured out the extent of the first Presidio and a later and larger version put up in 1815, but what exactly is underneath is a bit of a mystery.

Blind has a good idea of what's there: foundations of houses, pieces of what the settlers left behind. He says there were more civilians than soldiers in Spanish days. Half of the members of the original expedition led by Juan Bautista de Anza to found a colony in San Francisco were under 14 years of age.

'Center of secular authority'

"This was the center of secular authority in the Bay Area from Sonoma to Santa Cruz," Bland said.

It also had a different purpose than the missions, which aimed to convert the native Indian people to Christianity. The Presidio was meant to hold the land and to be the center of a colony, like the English in Virginia or the Dutch in New Amsterdam.

"It's the birthplace of San Francisco," said Michael Boland, chief of planning and projects for the Presidio Trust, which runs the Presidio.

The trick is to find what's under the ground without digging everything up, said David Morgan. Morgan is chief of archaeology and collections at the National Center for Preservation Technology. "To remove it, you have to destroy it."

"We have to figure it out. Are we right? Do we have to tear up a whole plot to find out what's underneath?" said Blind.

So the Presidio archaeologists use radar and electronic devices to see under the ground.

Gopher volunteers

One of their searches this week was centered on a spot of green lawn about 30 feet southeast of the Presidio's main flagpole.

The spot was covered by green grass and a couple of gopher holes. "Volunteer archaeologists," Blind calls the gophers.

Wednesday, the archaeologists dug a hole 3 feet long by about 1 1/2 feet wide, like a surgical strike. Bingo! Under the lawn were some sandstone rocks, the foundations of some outbuildings of the long-ago Presidio.

"It was as if we had a jigsaw puzzle with a thousand pieces and we didn't know how it went together," Morgan said. "This," he said, "is now a piece of the puzzle."

"We are literally only scratching the surface," Blind said. The technology they are using is not new, but the application to digging the past is, Morgan said.

"Now we are using technology solutions to address preservation problems," he said.

Buried but not destroyed

One of the advantages of working to uncover the colonial Presidio is that, unlike other European colonies in American cities, the Presidio is mostly unchanged. "Manhattan grew up over Dutch New Amsterdam, but the city of San Francisco grew up away from the Presidio," he said.

So what is past is only buried, not destroyed.

The Presidio digs are also being used as a classroom to help other archaeologists learn cutting-edge techniques. It is also useful for archaeology students at Stanford, UC Berkeley, Sonoma State University and San Francisco State, which all have archaeology departments.

The presidio archaeology lab even has developed a course for grammar school kids, so they can understand California's roots.