Is it a secret getaway tunnel from the Wild West? An early 20th-century conduit for electrical cables? Or maybe a funky sewer line built in the 1970s?
Everyone, it seemed, had a pet theory about the mystery tube that was unearthed last week and appeared to run on a subterranean collision course with the future site of the Jewish Museum San Francisco.
Construction crews discovered the immense wooden tunnel while digging a deep hole for a four-level underground parking garage that will be built under and next to the Jessie Street museum.
At first, a hard-hat worker mistakenly thought that he’d uncovered the wreckage of a Gold Rush-era ship. Days later, it was still unclear exactly what he’d dug up.
“We will find out what it is,” pledged Allen Pastron, president of Archeo-Tec, an Oakland-based archaeology firm hired to study the site.
Believed to be made of Douglas fir, the tunnel measures 12 feet in diameter and looks like an enormous barrel lying on its side in the sandy pit.
It rests about 20 feet deep and heads in the direction of the historic Pacific Gas & Electric Co. substation where the Jewish museum will be built. The building’s towering brick walls are being braced by metal poles during the excavation process.
Unlike the substation, the tunnel is “hardly an architectural gem,” Pastron observed. He proclaimed its construction as “rather haphazard.”
So far, nobody knows how far the tunnel goes. Because the tube was filled with sand and of questionable construction methods, workers refrained from venturing inside.
“There’s no way OSHA in a million years would give its blessing to that kind of structure and let someone go in there,” said Pastron, who was initially skeptical of speculation that the tunnel was a sewer pipe from the 1970s.
After giving Pastron’s archaeologists a chance to study, measure and videotape the thing, workers demolished the 31-foot section they had unearthed.
Shortly before noon last Friday, the powerful shovel of an excavator smashed the tunnel’s wooden slats like so many match sticks. The result was a loud crunch.
“Ah. This is always the part of these jobs I don’t like so much,” said Pastron, as he watched — and listened — up on ground level near Mission Street.
Two young archaeologists on his staff scrambled into the hole to retrieve a section of metal banding and a couple of slats of wood. Both the glint of the metal and an ink stamp from a Cloverdale lumber mill suggested that the structure might be relatively recent after all. Some pieces of wood examined earlier bore the numbers 1972. That could either refer to a date, an address or some other coding, Pastron said.
The archaeologists planned to consult with wood experts at U.C. Berkeley and pore over historical records to uncover the tunnel’s vintage and raison d’etre.
Noting that a paved parking lot had rested at the site since the 1960s, Pastron questioned why anyone would spend the money to bore underground to build “something that’s that shoddy looking.
“There still are a number of unanswered questions,” said Pastron.
Even if the tunnel isn’t historic, the lot where it’s located is, according to the archaeologist. Back in the 1850s, a quartet of cottages known as Howard’s Row sat on the South of Market spot.
Peering down at the tunnel before it met its demise, Pastron estimated that salvaging the structure would cost well into the “seven figures. I don’t think it’s that significant, whatever it is.”
As for theories of a purpose as a clandestine tunnel for 19th-century bandits, Pastron was dubious. “Secret tunnels don’t look that that. It’s too big. It’s too well built,” he said.
On the other hand, “it’s too crummily built to be some expensive public works project.”
Whatever it is, the tunnel will soon be history as crews continue digging out the underground garage. It is being financed with $43 million in bonds by the San Francisco Redevelopment Agency and New York-based Millennium Partners.
Slated to be completed next fall, the project will also create a plaza and new foundation for the Jewish Museum.
The museum itself has been stalled by a fund-raising campaign that fell far short of an original $100 million price tag.
Connie Wolf, the museum’s director and CEO, said board members will discuss the project’s future at a retreat later this month. Renowned architect Daniel Libeskind remains committed to working on the museum, she said.