Oft-adorned with brightly colored signs wishing residents "Happy Birthday" or "Congratulations," the landmark tree holds a lot of significance in town.
"Ever since the '70s, people have kind of watched the tree, and in a lot of ways it became the symbol of Danville," said Beverly Lane, curator of the Museum of the San Ramon Valley and a member of the original Danville Town Council.
People estimate the old oak is around 350 years old.
Its location off I-680 makes it something of a gateway into town, said Assistant Town Manager Marcia Somers.
"If you're going to come from downtown, you're going to go by that tree," agreed Lane.
When Danville incorporated in 1982, the shape of the towering oak was used to create the town logo. Over time it became known for the signs people post on it, usually to give shout-outs to friends and family. Residents have hung yellow ribbons to honor the service of veterans during both Iraq wars.
"People have loved writing messages on the tree. Because of its location and its age, if you want to do a 'congrats,' people would notice it there," said Lane.
The town welcomes the postings, but with a few rules: Signs are supposed to be up for no more than 48 hours, and no soliciting or advertising is allowed. They must be hung on the steel frame, not the tree itself.
"It's a fairly informal process," said Somers.
Residents are expected to date the signs and be responsible for taking them down. If they're not taken down in time, the town will step in, and the maintenance department or code enforcement officers will remove the signs.
When inappropriate signs go up, residents often notice right away and take their complaints to the town. But usually the community is respectful about following the guidelines, Somers said.
The oak is also the site of Danville's annual tree lighting ceremony. Each year in November, hundreds of people gather near the tree to celebrate the popular tradition, which includes choral music and a visit from Father Christmas.
The ceremony began in 1976, after Diablo Road was widened to four lanes. However the widening of the road created some problems for the oak, too.
The tree stands in the median, surrounded by road on both sides. People became concerned the high traffic spot was stressing the old oak. In 2000, arborists gave weight to those fears, telling the town that the tree was unstable and unsafe for the public, because the roots were rotting.
"They do quite extensive readings of the health of the tree and what they found is there had been some decay at the root crown," said Somers.
That's when the steel structure was built to surround the oak. The 16-foot-high frame, mounted on six columns, circles the tree's trunk and branches to support it in its old age. The structure was erected in early 2001 and cost $70,000.
"We were concerned there might be some safety hazards potentially and so a number of options were looked at," Somers said.
The Town Council at the time also considered an alternative steel framework that would span all four lanes of Diablo Road to catch the tree if it fell. That solution was estimated to cost $150,000.
One council member even suggested taking the tree down, but residents banded together to preserve it. They formed the Support the Oak foundation and raised money toward the cost of the steel frame.
Today the tree still stands and still holds special significance for the community.
"It's really a gateway, you know, the main entrance into town," Somers said. "I think it holds a lot of positive memories as well as symbolism for people here in Danville."