The report focuses on the canyon's large population of Blue Gum eucalyptus trees, an invasive species originally imported from Australia.
Historical photographs show Glen Canyon was largely treeless in the late 1800s, when the land was used primarily as a dairy farm.
The eucalyptus trees were planted after investors believed the fast-growing species could be harvested for timber.
"And these people were so stupid, they didn't realize they were going to build railroad ties and use the wood for building, and it's worthless. It warps, it splits. it has no commercial value," said Rick Carell, a member of the Civil Grand Jury.
While the timber venture failed, the trees remained.
Today, their flammability is a concern for fire safety officials and grand jury members.
MORE: 600 goats graze Poplar Beach in Halfmoon Bay to reduce wildfire risk
"The leaves have a lot of oil in them, and so actually, if it's very hot, and it's been very, very dry, they actually explode, because it's highly flammable. And so, you can see here, look at all the debris right next to this road. So somebody throws a cigarette out into there, and you have a potential fire," Carell said.
Carell said assessments of the trees have raised additional concerns.
"They evaluated something like 427 eucalyptus trees and 80% of them, back in 2012, were in bad shape," he said.
Although CAL FIRE has repeatedly rated San Francisco's wildfire risk as low because of the city's cool, foggy climate, the grand jury report points to the 2025 Pacific Palisades fire in Los Angeles as an example of how fires can occur in urban areas where vegetation management is inadequate.
The report notes that Glen Canyon has only two fire hydrants, one near the Glen Park Recreation Center and another near a day camp building.
However, San Francisco's Emergency Firefighting Water System provides additional resources through reservoirs, high-pressure hydrants and underground cisterns.
One nearby cistern at Chenery and Surrey streets can supply 75,000 gallons of water. Based on a fire engine's typical pumping rate of 1,500 gallons per minute, that amount of water would be exhausted in about 50 minutes. Additional cisterns are located in surrounding neighborhoods.
MORE: CAL FIRE urging Bay Area residents to create defensible space as wildfire season begins
Despite the concerns, the report concluded that removing all eucalyptus trees is not a practical solution because of the canyon's steep terrain. Large-scale removal could increase the risk of landslides. Instead, the report recommends managing vegetation by clearing brush and fallen debris and removing diseased trees.
"To remove any brush that might be a fire hazard, if something could really ignite quickly. We're going to raise up the branches, the lower branches of the tree because that's where a lot of the problem is for the spread of the fire, and if there are any dead trees that are really hazardous or branches that may hang over the roadway, that we can take them out as well," said Rachel Gordon of the San Francisco Department of Public Works.
Public Works officials are expected to coordinate closely with CAL FIRE on vegetation management efforts.
"CAL FIRE guys, they train in the type of environment, and so what they do, they get their chainsaws out, they eliminate. They limb the trees, they bring out the debris and that sort of stuff so this is an ideal training site for them," Carell said.
The San Francisco Public Utilities Commission, which manages a small portion of the canyon, has already removed trees on its property to prevent them from falling across O'Shaughnessy Avenue, a potential emergency evacuation route.
The agency has also hired habitat experts to remove non-native vegetation and replace it with fire-resistant native species, including coast live oaks.
"That has all these tannins in the foliage that resist fire. You can put a lighter right under that thing in the middle of the hottest day of the year, and it will not burn like these willows. They will not burn, and so that's what we want to load our parks with instead of having things like the eucalyptus and the pine -- which, as we all know, they just burn like a crazy Christmas tree fire," said Habitat Specialist Josiah Clark.
The majority of the 66-acre canyon is managed by the San Francisco Recreation and Parks Department, which agrees that improved coordination among city agencies is essential to maintaining fire safety in the area.