A crisp coastal breeze sweeps up the slopes of San Bruno Mountain, a landscape with deep significance to longtime conservationist David Schooley.

For decades, he has fought to shield this rugged terrain from overdevelopment.

“I discovered San Bruno Mountain in 1969,” said Schooley, co-founder of San Bruno Mountain Watch. “And I found this incredible set of canyons. Shortly after, I learned they were about to shave off the top of the mountain and fill in the Bay. I was just horrified.”

Schooley was referring to a plan by the New York-based Rockefeller family to level the mountain’s peak and use the material to fill in parts of the Bay, creating an artificial island. The battle to stop the project helped launch what became the “Save the Bay” movement, leading to stricter regulations against landfilling and stronger protections for shoreline ecosystems.

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Decades later, the mountain remains vulnerable to development pressures.

Schooley, along with environmental advocates Tera Freedman and Del Schembari of the Mountain Butterfly Collective, has ramped up door-knocking efforts to alert the community about a massive proposed development they say could threaten endangered butterfly species.

The project in question is a 1.3 million-square-foot warehouse at the former quarry site — an eight-story structure that could employ between 800 and 1,500 people.

“The warehouse or distribution center project will introduce traffic, potentially at all hours of the day and night, along with light and air pollution,” the Sierra Club said in a statement. “It will also decimate critical wildlife habitat. The plan includes a new access road with regrading, causing erosion issues and the loss of many heritage and habitat trees. It could be a 24/7 operation.”

It remains unclear what the quarry will be used for. Plans such as data storage or a commercial distribution center are among some of the ideas.

San Bruno Mountain is an unexpected sanctuary in an area dominated by industry, commercial development, and the busy San Francisco International Airport. It is home to at least 14 rare or endangered plant species, as well as critical host and nectar plants for threatened butterflies, including the San Bruno Elfin, Mission Blue, Callippe Silverspot, and Bay Checkerspot — species found in only a handful of locations worldwide.

“This is it — there’s nowhere else,” Freedman said. “This is the last of it.”

Renowned biologist E.O. Wilson once described San Bruno Mountain as a “global biodiversity hotspot” and an area that should be protected.

In addition to butterflies, the mountain supports 195 species of birds, 13 reptile species, six amphibian species, small mammals, and rare insects such as the San Francisco Forktail Damselfly, according to San Bruno Mountain Watch.

Freedman said she first heard rumors about the development a year ago.

“I was outraged,” she said. “A big development group had spent years planning this. The information came out around 2021, and they’ve invested a lot of money to make sure they can get this through.”

The developer behind the project, Lafayette-based Orchard Partners Inc., did not respond to requests for comment. However, according to the project’s website, the overall property spans 144 acres. The proposal includes closing and reclaiming the quarry, as well as annexing about 104 acres into Brisbane’s city limits.

“Approximately 82 acres will be conserved habitat,” the developer states on its website. “That includes 36 acres of annexed land protected under a conservation easement, with an additional 46 acres offered for dedication to the county as open public space.”

John Swiecki, Brisbane’s community development director, said city staff is preparing the final environmental impact report before it goes to the planning commission and, ultimately, the city council later this year.

As of now, city staff has not taken a position on the project.

“There is no recommendation yet, as we are awaiting the final environmental impact report,” Swiecki said. “Threats to butterfly and plant species have been identified as potential impacts, but the developer has proposed mitigation efforts, including conservation and land dedication to the county.”

For conservation groups, the assurance isn’t enough. And their efforts to inform the public about the looming project seem to be working.

While a city council vote on the project is still far off, the public comment period for the environmental impact report has already generated nearly 400 pages of feedback, mostly raising concerns about its environmental impact. The comments are available on the city’s website.

Councilmembers have yet to state their position on the proposal publicly ahead of city staff’s recommendation.

For Schooley, who has dedicated most of his life to protecting the mountain, there is no room for complacency.

“Every 20 years or so, you think you saved it, and things are good, then suddenly you get hit again,” he said. “We’ll continue to go out and protect it in some other way.”