In the early 1970s, at the height of the struggle to stop development of San Bruno Mountain, activists climbed Sign Hill  on a full moon night and changed the South San Francisco letters to: "Save San Bruno Mountain. No Industrial City."

Members of the Save San Bruno Mountain Committee also baked a cake in the shape of the expansive mountain inviting city officials to cut out a piece and brought out a billy goat to a San Mateo County Parks and Recreation Commission meeting to make their point.

The documentary "Butterflies & Bulldozers" depicts these humorous tactics as part of a landmark environmental struggle over the largest undeveloped landmass in an urban area in the United States.

The South San Francisco Public Library and Historical Society of South San Francisco hosted a screening of the film Thursday night at the Municipal Services Building.

The film features David Schooley and Fred Smith, who once fought side by side against the bulldozers, but later parted ways.

Schooley said he hopped on a Greyhound Bus and got off at the first stop south of the city to discover the mountain where he has led interpretive tours since 1969.

"It's a really special place," Smith said in the film. "This mountain kind of gets under your skin."

The location of a landfill on the waterfront near Brisbane kept developers away from San Bruno Mountain during the first half of the 19^th century, but houses started to sprout up on the hillsides outside Daly City, inspiring folk singer Malvina Reynolds to write her famous song, "Little Boxes."

In 1960, the Crocker development proposed to flatten the mountain and build a whole new city on top. Although this project never gained ground, the Visitation Rancho development was next on deck, sparking the formation of the Save San Bruno Mountain Committee.

The film shows black and white photos of committee members and old news articles.

In 1976, the San Mateo County Board of Supervisors approved a compromise plan that allowed development of some sections of the mountain in exchange for preserving the majority of it as open space. Smith saw this is a victory but Schooley didn't want any development.

The discovery of several endangered butterflies, including Mission Blue and Callippe Silverspot, complicated matters. This led to the country's first habitat conservation plan, allowing development of some critical habitat in exchange for money to ward off invasive species.

Schooley argued against the plan: "You can't compromise and play games with something that is so living and real," he said. He split from the committee and formed San Bruno Mountain Watch.

Smith got elected to the Brisbane City Council and later became mayor.

The two men also differed about a hermit named Dwight who once lived in a shelter on the mountain. Smith wanted him out while Schooley led tours to his hut.

Toward the end of the film, Schooley claims that the habitat plan had little scientific study behind it, while Smith admits that the plan didn't provide enough money to deal with invasive and native species that are taking over the butterfly grassland habitat.

After the screening, filmmakers Ann and Steve Dunsky answered questions from the audience.

Ken McIntire, executive director of San Bruno Mountain Watch, said his organization is still adamantly opposed to the habitat conservation plan.

"We feel that the film didn't go into the rational reasons for not going along with that compromise," McIntire said. "It's not just a matter of principal and moral backbone that David obviously has."

Steve said they didn't take a position in the film and tried to present a variety of viewpoints. The unifying theme was compromise, which he said typically isn't explored in environmental documentaries.

"What I found was most compelling is these two men, who have both dedicated their lives to saving this mountain," Ann said.

Valerie Lambertson, a South San Francisco resident, said she remembered seeing front-page articles about the conflict.

"This was like catching up on a story that I knew of many years ago," Lambertson said.