Local lore has it that the then-50-year-old prefabs in the Hollywood Hills into which fledgling nonprofit TreePeople moved in 1977 were once the offices of California’s most notorious eco-villain: William Mulholland. Unlike Mulholland, who diverted, dammed, and plundered California’s water supply in the 1910s and ’20s for the benefit of Angelenos (and their golf courses), Andy Lipkis, founder and president of TreePeople, has a take on greening L.A. that’s markedly more arboreal.

“By 1975 I had moved my nursery up to Coldwater Canyon, and in 1977 our offices got up there too,” says Lipkis. Taking up residence on the site of an abandoned fire station off Mulholland Drive, TreePeople has worked for the last three decades planting hundreds of thousands of trees around L.A., encouraging conservation, and serving as caretakers of Coldwater Canyon Park, a 45-acre urban forest replete with hiking trails, a tree nursery, and a brand-new, and highly green, conference center.

“Fifteen years ago we hired Marmol Radziner when they were just out of architecture school to design an off-the-grid campus on our site that would inspire people to live more sustainably,” says Lipkis. But like countless architectural projects, this one saw more delays than action. “Back when we started, green building was even more expensive than it is now, and we just never had the money to build everything. For the last five years we’ve been working out of yurts.”

Only TreePeople’s conference center, which was designed to fly through LEED certification, has been constructed. The structure employs numerous recycled and natural materials, including kitchen cabinets made of pressed sunflower seeds; a 225,000-gallon cistern located beneath the center catches rainwater and runoff and uses it for irrigation. With its rough concrete walls and canted roof marking a clear nod to SoCal modern past, it is not the least bit dated. The conference center makes a forthright aesthetic statement about its environs, but it’s the environment that’s really on Lipkis’s mind. “The plan was to build a really attractive beyond-LEED building so that then no one will have any reason not to build green.”