And while these events have typically been the natural environment for the Birkenstock crowd, more and more are coming out for a different kind of green: cash. They want to save money and realize that a one-time investment in something like solar panels can often reap years of rewards.
Laura Ryan, Pleasanton's energy and sustainability manager, is glad that green is the new black.
"It's not a niche market any more. As people get involved in these things it drives prices down because of high demand. The economy being as bad as it is, that's even more of a motivation," Ryan said at the second annual fair at CarrAmerica on Rosewood Drive.
The fair featured much of what one would expect at this sort of event: people selling solar panels, electric bikes, motorcycles and chargers for electric cars, others from BART and other transit agencies and rideshare companies encouraging people to use public transportation or vanpool.
Companies offered everything from high-end water purifiers to whole home remodeling, banking on the idea that green thinking will mean black ink in their ledgers.
It also brought in some unexpected vendors. Nuubia Chocolat was a crowd favorite largely because of its free samples. The company, which recently opened on W. Las Positas Boulevard, sells chocolate that's green in attitude, not color, according to CEO Alexandra Saunders of Danville.
"My background is conservation and sustainability," Saunders said. "We have an environmental mission and we have a mission to produce the finest chocolate."
The company goes as far as buying only from dairy farms that treat their animals humanely and paper free of hardwood or rainforest fibers and using soy-based inks. It's also just been named best chocolate in the U.S.
Another local vendor was Rhonda Chase Design, a Pleasanton-based jeweler who recently began a line made from recycled materials like newspaper comics rolled and varnished into beads, cans cut and lacquered to create earrings and necklaces made from reclaimed bottle glass.
Chase said people are often obsessed with things that are brand new, like the latest phone.
"I've been working on ways of making my jewelry more environmentally friendly," she said. "I want people to have the idea that they can have something beautiful and functional without getting it new off the shelf."
Although 93 vendors were signed up to participate, along with a number of informational booths manned by Pleasanton staff, the rain forced a number to drop out.
Ryan estimated 87 vendors were in attendance. Thomas Cosgrove of Clean Energy Associates, who organized the event, said he expected between 500 and 600 people to show up, slightly fewer than last year, despite a last-minute push to let people know the event had been moved indoors.