People have been toking up in the Cow Palace parking lot for more than 50 years.

This was the first time it was legal.

The International Cannabis and Hemp Expo, the first trade show in the United States to allow on-site pot smoking, attracted an estimated 15,000 enthusiasts to Daly City over the weekend. They talked bud, sold products ranging from a $500 water bong to a $19,500 mobile grow house, and discussed how efforts to legalize marijuana would impact their livelihoods.

"We're exercising our rights as patients to peacefully gather," said Bob Katzman, chief operating officer of the expo, as he stood near the designated puffing area. "We're here to talk about changing some of the existing laws, but we're not here to break the law."

Katzman said it took organizers four years to negotiate a permit with a venue that would allow marijuana consumption. It wasn't possible, he said, until a "massive change in the political climate."

That climate is set to be tested in November, when an initiative that would legalize marijuana is to be decided by California voters. Now, marijuana is available only to those with a medicinal use card.

Such cards were easy to attain at the exposition.

For $99 - cash only - attendees such as Shawna Spencer of San Jose received a temporary "recommendation" from doctors that allowed her to smoke at the event. Spencer, who said she suffers from bipolar disorder, said she had waited for more than an hour.

"It's worth the wait because I need it," Spencer said.

Dr. Daniel Susott said he expected to sign off on 1,600 people by the end of the weekend. He said a portion of the fees would go to charity.

"We're making history today," he said as his visitors complained of chronic pain, depression and insomnia, among other ailments. "We're operating within the guidelines of Prop. 215 and helping people get the medical marijuana they need."

If marijuana becomes legal, Susott expects that his patients will self-prescribe.

"People will start growing their own medicine in their homes," he said. "And the big pharma companies aren't going to like it."

For those concerned with the conspicuous equipment needed to grow plants inside the home, Tim Ellis of Orange County had the solution: An 18-foot trailer that can yield up to 6 pounds of pot every two months. The Grow n' Mobile starts at $19,500.

Ellis, a father of two, said he had the family grower in mind - a person who desires to cultivate outside the house, but in a secure location.

Showing off every detail of his invention, Ellis said he rigged the trailer's hitch so thieves would need a blowtorch to hook the trailer to their own truck. Fumes are routed through a charcoal filter. And the roof has an infrared shield to thwart weed-hunting helicopters.

"Can't steal it, can't smell it, can't find it," Ellis said, offering his sales pitch. "Built by a grower for a grower. Grow mobile!"

The event hosted a panel discussion Saturday on how legalization would impact large California growers. A contingent from Humboldt County argued against the ballot initiative, complaining it could devastate a key local industry.

"Radical" Russ Belville, the outreach coordinator for the National Organization for the Reform of Marijuana Laws, said that if California's initiative passed, he expected home-growers to enter the market and drive prices down.

But he was unsympathetic to the group from Humboldt County.

"To that end, I would say, 'Tough,' " Belville said. "We should have to put people in prison so you can continue to make a living?"