SAN FRANCISCO (KPIX 5) – Crews were out in force at Golden Gate Park early Thursday morning, cleaning up trash left behind by thousands of marijuana smokers who converged on Hippie Hill for the annual 420 celebration.

Workers with the Recreation and Park Department arrived at 6:00 a.m. to continue a cleanup that began after the so-called “Smokeout” ended. While the celebration was mostly peaceful, revelers left behind 22,000 pounds of garbage. Earlier estimates ranged from 10,000 pounds to 15,000 pounds of trash.

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“Not exactly a leave no trace moment out there,” San Francisco Recreation and Park Department manager Phil Ginsburg told KPIX 5.

Ginsburg said his crews were out there until 10:00 p.m. Wednesday night.

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In what has become an annual tradition, at least 10,000 people gathered to smoke pot on Hippie Hill, despite the park’s smoking ban.

The celebration was not without drama. Around 6:00 p.m. Wednesday, a stampede broke out after witnesses said someone pulled out a gun. A separate armed robbery was also reported.

“We definitely have public safety concerns…SFPD had 30, 40 officers out here, we had our entire park ranger unit out here. So we’re very relieved that the event ended safely,” Ginsburg said.

Like last year’s event, the cleanup will be costly. “It’s a mess out here, and I have 40 people working out here this morning. This will cost the city $100,000. Probably by the time we’re done, this will cost my department $30,000 to $50,000 in staff time,” Ginsburg said.

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“To put that in perspective, we can send one kid to summer camp for a week, for free, for about $300,” the Recreation and Park director went on to say.