A large crowd cleared out fast after reports of gunshots around 6:30 p.m.
Thousands of people gathered at Golden Gate Park to celebrate "420" on Sunday.
The date 420 has become an unofficial, annual event that is not sanctioned by the city.
The informal gathering held annually on April 20, brought pot smokers and weed vendors together for the day in the area known as Hippie Hill on the eastern end of Golden Gate Park.
San Francisco police officers were patrolling the Haight-Ashbury neighborhood, Hippie Hill and Sharon Meadow areas earlier in the day issuing hundreds of advisements to citizens.
Officials said the officers issue advisements when they see a violation and instead of arresting or citing an individual, advise the person to obey the law. Officers issued advisements for people for infractions such as carrying open containers of alcohol.
Shortly after 4:20 p.m., officials said that the crowds of marijuana smokers had just finished "their big smoke-off."
After the crowd dissipated, 35 volunteers with the Green Cross Medical Marijuana started cleaning up the park.
"We started picking up all the trash and make sure that what was reported on last year is not a repeat this year," Green Cross Dispensary spokesperson Kevin Reed said.
A huge mess was left behind last year. The city said it costs thousands of dollars and took days to clean up. There were also complaints that 420 partiers didn't behave too well as they left through the surrounding neighborhoods.
Reed said an event sponsored could keep that from happening again.
"People peeing in people's lawns as they get back to their cars because there weren't enough restrooms and I'm hoping in the future that the city sees the benefit and actually allowing someone to host an event like this," Reed said.
This is not a sanctioned event and there has been some question if the city can sign off on a day long party focused on what's technically recreational drug use by many attendees.
This year streets surrounding the Hippie Hill and Haight Street areas were blocked off to traffic, largely due to a bad traffic jam on Stanyan Street in 2013. Traffic this year was pushed into surrounding neighborhoods such as Cole Valley and Lone Mountain.
San Francisco Recreation and Park Department is spearheading the cleanup following the event with the assistance of the Department of Public Works.
Bay City News contributed to this story.
