DENVER — Once the province of activists and stoners, the traditional pot holiday of April 20 has gone mainstream in the first state in the nation to legalize recreational marijuana.
Tens of thousands gathered for a weekend of Colorado cannabis-themed festivals and entertainment, from a marijuana industry expo called the Cannabis Cup at a trade center north of downtown, to concerts at the Red Rocks Amphitheater that included Slightly Stoopid and Snoop Dogg.
A massive festival was held at Civic Center Park, in the shadow of the state capitol, with clouds of cannabis smoke wafting through the crowd. Revelers raised joints, pipes, and vaporizer devices to the skies in a defiant toast.
Public consumption of marijuana is still illegal in Colorado, and sales are regulated.
There were no mass arrests Sunday, but Denver police said they issued 37 citations, 31 for public consumption of marijuana and the rest for unspecified violations. A day earlier, they issued 21 citations for marijuana-related offenses and arrested one person accused of attempting to distribute the drug.
The park event is the most visible sign of the pot holiday’s transformation. It started as a defiant gathering of marijuana activists, but this year the event has an official city permit, is organized by an events management company, and featured booths selling funnel cakes and Greek food next to kiosks hawking hemp lollipops and glass pipes.
Gavin Beldt, one of the organizers, said the event is now a ‘‘celebration of legal status for its use in Colorado and our launch of an exciting new experience for those attending.”
Denver is just one of many cities across the country where 4/20 marijuana celebrations were held Sunday.
In Trenton, N.J., speakers urged a crowd of about 150 gathered at the State House to push state and federal lawmakers to legalize or decriminalize marijuana and called on Governor Chris Christie to do what he can to help medical marijuana patients.
Thousands celebrated in Washington, the only other state to legalize marijuana. Events included a Snoop Dogg show Saturday night as well as an event sponsored by Seattle’s Dope Magazine, with a $99 ‘‘judge’s pass’’ available that included 10 marijuana samples.
In San Francisco, Police Chief Greg Suhr said his officers would be cracking down on illegal parking, camping, drug sales, underage drinking, and open alcohol containers at Golden Gate Park’s Hippie Hill. Officials didn’t want the unofficial pot holiday to disrupt Easter activities in the park.
In Boulder, University of Colorado officials closed campus to all but students, faculty, and staff on Sunday to ensure no 4/20 celebrations were held.
Spokesman Ryan Huff said the tactic was working, with no arrests reported Sunday. The university says marking 4/20 is contrary to its mission of research, teaching, and learning, and in the past, has seeded a main lawn with fertilizer to keep revelers away.
On Saturday, the first day of a two-day festival in Denver, only a few people lingered on the steps of a Roman-style amphitheater where marijuana activists spoke angrily about bans on the drug in other states.
Thousands instead lingered on the park’s broad lawns, listening to hip-hop music blasting from the sound stage and enjoying the fresh, albeit marijuana-scented, air.
‘‘It’s a lot mellower this year,’’ said Cody Andrews, 29, of Denver. ‘‘It’s more of a venue now. More vendor-y.’’
While the weekend was for celebrating, recent events have brought serious scrutiny to Colorado’s experiment with legalizing marijuana. Denver police say a man ate marijuana-infused candy before shooting and killing his wife last Monday, an attack dispatchers heard during a 911 call the woman placed. Her death followed that of a college student who traveled from Wyoming to Colorado with friends for spring break, ate more than the recommended dose of a marijuana-laced cookie and jumped to his death from a hotel balcony in Denver.
State lawmakers are debating how to increase safety regulations.
Marijuana festivities got off to a slow start Sunday. But as the clock counted down to 4:20 and crowds surged into Civic Center Park, festivalgoers noted the big changes from previous years — more merchandise and more police.
The whole scene was wonderfully surreal for Bud Long, 49, from Kalamazoo, Mich., who recalled taking part in his first 4/20 protest in 1984.
‘‘Nationwide, it’ll be decriminalized,’’ he predicted, ‘‘and we’ll be doing this in every state.’’
The two recent deaths in Colorado have raised concerns about the recreational marijuana industry and the effects of the drug, especially since cookies, candy, and other pot edibles can be exponentially more potent than a joint.
Al Bronstein, medical director of the Rocky Mountain Poison and Drug Center, said the center is seeing cases of hallucinations, nausea, dizziness, and anxiety.
Studies are mixed about whether there is any link between marijuana and violence. Still, pot legalization opponents said the deaths are a sign of future dangers.
Twenty-six people have reported poisonings from marijuana edibles this year, when the center started tracking such exposures. Six were children who swallowed innocent-looking edibles, most of which were in plain sight.
Five of those children were sent to emergency rooms, and two to hospitals for intensive care, Bronstein said. Children were nauseated and sleepy, and doctors worried about their respiratory systems shutting down.