San Francisco park workers and volunteers spent much of Sunday picking up and hauling away 10,000 pounds of garbage strewn all over the eastern part of Golden Gate Park known as Hippie Hill, the remnants of Saturday's annual yet unofficial pot-smoking bacchanalia.

But this year's annual celebration - which falls each year on April 20 and is known as "420" - drew a larger-than-average crowd of between 10,000 and 15,000 revelers on the warm weekend day. They proceeded to smoke, drink, eat and rack up more than $10,000 in costs for city crews to clean up the mess, ironically just before Earth Day.

Even by early Sunday afternoon, mounds of empty bags of chips, candy wrappers, snack containers, plastic cups, bottles and other debris still remained to be picked up, the fallout of what appeared to an enormous, collective case of the munchies.

Dan Kling, a nearby resident who was playing in the park with his 2 1/2-year-old daughter Sunday, was disgusted. Kling, 39, said he didn't have an issue with the event, just with what was left behind.

"If you can't be responsible for yourselves, you can't have a party," he said.

The April 20 countercultural event supposedly has its roots in the early 1970s in San Rafael, where a group of pot-smoking teenagers used to gather and get high at a designated meeting spot at 4:20 p.m. Now various unofficial 420 celebrations are held throughout North America.

Significantly larger crowd

While 420 celebrations have drawn people to Golden Gate Park in the past, city officials acknowledged that Saturday's crowd was significantly larger than in recent years.

"The nice weather and fact it (fell) on a weekend worsened the situation," said Connie Chan, a spokeswoman with the San Francisco Recreation and Park Department.

Despite the large number of people city officials know will gather every year on April 20, the city does not provide any additional garbage cans or portable toilets for the event. Unlike sanctioned activities such as Bay to Breakers or the Outside Lands Music and Arts Festival, the April 20 smoke-in lacks official organizers or any permits for those amenities.

"Permitted events are well organized and planned much in advance with multiple city agencies to ensure public safety and patron enjoyment," Chan said.

Still, extra police officers are called in, and additional services, such as ambulances, are needed.

"It's almost completely unmanageable. There are no officials you can contact to deal with things so that's a frustration for us," said Lt. Simon Silverman of the San Francisco Police Department's Park Station, located near Hippie Hill. "The people paying for all of this are going to be the taxpayers, so it's not without cost."

Volunteers help clean up

Many other unofficial events - like spontaneous gatherings for July Fourth - can draw hundreds if not thousands of people to parks. But July 4 activities do not typically involve as much excessive drug and alcohol use as the April 20 festivities, Silverman said.

Still, Silverman described Saturday's activities as relatively smooth and free from violence, other than a robbery and the numerous ambulances called for medical problems related to the drugs and alcohol. He said issuing tickets for littering or other infractions would have overwhelmed the department's resources.

In addition to city employees, many volunteers, some of whom had been giving the park extra attention for Earth Day, helped with the cleanup. And some of those helping to clean up had attended Saturday's 420 celebration.

Amir Holmes El of San Francisco spent the whole day at the event on Saturday and came out Sunday morning to lend a hand. He said the event was joyous and peaceful, but acknowledged the aftermath was a mess.

"There was so much garbage, you'd swear we'd just had Woodstock," he said.

Victoria Colliver is a San Francisco Chronicle staff writer. E-mail: vcolliver@sfchronicle.com Twitter: @vcolliver