Protests in New York and Missouri have died down, but angry crowds in California spent much of the weekend blocking traffic and clashing with police in this ultra-liberal bastion thousands of miles from the where Michael Brown and Eric Garner were killed.

Although many activists in other parts of the country have gone home, protests in Berkeley and Oakland are still active, reflecting the area's long history of protest dating back to the 1960s and strict limits on local police powers.

The crowds that came out to protest in Berkeley numbered only a few hundred, but some are not college students or residents so much as full-time demonstrators who protest anything — war, prison conditions and economic inequality — and sometimes use demonstrations as a pretext for violence and vandalism, just as they did during the Occupy Wall Street movement.

Berkeley Mayor Tom Bates said a tiny fraction of protesters are obscuring the wider message calling for reform of policing policies nationwide.

"The people in the Bay Area are sensitive to worldwide issues," Bates said. "Unfortunately, there is a small element that uses violence at times to make their point."

Merchants on Monday cleaned up broken glass and took stock of the previous night's looting from downtown Berkeley stores.

Bates called the violent elements of the demonstration "cowards and thugs who need to take off their masks."

It was not immediately known how many businesses were damaged, and no damage estimate was offered. Five people were arrested, police said.

Aakash Agarwal, a sophomore at the University of California at Berkeley, witnessed the looting of a Radio Shack. He said about three dozen people cheered when the store's front window shattered.

"The whole peaceful protest thing went out the window," Agarwal said.

In keeping with the city's protest history, Berkeley leaders have put limits on their police. Officers cannot have search dogs, stun guns or helicopters and are restricted in the type of gear they can wear, said Berkeley police union President Sgt. Chris Stines.

"All of us are out there wearing what we wear on patrol, and as a result, we are getting pretty banged up," he said, explaining that shin and chest guards and padded vests would help prevent injuries. At least three officers suffered minor injuries.

Stines said he did not believe there was any "legitimate political message" behind Sunday's protest. "It was just criminal behavior."

The unrest is not limited to Berkeley.

Seattle police arrested seven people Saturday during a protest that included a group trying to block a state highway. Rocks were also thrown at officers and storefronts smashed. More protests were scheduled for Monday.

The protests started after a Nov. 24 decision by the grand jury not to indict officer Darren Wilson in the killing of Michael Brown. A New York grand jury on Dec. 3 declined to prosecute a police officer captured on video applying a fatal chokehold on Eric Garner. That decision set off another series of demonstrations nationwide.

Oakland police have arrested about 200 people since the protests started.

The Rev. Jesse Jackson said much of the violence can be attributed to an "organized element" of activists based on the east side of the San Francisco Bay who seek attention with rocks and bottles. He said he's disappointed that the violence obscures the efforts of the peaceful demonstrators.

Other issues such as University of California tuition hikes and general dissatisfaction with gender, race and economic inequality appear to be driving the Berkeley protests, he said.

Sunday's protest began peacefully on the University of California's Berkeley campus but grew rowdy and spilled into neighboring Oakland. Activists forced their way onto a freeway and blocked traffic, but officers chased them off, police said.

California Highway Patrol officers fired tear gas after protesters threw rocks and bottles at them and tried to light a patrol car on fire. Police also said explosives were thrown at officers, but it was unclear how potent the explosives were.

By late Sunday, groups of protesters were roaming through the downtown area, throwing trash cans into streets lighting garbage on fire, smashing windows and looting businesses, police said.

There also were reports of vandalism at Berkeley City Hall. A Whole Foods on historic Telegraph Avenue was looted, with people stealing bottles of champagne and passing them around the crowd.

Since last month's grand jury decision in Missouri, Seattle protesters have frequently gathered downtown and in the city's Capitol Hill neighborhood. Hundreds of people marched on police headquarters Saturday without incident, but later a group tried to block a state highway and hurled rocks at officers. Seven people were arrested.

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Associated Press writers Lisa Leff in Berkeley and Chris Grygiel in Seattle contributed to this report.