Dozens of protesters walked across Interstate 880 in Oakland at the tail end of rush hour Monday evening, stopping traffic in both directions for several minutes. Several protesters laid their bicycles on the ground in front of stopped cars.
"You've got to go. You will go to jail," one police officer shouted at demonstrators who were blocking traffic, the Oakland Tribune reported. However, police decided not to make arrests as the marchers, chanting "Justice for Trayvon Martin," were directed back to surface streets.
The freeway protesters broke off from a larger group organized via social media that gathered at Oakland City Hall about an hour earlier. Several people were arrested while marching from City Hall, authorities said.
In Los Angeles, a group of several hundred mostly peaceful protesters gathered Monday night at Leimert Park southwest of downtown, many of them chanting, praying and singing.
A group of about 100 people splintered off and began blocking traffic on nearby Crenshaw Boulevard, some of them jumping on cars trying to pass, police said. There were no reports of any arrests.
Over the weekend, demonstrators in Oakland and Los Angeles blocked traffic and clashed with police in protests over a Florida jury's acquittal of neighborhood watch volunteer George Zimmerman in the shooting death of the unarmed black teenager.
LA Mayor Eric Garcetti called for peace and cut short an East Coast visit following police confrontations early Monday.
Police shot beanbag rounds and arrested six people—including one on suspicion of assaulting an officer—while breaking up relatively small demonstrations before dawn.
No injuries were reported to either demonstrators or officers.
Most demonstrations around the state were peaceful.
Democratic Sen. Barbara Boxer sent a letter Monday to U.S. Attorney General Eric Holder supporting the Justice Department decision to review the case to determine whether Martin's civil rights were violated.
"I respect the fact that the jury has spoken ... but I don't think this should be the last word," Boxer wrote in the letter.
"Trayvon Martin's death was a tragedy and has raised many sensitive and important issues," she wrote. "We should explore every avenue in an effort to ensure that something like this never happens again."