Violence has flared in Oakland, California, after a white ex-police officer was convicted on a lesser charge for shooting dead an unarmed black man.
Johannes Mehserle was found guilty of involuntary manslaughter.
He shot Oscar Grant in the back on the subway on 1 January 2009, while attempting to subdue him after a fight.
The BBC's Peter Bowes in Los Angeles says it was one of the most racially divisive trials in recent history.
After the Los Angeles jury rejected charges of murder or voluntary manslaughter a crowd of about 500 people marched in protest in Oakland at the outcome of the trial.
Later sporadic violence broke out in the town with rioters damaging shops, cars and setting fires.
Police in Oakland made 83 arrests during Thursday night for such offences as vandalism, assaulting a police officer and failure to disperse.
Mobile phone footage
Mehserle had told the Los Angeles court that he had mistaken the pistol for an electric Taser weapon on his belt.
The incident, recorded by onlookers on their mobile phones, sparked a period of violence, with protesters clashing with police and rioters setting cars ablaze and damaging businesses.
The trial was moved to Los Angeles because of the tensions in Oakland.
Speaking after the jury's finding, California Governor Arnold Schwarzenegger called on state residents "to remain calm in light of the verdict and not to resort to violence".
Mehserle, 28, faces years in prison. He will be sentenced next month.
He resigned from the 200-member Bay Area Rapid Transit (Bart) police force soon after the shooting.
The Bart system serves cities in the San Francisco Bay area.
On the night of the shooting, police officers identified Grant, a 22-year-old African-American man, as a participant in a fight on a train.
Mehserle and another officer attempted to subdue him, and Mehserle testified that he saw Grant digging in his pocket and feared he had a gun.
He told the court he had intended to use an electric Taser weapon but mistakenly pulled and fired his duty handgun instead.
Grant had recently been released from jail after serving time on a gun possession charge.
Mehserle fled to Nevada following the shooting and was arrested about two weeks later.