The Watts Riots was a race riot that took place in the Watts neighborhood of Los Angeles from August 11 to 17, 1965, and that resulted in 34 deaths, 1,032 injuries, 3,438 arrests, and over $40 million in property damage. It was the worst riot in the city's history until the Los Angeles riots of 1992, and is considered by many to be a key turning point in the Civil Rights Movement.
The riots were sparked by the arrest of 21 year old Marquette Frye for reckless driving. The arrest took place blocks from his home, and his mother, when seeing her son forcibly arrested, began fighting with the police. During the arrest, hundreds of onlookers gathered to watch the fight, and rumors quickly spread through the neighborhood. By the evening of the following day, the neighborhood was in the grips of full scale rioting.
[Source: Wikipedia, http://en.wikipedia.org/wiki/Watts_Riots]