The protest against the war in Vietnam and La Raza in Los Angeles on August 29, 1970 was broken up by armed police who attacked the crowd and then just kinda' went crazy. A popular liberal Chicano journalist named Ruben Salazar was murdered by police. Hunter S. Thompson, who was hanging with his friend and attorney Oscar Zeta Acosta (later known as Dr. Gonzo), wrote a great piece about the protest that appeared in Rolling Stone in 1971....here is a link (there's a pdf you need to click on to read the piece)
Oscar Zeta Acosta wrote an entire book about the protest and the movement. That book is titled The Revolt of the Cockroach People.