Tom Sawyer Island is a Disneyland attraction. While not as exciting as some of the other rides, the island was particularly appealing to some enthusiastic hippies.
These particular hippies were part of a political movement called the Youth International Party (Yippies), who were riding the anti-war, free speech movement of the 60s. They used a lot of theatrical gestures as a way of protesting and making social commentary. For example, they once had a Pig run for president to mock the status quo.
On August 6, 1970, nearly 300 members of the Yippies invaded the island as a form of protest. They hoisted the Viet Cong flag and marched down Main Street. Disneyland responded by calling the riot police. The park closed early for the first time in history.