A witness said "It looked like Superman had thrown a car right off a bridge,"
Unfortunately the truck that fell from the sky into the festival at Chicano Park was no Hollywood stunt.
According to police reports, The truck was driven by Richard Anthony Sepolio, 25, a US Navy member who police suspect was drunk. Police say the vehicle jumped the guard rail and landed on a tent selling T-shirts.
The park was the end point for La Raza Run, a motorcycle ride from Los Angeles to San Diego that had started about 8am on Saturday.
The San Diego Tribune reported that up to 2000 bikers left downtown Los Angeles on Saturday morning headed for San Diego.
Motorcyclists and others arrived at Chicano Park about 12.30pm. By 3.30, a large crowd had gathered, looking at art and listening to live music.
On the freeway above about the same time, Sepolio was trying to get from a northbound lane onto Interstate 5, troopers said.
He lost control of the truck, which ran through a guard rail and plunged into the park.
The scene was "instant chaos and panic", one attendee told the Tribune.
Bystanders immediately rushed to lift the truck off those crushed underneath.