SIMI VALLEY, Calif. - As many as 10,000 Fourth of July revelers were just settling into their seats for the fireworks show at a Simi Valley park when a bright plume of red and white bursts spread across the ground, injuring 39 people and sending others fleeing for safety.
Police in the city northwest of Los Angeles were still investigating what caused Thursday night's explosion. While the cause was still unknown, they had earlier said it appeared a firework detonated prematurely in its mortar, knocking over a row of others.
A view of the scene from a distance Friday morning showed groups of mortars held vertically in box-like wooden structures sitting on the ground. In front of them, a number of mortar tubes lay horizontally scattered on the ground. Cellphone videos captured fireworks exploding in spheres of sparks close to the ground, amid smoke and people screaming.