Speaking to CNN affiliate KGO-TV, an eyewitness at Gilroy described fleeing the scene of the shooting with his 12-year-old cousin, who had been shot.
"We saw a hole in her leg and she was crying," he told reporters.
"She was hurting a lot," he said. "She was running fast -- that's why we didn't know if she got shot, she was running normally ... It was probably just adrenaline because she wanted to get out of that situation."
The girl has since been driven to the hospital, he said.
At least one person has died from the shooting, and at least 11 are injured, officials say.