Rodrigo Lopez identified the boy as his son, Andy, to a newspaper and said the young teen was carrying a toy gun that belonged to a friend.
After spotting the boy, the deputies called for backup and repeatedly ordered him to drop the gun, O'Leary said in a news release. It wasn't clear whether he pointed the replica assault rifle at the deputies or made any type of threatening gesture. The sheriff's office referred calls to the Santa Rosa Police Department, which did not immediately return a call for comment.
O'Leary said the deputies fired several rounds from their handguns immediately after issuing the orders to drop the rifle.
A neighbor in the area, Brian Zastrow, told the Santa Rosa Press Democrat (http://bit.ly/1eJymxx ) he heard seven shots.
"First, I heard a single siren and within seconds I heard seven shots go off, sounded like a nail gun, is what I thought it was," he said.
The boy fell to the ground on top of the rifle, according to O'Leary. He said the deputies ordered him to move away before approaching him and putting him in handcuffs.
They began administering first aid and called for paramedics, who pronounced him dead at the scene. Deputies also found a plastic handgun in the boy's waistband, O'Leary said. The deputies, who have not been identified, have been placed on administrative leave, which is standard after a shooting, O'Leary said.
Community members left candles, teddy bears and flowers at the edge of the field where the teen was shot and questioned deputies' decision to open fire.
"I'm sure you can tell he's a 13-year-old boy," Abrey Martin told KGO-TV. "He's not some maniac."
Rodrigo Lopez told the Press Democrat he last saw his son Tuesday morning.
"I told him what I tell him every day," he said in Spanish. "Behave yourself."
The family was back at their mobile home Tuesday night after identifying the boy's body, the Press Democrat reported.
The newspaper quoted the boy's mother, Sujey Annel Cruz Cazarez, as saying, ""Why did they kill him? Why?"
Andy Lopez was an eighth-grader at Lawrence Cook Middle School, where assistant principal Linsey Gannon said he played trumpet in the band.
"Andy was a very loved student, a very popular, very handsome young man, very smart and capable,'" she said Wednesday. "Our community has been rocked by his loss."
Information from: The Santa Rosa Press Democrat, http://www.pressdemocrat.com