A brush fire that sparked Monday near San Pasqual Road at State Route 78 was first thought to be arson but investigators are now saying that's not the case.
The San Diego Metro Arson Strike Team initially said they believed the fire was deliberately set.
On Tuesday, after interviewing several witnesses, arson investigators said the rim of a vehicle's tire threw sparks into the brush along the side of the road, sparking the fire.
The Cloverdale Fire started just before 3 p.m. Monday and quickly grew to 100 acres as it spread in an east-northeast direction, San Diego Fire-Rescue confirmed.
As of Tuesday afternoon, the fire was 65 percent contained.
"Multiple fires along the San Pasqual Valley corridor along wit multiple points of origin had the investigative team thinking intentional yesterday," SDFD spokesperson Mónica Munoz said.
The Rangeland Fire sparked Thursday near Rangeland Road and State Route 78 and burned 250 acres before it was fully contained by fire crews. At one point homes were in immediate danger, according to Cal Fire, but none was damaged.
The Pasqual Fire broke out amid a triple-digit heat wave in late July and scorched nearly 400 acres just east of the San Diego Zoo Safari Park.
One firefighter suffered a minor injury and was treated at the scene, SDFD said.
The San Diego County Sheriff's Department issued an emergency evacuation warning for the San Pasqual area near the intersection of San Pasqual Road and SR-78. The warning was lifted at around 8:45 p.m.
Evacuation warnings are voluntary, but residents should be prepared to leave if an order is issued.
An evacuation shelter was set up at San Pasqual High School at 3300 Bear Valley Parkway.
All lanes of SR-78 were closed between east of the San Diego Safari Park and Cloverdale Road, Caltrans San Diego said. Caltrans reopened the highway Tuesday at around 8 p.m.
The fire forced the San Diego Zoo Safari Park to close early.
"The Park is not threatened but we are exercising due diligence to protect animals, staff and guests," the Safari Park said in a tweet. The park said late Monday it would open as scheduled Tuesday morning.
No structures were threatened.
Wind, heat and the terrain are the main contributing factors in the spread of the fire, officials said.