Investigators on Thursday confirmed the cause of the Casner Fire near Ramona that forced evacuations and grew up to 180 acres.
Cal Fire told NBC 7 that the fire was caused by a tractor that was clearing brush and hit a rock creating a spark that created a fire that the tractor driver could not control.
The Casner Fire began burning at around noon Wednesday near eastern Ramona, close to where state Route 78 intersects with Casner Road.
Multiple structures were threatened and nearly 20 homes in the area were temporarily evacuated but no homes were damaged, according to the CHP.
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On Thursday, firefighters continued to cut a containment line around the blaze and temper any hot spots that remained. The effort was expected to last throughout the day, Cal Fire said. Containment of the blaze was 70% by Thursday evening.
When the fire started, a large plume of smoke was visible likely from miles around. At least one fixed-wing firefighting aircraft was making water drops on the blaze.