Investigators determined that arson caused a wildfire that has burned more than 21 square miles of grass, brush and timber in northeastern San Diego County, the California Department of Forestry and Fire Protection said Wednesday.
No further details on the cause would be released until the investigation into the week-old blaze was completed, the agency said in a statement.
The fire slowed its advance Wednesday into the backcountry, but hot weather and low humidity still posed a challenge for firefighters trying to surround it.
The fire was 65 percent contained after burning 14,100 acres on the Los Coyotes Indian Reservation and Anza Borrego Desert State Park. No homes were threatened.
More than 2,100 firefighters were on the scene, aided by 18 bulldozers and 27 aircraft. Twelve firefighters have sustained minor injuries since the blaze began, mostly heat exhaustion.
The fire was burning east and northwest through steep, rugged terrain.
A statement from the California Department of Forestry and Fire Protection said the fire's spread to the east had slowed considerably, while the northern portion continued to burn in heavy vegetation through an area with no known fire history.
The blaze was not expected to threaten any structures or populated areas, but winds could send smoke into the eastern Coachella Valley and the community of Borrego Springs.
About 500 miles to the north in Calaveras County a wildfire burned 83 acres and forced the temporary evacuation of three homes east of the town of San Andreas.
The fire was reported Monday in an area of rocky hills and heavy brush about 50 miles northeast of Stockton. It was fully contained late Wednesday.