A 14-year-old girl was convicted Tuesday of setting the fire that burned nearly 2,000 acres and destroyed or damaged 40 structures in the San Marcos area in May 2014.
The fire raged from May 14 to May 22 and, at its height, was battled by more than 500 firefighters. It destroyed structures in San Marcos, Escondido and the Harmony Grove Spiritualist Assn. retreat.
The girl, tried as a juvenile, did not testify during the trial in San Diego County Superior Court.
Her name has not been publicly revealed and the media were warned by the judge not to show her face during the trial. Sentencing was set for April 15.
Judge Howard Shore, hearing the case without a jury, found the girl guilty of three felonies but concluded that she did not intend to start a fire that destroyed property.
Testimony by her mother and sister indicated that the girl admitted using a lighter in the family backyard to start two fires. She also confessed during interrogation by a sheriff's deputy while her mother was present, according to testimony.
Prosecutors argued that one of the fires sent an ember nearly a half-mile that ignited the Cocos fire. It caused more than $10 million in damage, officials said.
The Cocos fire -- named for a street near its origin -- was one of 20 that raged through northern San Diego County in May, driven by hot, dry Santa Ana winds. None of the other fires have been determined to have been arson.
The Cocos fire was investigated by the California Department of Forestry and Fire Protection, the San Marcos Fire Department, the Sheriff's Department and the federal Department of Alcohol, Tobacco, Firearms and Explosives.