Santa Barbara County officials said they believe power tools were being used along the Jesusita trail between 10:30 a.m. and 1:30 p.m. May 4 and 5, the Los Angeles Times reported.
Cooler air in the region provided a boost for firefighters and the wildfire -- which has charred almost 9,000 acres, destroyed at least 31 homes and damaged at least 47 others -- was 55 percent contained by late Sunday.
"I think everybody could feel the difference," Tom Davis, the fire chief of Santa Barbara County, said after cooler air moved into the region late Saturday.
Firefighters said they expected the wildfire would be fully contained by Wednesday.
Most of the estimated 50,000 people who had been evacuated from their homes have been cleared to return home.
A fire in the same area destroyed an estimated 200 homes about six months ago.