The Springs fire, which started last Thursday in Camarillo south of the 101 Freeway burned 24,251 acres, according to the California Department of Forestry and Fire Protection.
Earlier estimates put the fire's damage at 28,000 acres.
The fire is 95% contained and should be fully under control Thursday, according to the Cal Fire website. Small fires reignited within the footprint the blaze made across the Point Mugu and Newbury Park mountains and vegetation-filled hillsides.
Nine people, including eight firefighters, suffered minor injuries in the blaze.
Although the cause of the fire remains under investigation, officials said Sunday that they had ruled out arson and instead believed the blaze was started by a small "undetermined roadside ignition of grass/debris."
"The area is considered a collection point for fuels and ignition sources. Due to the topography, the fire quickly spread, fanned by strong east winds," Cal Fire said in a statement.
A spell of cool, wet weather over the weekend helped firefighters regain the advantage over the blaze.
At its peak, the fire threatened about 4,000 homes, authorities said. Fifteen houses were damaged but none were destroyed. Ten storage sheds and barns were destroyed.