Aided by cooling temperatures and rain, firefighters battling the massive Springs fire in Ventura County have the blaze 80% contained, the Department of Forestry and Fire Protection said Monday.

The fire has burned 28,000 acres and is expected to be fully contained by Tuesday.

At its peak, the blaze threatened some 4,000 homes, authorities said. Fifteen houses were damaged but none were destroyed. Five firefighters and one civilian suffered minor injuries.

PHOTOS: Springs fire

The blaze was started by a small, "undetermined roadside ignition of grass/debris" and not thought to be the result of arson, authorities said Sunday.

The fire started at the edge of southbound Highway 101 near Thousand Oaks, about a quarter-mile north of the truck scales on the Conejo Grade, according to Cal Fire.

"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," the state fire agency said in a statement.

The fire erupted Thursday and quickly gained momentum, burning all the way to the Pacific Ocean. But the weather changed dramatically Saturday, with lower temperatures and high humidity helping firefighters.

On the western outskirts of Thousand Oaks on Saturday, as fire crews attempted to use controlled burns in an effort to ensure containment of the blaze, residents in nearby neighborhoods watched from their properties.

The potential for a devastating blaze became clear early in the week, when Cal Fire authorities and meteorologists determined that ominous weather patterns were setting up over Southern California: Hot Santa Ana winds, unseasonably high temperatures reaching the 90s and low humidity.

Cal Fire authorities dispatched hundreds of firefighters from across the state to Ventura County. Firefighters and additional ground personnel were also deployed from Oregon, Arizona, Idaho and New Mexico.

"We knew big fires were imminent; we just didn't know where," Cal Fire Battalion Chief Nick Schuler said.

At the peak of the fire, more than 1,800 fire personnel were on the scene. But late Saturday, fire officials began releasing some engine companies and all mandatory evacuations were lifted.

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