Ventura County Fire spokesman Tony McHale said the wet weather significantly reduced fire activity but also caused crews to work more slowly and methodically on steep rain-slicked hillsides.
There were no remaining open flames but firefighters continued to be on the lookout for flare-ups as they dug lines around the burn area, McHale said.
The blaze was 80 percent contained. Officials expect full containment late Tuesday.
Investigators ruled out arson as the cause of the fire that charred 44 square miles at the western end of the Santa Monica Mountains. Instead, they believed it was started by a small, "undetermined roadside ignition of grass and debris" on the edge of U.S. 101 near Thousand Oaks, said Tom Piranio, a spokesman with the California Department of Forestry and Fire Protection.
The area near an uphill incline is considered a collection point for fuel and ignition sources, and it's possible a piece of debris fell into the tinder-dry brush early Thursday and sparked the fire, Piranio said.
"The topography plus the hot, windy weather created a perfect storm for the fire to spread fast," he said.
At its peak, the fire threatened some 4,000 homes as it moved through neighborhoods of Camarillo Springs and Thousand Oaks. It damaged 15 homes.
Classes were in session again Monday at California State University, Channel Islands. The school, attended by about 5,000 students, was evacuated Thursday as flames neared the campus.
Eight firefighters suffered minor injuries while battling the flames.
The blaze was one of more than 680 wildfires in the state so far this year - about 200 more than average.
East of Los Angeles in Riverside County, a fire that burned 510 acres south of Banning was fully contained Sunday.
In Northern California, a fire that has blackened 11 square miles of wilderness in Tehama County was a threat to a pair of commercial properties near the community of Butte Meadows, according to Cal Fire.
Thunderstorms were expected to bring erratic winds but little rain to the area about 200 miles north of San Francisco.
Nearly 1,300 firefighters were on the lines and the blaze, which started Wednesday, was 60 percent contained.