The blaze was started when a tree fell onto a power line, according to the Ventura County Fire Department.
It was first reported in the Santa Clara River bed near the Santa Paula Airport just before noon Monday.
It was initially estimated at 3-5 acres but rapidly spread to at least 10 and then 174 within about three hours, with strong wind gusts in the area up to 35 mph.
By around 5 p.m., firefighters said they had stopped forward progress and determined the cause.
A secondary spot fire also burned near the Briggs Road interchange with the 126. The freeway remained open but the Briggs Road ramps were closed in both directions.
Evacuation warnings were issued for Shell Road east of the 126 to Todd Road.
South Mountain Road was also closed.
The blaze was named the Cornell Fire, for Cornell Drive.
While it spread quickly, the location in the riverbed and quick response by firefighters helped keep it in check as the flames ran out of fuel to burn.
Most of Southern California is facing an elevated fire danger Monday as strong Santa Ana winds return and humidity remains low. In some areas, Southern California Edison was turning off power to reduce the risk of fires starting from damaged power equipment.