Investigators have determined that high winds carried a tree branch into a Department of Water and Power line, setting off an electrical arc and sending sparks to the ground that ignited the blaze.
The video from a car driving along the 405 Freeway shows a white electrical arc and explosion along the side of the road not far from the Getty Center.
Investigators say the video helped them pinpoint the cause and time of origin of the blaze.
They determined the blaze started around 1:30 a.m. Monday near the 1800 block of North Sepulveda Boulevard.
They say there was no evidence of arson or a homeless encampment in the area.
Fueled by dry terrain and strong Santa Ana winds, the blaze grew to more than 600 acres in less than 12 hours of ignition before firefighters were able to get the flames under control. They remain vigilant as the Santa Ana winds are expected to pick up again late Tuesday night.