What you see there is a flammagenitus cloud rising to the north above Ranch 2, a wildfire about fifteen miles east of here in the San Gabriel Mountains, just north of Asuza (one of too many towns to remember, in greater Los Angeles). If the video works, you’ll see how how the clouds give shape to the heat from the fire, even as smoke (darker and with a gray/magenta color) stopping at a lower elevation, spreads northward in the same direction.
The fire was caused by arson, says the guy who confessed to starting it.
It’s interesting to see how much reporting on fires has changed in the time I’ve been following stories like this in Southern California. Inciweb, the canonical close-to-live running catalog of wildfires in the U.S. has moved from the .org where it started to NCWG.gov, the National Coordinating Wildfire Group. When I first wrote about Inciweb, back in ’06, I didn’t mention that it was entirely the heroic work of one Linux hacker at the Forest Service who didn’t wish to be identified.