A short [edit: long] summary for people who haven't heard
Beginning on Sunday, there was a very heavy system of Santa Ana winds (a name for the warm dry winds that come from the desert and head to the coast) that would last about 3 days. Officials had noted that these conditions would be identical to those of October 2003, when the Cedar fire burned over 700,000 Acres, 1000 homes and killed 22 people. They prepared to send out firefighting assistance should it be necessary.
On Sunday morning/ early afternoon, a fire was started (I don't the specifics of each fire) somewhere in SoCal either by downed power lines (Gale-force winds) or other. The santa ana winds blew the fire out of control. By Sunday night, at least 6 other fires had sprung up around Southern California, (7 counties in SoCal declared states of emergency the next day). San Diego was the hardest hit, with a large fire in north country suburbs and those in So. East County.
Although fire departments from all over the state were deployed and those from other states were brought in, the extreme winds fueled the fires out of control and it was all firefighters could do to direct the fire away from homes, let alone put it out. Hundreds of thousands of people were evacuated [including me 🙂] as well as entire cities in the suburbs of San Diego. The winds have died out, but firefighters are still battling the blazes and many people are still evacuated from their homes.
I don't know the exact numbers, but over 2300 structures have burned and in terms of damage, this fire likely sets a record in California history. 7 People have also died in the fires. Nearly all schools in San Diego county were closed for the entire week due to smoke/air quality (and displaced students/staff).