I was once informed by someone working at a major energy company that if the utility frequency dropped to a certain specific value it could cause uncontrollable systemwide cascading blackouts. I don't remember the value, but I wish I did.<p>A large outage like SF, if it wasn't done in a controlled manner, could be grid overload. Or to prevent grid overload, utilities might need to shut down a regular on a high voltage supply line, which causes an overload somewhere else in the system, and automatic cutoff switches force a blackout.<p>Similar events have happened over the years starting in a remote state and ending in a California blackout. Often it's due to aging infrastructure which goes down unexpectedly, which then causes a chain reaction that hits other parts of the grid. If winds took down power lines in LA, this could cause a backup which could take out SF. It's possible that either LA or New York could have caused the SF blackout, or vice versa. If one part of the grid starts to go down it puts pressure on the rest, and things start to pop.<p>Note: I'm talking out my ass here, but it's based on news reports of previous outages.