The planning is one of the two key parts. The second is, rather than asking what does hit SoCal, it might be easier to ask what doesn't. California and it's people have had a lot of practice at dealing with disasters and crisis, so they know what parts of their plans didn't work last time.

There is another thing that I think is being overlooked. If you say it fast enough, a million people sounds huge. Normally, a crowd of a million IS huge. But what percentage of the effected counties is that?