Help us identify this awesome butterfly

Can anyone identify this fairly large butterfly?

In Southern California, my daughter and I each got a good look at Daughter of Mothra. I then grabbed a few snapshots and a bit of video. Each wing was about 5.5" tall and at tip-to-tip, and at its widest we estimate 7" across?

We see lots of monarchs, but nothing like this guy.

What say you?

Here is some video of it flitting around.

A true Happy Mutant and long-time friend of the site, KentKB, guesses it is a Swallowtail. A quick search on the internets shows that's a pretty darn good guess?