I contacted the proprietor of the Contrail Science blog regarding my belief that the contrail I observed was north of Catalina Island, as opposed to his theory that it was flight UPS902. He sent me a Google Earth file that convinced me I was wrong.
Using Google Earth, you can open the file regarding that particular flight here. A tour of how to use it follows:
As a reminder, here is the drawing I made on top of a photo from my approximate vantage point:
We face south/southwest, so north is basically to the right.
And here is the Google Earth image from somewhere around my vantage point:
Keep in mind that my drawing was from what I saw inside the house. It undoubtedly continued its arc up and to the left, and if I had gone outside I think the arc would have looked just like the Google Earth screenshot you see above.
But while it looks like it is north of Catalina from that vantage point, it is not. Using the Google Earth file, this is what it looks like from overhead:
This is pretty good evidence. I think this guy has nailed it.
P.S. As I noted in the post below, he says the blue arc is a shadow. He clarifies by e-mail that it is a crepuscular shadow. You can see photos of similar shadows here. He says it appears odd because it is a single shadow.