I would bet that to be true, Laaz. I think Tristeza was more an issue in Florida and surrounding gulf citrus states than California. But, all commercial groves planted after the 1940's here in California I'm sure are on Carrizo/Troyer.

I really don't understand that warning sign that comes with those seville oranges!
My first sour orange I ate fresh, today I juiced one and drank the juice. Believe it or not, I really liked the juice! It had a very lemony taste but much less acid. I think this juice could be very suitable to spice up the juice of sweet oranges, that I often find too sweet!