UC Davis Athletics Joining Mountain West - Football to Follow There's not a chance in hell USC and UCLA are leaving the Big 10 unless whatever conference they move to offers a similar amount of TV money, which an all California conference wouldn't come anywhere close to doing.
Cal and Stanford might be different since it seems like their move was more out of necessity and they're not getting anywhere near the TV money that UCLA and USC are. But even then, I doubt and all-California conference would match what they get in the ACC.