Any chance the feeders leaked?
Mites and most diseases would have been a much slower decline in your climate, I think. CCD usually has empty hives, no dead bees.
If you are sure that a couple of weeks ago there was a healthy queen, brood, and a decent size cluster, I'd say that there was some external catastrophe that killed them. I really do hate to say it, but one of the leading causes of bee death is beekeepers at least from my own experience :roll:.
I am sorry for your loss and I do know how you feel.