Maridol Papaya with large fruit in Hayward.
GROWS ON YOU.com has a photo posted by "Delonix" of a Hayward yard with Papaya fruit- about 6 of them?- and a plant about 5'? tall. I think I've seen that yard..the fountain.
It can be done. The last two years have been warm. I'm still kind of shocked looking at the photo.