Sunnydale is one of the hottest stars we’ve colonized, her surface nearly white-hot against the darkness of space.  Only spectacularly inefficient greenhouse effects make any of the worlds under her powerful fires habitable at all.  The Republic of California acquired colonization rights after Contact, and named it after the famous fictional city of the same name.  It truly is just a nice place to live, rich in minerals, sunshine, and wide-open spaces.