I'm Looking for a book series I read back in junior high.?

I remember the bindings were all black, and none of them were very thick. I think there were 5 books in the series. The books were about California breaking off the continent after a major earthquake, and then being quarantined because of nuclear radiation or something like that. I also remember something about rampant biker gangs terrorizing people. But the series were all about this one guy and how he survived, and tried to escape. His wife and child (son, I think) get killed by the evil biker dudes at the end of the first or second book. And in the next book he hooks up with his wife's best friend...? That's pretty much all the details that I remember except that there were some fairly explicit parts. (The bikers gang a convenience store clerk girl in I think the first book.) I just remember thinking these books were kinda like a Californian "Road Warrior" series. Thanks for any help.