Are motorized bikes legal in California?

[Garrett]

I was thinking about putting one of these motorized kits on my mountain bike and was curious about the laws. I live in Southern California and was wondering if there were any laws against motorized bikes before i bought one. If there are laws what are the restrictions? I was looking at the kits on this website (http://www.kingsmotorbikes.com/) Are these decent kits? They seem pretty cheap. Thanks