I don't think (or know) if there is a specific law against kissing a minor in California. But since you're of the age to be a college sophomore and she is of the age of a high school sophomore, this sounds like an incredibly bad idea, legal or not. There is no way around what usually happens next and, in addition, you should know that there is no "consent" that can be given by a minor when it comes to certain acts and actions. And understand that in the event you break it off with her and she gets upset and makes claims that could be her perspective of your interaction, then even if you successfully defend yourself you're still a 19 year old who has had a relationship with a minor.
What's the safest way? If you're worried about her parents, you should already be thinking about whether this is the right time to pursue the relationship further. The way around it? Perhaps to get married, with consent of her parents.