is it unlawful for two consenting women, one who is 16 1/2 and the other who is soon to be 19 to have sex (they are girl friend and girl friend). The 19 year old's mother has threatened to call the police if she continues to see the 16 1/2 year. The parents of the 16 1/2 year old do not have a problem with the situation. Could they be held responsible as well.

The law in California has no gender lines. It applies to both male-female and same sex relationships. The age of consent is 18. In the situation you describe, the 19 year old could be at risk for legal action if a complaint is filed with authorities.

It would highly unlikely that the parents of the 16 year old would be found criminally negligent; unless the parents were promoting, coercing, and/or participating in sex acts involving a minor.