My name is ***** ***** I am an experienced criminal
I am very sorry to hear about this, as you probably know your son may be in serious trouble here. The age of sexual consent in California is 18. That means his 16 year old girlfriend is under the age of consent. The fact that he did not force her to have sex is important, but the fact that she consented isn't helpful. California won't recognize her right to consent for 2 more years.
So the charges here, if the girl's parents wish to prosecute, would be statutory rape
(pc. 261.5), possession of/making of child pornography (pc 311.11) to say nothing of furnishing illicit drugs to a minor (HS 11360).
The two sex charges and the drug charge are wobblers. That is, depending upon the facts and circumstances of the case and the discretion of the prosecutor, the state can go forward with each count as a misdemeanor
or a felony. As a felony, he risks years of prison and lifelong registration as a sex offender. What you should do is to start looking for a very good lawyer, who can get these charges reduced and do maximum damage control.