Legal Question in Sexual Harassment in California

Because the legislature has made one illegal and the other not.

The federal law prohibits "accessing with the intent to view" "child pornography" which could well include "looking at pics of nude underage girls." Avoid viewing, accessing, or having any such images in your possession, whether stored on physical media or electronically. As far as looking at actual naked people, if you are in a place where you have a right to be, I am not aware that it's against the law to look at any naked people you might encounter regardless of their age or gender; or whether they are situated at a naturist resort or riding the subway. But it is rude to stare.