The 48-year-old teacher met the alleged victim when she was his student at the school. Deputy District Attorney Katherine David said Peterson would hang out with the 17-year-old after classes let out.
Peterson allegedly took sexually explicit pictures of the two of them together in April. David also said Peterson sent sexually explicit text messages to the teen.
The two would regularly meet at a motel near the Angel Stadium to have sex, said David.
One of the victim's family members grew suspicious and found Peterson's text messages on the girl's phone. The family member alerted police.
Peterson was arrested Dec. 2 when he emerged from a motel shortly after the victim left.
Peterson posted $100,000 bail.
City News Service contributed to this report.