Police have arrested a 20-year-old Grand Junction man after they say he sexually assaulted a 13-year-old girl he met on MySpace, the social networking Web site.

The Mesa County sheriff's office arrested Martin Martinez, 20, and charged him with sex assault on a child and contributing to the delinquency of a minor.

Investigators learned in early December that the 13-year-old had met Martinez on MySpace in November, and agreed to meet him in person.

The victim told police that she met Martinez and after drinking alcohol and smoking marijuana allegedly supplied by the suspect, they had sex. Colorado law states that anyone 13 year old cannot consent to sex with someone more than four years older than them.

The arrest caused the usual warning from police about monitoring children's Internet use. For more tips, go to myspace.com and choose the "safety tips" at the bottom of the page.