The video shows a man hanging outside his truck holding on with just one hand and dancing as the vehicle heads northbound toward Corona.
Jennifer Frerichs spotted the stunt as her husband was driving her to get her nails done Saturday morning. She broke out her smartphone and recorded video.
"My only thought was how stupid could you be," Frerichs said.
The stunt, she said, was not only dangerous for himself, but for other drivers on the road.
"He could have easily fallen, I could have ran him over, it could have caused more accidents."
A spokesperson with the CHP says they are investigating.
If they find the person who did it, both he and the driver could be facing two infractions. One for what they call unlawful riding, the other for not wearing a seat belt.
The vehicle appears to be a raised black truck with red rims. If you recognize it, call the CHP at (951)637-8000.