Thursday's crash was so violent that firefighters had to use the Jaws of Life to get the officer out.
The officer was seriously injured but is expected to survive. The tow truck driver was also injured but is also expected to survive.
The California Highway Patrol is investigating the accident.
A witness said the tow truck driver had pulled over but the officer, who was going very fast, lost control while trying to get around another vehicle.
The tow truck driver "was not moving," said a bystander, Alberto Lemus. "He saw the police and pulled over."