No one was in the patrol car when the collision took place in the late morning, the Laguna Beach Police Department said in a message posted along with photos on Twitter.
"When using Autopilot, drivers are continuously reminded of their responsibility to keep their hands on the wheel and maintain control of the vehicle at all times," a Tesla spokeswoman said in response to an AFP inquiry.
"Tesla has always been clear that Autopilot doesn't make the car impervious to all accidents."
Responses to the police department Twitter post ranged from thoughtful analysis of the accident to mistrust of self-driving cars.
"For automation to learn from mistakes, their developers need to admit making them," read a comment tweeted from the account of @SafeSelfDrive.
"Human error behind the wheel has been replaced with human error behind keyboard."
Tesla chief Elon Musk complained in a recent earnings call that accidents involving self-driving cars get sensational headlines while the potential for the technology to save lives is downplayed or ignored.