It’s standard procedure to write a ticket to drivers that hit deer and other large wildlife. I would imagine the rock is viewed the same way. If you hit a deer, it’s your fault no matter what and you get a ticket. Technically according to the law, that is. But many cops just ignore it.
Honestly?
Jeez what a load of BS.
I had this “conversation” with a friend following a collision I had with a deer a year and a half ago. I did some research on this subject. I can’t speak for all states, but in CA it isn’t an automatic ticket for a vehicle collision with an animal. It is also not an automatic ticket when an act of nature occurs (e.g., a large rock rolling down a steep rocky hill directly in front of your vehicle while traveling at below the posted highway speed in inclement weather - which severly impacts the vehicles ability to stop and it’s too dangerous to swerve to avoid the rock).