Take down their plate number....report it to the authorities.
If the cop doesn't want to deal with it, ( which has happened many times in the interior) go to the staff sergeant, or report it to Wildfires....bear in mind there's a good chance you may have to testify as a witness.
I've written a few tickets over a thousand for careless behaviour, including tossing cigarettes .....if they start a forest fire, and Forestry is over budget for fighting fires that year, they are on the hook for the cost of that fire.
So that means even though they may not incur the cost at the time of the fire, it may come to bite them in the ass a few months after sweating about it.
Don't let them think they can just carelessly toss one out and keep driving, thinking it doesn't matter....they are a threat to some people's homes and livelihoods,and our economy.