They would probably have one or two security guys in the van or car with them armed with assault rifles to take on any state trooper, sheriff, or citizen that tried to interrupt.
How to stop it? Unfortumnately, we're not prepared to stop anything on this scale. We have a lot of volunteer fire departments throughout the west and we have smoke jumpers and the national guard ... but they are all reactive after it's really going.
Until more and more citizens are armed and can interdict it at force of arms when it occurs, all we can do is react IMHO.