Must have been one of those 50lb Walmart fat bikes.
Sadly, I see this being a problem pretty much every spring. Does cam rock have a physical barrier or gate when closed? I know Blue Mounds has one although I've seen it circumvented, and it's probably not always up when it should be. Physical barriers and signage are I think the only (legal) things we can do. Trail cameras, public humiliation, and castration won't do much, at least in the short term. Minimizing and repairing the damage are unfortunately the only options.
There's always going to be the random idiot or two and as the saying goes, you can't make anything idiot-proof because idiots are so ingenious. Sad but true.