This website is a good read: http://trailkillerz.blogspot.com/
The guy who writes the site has dedicated his life to documenting and cataloging all acts of illegal trail building and illegal trail riding by mountain bikers everywhere ever.
You know when you want your city to build what seems like the smallest thing ever, and you’re really only asking for left-over crumbs from under the bargaining table, and it’s like pulling teeth with the city administrators, like by choosing whether to allow bikes on a piece of property that’s already zoned for hikers, camping, fires, horses, ATV’s, shooting, logging, and space shuttle landings, it’s like they’re choosing which of their children will live and which will die.
When mountain bikers propose something completely harmless, like Timberline Bike Park, singletrack in Forest Park, the continued presence of bikes in the recently purchased Riverview property in Portland, or any number of other projects from any number of other cities, “concerned citizens” come out of the woodwork saying that bikes will kill children, dogs, butterflies, owls, lichen, old growth trees, salmon, trilliums, and all that is good and holy. And invariably, before twisting in the dagger at the public meeting, these people claim the moral high ground by stating they “also ride mountain bikes,” as if they are the only objective ones who can rise above the fray and render a wise and judicious conclusion on this topic. “As a hiker, mountain biker, and concerned citizen, I believe that… (insert your choice of curmudgeony statement that precludes the possibility of ever allowing mountain biking anywhere).” But no one told them that this doesn’t count as mountain biking:
And if mountain bikes weren’t bad enough, mountain bikers are nothing but renegade thrill seekers looking to leach off and destroy other people’s resources (and mother nature, man!) in their “do whatever it takes, ruin as many people’s lives, so long as you can make a name for yourself as an investigatory journalist, no matter how many friends you lose or people you leave dead and bloodied along the way, just so long so you can make a name for yourself as an investigatory journalist, no matter how many friends you lose or people you leave dead and bloodied and dying along the way?”
Typical mountain bike trail building
A typical mountain biker
If any of what I just said makes sense, you will enjoy that website.