It used to be possible to ride on Powell Butte here in Portland way back. As long as you walked your bike there, you could ride the trails. My dad was apparently on a first-name basis with all the cops in that area because they'd catch him riding his '74 Maico (which was new at that time) on the sidewalk. It started fairly innocently, just sitting side-saddle and going along in first at idle. Then the revs built up slightly, then a reach down to bring it up to second. Pretty soon, he was on the sidewalk in 4th gear, legs danging casually to one side, passing cars at 45 without really realizing it.
But of course, Powell Butte is now restricted to no motorized vehicles, which makes it great for the bicyclists. If you have a bicycle in Oregon, you are a god among men. You can ride in the main traffic lanes, in the dedicated bike lanes, on the sidewalks, through a random field, on dirt roads, on any hiking trail, up any mountain, and so on. The only time you'll ever get hassled is if you are slowing traffic too badly (keeping me 10 under the limit downtown apparently isn't "too badly," though), or if you go on the freeway, or happen to get onto the Indian reservation.
But add a motor to that, and you're through. It was so bad, at one point, that bikes weren't even allowed to ride gravel in the McCubbins area where I ride now. If you wanted to go on a ride, you could only go for fifteen minutes MAX without having to re-trace your steps. The result of that was that everyone stopped going there, and now they don't have enough budget for their army of Men in Beige. Outside of the actual campground itself, it's basically anarchy, which is pretty cool.