Bikes don't ruin trails.
Quads don't ruin trails.
4x4's don't ruin trails.
Heck for that matter guns don't kill people.
Its the irresponsible idiots that either are not properly "trained", the ignorant people who don't care, and or the careless that don't pay attention (among others I'm sure) that ruin it for the rest of us.
The Pacific Northwest Fourwheel Drive Assoc. fights to keep trails open, and whether or not a trail or area is used by everyone or not, if it is closed for some reason or another, IT IS CLOSED! Whether it is only a $100 fine, or a $10,000 fine, its still trespassing, It still makes the rest of us who do obey the laws suffer the consequences of YOUR actions. Why do you think those areas are closed? Just to spite you?
There has been a few people creating new trails at TSF in the PAC/NW, other see them and try them too, pretty soon they are torn up badly and starting to erode when the rain hits which in turn kills trees, plants, etc. So, rather than let these actions go on unchecked, the rangers close a trail or area, then what? We lost yet another area to wheel thanks to people like yourself that think they have the right to do as they please where ever, whenever, and however they please.
Think before you act.
[/rant off]