Search for "trespass grow" to find a lot of magazine articles and videos on the subject.

I may shake my head at clear-cutting and overgrazing but I'll say that I've never been chased off public land by a rancher nor fired upon by lumberjacks. The marijuana growers are ... unique.

You might be surprised by the scale. I know a few folks doing water management in California, and they've all independently brought up the exacerbating effects of unmonitored but significant water usage by illegal farms during the last few years of drought.

Don't have a link handy, though.

As a cyclist I shudder at the thought of motorcyclists ruining the trails, making noise and generally trashing the place.

My hill walking dad curses the mountain bikers and their damage to the terrain - leave nothing but footprints, take nothing but memories.

I hear you. The thing about a national forest is there are already roads, and already the sounds of logging. These are working lands. We set aside wilderness areas without roads, that are not even welcoming to horses, for those seeking peace.

Enjoy your lands.

Pretty common occurrence - http://mobile.reuters.com/article/amp/idUSKBN1AM0C3

I'd rather run across an old composting toilet while biking than an old meth lab, so you have a point