Bob's right. USFS doesn't have the resources to get rid of dope growers. It's the local sheriff in conjunction with whatever LE the USFS has (usually only one or two per forest). There's assorted agreements that DEA and Border Patrol can be brought in as logistical support to clean these areas up. As an investigator once remarked "large areas of US federal lands have been taken over by foreign nationals." It's absolutely correct.
I have nothing against the use of MJ by adults in social situations. But the true cost of, say, medical marijuana is not part of the equation. These growers take over federal lands, make it dangerous for recreational hikers, spread all manner of truly toxic rodenticides and fertilizers; poach bear and anything that moves; leave miles of irrigation tubing; piles of garbage to say nothing of the danger to law enforcement who try to get rid of this stuff.. . All of it supported by trying to present it as a benign and harmless use of dope by medical marijuana and recreational users.
Even the quasi-legal growers in Humboldt dump all manner of pesticides and rodenticides on the environment because they have to stay competitive. (and, really, because they're no different than any other greedy and unregulated market...).
Which is all to say it's not just harmless stoned out MJ users. This stuff has a real effect on our public lands, wildlife and society that has to be realistically looked at.
g.