Southern California is especially bad, but this is spreading everywhere in CA. I've had a friend or two find (empty) plantations in the off season, and some of them are pretty well developed. If it's a site operated by the Mexican Mafia (I'm serious... search news sites), and they're around, you run the risk of getting shot at with assault weapons. Some areas are allegedly protected by tripwires, traps, etc, and it's a good idea to be careful and stay clear if you see anything like cultivation, out in the back country. From what I've read, the Los Angeles area rangers are having enormous, life-threatening problems on a routine basis.

As for trashing the environment, it really ticks me off that the land is cleared, then used for effectively agriculture, with pesticides often used. Bah.