Clandestine meth labs are always both toxic and explosive. A lab can be as little as a couple of jars and buckets, depending on the type of cook, or it can be a full-on lab-looking setup. There will likely be the remnants of pseudo-ephedrine packages, lithium batteries that have been taken apart, white gas and/or starter fluid cans, and in some cases a propane tank. What you find as a "lab" depends on the sophistication of the cooks. Trailers, motel rooms, motorhomes, vans, and abandoned buildings are all favored places to set up a cook; anywhere that likely won't be discovered for a while. If you find one, don't examine the remnants; leave the area as soon as possible and notify law enforcement who will have a hazmat team clean it up. If you smell acetone, or other odd chemical smell coming from a trailer or building, leave immediately as the atmosphere is likely explosive, and call law enforcement.
Marijuana grows have always been a problem on public lands. Generally if there are booby traps, they're set up to scare off critters, but they are often potent enough to do you significant harm. If the grower is in the garden, that can be problematic as well.
When you're out in the back country, be alert for anything out of place; trash, black pipe water lines, fertilizer bags, or other unusual waste. If you begin to see odd things that you wouldn't normally see in the area you're in, pay heed, back out and call law enforcement. The life you save may be your own.
ON EDIT: I found an article you may find interesting:
http://www.nydailynews.com/news/crime/u-s-grapples-rise-rolling-meth-labs-article-1.1320625
