Oh that it were that simple, to predict where the "fields o' plenty" are, that is. Remember that these guys are trying to place them where they won't be found, so you can play the odds that it'll be someplace remote. The DEA fly guys tell me that marijuana plants are easily spotted from the air and they do occasional fly-overs of the rural areas around here. Sometimes the growers will place their plants randomly interspersed with weeds along a creek bank, etc., to make them more difficult to spot. The only rule of thumb I can give you is that the growers usually booby trap the perimeters of their plots, so if you stumble on a field of it, act like you're in a mine field ('cause maybe you are), turn about and retrace your exact steps out of there examining the ground of each step before you put your foot down, and don't touch anything. I attended an explosives and booby trap seminar a few years ago, and they demonstrated one really nasty device that was favored by Calif. growers in the late 70's & 80's. It consisted of a piece of 2x4 with an "L" bracket screwed to it. A couple of hose clamps held a 6" piece of 3/4" diameter steel pipe to the other leg of the bracket. On the other side of the 2x4 was a Victor's rat trap. A hole was drilled through the 2x4 directly under where the killing bar would strike, and out the other side dead center in the pipe. The pipe is loaded with a 12 ga. shell and a 10 penny nail is placed in the hole for a firing pin. Some fine monofiliment fishing line is tied to the trap's trigger and strung across a path. Trip the line and the trap goes off driving the nail into the shotgun shell's primer, and... boom!
There were lots of other ingenius devices there too used to maime and kill. After that seminar, I walked in the woods feeling like I was on point in Viet Nam. Not cool!