POLK, Ore.-- Police are patrolling the skies looking for outdoor marijuana grow operations inOregon this harvest season.

But finding them is not easy.

It has a distinct color and a different shape from everything, says an undercover drug investigator as he peered out the window of an Oregon National Guard helicopter.

Last year, police confiscated more than 125,000 marijuana plants in Oregon. But so far this year, the numbers are down significantly.

Investigators theorize the drug cartels have moved elsewhere. This year, Idaho has seen a spike in outdoor grow operations on public land.

Intelligence reports suggest most of these marijuana grow operations are run by Mexican drug trafficking organizations. And there is big money at stake.

We've seen people, growers in the past that have been armed with assault rifles, scoped rifles, they conduct active counter surveillance, said Lt. Bill Fugate of Oregon State Police.

Investigators have also found hidden traps.

Anything from explosive devices to just rigged up shotgun shells, said Fugate. Police worry about hunters or hikers stumbling into a drug operation.

The growers rig intricate water systems. They douse their plants and the surrounding forest with commercial grade fertilizers and pesticides.

Police video shows heaps of trash and chemicals leeching into the ground polluting soil and streams.

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