Agents with the San Diego County Narcotics Task Force discovered more than 3700 marijuana plants growing illegally in San Marcos Monday.
The illegal grow operation was uncovered on a hillside just above Cal State University San Marcos and just below a line of homes.
A drug agent riding in a helicopter spotted the marijuana from above.
"The color of marijuana reflecting from different angles looks different from natural foliage," explained Lt. Hank Turner with the Narcotics Task Force.
Because there was no trail, agents had to crawl at times to maneuver their way through the thick vegetation.
Once they made it to the site, they found thousands of plants up and down a hillside and hidden from the sight of nearby residents.
The plants had a sophisticated irrigation system with water coming from a nearby hydrant which is illegally tapped into.
The time between June and October is the typical grow season for marijuana and during that time agents say they will spot and cut down hundreds of thousands of plants all over the county.
"We went to one last month, the people were armed found ammunition, found magazines for weapons," Turner said.
Agents say they believe most of the illegal crops are backed by Mexican drug cartels that send workers across the border to secretly cultivate the fields.
And they are good at what they do Turner said.
As agents made their way through the brush at the San Marcos site, a law enforcement helicopter flew low to try and flush out anyone who may be hiding. No one appeared. No arrests were made.
Not only are these types of operations feeding into the trafficking and use of illegal drugs but growing the plants can also cause serious damage to the environment because of the chemicals used.
For the agents like Hank Turner, this isn't only about stopping illegal drug trade, it's also about protecting innocent people who have no idea what could be growing just a few yards away from their home.
"I don't want my kid to go for a walk and walk across one of these and get threatened or find
themselves in harm’s way," Turner said.