For weeks, LAPD narcotics officers kept watch over hundreds of marijuana plants they had discovered in O’Melveny Park in Granada Hills, hoping to catch the person cultivating them.

They would hike the mile and a half from the parking lot and wait in the bushes. A man showed up Aug. 12 and began tending the plants and the extensive irrigation system. The officers followed the man to his car, where they arrested him.

Natale Gabriele, 49, of West Hills, was booked on suspicion of possessing marijuana for sale.

There were 2,700 plants growing in the park, some more than 10 feet high, Det. Robert Holcomb of the LAPD’s narcotics enforcement unit said Thursday. Their street value was estimated at more than $24 million.

“In my 22 years of being a narcotics officer,” he said, “this is the largest narcotics growth I have ever heard of.”

Officers also discovered a sophisticated irrigation system, complete with a dam to block a nearby stream, irrigation tubing and a battery-operated pump and timer that would automatically distribute water to the plants.

Holcomb estimated the plants had been growing in the park for two years, probably starting up after the Sesnon fire ripped through the area in 2008.