WAXAHACHIE -- A hidden key, a magnetic lock, and a secret door behind a bookcase led Ellis County sheriff's deputies to an underground pot-growing room containing more than 150 plants. 

The indoor farm was thriving under the detached garage of a house in the 300 block of Pebble Creek in Red Oak, deputies said. 

The owner of the house, Dwayne Marshall Nielsen, 46, was charged with possession of marijuana and released from jail on a $40,000 bond, Sheriff’s Capt. Danny Williams said today. 

The pot plants were in various stages of growth. One was a “mother plant" that produced cuttings and seedlings. 

The underground operation included an irrigation system, grow lights and chemicals to help the plants mature, Capt. Williams said. 

"The odor was hard to describe, but it wasn't good," Capt. Williams said. "We had to get the fire department in there to help air it out so we could work." 

Officials said the operation was capable of producing 30 to 40 pounds of marijuana every two months.

 A task force that included the sheriff's department, Red Oak police and the U.S. Drug Enforcement Administration had been working on the case since October, Capt. Williams said.

 Finding the secret passages wasn't difficult, since authorities had been tipped off about where to look, Capt. Williams said. 

"We knew there was a key, but we had to look to find it," he added.