Marijuana that's legal in Nevada still isn't legal on a plane, so Clark County airports have installed boxes where passengers can safely unload the product before getting on board.

So-called "amnesty boxes" were installed last week at McCarran International Airport to help patrons comply with a county ordinance passed in September that bans cannabis on airport property. It could also stave off trouble at federally manned Transportation Security Administration checkpoints.

The boxes, which are located outside of the actual buildings, feature a drawer-drop that prevents people from reaching inside and plucking out drugs that prior patrons have dropped off. They are bolted into concrete and placed in high-traffic areas of the airport as a precaution against those who might steal or break into the boxes.

Airport spokeswoman Christine Crews said the first batch of boxes was installed on Friday, and the rest of the 20 planned boxes will be placed at county properties including the Henderson Executive Airport, North Las Vegas Airport and McCarran's consolidated car rental facility.

She said a contractor will be checking the boxes a few times a week and adjusting stops as usage patterns are determined. Crews said she didn't know if anybody had used the boxes yet.

TSA notes that possessing marijuana remains a federal crime.

"Our officers aren't looking for illegal narcotics, but they have to report them to law enforcement when discovered," the agency's Twitter account said.