Officials at McCarran International Airport say "amnesty boxes" — designed so passengers can dump legal marijuana instead of carrying it illegally onto a plane — generally have some products in them when a contractor comes to empty them twice a week.

But airport spokeswoman Christine Crews said this week it's impossible to offer a weight or quantify exactly how much has been collected in the six months since the boxes were installed because of the diversity of marijuana products that's turned in — everything from cannabis-infused drinks to marijuana flower to vape pens. She also said passengers sometimes toss non-cannabis-related trash into the bins.

Marijuana that's legal in Nevada still isn't legal on a plane, so Clark County airports installed some 20 boxes to help patrons comply with a county ordinance that bans cannabis on airport property. The installation, plus a year of servicing, costs $114,000, and the contract has four one-year renewal options.

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.

Crews said there haven't been reports that any of the boxes, which cost almost $1,500 apiece to set up and install and $75 per week, per box to service, have been vandalized.

In addition to McCarran, boxes were placed at Henderson Executive Airport, North Las Vegas Airport and McCarran's consolidated car rental facility.

Crews said the contractor, Logistical Solutions, checks the boxes twice a week. Cannabis products found inside are first chemically rendered unusable before they are transported away to the landfill.

The federal Transportation Security Administration notes that possessing marijuana remains a federal crime in spite of the state law.

"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.