Three years ago, the first of three marijuana amnesty boxes was installed at Aspen-Pitkin County Airport. The idea behind the boxes was to give flyers a way to dispose of legal cannabis before they boarded a plane bound for a destination where the substance might be against the law, and Pitkin County Undersheriff Ron Ryan considers the containers to be a success, even though weed isn't the only aromatic thing sometimes left in them.

Other examples? "Dirty diapers," Ryan says. "Garbage. And leftover Starbucks. That's one of the worst, because a lot of the drinks from there are milk-based. If they're left inside for a week, the smell becomes pretty horrendous."

As we reported back in January 2014, the airport in Colorado Springs also installed marijuana amnesty boxes after limited recreational cannabis sales became legal in the state.

Here's a look at one such box.

News of the Springs pot boxes soon became a gag line on national TV outlets such as the Fox News panel discussion show Red Eye. This reaction may explain why the airports in Colorado Springs and Aspen are the only such facilities in the state to provide this service at present.

Nonetheless, Undersheriff Ryan, who previously spoke to the Aspen Times on the topic, is glad they remain on display in Aspen.

"We get every kind of marijuana product that's sold in the retail community dropped in them," he says. "Edibles, the raw product itself and the paraphernalia that goes into the consumption of it: vaporizers, rolling papers. And everything we remove out of the box is something that wasn't disposed of improperly — which means it didn't end up in kids' hands."

This was a larger issue shortly after legalization, Ryan maintains.

"Things were being left in hotels and residential refrigerators, and there were a few reports of maids who took the product home and either family members or children consumed it," he notes. "But that isn't as much of a problem now as it was then. The Valley Marijuana Council, which is a cooperative of stake-holders, including people from the public-safety community and schools, has spent a lot of time letting people know that items left behind shouldn't be consumed unless they're clearly in a sealed container."

In Ryan's view, the boxes are safer pot disposal sites than garbage receptacles, including those at the airport. But early on, it was hard to tell the difference between them.

"For a while, they looked more like trash cans than they did secure boxes for marijuana," he acknowledges. "Originally, the airport was reluctant to advertise too overtly that it was a marijuana amnesty drop box. Now they have better signage on them, so there's less garbage being dropped, and more of the things they were designed for."

The frequency with which the boxes are used varies by the time of year: more during ski season, less during the off-season. As such, several days may go by before a sheriff's department representative checks the boxes, which can increase the strength of their scent whether they contain a particularly pungent strain or something non-pot-related.

"Things that tend to decompose definitely create a little bit of a hassle," Ryan admits. "But it's a small price to pay."

He adds: "Maybe we should put a dirty-diaper amnesty box next to the marijuana-amnesty box."

After all, a lot of people would consider leaving a diaper behind in a public space to be a lot more serious offense than dispensing of some pot.

Here's a larger look at the Aspen airport's marijuana-amnesty boxes.