At Colorado’s newly minted recreational marijuana shops, cash is king.

Because the drug is still illegal at the federal level, most pot shops in Colorado are not taking credit cards or other forms of electronic payment, thanks to the complications that could come from federal authorities tracking down customers and store owners through those transactions. It’s a legal business, but one that’s forced to operate as if it were still partially in the black market.

To make things easier for their customers — and to keep people from having to carry large stacks of cash with them as they come and go, which could attract criminals — many shops have installed ATMs inside.