One day while driving along Highway 50 in Nevada, photographer David Gardner spotted a giant cottonwood tree draped with what seemed to be hundreds of pairs of shoes. It was a strange sight to find in the middle of nowhere, so naturally he got out and started taking pictures, all the while wondering why anyone would feel compelled to do something like this.

“The only thing I could come up with was that it must have something to do with communication,” he says. “People were using these shoes to create this kind of conversation with each other. They didn’t know what they were talking about, but they were communicating.”