Fiddler Darol Anger might have summed up the fourth annual RiverCity Bluegrass Festival best with an odd observation: "You can't have a bluegrass festival without Stevie Wonder," he said, before he and his band, Republic of Strings, along with guest vocalist Stephanie Schneiderman, launched into their version of Wonder's funk classic "Higher Ground."

If it seemed a counterintuitive way to describe the festival, held Friday, Saturday and Sunday at the Oregon Convention Center, it is, on reflection, a deeply hopeful description. Though the festival focuses on bluegrass, a narrow idea of that genre doesn't cover all the music that was played, including styles influenced by bluegrass and bluegrass influenced by different styles. That kind of musical back-and-forth is what ultimately will give bluegrass longevity, what will allow it to move into the future and stay vital. And that process was very much on display over the weekend, at a festival that, while drawing on traditional music, looked repeatedly to the future of bluegrass.

Take Saturday headliner Marty Stuart, who's long combined genres such as country, rock, bluegrass and gospel. Now add disco to the list: He and his band, the Fabulous Superlatives, played a bluegrass version of the Bee Gees' "Stayin' Alive" that brought down the house. It was an unexpected moment of musical plaids and stripes, and a pure delight, coming near the end of a set that had already been full of joy. The result sounded new, fresh, in a way the song hasn't sounded in years (if not decades).

By Luciana Lopez