Alabama Shakes' headlining set at Mountain Jam's fourth and final day was wonderful, in the literal sense. Brittany Howard's voice is a wonder; its power is wonderful. The Grand Canyon is a wonder -- or the Great Pyramid, or Kind of Blue -- because when people walk up to these things, they have crazy emotional responses they can't explain: They get goosebumps, or freeze, or start crying.

In the presence of the wonder of Howard's voice, it was impossible not to be moved -- like during the early-set crescendo of "Miss You" (dedicated to "Ricky," who "can't stay out of jail") and the late-set crescendo of "You Ain't Alone," a seduction via intimidation. It was simply overpowering.

Conventional blues forms typically give Howard the ideal platform for that voice, but the new songs from Sound & Color, like "The Greatest," used the power of Howard's voice to drive to band to even greater heights. As a performance that strove to push blues out of the box, it was a fitting final show for a festival that explored all kinds of ways into American music tradition.

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