FLORENCE – A guy in the fifth row screamed out “Hell yeah! Hell Yeah! Don’t change a thing.”

It was perhaps the biggest compliment that Tucson’s own Run Boy Run could get from the crowd of several hundred milling in and about as Country Thunder settled into Day 2 here.

RBR is the only Tucson band on the main stage — Cooper Meza Band is playing the KIIM FM VIP skyboxes throughout the weekend — and the they are the only ones proudly billed as bluegrass, the noble forefather of country.

The quintet — siblings Matt and Grace Rolland; sisters Bekah and Jen Sandoval; and Jesse Allen – performed what will likely go down as the most musical show of the four-day festival. Their instrumental arsenal included twin fiddles, stand-up bass, mandolin, guitar and cello, and several of them double-dipped on more than one instrument. And boy could they play the dickens out of them. On “Little Girl,” award-winning fiddler Matt Rolland kicked off the soaring intro after the Sandovals and Rolland’s sister soared on the a capella vocal harmonies. Bekah Sandoval followed Rolland’s lead and one by one each member chimed in, all at different tempos until the music built to a glorious swell.

And that’s when the guy in the fifth row yelled out for this Tucson quintet not to change a thing.

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