An electric guitar made its way to the depths of Cumberland Caverns on Friday night, bringing Southern rock to a stage normally reserved for banjos.Drivin n’ Cryin brought the crowd to its feet with a guitar-driven version of “Honeysuckle Blue” as the sixth season of Bluegrass Underground took a decidedly different turn.That act was followed by Jason & the Scorchers, a Nashville-based group that helped define the Southern rock movement in the mid-1980s. It was an energy-filled performance that saw band frontman Jason Ringenberg swinging the microphone cord like a lasso for parts of the show.“If you’re a musician, you have to perform all the time because the alternatives aren’t good,” Ringenberg told the Standard moments before taking the stage for the final set Friday night. “We’ve made a lot of records and toured the world a couple times, but playing in a cave, this is a first for me.”The Cox Family presented a more traditional Bluegrass Underground offering with a stand-up bass and banjo.