Ry Cooder has a guitar in his hands. He’s playing “Jesus on the Mainline.” It’s 1987 in Santa Cruz, and the gospel traditional has changed, on this day, into something supercharged and incendiary, run through an overdriven amplifier to produce fat, chunky crunch. Cooder’s eyes dart across the stage, locking first with trombonist George Bohanon, as he swings the bluesy lines of a solo, and then over to pianist Van Dyke Parks, as he hammers out a ragtime-inflected chord progression. Cooder’s own guitar playing seems to knit the two threads together: first, he comes down hard on Bohannon’s insistent downbeat, leaning into clipped, distorted blue notes, then somehow stumbles free of them, repeating the same syncopated tagline over and over. Just as the band seems to reach their peak, Cooder points his guitar up toward the ceiling and then bangs it downward, a gesture most bandleaders use to wrangle the ensemble, as if to say, “Hey! Play the notes like I told you to play them!” or “Let’s end this song now!” But, with Cooder, it’s just the opposite. Rather than leading, he’s reacting to the deep groove laid down by the other musicians. He’s dancing a hip-shaking, shoulder-shrugging shuffle. What he’s really saying is “Don’t stop now, we got it, let’s boogie.”