Bob Weir, Chris Robinson and Jackie Greene made their debut as a trio at last summer’s Rocky Mountain Folks Festival in Lyons and they were, quite simply, the talk of the weekend. Weir, the venerable Grateful Dead frontman, led his younger companions through Dead favorites and deep cuts — all three playing guitar and harmonizing. As the bandleader of the Black Crowes, Robinson’s piercing rock ‘n’ roll howl is unmistakable, and he adds grit and soul to counter Weir’s mellow lullabies. Meanwhile, Jackie Greene may simply be Americana’s best-kept secret. Tickets for Saturday’s show at the Boulder Theater are sold out, but try your luck outside the venue.