Colorado bluegrass-heads Yonder Mountain String Band spin the genre deep into jam-band land on their fifth album. They’ve been doing this for more than a decade, but The Show sounds more like the Grateful Dead than Bill Monroe. The quartet flashes its virtuosity at every turn: fancy picking here, speed-of-light fretwork there. They even score a hook or two (“Complicated,” “Dreams”). But on some cuts — like the nearly eight-minute “Honestly” and the closing “Casualty,” which runs more than six minutes — they undercut one of bluegrass’s prime assets: brevity. But that’s the jam band in them taking over. When they stick to the mandolin and banjo strumming they do best, it’s show-offy without the baggage or plodding self-indulgence that usually weighs down the music.