You don't have to be from the boondocks to savor Yonder Mountain String Band's down-home sound. In fact, its inspired blend of folk and fusion has less to do with hillbillies and more in common with such genre-defying outfits as Nickel Creek and Bela Fleck and the Flecktones. Although it's often tagged as a bluegrass band, terms like jamgrass or newgrass provide a better fit. Then again, the group's more esoteric covers (it's not unusual to find songs by the Beatles, Zappa, or Ozzy Osbourne tossed into the freewheeling mix) make a definitive description somewhat elusive. It recently blurred the boundaries even further by enlisting veteran rock producer Tom Rothrock the man behind the boards for the Foo Fighters, James Blunt, Beck, and Elliott Smith to steer its self-titled fourth album. While eschewing rock 'n' roll flair, this Colorado quartet creates its real appeal by simply using guitar, bass, banjo, and mandolin to tweak the traditional with an irresistibly infectious mountain brew.