After 11 years of heavy touring and building a solid fan base for their string-music-inspired prog-grass, Railroad Earth have earned the right to brag. Still, their publicity e-mails and official bio make claims bold enough to warrant attention in this write-up: “Railroad Earth is one of America’s greatest bands playing today, plain and simple,” states the release. That’s either an indictment of a sorry state of American music or a heaping load of self-praise. What’s virtually undeniable is that Railroad Earth is the best semi-bluegrass band to ever emerge from New Jersey. The sextet hails from the tiny township of Stillwater, just outside the Delaware Water Gap National Recreation Gap. They’re from the northwest sliver of the Garden State that even staunch haters of suburbia would call “nice.” Those hilly, rural environs rubbed their Appalachian foothills juju all over Railroad Earth, helping to develop their sound into an amalgam of tight fiddle, mandolin, and guitar that work their way on stage into tight grooves and intense buildups. Still on the road a 2010 eponymous release, the band plans to record their seventh album later this year. They’ll headline at the Music Farm on Friday as part of Atlanta-based micro Sweetwater Brewing Co.’s fundraiser for the Waterkeeper Alliance. The show is one of several events during Sweetwater’s “Save the Cooper” campaign which benefits the Charleston Waterkeeper efforts to protect the Cooper River. That alone makes it worth staying on the train for another trip around the planetary tracks with one of the world’s greatest bands in all of history.