Folk music has had its ups and downs in America. The recent passing of Pete Seeger occasioned some reflection about the various revivals and retrenchments that the folk legend and his music experienced over a long career.

The Avett Brothers, who came to the Cumberland County Civic Center on Monday night, have found followers among those who appreciate their focus on both the roots and branches of a long tradition. Their mix of folk, country, bluegrass and rock has proven to have broadening appeal.

The North Carolina-based group, currently configured to include brothers Scott and Seth Avett with Bob Crawford, Joe Kwon, Mike Marsh and Paul Defiglia, has been playing ever-larger venues in recent years. The Civic Center, though not sold out, held a large and enthusiastic crowd for this early-week event.

They began the show in the original trio of the Avetts, Scott on banjo and Seth on guitar, plus Crawford on upright bass for a take on “Shame,” a tune which quickly reminded all that this band works into some interesting lyrical shadows while maintaining a bright sound. As they gradually added members, a version of John Denver’s “Thank God I’m a Country Boy” made things lively.

“Live and Die” was quickly recognized by the crowd, as Kwon’s plugged-in cello added another dimension. His cello was also prominent in the band favorite “Head Full of Doubt/Road Full of Promise,” a strong piece with an uneasy lyrical resolution.

The brothers’ vocal harmonies were a highlight of “Laundry,” which finished with a mini-hoedown that had them dancing. This was generally a very animated group, with lots of moving around the stage as they played.

There were moments of intensity when only the presence of acoustic instruments onstage could distinguish the band from hard-nosed rockers. But quieter moments revealed the group’s long apprenticeship in the subtle pathways of tradition.

Old Crow Medicine Show, a Nashville-based septet that plays a little closer to their down-home roots than do the Avetts, opened the evening. Their one-hour set was highlighted by the classic C.C. Rider and their own great “Wagon Wheel,” co-written by band member Ketch Secor and Bob Dylan. This latter tune will likely be heard again at the civic center later this month when Darius Rucker comes to town.

Steve Feeney is a freelance writer who lives in Portland.