Harpeth Rising’s fourth album, “Tales from Jackson Bridge,” drops Oct. 3.

The Nashville quartet, which fortifies passionate folk, Americana, blues, bluegrass and all things acoustic with classical training, previewed the new recording for Niles at Riverfest while crossing dragon boat racing on the St. Joseph River off their bucket list.

Violinist Jordana Greenberg, a Canadian-born, Kentuckiana transplant, began calling denizens of the City of Four Flags “Nile-ators” after a shouted suggestion while polling Friday night’s crowd gathered on the grass at the foot of Riverfront Amphitheater.

It fit better than, say, Nil-ihists.

Harpeth Rising opened with “The Wheelhouse,” a track from their new recording.

“We came in from Indiana today,” Greenberg said. “We’ve been having a wonderful, busy summer,” leaving Niles bound for Boston.

“We spent a lot of time last month in the outer parts of Michigan we haven’t explored before,” minus Mackinac.

“There’s a beautiful beach in Ludington. All of us saw the Northern Lights for the first time in Boyne Falls. It was amazing.”

Shivering at the memory of a frigid downpour which lashed Niles during last year’s Bluegrass Festival, Greenberg wore rubber boots just in case.

Her patchwork boots also made a good tie-in to “These Boots are Made for Walkin’,” Nancy Sinatra’s No. 1 1966 hit.

They also played an instrumental version of The Beatles’ “Norwegian Wood (This Bird Has Flown)” from 1965’s Rubber Soul.

A couple of covers aside, Harpeth Rising mostly creates original songs layering instrumental arrangements with four-part harmonies and lyrics about wanderlust, eternal curiosity, class struggle and extraordinary love.

The four met while earning performance degrees at Indiana University’s Jacobs School of Music. Despite their diverse beginnings from vastly different cultures and geographic areas, they unified around their novel musical hybrid.

Besides Greenberg, who grew up in Paoli, Ind., near French Lick, banjo player Rebecca Reed-Lunn hails from California.

The two women bonded during a youthful cross-country spiritual quest.

Their adventures through the desert and on to Hawaii via the Telluride Bluegrass Festival convinced them to follow folk music’s path.

Harpeth Rising became fully formed with the addition of Maria Di Meglio (cello) and Chris Burgess (percussion).

Burgess’ Kentucky roots and Di Meglio’s ethnic Brooklyn background added new dimensions to their sound, profuse enough to be emanating from a much larger ensemble.

Di Meglio transitions fluidly between providing the bass line and taking melodic leads, while Burgess builds a textured matrix from percussive elements.

Reed-Lunn’s claw hammer banjo style was learned mostly by watching YouTube.

Greenberg takes the place of a lead guitar, gliding effortlessly between concert violinist and accompanist.

After only a few months as a band, they booked a tour of England, which included a performance with The Bath Philharmonia.

They were invited to perform at The Cambridge Folk Festival the following summer, and have since played folk festivals across England and the United States.

They built their fan base in the tradition of all wandering minstrels — passionately and by word-of-mouth.

Previous releases include Harpeth Rising (2010), Dead Man’s Hand (2011) and The End of the World (2012), a collaboration with David Greenberg, Jordana’s dad.