Earl Scruggs provided the way in.

After the iconic bluegrass banjo player told John McEuen of the Nitty Gritty Dirt Band that he admired the young group’s cover of his "Randy Lynn Rag" on their 1970 album Uncle Charlie & His Dog Teddy, McEuen took a leap of faith. In the spring of 1971, the then-26-year-old asked: "Earl, I was wondering if, if you think you might, or would want to, uh, I mean, record a couple of songs with the Dirt Band?"

The answer, as McEuen later recalled in his book The Life I’ve Picked: A Banjo Player’s Nitty Gritty Journey, was an enthusiastic yes—paving the way for one of the most important recording sessions in country music history: the three-LP Will the Circle Be Unbroken.

It came at a pivotal time in country music. As trends shifted away from the more traditional Appalachian roots ("hillbilly") music that was the bedrock of the Grand Ole Opry, and toward a smooth-as-margarine "countrypolitan" style known as the Nashville sound, a generation of legends were left out in the cold.

The Nitty Gritty Dirt Band, however, weren’t ready to let artists like Scruggs, Roy Acuff, Jimmy Martin and Maybelle Carter slip away.

Formed as a jug band in Long Beach, California, in 1966, the quintet was part of the West Coast’s burgeoning country-rock scene. (Jackson Browne was an early member for a bit, before McEuen—talented on banjo, fiddle, mandolin and steel guitar—replaced him.) But they also had a love of real country and bluegrass and those genres’ roots.

Just as important, this embrace came at a crossroads for America, as generations were divided over polarizing issues like the Vietnam War and the counterculture, from music to hair styles, marijuana to the sexual revolution.

But the Dirt Band—at the time, McEuen, singer-guitarists Jeff Hanna and Jim Ibbotson, and multi-instrumentalists Les Thompson and Jimmie Fadden—found a way to make all that cross talk fade into the background. They would go into the studio with their heroes for a picking session. And they knew there was an audience for it. As McEuen told the website Sounds Like Nashville: "We had been playing colleges, and the kids would ask us about the banjo music. We found that a lot of the audience had never heard of Roy Acuff or Earl Scruggs or Doc Watson."

Scruggs began rounding up players but, famously, not everyone shared his enthusiasm. Bluegrass king Bill Monroe refused to join the session, allegedly skeptical of the young California hippies. And while Acuff agreed to do it, he came in suspicious.

"There’s no reason any group with the hippie dress—long hair, beards, dirty clothes—couldn’t sing on the Opry," he told Look magazine a month before the session. "But it wouldn’t be accepted as if you or I should walk on as we are in our good American way of life. The music is down to earth, for the home—not to get all hepped up and smoke a lot of marijuana and go wild about."