Like many American roots enthusiasts, I was introduced to Del McCoury when he and Steve Earle teamed up for “The Mountain” in 1999. But for bluegrass aficionados, McCoury had been a mainstay for years. He performed with the legendary Bill Monroe in the early 1960s, played the bluegrass circuit in the ’70s and ’80s, and influenced and played with Phish and the String Cheese Incident in the ’90s. While he hasn’t reached the status of Monroe, or Flatt & Scruggs, he is widely seen as a national treasure. Last weekend was the ninth annual DelFest in Cumberland, Maryland, in the hills of the Appalachia, spanning four days and dozens of artists.