Dave Johnston has just finished reading All the Pretty Horses, the first book in author Cormac McCarthy’s noted Border Trilogy series. And the Yonder Mountain String Band banjo player has noted a parallel between the book’s protagonist, John Grady Cole, and his nearly two decades-old, Colorado bluegrass band.

“There’s this great quote in there when the main character’s on the way back home, and it’s about how people are formed by their landscapes and by their environments,” Johnston says. “The inner life of a person is actually made more by the environment than by any decisions that the person could actually make. And that kind of dovetails with [Yonder Mountain]. I think the inner light of what makes a band is going to be influenced by its environment. It might have more to do with where you’re located than you want to acknowledge.”

In the same way that McCarthy’s novels migrated from the foothills of the Blue Ridge Mountains to the Wild West, bluegrass music made a similar journey. Born in the Appalachian Mountains, bluegrass has taken root in Colorado, where it’s meshed with the open-ended ideas and loose structures of progressive jam-band rock to rewrite the definition of the genre. And if any band typifies the Rocky Mountain approach to bluegrass, it’s Yonder Mountain String Band.

About as anti-dogmatic a bluegrass band as one’s likely to find, Johnston’s band has been straddling bluegrass’ new and old worlds since the late 1990s, bucking against its hidebound formalism while reveling in its hot-shit riffing.

Though Johnston can’t quite place his finger on it, he accedes that there’s just something about the mountains in the West that makes them different from the mountains in the East.

There are parallels, Johnston observes, in the political proclivities of Appalachia and the Rockies. Western North Carolina, for example, tends to be politically progressive and humanistic, and the same holds true for the Front Range of Colorado, which stretches from Pikes Peak to the Colorado-Wyoming state line and encompasses most of Colorado’s progressive bases, like Denver and Boulder.

Such free-thinking ideas trickle down into the Front Range’s music scene, creating an atmosphere comprising adventurous musicians and an adventurous audience. Forward-thinking Colorado bands like Hot Rize, Leftover Salmon, and String Cheese Incident acted as “older brothers” to Yonder Mountain, Johnston says, paving the way for traditional-sounding bands with progressive ideas and a proclivity for live improvisation. And in the same way that Colorado’s progressive enclaves support liberal ideas, audiences in Colorado are willing to support bands that push beyond traditional boundaries.

“It’s a place that, you know, they definitely honor the tradition, and they love the music that’s held up, from traditional mountain music to traditional bluegrass to jazz, all of that,” Johnston says. “But they also like things that are moving in another direction, I think you could say. I think the audience there likes music that takes chances and isn’t overly formal.”

Formally, Yonder Mountain String Band looks like a bluegrass band, lacking both electric instruments and percussion. But bluegrass’ inherent orthodoxy doesn’t limit Yonder Mountain String Band, Johnston argues — it actively spurs his band’s decidedly unorthodox explorations.

“The thing I loved the most about when I first felt like I really heard bluegrass was that I really loved the sentimentality of the speakers in the songs,” Johnston says. “It almost seemed like that was one of the big rules, that you had to be really direct, even if it meant appearing very sentimental. And I think that is missing in a lot of modern music. It makes the freer parts of what Yonder Mountain does, when we break out of the form, I think it feels more authentic with how we feel about music and how we feel about our influences.

“I don’t want to suggest that because we play something that might not resemble formal bluegrass that we’re somehow not fans of that music as well, because we are,” Johnston continues. “But that’s how we feel sustained by doing what we do.”

And that feeling sustained Yonder Mountain’s original lineup for 16 years, up until last spring, when founding mandolinist Jeff Austin bolted from the group for a solo career, casting doubts about the band’s future. But you either stick or you quit, McCarthy wrote in All the Pretty Horses, and Yonder Mountain is sticking. Rather than try to replace Austin, the group first subbed in special guests on the road and in the studio — including legends like dobro player Jerry Douglas and mandolinist Sam Bush — before bringing in young guns Jake Joliff, a monster mandolinist who was a founding member of the disbanded Americana outfit Joy Kills Sorrow, and fiddler Annie Kral, who’s spent time with progressive jam acts Railroad Earth and moe.

The new blood has reinvigorated the band, Johnston says, opening up new exploratory avenues and offering refreshing songwriting ideas. It places Yonder Mountain String Band in an unusual position.

“It’s two things happening at once,” Johnston says. “It is a new band, but it’s not entirely new, either. We’re in between — sort of like our relationship to formal bluegrass and nontraditional bluegrass. It all kind of feels like it dovetails pretty nicely.”