Halfway through Mountain Tracks, vol. 3, Yonder Mountain String Band’s newest live release, the Colorado quartet shifts into jamband gear. A pack of young, hip and talented players, YMSB represents the best of modern progressive bluegrass — a style of playing which weaves bits of folk, rock, and even jam into mountain music’s acoustic frame. Yet, throughout Mountain Tracks’ first five cuts, YMSB plays it relatively straight, offering a series of tight, and relatively traditional, bluegrass tunes.

In fact, it's not until the segue connecting "If There's Still Ramblin' in the Rambler" and "Steep Grade, Sharp Curves," that YMSB proves its jamband colors. The change happens quickly and smoothly, without disrupting the tight banjo picking of Dave Johnson. But, during an extended reading of "Steep Grade," the group's jamband underbelly shines through brightly. Perhaps a testament to the group's relaxed, yet effective, style of improvisation, Yonder slips from bluegrass covers into more experimental territory with advanced ease. Yet, despite their overt bluegrass leanings, YMSB are firmly grounded on jamband soil.

A two-disc set, which collects highlights from the band's September 2003 appearance at Planet Bluegrass, Mountain Tracks isn’t for novices. Filled with uptempo bluegrass romps, such as the album closing original "Peace of Mind," this meaty collection offers the full YMSB experience. Spread across 24 songs, including an unlisted cover of Johnny Cash’s "Ring of Fire," Yonder Mountain jumps from tight traditional songs ("Queen of the Faith") to long-winded originals ("Traffic Jam") to choice country-rock covers (Willie Nelson’s "Bloody Mary Morning"). Yet, throughout, the group manages to be cohesive, mostly through its rock and roll energy. Yonder Mountain also offers its share of asterisk-worthy surprises, including a spoken word appearance by Kinfolk celebrity Pastor Tim, and guest spots from fiddler Darol Anger. Fleshing out a number of key tracks, including "Maid of the Canyon," Anger offers a number of choice solos, functioning as a quasi-fifth member.

In fact, after a few relatively straightforward bluegrass tunes, including a duet between mandolin player Jeff Austin and guitarist Adam Aijala on "Coo Coo's Nest," YMSB offers a setlist of segues, turning the second portion of both shows into mini-medleys. And, like any great jamband, Yonder Mountain use certain songs as thematic hooks, tying disc one together with bassist Ben Kaufman's bright "Traffic Jam," and disc two with Austin's abovementioned "Peace of Mind."

Like String Cheese Incident before them, Yonder Mountain also work as a bluegrass songbook of sorts, introducing a new generation of music aficionados to the works of Bill Monroe and others. While traditional music is driven by its story, Yonder Mountain's progressive blend favors rhythm, provided throughout by Kaufman's upright bass. Though the group's lyrics are well composed, Yonder Mountain tends to favor the whimsical over traditional old time stories (best exemplified during on odd take on Monroe's "Kentucky Mandolin"). And, in the end, perhaps it's this sense of ease, which has allowed Yonder Mountain String Band to extend their traditional sound into the present.