Leftover Salmon have never been a band to sit still and rest on their success. Celebrating 35 years at the vanguard of the scene, the Boulder-born heroes of jam grass are back with Let’s Party About It, an album that could be seen as a victory lap but is more a rowdy declaration that the party’s far from over. Recorded once again at the hallowed Compass Sound Studio, Let’s Party About It is a showcase for Leftover Salmon’s always-evolving blend of down-home bluegrass, rock n’ roll swagger, Cajun spice, with plenty of improvisational freedom. It’s the sound of a band that helped invent the jam band genre and still plays like they’ve got everything to prove.

The record opens with “Big Wheel,” with its banjo bounce and philosophical ease, and co-founder Vince Herman steering the song through cycles of time and change. On “Twisted Pine,” mandolin master Drew Emmitt trades lines with bluegrass royalty Del McCoury, their harmonies soaked in mountain melancholy. But just when things start to drift into traditional territory, the band shifts gears on “Good Dog,” a swampy, horn-fueled celebration of their Cajun side, where Jeff Coffin’s sax sizzles and Jay Starling’s Dobro beckons with Southern charm.

There’s also pure pickin’ joy on the instrumental “Salmon Scales,” where banjoist Andy Thorn leads the charge with guest Jason Carter on fiddle, and the band lets loose in technicolor jam fashion. The title track, “Let’s Party About It,” is a two-steppin’ rave-up that unites bluegrass great Sam Bush with funk-inflected sax runs from Coffin. It’s emblematic of the whole record - joyfully loose and rooted in tradition without being bound by it. Other highlights include “Redbird,” a nod to their early bluegrass days, and the emotional anthem “River Take Me,” carried by Emmitt’s weathered, soulful vocals.

Since the late ’80s, Leftover Salmon have defined the spirit of American roots improvisation. More than a jam band, they’re architects of a scene, pioneers who cracked open the bluegrass tradition and let in the funk, the swamp, the jazz club, and the dive bar. Sure, with Let’s Party About It, they’re celebrating a milestone, but they are also proving, once again, that no one throws a musical party quite like them.