With their latest album, “Get Yourself Outside,” Colorado-based Yonder Mountain String Band once again echoes out into the universe their place as not only a pioneering jam-grass act, but also one of the most innovative groups in the live music scene — something the groundbreaking ensemble has proudly held high for the better part of a quarter-century. From selling out Red Rocks Amphitheatre at a time that was unheard of for string acts, to performing for tens of thousands at festivals like Bonnaroo, Yonder Mountain was the initial spark in an acoustic inferno decades ago that endures headlong into the 21st century.