Back in 1993, b.h.t.m had its first big paid gig. The band brought its super-charged blues rock to the denverzoo, where the members found lifelong friends in Blues Traveler — whose frontman, John Popper, shared some portentous words that Todd Park Mohr never forgot. “When you’re young, you don’t know how long you’re going to be around; you don’t realize what you’re getting into,” Popper told the group’s titular vocalist and guitarist. “But people are always going to want to see you play, and I’m always going to want to see you play.” It’s rare to hold a friendship for forty years, much less a band, but Big Head Todd and the Monsters has beaten the odds. And while Denver has undergone massive changes since Mohr, drummer Brian Nevin and bassist Rob Squires formed the group in 1986 at Columbine High School, BHTM is much the same — as energetic and inexhaustible forty years in as when it released its breakout third album, Sister Sweetly, which went platinum, and built a widespread follow...