Quicksilver Messenger Service is an American rock band that emerged from San Francisco's psychedelic music scene in the mid-1960s. Known for their extended, improvisational jam sessions, their music combines elements of blues, folk, and jazz. The band's notable members include guitarists John Cipollina and Gary Duncan, whose dual lead guitar work was a distinctive part of their sound. Their most influential work is arguably the album "Happy Trails" (1969), which is considered a cornerstone of psychedelic rock.