Rooted in the free-form extended jams of psychedelic icons the Grateful Dead, the bluesy riffs of the Allman Brothers, and the Latin-tinged music of rock legends Santana, jam rock came into its own in the 1980s and '90s. The Dead were the quintessential point band for the jam rock movement, gaining a grassroots fan base through constant touring and word-of-mouth evangelism. Bands like Phish and Widespread Panic continue that tradition today, while the success of the platinum-selling Dave Matthews Band is one exception to the slow and steady sales normally enjoyed by bands in this school. The essence of jam rock naturally lies in live performance, as recorded formats place limits on expansive guitar spontaneity. Jam bands minimize the importance of song structures, relying instead upon an improvisational sprit that has its roots in the free jazz of Ornette Coleman and John Coltrane, even though their music is distinctly grounded in rock.