Born in Colfax, California in 1935, Riley began performing as a solo pianist during the 1950s. During that decade, he studied composition at San Francisco State University, the San Francisco Conservatory, and University of California, Berkeley, studying with Seymour Shifrin and Robert Erickson. He befriended composer La Monte Young, whose earliest minimalist compositions using sustained tones were an influence; together, Young and Riley performed Riley's improvisatory composition "Concert for Two Pianists and Tape Recorders" in 1959–60. Riley later became involved in the experimental San Francisco Tape Music Center, working with Morton Subotnick, Steve Reich, Pauline Oliveros, and Ramon Sender. Throughout the 1960s he also traveled frequently in Europe, taking in musical influences and supporting himself by playing in piano bars. He also performed briefly with the Theatre of Eternal Music in New York.