Morton Feldman (1926 - 1987) is known for his work in indeterminacy, or chance music
Leo Ornstein (1893 - 2002) was born in Russia then migrated to the Lower East Side. He pioneered the tone cluster, close-knit groups of notes with a harsher sound than traditional chords.
Arnold Schoenberg (1874-1951) was an Austrian Jew who migrated to California when Hitler rose to power in 1933. His twelve-tone serial technique ushered in a new era of musical aesthetics, and would have been suppressed by the Nazis. In California he was free to develop it further and teach it to others. His influence is still felt and heard today.
John Zorn (1953 - ) blends popular music genres with classically-derived forms in experimental music. He has also composed film scores.