Complex sentence: Moskowitz returned to New York, but she and Byrd stayed in contact and, in early 1967, she returned to California as Byrd started to form a band, the United States of America, with another politically radical composer, Michael Agnello.
Split into simpler sentences: Moskowitz returned to New York, but she and Byrd stayed in contact. When Moskowitz returned to California, she and Byrd started the United States of America, with another politically radical composer, Michael Agnello.