Complex sentence: The Opposite Six were and American garage rock band from California, California who were active in the 1960s, not to be confused with another band of the same name also from the Bay area but from Marin County.
Split into simpler sentences: The Opposite Six were and American garage rock band from California, California who were active in the 1960s. They are not to be confused with another band of the same name also from the Bay area but from Marin County.