The sound of the 70's was shaped by British band Led Zeppelin. The y were hugely popular throughout the entire decade. Every single one of their studio albums reached either #1 or #2... that is an outstanding track record.
Oddly enough with their beautiful song "Going To California" (1971) Led Zeppelin helped to define the laid back Southern California sound (which became extremely popular in the 70's with groups like Eagle, Carpenters and others.