Complex sentence: The band appeared at The Coachella Valley Music and Arts Festival on 13 and 20 April in Indio, California and Hard Rock Calling 2011 on 24 June in Hyde Park, London, where they were joined by Kaiser Chiefs and headline act The Killers.
Split into simpler sentences: The band appeared at Hard Rock Calling 2011 on 24 June in Hyde Park, London. They were joined by Kaiser Chiefs and headline act The Killers.