Barry McGuire once played with the New Christy Minstrels, composing and singing lead on their biggest song, "Green, Green". His "Eve of Destruction" was done in one take and went to number one. During this time he met the Mamas and the Papas and introduced them to produced Lou Adler and they ended up singing backup on Barry's album "Child of Our Times". Barry's version of "California Dreamin'" was supposed to be the second single from the album "This Precious Time" but, at John Phillips request, it wasn't released.
The Mamas and the Papas version of "California Dreamin'" was essentially the same as Barry McGuire's except they replaced Barry's voice with Denny Doherty's and added a flute.