When the group was just starting out in 1965, their friend Barry McGuire helped them get a contract with his record label, Dunhill Records. McGuire recorded the first version of the song with The Mamas & The Papas as his backing band and a harmonica solo instead of a flute. It was going to be used as the follow up single to his hit, "Eve Of Destruction
." The Mamas & The Papas then decided to record it on their own, with Denny Doherty (the other Papa) singing lead and some chord changes he came up with after consulting the session guitarist, P.F. Sloan, who had him listen to "Walk - Don't Run
" by The Ventures. The results were impressive, and Dunhill Records agreed to use it as their first single, holding off on McGuire's version so there wouldn't be competition from an established artist.
At the same time, The Mamas & The Papas' version of their song "Go Where You Wanna Go" was pulled to focus on "California Dreamin'," allowing The Fifth Dimension to score their first chart it with the song a few months later. (thanks to Kent Kotal at Forgotten Hits