“California Girls" is from the Beach Boys 1965 album Summer Days (And Summer Nights!!).

It was late at night and Brian Wilson, who had just taken LSD for the first time, was in the bedroom of his Hollywood apartment with a pillow over his head. He had images of his mother and father on his mind and most of all, fear. He was said to have pushed through those thoughts and walked downstairs to the piano.

In a 2007 interview, Wilson explained that he went to his piano and "was thinking about the music from cowboy movies.  I sat down and started playing it, bum-buh-deeda, bum-buh-deeda.  I did that for about an hour and got these chords going.  Then I got this melody, it came pretty fast after that."  He said that "California Girls" was intended to encapsulate the feel of the Drifters' version of "On Broadway" and on other occasions, said that the shuffle beat in the song was influenced by Bach's "Jesu, Joy of Man's Desiring".

The next day, Mike Love came by the apartment on Gardner Street and the pair took turns building a hit.  Wilson said that he came up with the subject matter and opening lines and that "Every other line was his or mine. ... Everybody loves girls, right? Everybody loves California and the sun.  That’s what I wanted from the song. And to mention all the parts of the country, that’s fun, people will like that."

Love was not originally listed as the song's co-writer but was awarded a credit after his successful 1990s lawsuit for songwriting credits.  He said that he approached Wilson about the omission when the song was released, and that Wilson had told him that the mistake was the fault of Wilson's father Murray, the band's publisher.

Lead vocals on the song were by Love, but you can also hear Bruce Johnston on the track along with Brian Wilson, Carl Wilson, Dennis Wilson and Al Jardine.  Johnston was brought in to tour with the group when Brian Wilson decided to stay off the road, and this was his first vocal appearance on a Beach Boys song. 

Various Sources