I always found sixties beach movies pretty dull: though I love Buster Keaton, his appearances in them were pretty much the nadir of his career, I would say. So I would only really watch them in fast-forward mode, looking for the rare appearances of minor surf and garage bands. That's why I guess I entirely missed this song, from Pajama Party. I always associated the song with the Ramones, although I vaguely knew that it was a cover.
Update: I really should do my research before I post: turns out first hit version of California Sun was by The Rivieras, from South Bend, Indiana, and the original recording was by a guy called (showbiz Alliteration Alert) Joe Jones. Here's an article on the history of this song in, of all places, the Jewish World Review.
Listen:
Download: Annette Funicello - California Sun MP3 (rapidshare)