I found this story on the radio a couple of weeks ago:
“Filmmaker Lee Mendelson was looking to make a documentary about Peanuts creator Charles M. Schulz. One day, Mendelson was traveling across the Golden Gate Bridge in San Francisco and heard Guaraldi’s minor hit “Cast Your Fate To The Wind [on the radio].”
“Well, as jazz hits go, it was a smash,” Ramsey says. “But in the overall pop scene, it made its mark.”
So Mendelson contacted Ralph J. Gleason, a jazz critic in San Francisco, who put him in touch with Guaraldi. It was the beginning of a long partnership that resulted in commissions for many animated Peanuts specials.
http://www.npr.org/templates/story/story.php?storyId=120892574