It's hard to believe that this song was only a B-side when it was first released in 1958 with the single 'Donna'.
'La Bamba' is a Mexican folk song, so was not actually written by Ritchie Valens (May 13, 1941 - February 3, 1959), but Valens' adaption has been ranked highly in Rolling Stone magazine's top 500 songs of all time.
It was later covered by Los Lobos and featured in the 1987 biographical film 'La Bamba', and issued on the subsequent film soundtrack.
The version played here (in the key of B) features guitar and 'claves', the latter of which appear in Ritchie Valens' recording, and are a popular instrument in Afro-Cuban music.