Stephen Stills formed the Buffalo Springfield with Neil Young and the rest in 1966. Peter Tork, of the Monkees, was a friend of Stephen Stills, of Buffalo Springfield, then CSNY. Stills was the one who told Tork about the Monkees audition after being turned down himself. Buffalo Springfield appeared at Monterey Pop, and it was Tork and Stills who grabbed up Hendrix for a post-Monterey Pop jam that lasted for days. Stills later jammed with Hendrix on other occasions, in after-concert jams and in the studio. 
Hendrix made a guest appearance on Stills first solo outing, Stephen Stills, on a song titled Old Times, Good Times. (Eric Clapton played guitar on another track on the album.) Hendrix had died by the time the album was released, so Stills dedicated it to ‘James Marshall Hendrix.’
Stills claims to have recordings of jams with himself and Hendrix and others, but says they aren’t of any commercial value, so he has not released them. After Buffalo Sringfield, Stills went on to even greater success, forming Crosby, Stills, Nash and Young in 1968. Crosby, Stills, Nash and Young made their second live appearance at the Woodstock Festival in August 1969.