Photographer Henry Diltz and the members of Crosby, Stills & Nash were driving around West Los Angeles looking for an interesting shoot locale when Graham Nash remembered recently noticing a funky old building on Palm Avenue. After finding the location—and no one around to ask for permission—the trio sat on a couch on the porch, singing, talking and laughing as Diltz snapped away. Two days later the group decided that a straight-faced shot...