My classmate, Hass, and I were standing on a rooftop on the lower west side of Manhattan watching a dance performance taking place in a vacant lot across the street when he nudged me and whispered, “That’s Robert Smithson.” The tall guy to my left at the parapet, in a cowboy hat and black trench coat, was solemnly staring down at the ground, along with a couple dozen other bohemes of the downtown art scene who had climbed four flights of rickety stairs in a derelict, cheese warehouse to view the show.