In the 1970’s, New York artists began moving into large empty lofts in neglected downtown neighborhoods like SoHo. With all that space, their art got bigger and bigger – a perfect match for the egos of the nouveau riche collectors of the go-go ‘80s. But for some artists, even the lofts were too small. They left their studios altogether to work on a really monumental scale,  using the earth as a canvas and the backhoe as their paintbrush. A new documentary tells the story of the “land art” pioneers like Michael Heizer, Robert Smithson, and Walter De Maria. Madeleine speaks with the director.