Also known as Earth art. It can be seen as part of the wider Conceptual art movement in the 1960s and 1970s. Land artists began working directly in the landscape, sculpting it into earthworks or making structures with rocks or twigs. Some of them used mechanical earth-moving equipment, but Richard Long simply walked up and down until he had made a mark in the earth. Land art was usually documented in artworks using photographs and maps which the artist could exhibit in a gallery. Land artists also made Land art in the gallery by bringing in material from the landscape and using it to create installations. The most famous land art work is Robert Smithson's Spiral Jetty of 1970, an earthwork built out into the Great Salt Lake in the USA. Other Land artists include Walter de Maria, Michael Heizer and Dennis Oppenheim. Many others have made land art works.