Land art, also called Landscape Art or Earthworks, refers to works made from materials derived from the earth or situated on or within a landscape. Land art is usually site-specific—created for and utilizing characteristics of a particular location—and often invites human interaction and the passage of time to drive the work’s constant evolution. In the 1960s, American and European artists began to use dirt, rocks, and sand as media and subject matter, experimenting with diverse approaches. In 1967, the artist Richard Long paced up and down a stretch of meadow over and over, creating a visible path depicted in the photograph A Line Made by Walking. This understated meditation on a simple landscape contrasts with land art that seeks to dramatically alter a site, such as Robert Smithson’s 1970 sculpture and film, Spiral Jetty, which uses 7,000 tons of boulders, mud, and salt crystals mined from the area around Utah’s Great Salt Lake to form a massive spiral that snakes 450 meters from the lakeshore. Other emblematic works of land art include Walter De Maria’s Lightning Field (1977) in New Mexico, Nancy Holt’s Sun Tunnels (1976) in Utah, and Michael Heizer’s Double Negative (1969) in New Mexico. While many examples of land art are now managed by permanent collections or foundations, works associated with the installations, such as blueprints and plans, original photography, and artist films, are available to collect.