The Land Art movement was part of the anti-gallery uprising of iconoclastic artists in the 1960s and 1970s. This new film by James Crump is an excellent primer, and it features the movement's largely-reticent voices, including Robert Smithson, Walter De Maria, and Michael Heizer.
Here's a contemporary piece on the making of Spiral Jetty (pictured above from the film):
Here's a short clip of what Double Negative looks like today:
• Troublemakers website (troublemakersthefilm.com)