Short answers, pulled from the story.
Land art is an art movement that emerged in the 1960s and 1970s, also known as Earth art, environmental art, and Earthworks. It used the materials of the Earth, including soil, rocks, vegetation, and water found on-site, and placed works in locations often distant from population centers.
Robert Smithson created the Spiral Jetty in 1970, arranging rock, earth, and algae into a 1500-foot spiral-shaped jetty protruding into Great Salt Lake in northern Utah. Its visibility depends on fluctuating water levels, and it has been completely covered and uncovered again by water.
Land artists rejected galleries and museums because their work could not easily be turned into a commodity for the commercial art market. The movement centered on rejecting the commercialization of art-making and embracing an emergent ecological movement, though photographic documentation was often shown in gallery spaces.
Prominent American land artists included Robert Smithson, Walter De Maria, Michael Heizer, Nancy Holt, James Turrell, Carl Andre, and Alan Sonfist. The most prominent non-American land artists were the British Chris Drury, Andy Goldsworthy, and Richard Long, along with the Australian Andrew Rogers.
The Land art movement declined after the mid-1970s economic downturn, when funds from wealthy patrons and private foundations largely stopped because land art was not marketable in the commercial art trade. The death of Robert Smithson in a plane crash in 1973 cost the movement one of its most important figureheads.
Land art drew on much older traditions of hill figures and geoglyphs, and its 1960s Earth art recalled works such as Stonehenge, the Pyramids, Native American mounds, the Nazca Lines in Peru, and the Carnac stones. It was also inspired by minimal art, conceptual art, De Stijl, Cubism, and the work of Constantin Brâncuși and Joseph Beuys.