Spiral Jetty is a basalt spiral 1500 feet long and 15 feet wide, which protrudes from the shore of the Great Salt Lake, on submerged land leased from the government. Given his preoccupation with entropy, it is fitting that each of the three existing earthworks designed by the artist Robert Smithson in the United States are severely degraded, and each in a different way. Spiral Jetty is usually invisible, lying a few feet under the fluctuating surface level of the lake. Smithson built the piece in 1970 at a time when the lake was at a particularly low level. As a result the piece only occasionally rises to the levels of perceptibility, within the visual conundrum that is the Great Salt Lake. In 2004, regional drought led to the emergence of the Jetty for over a year, a period that conveniently corresponded with a major traveling retrospective of the artist's work. Smithson had also conceived of a museum for the jetty, to be located near Golden Spike Monument. The Dia Art Foundation of New York acquired the piece from Smithson's estate in 1999.