Built on the northeastern shore of the Great Salt Lake near Rozel Point in Utah entirely of mud, salt crystals, basalt rocks and water, Spiral Jetty forms a 1,500-foot-long (460 m), 15-foot-wide (4.6 m) counterclockwise coil jutting from the shore of the lake. The water level of the lake varies with precipitation in the mountains surrounding the area, revealing the jetty in times of drought and submerging it during times of normal precipitation.
Smithson reportedly chose the Rozel Point site based on the blood-red color of the water and its connection with the primordial sea. The red hue of the water is due to the presence of salt-tolerant bacteria and algae that thrive in the extreme 27 percent salinity of the lake's north arm, which was isolated from fresh water sources by the building of a causeway by the Southern Pacific Railroad in 1959.
Smithson was attracted to the Rozel Point site because of the stark anti-pastoral beauty and industrial remnants from nearby Golden Spike National Historic Site, as well as an old pier and a few unused oil rigs. While observing the construction of the piece from a helicopter, Smithson reportedly remarked "et in Utah ego" as a counterpoint to the famous pastoral Baroque painting et in Arcadia ego by Nicolas Poussin.
To move the rock into the lake, Smithson hired Bob Phillips of Parson's Construction of nearby Ogden, Utah, who used two dump trucks, a large tractor, and a front end loader to haul the 6,650 tons of rock and earth into the lake. It is reported that Smithson had a difficult time convincing a contractor to accept the unusual proposal. Spiral Jetty was the first of his pieces to require the acquisition of land rights and earthmoving equipment.
He began work on the jetty in April 1970. Construction took six days.
In 1970 during the construction of the jetty, Robert Smithson wrote and directed a 32-minute color film, "Spiral Jetty". The film was shot by Smithson and his wife Nancy Holt, and funded by Virgina Dawn and Douglas Christmas.