In 1967 Smithson began exploring industrial areas around New Jersey and was fascinated by the sight of dump trucks excavating tons of earth and rock that he described in an essay as the equivalents of the monuments of antiquity. This resulted in the series of 'non-sites' in which earth and rocks collected from a specific area are installed in the gallery as sculptures, often combined with mirrors or glass. In September 1968, Smithson published the essay "A Sedimentation of the Mind: Earth Projects" in Artforum that promoted the work of the first wave of land art artists, and in 1969 he began producing land art pieces to further explore concepts gained from his readings of William S. Burroughs, J.G. Ballard, and George Kubler.
As well as works of art, Smithson produced a good deal of theoretical and critical writing, including the 2D paper work A Heap of Language, which sought to show how writing might become an artwork. In his essay "Incidents of Mirror-Travel in the Yucatan"  Smithson documents a series of temporary sculptures made with mirrors at particular locations around the Yucatan peninsula. Part travelogue, part critical rumination, the article highlights Smithson's concern with the temporal as a cornerstone of his work.Home Depot Travelocity