1968
Robert Smithson, "A Sedimentation of the Mind: Earth Projects," Artforum 7, no. I (September 1968), p. 50

https://holtsmithsonfoundation.org/sites/default/files/2024-10/Smithson%20A%20Sedimentation%20of%20the%20Mind%20102524.pdf

reprinted in Robert Smithson: The Collected Writings, ed. Jack Flam (Berkeley: University of California Press.1996), p. 112.

https://monoskop.org/images/b/bd/Smithson_Robert_Collected_Writings_no_OCR.pdf