IN HIS “SITE/NON-SITE” projects of the late ’60s and early ’70s, Robert Smithson mapped the ravages and beauties of the twentieth-century landscape. His chosen sites were poisoned lakes, rubbish dumps, and construction zones, by-products of industrial capitalism. Intervening and scavenging in these wastelands, he carried back from them evocative fragments—stones, salt crystals, tar samples—which, in the gallery, became non-sites, abstract reminders of the absent site’s meaning. “My view of art,” Smithson wrote in 1969, “springs from a dialectical position that deals with whether something exists