Mt. Rushmore is a famous landmark in the Black Hills of South Dakota. The faces of four American Presidents are carved into the mountain. According to a new book, this faces may last 7.2 million years (not forever but still a long time.)
The book is The World Without Us by Alan Weisman. A review in the New Yorker noted, "Teasing out the consequences of a simple thought experiment—what would happen if the human species were suddenly extinguished—Weisman has written a sort of pop-science ghost story, in which the whole earth is the haunted house. Among the highlights: with pumps not working, the New York City subways would fill with water within days, while weeds and then trees would retake the buckled streets and wild predators would ravage the domesticated dogs. Texas’s unattended petrochemical complexes might ignite, scattering hydrogen cyanide to the winds—a mini chemical nuclear winter. After thousands of years, the Chunnel, rubber tires, and more than a billion tons of plastic might remain, but eventually a polymer-eating microbe could evolve, and, with the spectacular return of fish and bird populations, the earth might revert to Eden."
While most signs of humanity vanish fairly quickly, not so the Presidents on Mt. Rushmore. Weisman wrote, "According to geologists, Mount Rushmore's granite erodes only one inch every 10,000 years. At that rate, barring asteroid collision or a particularly violent earthquake in this seismically stable center of the continent, at least vestiges of Roosevelt's 60 foot likeness, memorializing his canal, will be around for the next 7.2 million years" (p. 182).
If society collapses, and then comes back some distant time in the future, I wonder what they will make of Mount Rushmore? I am guessing they will think the Black Hills were sacred and that these men are the representation of gods. Or maybe they will just think that whatever society built the monument had an overdeveloped ego.