This chapter imagines what would happen to engineering masterpieces if humans were no longer around to maintain them. The English Channel Tunnel, connecting England and France, would not flood quickly—unlike many other tunnels—because it was dug within a single geologic layer of chalk marl with minimal filtration, giving it “one of the best chances of any human artifact to last millions of years, until continental drift finally pulls it apart or scrunches it like an accordion” (172). The Panama Canal was an unprecedented feat of engineering in the early 20th century. To move massive ships over the continental divide between North and South America, it uses a series of locks to lift them 137 feet above sea level to an enormous manmade lake and back down again on the other side. Without humans to maintain and replace the lock seals, the water would drain out; alternatively, with no one to open the floodgates, the dams would burst during storms, or eventually the gates would just rust away. Earthen dams would be gone within 20 years without maintenance, a Canal official predicts. In contrast, the giant sculptures at Mount Rushmore would likely last for millions of years because they are carved into Precambrian granite that erodes only once inch per 10,000 years.