Cajón del Maipo

This guide to Cajón del Maipo outside Santiago starts with a strange find: fossilized seashells cemented into rock two thousand meters up, toward Baños Morales, evidence that this whole canyon once lay on an ancient sea floor. It follows Charles Darwin's own visit here in 1835, when he read those stranded shells as proof the Andes had been shoved skyward out of the ocean by colliding tectonic plates. Split open a stone along the trail, and you might find the shell of an ammonite, a distant squid relative, more than one hundred thirty million years old.