SANTIAGO XALITZINTLA, Mexico Each spring, residents of this village tucked at the base of one of the world’s most dangerous volcanoes trek up to a cave near its crater to make a peace offering. Their gifts of fruit, flowers and turkey cooked in sweet mole are meant to placate Popocatépetl, the nearly 18,000-foot-high volcano viewed by many here not just as a geological wonder, but also as a mythological being whose whims have long shaped the lives of those in its shadows.