David Roberts in Smithsonian Magazine:
The Grand Canyon occupies such an outsize place in the public imagination, we can be forgiven for thinking we “know” it. More than four million tourists visit the canyon each year, and the National Park Service funnels the vast majority of them through a tidy gantlet of attractions confined to a relatively short stretch of the South Rim. Even people who have never visited America’s greatest natural wonder have seen so many photographs of the panorama from Grandview Point or Mather Point that the place seems familiar to them.
But the canyon is a wild and unknowable place—both vast (the national park alone covers about 1,902 square miles, about the size of Delaware) and inaccessible (the vertical drops vary from 3,000 feet to more than 6,000). The chasm lays bare no fewer than 15 geological layers, ranging from the rim-top Kaibab Limestone (250 million years old) to the river-bottom Vishnu Schist (as old as two billion years). The most ecologically diverse national park in the United States, the Grand Canyon embraces so many microclimates that hikers can posthole through snowdrifts on the North Rim while river runners on the Colorado below are sunbathing in their shorts.