Thor's Overlook

Eight spaces, no sign, on your left. That's Thor's Overlook, and it's worth pulling in. Parked? Read the walls from the top, starting with the rock at your feet. That's the Kaibab, two hundred seventy million years old, the stone that holds up both rims, and it began as the floor of a shallow sea. Brachiopods, corals, sponges and shark teeth have all turned up in it, so look down before you look out. Fossils stay where they lie, though. That's the law. Now find the great red cliff. Its name, the Redwall, is a fib. The rock is light gray limestone, only stained red, and its cliffs stand as high as eight hundred feet. Deeper still, at the Great Unconformity, layered rock sits directly on the old basement rock. About one point two billion years are missing there, some thirty percent of Earth's history. You're standing on a gap too. The surface under your shoes has two hundred seventy million years of its own missing. How old is the canyon itself? People have argued about that for over a hundred years. One camp says seventy million, the other says under six. A University of Colorado team read the older number from helium in tiny crystals, and argues the canyon was cut in stages. The park puts today's canyon at five to six million. Both camps agree on one thing. The Colorado, running through the whole of it, arrived about six million years ago. Stay well back from the edge. If you pulled in, turn left when you leave, heading east. You'll cross two hundred seventy million years of nothing.