At Horseshoe Bend the Colorado swings a full 270 degrees around a lone butte of red sandstone near Page, in northern Arizona, and flows on, leaving the rock cut off on three sides 305 metres below the rim. The river arrives here the wrong colour. Colorado is Spanish for reddish, after the silt it once carried. But Glen Canyon Dam stands a few kilometres upstream and draws its releases from deep in the reservoir, so the water leaves cold and drops its sediment behind the wall. It reaches the bend as a clear emerald ribbon between rust-red cliffs. Those cliffs are Navajo Sandstone, the hardened remains of one of the largest sand-dune deserts the planet has known, laid down around 190 million years ago. The long curved lines etched across the rock are fossil dune faces, the shapes the wind left in a Jurassic Sahara. Iron has stained the exposed surface red, while the stone just beneath it stays almost white.
From the car park a wide path of soft red sand takes you gently uphill for about a kilometre and a quarter, past a pair of shade shelters. Then the ground simply falls away, and the whole loop opens in a single step. Beyond the fenced platform the bare rim runs on with no barrier at all, and from the edge the rafts on the river below you shrink to white flecks. The same bend gives two different pictures. Around midday the high sun reaches all the way to the canyon floor and the cold water blazes green against the walls with almost no shadow on it. As the sun swings west the whole amphitheatre of cliffs turns amber and the river sinks to indigo. There is one more thing the drop does. Leaning toward the rim, you watch ravens and white-throated swifts wheeling far beneath your feet, riding the updraughts off the sunlit walls — which is not the way anyone usually sees a bird fly.