Using a long 400mm telephoto lens, I focus on only a tiny part of the river as it roars between the towering cliffs and the piles of rocky debris that surround it. The tiny slash of bluish green contrasts strongly to the golden brown rocks and dark shadows that frame its course. We are looking at the work of nature here – centuries of it. It is a sight such as this that makes the Grand Canyon one of the wonders of the natural world.