On 5 August 1869, John Wesley Powell and his nine companions launched their four boats into the Colorado River near Lees Ferry and soon entered what is now known as the Grand Canyon of the Colorado. Thus began the most hazardous and exciting phase of their exploration of the upper Colorado River, a journey that had begun 74 days earlier, upstream on the Green River. Their aim was to fill in one of the last remaining unmapped regions in the American West by reporting on 300 miles of inaccessible canyon lands. Having entered Marble Canyon, Powell’s expedition was immediately confronted with vertical rock walls and death-defying white-water rapids, only some of which could be bypassed by portaging their boats. Sand bars provided temporary campsites, but with food running low and little opportunity for hunting, their emergence mostly safe and sound, 24 days later, was seen as little short of miraculous. Vividly recorded in Powell’s The Exploration of the Colorado River and Its Canyons (Powell, 1961; first published in 1895), the expedition was deemed an outstanding success, as evidenced by public acclaim back in the east. More significantly, it triggered investment by the Federal government into mapping and developing the resources of this hitherto unknown region in the American West.