S1 | E6 | Airdate: 12/16/2007
How did the Grand Canyon get so deep? What are the secrets revealed in its mile-high walls, and what makes a world-class white-water rapid? Will Gadd climbs a sheer 400-foot pinnacle to see what the birth of the Grand Canyon looked like 70 million years ago. He reveals the hidden worlds buried in the layers of rock in the canyon's walls. From deserts to oceans to tropical forests, it's all there as you go down. When he reaches the bottom, one mile down, he goes white-water kayaking down the canyon's interior to see exactly how those famous rapids are made. And just beneath the waterline he reaches the bottom of the Grand Canyon. He discovers America's basement, a layer of dense black rock that the United States is built on. This is the story of lost mountains, epic adventurers and gigantic volcanoes that have shaped one of the most iconic natural wonders in the world. In the biggest, most dangerous stunt of the series, Gadd flies across the Grand Canyon using just the power of the massive thermal lift generated by the intense temperatures formed deep within the canyon.