In 1869, John Wesley Powell set off down the Colorado River with nine men, four wooden boats, and no idea what lay ahead. The Grand Canyon, 300 miles of unmapped canyon, unknown rapids, and sheer rock walls, was the last blank space on the map of the continental United States.

Author John F Ross joins Hugh to tell the full story: how a one-armed Civil War veteran turned geologist became the first person to navigate the entire length of the Grand Canyon, racing against starvation through 360 rapids in boats that were entirely wrong for the job.

From losing a third of their food supply on the very first day, to the desertion of three desperate men - it is a thrilling snapshot into a moment in time. We ask what Powell's extraordinary journey revealed about the American West, about leadership under impossible pressure, and about what it m ...