BBC News - John Wesley Powell: The one-armed explorer 4 January 2014 Last updated at 01:07 While much of the US was being rapidly settled in the 19th Century, large parts of the West remained unknown. Determined to change that, one man led an expedition along the "impassable" Colorado River and into the unexplored Grand Canyon, writes historian Dan Snow, who followed in his footsteps for the BBC. In May 1869, 10 men in four boats - loaded to the gunnels with food and scientific equipment - set off from Green River in the American territory of Wyoming. The current bore them swiftly southwards. It was the start of one of the greatest journeys of exploration in American history, one that owed everything to the energy, ambition and towering curiosity of US Civil War veteran John Wesley Powell. His aim was to fill in the vast blank space, the area of a medium-sized European country, which still dominated the map of the American West. Running through this unknown territory was the world's mightiest canyon - a jagged, deep, yet breathtakingly beautiful scar carved by the Colorado River, known simply as the Grand Canyon. No man had ever boated the length of the Colorado, its massive cataracts were simply considered impassable. As the rest of the US was rapidly being settled, this area remained a mystery. The team succeeded in its mission, but at a terrible cost. Three months, and 1,000 miles (1,600km) later, only two boats carrying six emaciated survivors made it to a settlement at the mouth of the Virgin River in Nevada. Terrible hardship and privation had forced four men to abandon the expedition and driven the rest to the brink of insanity. This summer I set off in boats exactly like Powell's, to recreate a sizeable portion of that journey. We could never experience the full horror of what Powell's men went through. For a start, we knew where we were going. Powell and his men constantly stared at the horizon, straining for any signs that a mighty waterfall was about to cast them to their deaths. Spared that threat, we had it easy. Dan Snow looks into John Wesley Powell's 1869 expedition Powell was a true child of the 19th Century. He threw off the influence of his father, who was a poor itinerant preacher, an immigrant from Shrewsbury in England. Immersing himself in books, science was his creed. The voracious thirst for knowledge and advancement marked him out from childhood. Powell was in a hurry. He rowed down the Ohio, Illinois and Mississippi rivers before the age of 25. But his exploring was brutally cut short by the Civil War. Fighting for the Unionists, he witnessed the horrors of the Battle of Shiloh in 1862, where the wounded were burned to death as fires tore through the long grass that covered the battlefield. At Shiloh he was shot by a rifle bullet, lost an arm and almost died. Nerve damage would cause him great pain for the rest of his life. Powell launched his expedition after becoming obsessed with the West during rock and fossil collecting trips during previous summers. He was joined by a colourful collection of characters, from those with no experience to hardened mountain men, and called himself The Major. In his journal and a later account of the journey, he never once made reference to his disability and it never stopped him scaling the canyon edges to collect specimens. Dan Snow and crew members have a dramatic moment riding the rapids Some days the river was benign and progress easy. Other days the Colorado turned wild. While rowing on the stretches of flat water is exhausting, nothing compares to the stomach churning terror and physical exertion of being sucked into white water. Powell's expedition encountered about 500 significant rapids. Any one of these could have wrecked boats and killed crew. Some rapids he risked. The boats would, he said, "go leaping and bounding over these like things of life." Other rapids were death traps, "the rushing waters break into great waves on the rocks, and lash themselves into a mad, white foam." One of his men described an approaching rapid as "a perfect hell of waves." It would have been madness to run these rapids, so they would pull into shore, unpack all their supplies and portage everything along the precarious river bank. During my own trip, nine of us struggled to lift one boat. A portage of 400m took us the entire day, leaving the boat bumped and scraped, and our legs and ankles battered. Watch episode one of Operation Grand Canyon with Dan Snow on BBC Two at 21:00 GMT on Sunday 5 January, or catch it later on iPlayer In white water, the boats rapidly became waterlogged and filled up. They span around, impossible to control. Powell wrote that if the boat is "turned from its course so as to strike the wave broadside on, and the wave breaks... the boat is capsized; then we must cling to her for the watertight compartments act as buoys and she cannot sink; and so we go on, dragged through the waves." Once flat water was reached the exhausted men would scramble aboard and starting bailing. Powell's expedition lost two of its boats - one carrying a third of the remaining food and supplies. They were always collecting tree sap to help patch the remaining boats. By late August they were in a terrible condition. In a diary kept during the trip, soldier George Bradley wrote that it was, "a ceaseless grind... which taxed our strength to the limit." Three months before, on the very first day of the expedition, they had blithely thrown 500lbs (225kg) of bacon away to lighten the load. Now they were subsisting on musty flour alone. Bradley recorded that the thin rations had "reduced me to poor condition." On 28 August, discontent turned to outright mutiny. Three men hiked out of the canyon, preferring the uncertain dangers of the desert to what they felt was certain death if they stayed. Powell begged them to stay. "Some tears are shed," he wrote, "It is rather a solemn parting, each party thinks the other is taking the dangerous course." Tragically, these three men were never seen again, most likely killed by Mormons or Native Americans. The very next day, the two remaining boats with their starving crews finally emerged from the canyon. Their reappearance after months of silence thrilled a nation that had been waiting for news. Powell made the most of his new celebrity. He would become director of the US Geological Survey, the Bureau of Ethnology and the Smithsonian Institute. His experience in the canyon had taught him that, rather than being empty, the canyon was home to many Native American cultures. It was the start of an enduring fascination and he went on to lead further expeditions. He had entered the Grand Canyon as a pioneer, hoping that it could be exploited and settled, but the experience changed him. He realised that the presence of indigenous peoples, the landscape, water and ecosystems meant that it could not and should not be settled as the Eastern states had been. Now, as the Western states are threatened with a catastrophic water shortage, it is possible that he should be remembered not just as an explorer, but also as a prophet.