In May 1869, a group of 10 men set out from Green River in Wyoming Territory, their goal to float from the Green River to the Grand River, and then onto the Colorado River through Grand Canyon. The inner canyon was terra incognito — unmapped and virtually unknown to anyone except local Indian tribes. Nineteenth-century America waited for news of the expedition with the same fascination that later generations felt for the Apollo missions.

The leader of the expedition, John Wesley Powell, was a Civil War veteran who’d lost his right arm to a cannonball during the Battle of Shiloh. He returned to the war after the wound healed and was promoted to major in the Union army. He later taught geology at Illinois Wesleyan University, having been fascinated by natural history since childhood. As a professor, he made field trips West, sparking his idea to explore the Colorado River through Grand Canyon.

When the expedition launched, the 35-year-old Powell was in charge of nine men, few with river experience, probably more than one interested in whatever gold they might find. One man left a month after they started out. When the remaining nine floated into Grand Canyon, they virtually dropped out of sight. Powell wrote in his journal, “We have an unknown distance yet to run, an unknown river to explore. What falls there are, we know not; what rocks beset the channel, we know not; what walls rise over the river, we know not.”

Fierce rapids battered the expedition’s four wooden dories, and the summer sun bore down on them. With food supplies dwindling and their clothing in rags, the men faced near starvation. In late August, three men left the expedition rather than face another brutal stretch of white-water. Powell named it Separation Rapid, and it proved to be the last difficult rapid they would face. Two days later, the remaining six reached the Colorado’s confluence with the Virgin River.

From Mormon settlements nearby, they were able to send word of their survival. Their journey took 99 days and covered a thousand miles. Powell learned that the three who’d chosen to leave were murdered on their hike to civilization. He included them in the dedication to his book about the expedition, The Exploration of the Colorado River and Its Canyons; published in 1875, it remains one of the finest adventure stories about Grand Canyon.

Powell repeated his canyon journey in 1872 and returned to the Southwest numerous times. Because of his strong interest in the native peoples of the region, Powell was named the first director of the Bureau of American Ethnology in 1880. He became the second director of the U.S. Geological Survey in 1881.

He was remarkably prescient about water issues in the West and warned that communities must carefully plan growth, cooperating to conserve water. Powell died in 1902, his warnings unheeded. The vast reservoir of Lake Powell bears his name, impounded behind the dam that forever changed the nature of the river he explored.