Early on the Green River, the Powell Expedition lost one of their large gear-carrying boats at a rapids they named Disaster Falls, washing up on Disaster Island. No one was killed, but many crucial supplies were lost, including all of the expedition's barometers. Fortunately, Powell and his men managed to recover some of the barometers - they were the only means Powell had at his disposal to determine his elevation. Knowing the elevation was essential for producing good maps, and it let the expedition know how much vertical drop remained before they reached sea level. The Powell expedition named many of the features along the Green and Colorado rivers, including the Gates of Lodore.
The expedition set out from Green River, Wyoming on May 24 with a company of ten men led by Powell, a veteran of the American Civil War who had spent much of his youth rafting on the Mississippi River and its tributaries in the upper Midwest, and who had lost his arm to amputation in the Battle of Shiloh. Prior to coming west, Powell had been a professor of geology in Illinois and established the Illinois Museum of Natural History. In addition to Powell, the company included his brother Walter, as well as a group of seasoned mountain men that Powell had recruited on his way to western Wyoming. The company consisted of