In 1867 he commenced a series of expeditions to the Rocky Mountains and the canyons of the Green and Colorado rivers. During his most famous expedition, from 24 May through 30 August 1869, he and his party made a daring nine-hundred-mile journey with four boats, traveling from the Union Pacific Railroad crossing of the Green River in Wyoming down through the Grand Canyon. He repeated much of the journey again in 1871 and 1872 to make a more thorough study of the Green and Colorado rivers.
In addition to his work in geology and botany, he studied the West's Native Americans and their languages. He founded and was named the first director of the Smithsonian Institution's Bureau of Ethnology, a position he held until his death. In 1879 the United States Geological Survey was organized and in 1880, following Clarence King's resignation, Powell became the director of the survey, a position he held until 1894.