In 1869, John Wesley Powell completed the first, and widely heralded, descent of the Green and Colorado Rivers. The previous summer he had been in Colorado on a field expedition. After his studies were completed, he spent the winter (1868-69) along the White River (tributary of the Green River).
In the early spring of 1869, he went back East, built boats, and then very quickly returned west to the town of Green River with the boats, pushing off down the river on May 24th. He later chronicled his harrowing journey in The Exploration of the Colorado River. The following map shows the various canyons through which Powell passed on that memorable journey.
(See also the map showing Powell's travels in the Colorado Rockies.)