Wallage Stegner is one of the writers I deeply respect. I have read only his fiction in the past, but while we were at The Grand Canyon, I bought this book about John Wesley Powell, titled Beyond the Hundredth Meridian, John Wesley Powell and the Second Opening of the West.
Spending time looking at this vast and forbidding rocky chasm it was hard to imagine deciding to run the river without any idea what would be involved, but that is just what Powell and his group of volunteer explorers did, in the 1870s.
Even now, the tributary creeks have flash floods, which dump boulders into the Colorado proper and create new rapids. Around many bends they found white water, losing their supplies and being dumped into the river themselves.
Apparently Powell became an influence on the creation of land-use policies for the Colorado Plateau, on which are many of the Western National Parks today. He learned many Native American languages and was respectful to the peoples of the area. He understood, as many did not at that time, that these peoples were very individual in their cultures.