When geologist Powell and his party of explorers first assayed the Colorado in 1869, it was North America's longest stretch of uncharted river. This is the story of that three-month, thousand-mile excursion, told in the words of the men who negotiated and mapped the river, through their journals, accounts, and letters. Black-and-white illustrations. Unabridged republication of the The Great Unknown: The Journals of the Historic First Expedition Down the Colorado River, published by Northland Publishing, Flagstaff, Arizona, 1988.
Here's a sample of other books in this Dover category
The Exploration of the Colorado River and Its Canyons by J. W. Powell Full text of Powell's 1,000-mile expedition down the fabled Colorado in 1869. Superb account of terrain, geology, vegetation, Indians, famine, mutiny, treacherous rapids, mighty canyons. 240 illustrations.