What is the theme in The Exploration of the Colorado River and Its Canyons by John Wesley Powell?

One of the most dominant themes of the book is adventure, even though the author points out that the purpose of the expeditions was science and not adventure. An experience of this sort could not be anything but adventure no matter what the purpose of the expedition. The men were exploring uncharted territory. They didn't know what to expect and had to be prepared to deal with any situation that they came upon. There was nothing to tell them what was around the next bend in the river or what the conditions were. They would climb the cliffs to look over the area to try to ascertain where the river was going and what the conditions were. They had to look ahead for rocks in the water and listen for the roar of upcoming waterfalls.