PBS
Pbs: American Experience: Grand Canyon: Powell's Expedition Colorado River
Part of the main feature called "Lost in the Grand Canyon," follow scientific explorer John Wesley Powell on his expedition down the Colorado River in 1869. This interactive map with its accompanying journal entries details the course of...
University of Virginia
University of Virginia: First Across the Continent: The Exploring Expedition
This 1902 work is available here from the University of Virginia. It includes illustrations and, according to the author, is taken largely from the accounts written by the explorers themselves.