In 1806, U.S. Army General James Wilkinson assigned Lieutenant Zebulon Montgomery Pike to explore the headwaters of the Arkansas and Red rivers. From St. Louis, the lieutenant's modest party traveled across the Great Plains to the Front Range of the Rocky Mountains. Throughout the journey, Pike maintained a journal, describing terrain, Indians, hardships, and the group's daily activities. In present-day southern Colorado's San Luis Valley, Pike and his men were captured by the Spanish and taken to Santa Fe, where many of his papers were confiscated by Spanish authorities, not to be...