Sight Unseen

John C. Frémont was the most celebrated explorer of his era. In 1842, on the first of five expeditions he would lead to the Far West, Frémont and a small party of men journeyed up the Kansas and Platte Rivers to the Wind River Range in Wyoming. At the time, virtually this entire region was known as the Great Desert, and many Americans viewed it and the Rocky Mountains beyond as natural barriers to the United States. After Congress published Frémont's official report of the expedition, however, few doubted the nation should expand to the Pacific.

The first in-depth study of this remarkable report, Sight Unseen argues that Frémont used both a radical form of the picturesque and an imaginary map to create an aesthetic craving for expansion. Not only did he redefine the Great Desert as a novel and complex environment, but on a summit of the Wind River Range he envisioned the Continental Divide as a feature that would unify rather than obstruct a larger nation.

In...