John C. Frémont’s official report on the 1842 expedition he led to the Rocky Mountains reads like a great adventure story. Frémont’s father-in-law, Thomas Hart Benton, a powerful senator from Missouri and strong proponent of western expansion, was a major supporter of the expedition, whose purpose was to survey and map the Oregon Trail to the Rocky Mountains. The senator hoped it would encourage Americans to emigrate and develop commerce along the western trails.

The party that included some twenty Creole and Canadian voyageurs and the legendary Kit Carson, started out just west of the Missouri border, crossed the present-day states of Kansas, Nebraska, and Wyoming, and ascended what the men believed to be the highest peak in the Wind River region of the Rockies. Frémont’s report provided practical information about the geology, botany, and climate of the West that guided future emigrants along the Oregon Trail; it shattered the misconception of the West as the Great American Desert.

Upon his return home to Washington, DC, Frémont dictated much of the report to his wife, Jessie Benton Frémont, a gifted writer. “The horseback life, the sleep in the open air,” she later recalled, “had unfitted Mr. Frémont for the indoor work of writing,” and so she helped him. Distilled from Frémont’s notes and filtered through the artistic sensibilities of his wife, the report is a practical guide, infused with the romance of the western trail.