Map of an exploring expedition to the Rocky Mountains in the year 1842 and to Oregon & north California in the years 1843-44

America Transformed: During the 1840s, Americans became interested in the Far West as they settled the Oregon Territory and entered the Mexican-American War. One American explorer who made major contributions during this period was John C. Frémont, who led five scientific expeditions. Charles Preuss, a German immigrant and the expedition’s cartographer, prepared this map depicting only the geographic information collected. Frémont’s official reports, written with the assistance of his wife Jessie (daughter of expansionist-minded Missouri senator Thomas Hart Benton), gave "manifest destiny" a popular text. Advocates of "manifest destiny" believed it was the nation’s mission and preordained right to spread American institutions and culture, thus justifying a policy of territorial expansion.
Courtesy of Boston Public Library