The era of continental expansion culminated with the Oregon Treaty of 1846 and the conclusion of the Mexican-American War in 1848 and was closely followed by the discovery of gold in California. Thus began a period of rapid exploration and growth in this huge region. Mitchell’s series of map of the American West, published between 1846 and 1859, provide a fascinating view of the rapidly changing region.

This map is filled with early territory and county configurations, the exploration routes of Lewis and Clark, Fremont, Kearney and Cooke, and the Spanish and Oregon trails. Washington and Oregon have their eastern boundaries at the Continental Divide in the Rocky Mountains adjoining Nebraska Territory and show updated county structure compared to earlier editions. County development is confined to west of the Cascades except for the newly formed Skamania and Walla Walla counties in Washington. Utah Territory extends to Middle Park and Long's Peak in present-day Colorado where it borders Kansas and Nebraska Territory. Denver and the early mining settlements are not on the map; however St. Vrains Fort is located. New Mexico Territory encompasses parts of present-day Colorado and Arizona and shows the Gadsden Purchase border with Mexico. County development in California is well underway except in the south where the huge counties of San Diego and San Bernardino dominate. Although dated 1850 in the copyright, this scarce map is from an 1855 Desilver edition of the atlas. It retains the Thomas, Cowperthwait & Co. copyright and decorative rope borders in the characteristic green color.

References: Rumsey #3008.001.

Condition: A

Contemporary color with a few minor spots and a bit of soil in blank margins.