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An Early Expedition through Wyoming and South Pass

Detailed map of the route taken by a detachment of American soldiers under the command of Stephen Watts Kearny in the summer of 1845.

The map was drawn to illustrate Kearny's report of a summer campaign to the Rocky Mountains, and covers the region between the Arkansas and Platte Rivers, reaching into Wyoming as far as South Pass and Green River. The dragoons departed Ft. Leavenworth and marched to South Pass via the "Oregon Trail" and returned 99 days later via the Arkansas River route, a distance of 2200 miles over the toughest western terrain.

Kearny's expedition began in Fort Leavenworth and proceeded on a circular march, heading northwest on what would later become the Oregon Trail, down along the Rocky Mountains to Mexican territory, and back up via the Santa Fe Trail. This march was intended as a display of the United States military power, both for the benefit of local Indian tribes and also for the British government, which at this time was trying to exert control over Oregon Territory.

Early Map by Future Major General William B. Franklin

The map is the work of Lieutenant William Buel Franklin (1823-1903),  a career United States Army officer and a Union Army general in the American Civil War. He rose to the rank of a corps commander in the Army of the Potomac, and also distinguished himself as a civil engineer before and after the war.  

Future President James Buchanan, then a Senator, appointed Franklin to the United States Military Academy in June 1839. Franklin graduated first in the class of 1843 and joined the Corps of Topographical Engineers. His first assignment was to assist in the survey of the Great Lakes. Then, he was sent to the Rocky Mountains for two years to survey the region with the Stephen W. Kearny Expedition.  After Kearny's expedition, Franklin served under General John E. Wool during the Mexican–American War and received a brevet promotion to first lieutenant after the Battle of Buena Vista.