The Raynolds Expedition was an United States Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 exploring and mapping party which left St. Louis, Missouri

St. Louis, Missouri

St. Louis is an independent city on the eastern border of Missouri, United States. With a population of 319,294, it was the 58th-largest U.S. city at the 2010 U.S. Census. The Greater St...

 May 29, 1859 and was intended to map the unexplored territory between Fort Pierre, Dakota Territory

Dakota Territory

The Territory of Dakota was an organized incorporated territory of the United States that existed from March 2, 1861, until November 2, 1889, when the final extent of the reduced territory was split and admitted to the Union as the states of North and South Dakota.The Dakota Territory consisted of...

 and headwaters of the Yellowstone River

Yellowstone River

The Yellowstone River is a tributary of the Missouri River, approximately long, in the western United States. Considered the principal tributary of the upper Missouri, the river and its tributaries drain a wide area stretching from the Rocky Mountains in the vicinity of the Yellowstone National...

. Led by experienced explorer and topographical engineer Captain William F. Raynolds

William F. Raynolds

William Franklin Raynolds was a U.S. Army Colonel, explorer, engineer, Mexican War and Civil War officer who is best known for leading the 1859-1860 Raynolds Expedition while serving as a member of the U.S. Army Corps of Topographical Engineers...

, other members included photographer James D. Hutton

James D. Hutton

James Dempsey Hutton was an artist, surveyor, cartographer and early photographer active in Montana, Wyoming, South Dakota and North Dakota in the years before the American Civil War. He served as an engineer in the Confederate States Army in that conflict, and died in exile in Mexico in...

, geologist and naturalist Ferdinand Vandeveer Hayden

Ferdinand Vandeveer Hayden

Dr. Ferdinand Vandeveer Hayden was an American geologist noted for his pioneering surveying expeditions of the Rocky Mountains in the late 19th century. He was also a physician who served with the Union Army during the Civil War.-Early life:Ferdinand Hayden was born in Westfield, Massachusetts...

. The expedition was guided by legendary mountain man

Mountain man

Mountain men were trappers and explorers who roamed the North American Rocky Mountains from about 1810 through the 1880s where they were instrumental in opening up the various Emigrant Trails allowing Americans in the east to settle the new territories of the far west by organized wagon trains...

 Jim Bridger

Jim Bridger

James Felix "Jim" Bridger was among the foremost mountain men, trappers, scouts and guides who explored and trapped the Western United States during the decades of 1820-1850, as well as mediating between native tribes and encroaching whites...

.