United States. Army. Corps of Topographical Engineers

The U.S. Army Corps of Topographical Engineers was a branch of the United States Army authorized on 4 July 1838. It consisted only of officers who were handpicked from West Point and was used for mapping and the design and construction of federal civil works such as lighthouses and other coastal fortifications and navigational routes. Members included such officers as George Meade, John C. Frémont and Stephen Long. It was merged with the United States Army Corps of Engineers on 31 March 1863, at which point the Corps of Engineers also assumed the Lakes Survey for the Great Lakes. In the mid-19th century, Corps of Engineers' officers ran Lighthouse Districts in tandem with U.S. Naval officers.

In 1841, Congress created the Lake Survey. The Survey, based in Detroit, Mich., was charged with conducting a hydrographical survey of the Northern and Northwestern Lakes and preparing and publishing nautical charts and other navigation aids. The Lake Survey published its first charts in 1852;

Major expeditions by the Corps:
Joseph Nicolas Nicollet, assisted by Second Lieutenant in the Corps of Topographical Engineers, John Charles Fremont, conducted a reconnaissance of the region of the Upper Mississippi River and Missouri Rivers in 1838 and 1839.
Boundary survey of the border with Republic of Texas (1841–42) by Maj. James Duncan Graham. Later discovered lunar tides in the Great Lakes in 1858-59.
Fremont conducted expeditions over the Oregon trail to the Columbia River and to California during 1842-1846. During his third expedition, Fremont detached Lieutenants James W. Abert and William G. Peck in August, 1845, at Bent's Fort on the Arkansas River to survey Purgatory Creek and the Canadian and False Washita Rivers.
Boundary survey of the Canada–US border (1844–46) led by William H. Emory.
Military Reconnaissance from Fort Leavenworth in Missouri to San Diego in California, Including Part Of The Arkansas, Del Norte, and Gila Rivers. By Lieut. Col. W. H. Emory, made in 1846-7, With the Advanced Guard of the "Army of the West" led by Brigadier general Stephen W. Kearny.
Boundary survey of the borders with Mexico; United States and Mexican Boundary Survey (1848-1855) led by William H. Emory.
Lorenzo Sitgreaves led the first topographical mission across Arizona in 1851.
Pacific Railroad Surveys, which consisted of five surveys to find potential transcontinental railroad routes. These survey reports were compiled into twelve volumes, Reports of Explorations and Surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean, made under the direction of the Secretary of War, in 1853-4. Volumes I-XII, Washington, Government Printing Office, 1855-61.
The Northern Pacific survey followed between the 47th parallel north and 49th parallel north from St. Paul, Minnesota to the Puget Sound and was led by the newly appointed governor of the Washington Territory, Isaac Stevens. Accompanying Stevens were Captain George B. McClellan with Lt. Sylvester Mowry out of the Columbia Barracks from the west and Lt. Rufus Saxton with Lt. Richard Arnold out of St. Marysville from the east.
There were two Central Pacific surveys. One followed between the 37th parallel north and 39th parallel north from St. Louis, Missouri to San Francisco, California. This survey was led by Lt. John W. Gunnison until his death at the hands of a band of Pahvants in Utah. Lt. Edward Griffin Beckwith then took command. Also participating in this survey was Frederick W. von Egloffstein, George Stoneman and Lt. Gouverneur K. Warren. Beckwith, subsequently explored the second Central Pacific route near the 41st parallel. This was the route subsequently closely followed by the Central Pacific and Union Pacific to complete the first transcontinental railroad.
There were two Southern Pacific surveys. One along the 35th parallel north from Oklahoma to Los Angeles, California, a route similar to the western part of the later Santa Fe Railroad and to Interstate 40, which was led by Lt. Amiel Weeks Whipple. Joseph Christmas Ives, Whipple's assistant, led the expedition that explored and mapped the Colorado River to the mouth of Las Vegas Wash. The southernmost Southern Pacific survey went across Texas to San Diego, California, a route which was later followed by the Southern Pacific Railroad which completed the second transcontinental railway in 1881. This survey was led by Lt. John Grubb Parke and John Pope.
The fifth survey was along the Pacific coast from San Diego to Seattle, Washington conducted by Lt. Robert S. Williamson and John G. Parke.
Exploration of the Colorado River of the West by Lt. Joseph Christmas Ives, 1858-59
Boundary survey of the borders with Canada, The Northwest Boundary Survey (1857–61)