Between 1860 and 1879 four major expeditions sponsored by the U.S government surveyed, mapped, and explored a large geographical region west of the Mississippi River.

The maps and reports were submitted from the U.S. Geological Exploration of the 40th Parallel, led by Clarence King; the U.S. Geographical Survey West of the 100th Meridian, led by Lieutenant George Montague Wheeler; the U.S. Geological and Geographical Survey of the Territories, led by Ferdinand Vandeveer Hayden; and the U.S. Geographical and Geological Survey of the Rocky Mountain Region, led by John Wesley Powell. In 1879, these were either concluded or consolidated under the newly created office of the U.S. Geological Survey.

Though many other expeditions occurred before and during the period between 1860 and 1879, including, but not limited to, the Lewis and Clark expedition, the Zebulon Montgomery Pike expedition and the Josiah Whitney expedition, only these four led directly to the creation of the U.S. Geological Survey and are referred to as the "Great Surveys" of the American West.

In 1867 the U.S. Congress appropriated funds to establish the Geological Exploration of the Fortieth Parallel under the War Department. Chief of the Army of Engineers, General Andrew Atkinson Humphreys, appointed Clarence King, a graduate of Sheffield Scientific School of Yale, to lead the survey. The mission of the survey was to examine the geological features and natural resources across a band of land between the 105th and the 120th meridians along the 40th parallel. Additional natural scientists to the survey included three geologists, a botanist, and an ornithologist. In order to document the survey, King hired Timothy O'Sullivan, a former photographer with Mathew Brady's Civil War photography corps.

The Fortieth Parallel Survey set up a base-camp in the Truckee Meadows, near present-day Reno, Nevada. Their first task was to make a 15,000 square mile map of the area between the California Sierra Nevada and the Shoshone mountain range 150 miles to the east. Though the survey did not make it to the 105th meridian, King and his men crossed the Humboldt Sink, the Carson Sink, and the Black Rock desert. They collected two thousand rock specimens, examined numerous mines, and set up 300 barometrical stations before ending the first season and returning to base camp.

While wintering in Virginia City, Clarence King and two other geologists explored and gathered data on Comstock mines, while photographer Timothy O'Sullivan took photographs from deep inside the Comstock mines, using magnesium flashes for illumination.

The Fortieth Parallel Survey's second season expanded the territory of the first season to cover all the Great Basin as far as Salt Lake. The U.S. Congress, pleased with the quality and amount of scientific information sent by the expedition, funded subsequent seasons until 1873, when General Andrew Atkinson Humphreys concluded the survey.

Seven volumes of research were published during and after the Fortieth Parallel Survey, including The Mining Industry (1870), Microscopic Petrography (1876), Descriptive Geology (1877), and Systematic Geology (1878).

In the same year as the Fortieth Parallel Survey, Ferdinand Vandeveer Hayden, a professor of geology and mineralogy at the University of Pennsylvania, was appointed geologist-in-charge of the United States Geographical and Geological Survey of the Western Territories. Hayden's orders were comprehensive and included, among other things, searching for deposits of oils, coals, clay marls, and other mineral substances. In addition, Hayden's survey was charged with gathering samples of geology, mineralogy and paleontology, and to note soils with regard to their adaptability to specific crops.

In the twelve years that Hayden led the U.S. Geographical and Geological Survey of the Territories, numerous scientists and artists contributed their talents to its purpose. An example of this contribution is the photographic work of William Henry Jackson, a photographer who had, prior to his appointment to the survey, been documenting the building of the Union Pacific Railroad as it journeyed westward to join the Central Pacific railroad. Jackson's images of the Yellowstone region accompanied sketches by Thomas Moran and a detailed report of the survey's findings. These were presented to the U.S. Congress, and on March 1, 1872 President Grant signed a bill making the region Yellowstone National Park.

Included in the vast output of the Hayden survey are Sun Pictures of the Rocky Mountain Regions (1870) with photographs by William Henry Jackson, The Yellowstone National Park (1876) illustrated by Thomas Moran, Geological and Geographical Atlas of Colorado (1877), and The Great West: Its Attractions and Resources (1880).

As with the Hayden survey, reports and collections made by John Wesley Powell helped to build interest in and perpetuate the exploration of yet another area of the American West, the Grand Canyon and plateau regions of Colorado and Utah. Powell, a former Civil War veteran and a professor of geology at Wesleyan College in Illinois, proposed a geological and geographical survey by boat of the Colorado River and its tributaries.

Powell's initial expedition exploring the Colorado River from May 24 to late August 1869 received favorable media coverage, in part due to Powell's entertaining lectures. Unfortunately, however, the survey yielded very little in the way of physical data.

For the second expedition Powell turned to the U.S. Congress as a means to supplement funds that he was currently receiving from the Smithsonian Institution in Washington, D.C. In June of 1872, Powell was granted $10,000 to lead a second expedition, the Geographical and Topographical Survey of the Colorado River of the West.

Powell's primary interest was in geology and ethnology, and his investigations centered on the problem of aridity and human adaptation in the lands of the West. Powell's travels by foot and by boat brought him into contact with what he called the plateau tribes; the Paiutes, the Shivwits, the Unikarits, the Utes, and others. Inspired by these encounters and by the ancient ruins of cities he saw while on the Colorado River, Powell later became the Smithsonian Institution's first Director of the Bureau of American Ethnology, a post he held from 1872 until his death in 1902.

The Powell expeditions yielded several books and reports: Exploration of the Colorado River of the West and its Tributaries (1875), Report on the Geology of the Eastern Portion of the Uinta Mountains (1876), Introduction to the Study of Indian Languages (1877), and Report on the Lands of the Arid Region of the United States (1878).

George Montague Wheeler had a similar practical interest in the exploration of western lands. A graduate of West Point Military Academy, Wheeler wanted to make maps that stressed human settlement and could be used to advance roads, railroads, dams, irrigation, agriculture, and settlement.

On June 10, 1872, the U.S. Congress granted Wheeler $75,000 to map the area west of the 100th meridian on a scale of eight miles to the inch, an undertaking that Wheeler estimated would take fifteen years to complete. All four surveys were now being conducted simultaneously.

In the summer of 1873, the Hayden and Wheeler surveys met at the headwaters of the Arkansas River in Colorado. Conflicts arising from the possibility that both were surveying and mapping the same territories caused the U.S. Congress to hold hearings to consider whether the surveys were conducted wastefully. At this time it was concluded there was enough work for all four surveys to continue with funding.

From 1874 to 1879 the Wheeler expedition surveyed, using a base-line and trigonometric triangulation method, over a third of the country west of the 100th meridian, including Colorado, Arizona, Utah, Nevada, and California. Wheeler's survey produced seventy-one geographical and topographic maps and seven economic land-use maps. Wheeler supervised over twenty-five publications on geography, astronomy, paleontology, zoology, botany, and archaeology, and seven of his own volumes of notes and reports. Over the course of the survey 43,759 specimens were sent the Smithsonian Institution in Washington, D.C.

At the end of the fiscal year in 1879, the U.S. Congress once again debated whether four independently funded and autonomous surveys were wasteful. A lobbying effort, headed by Powell but supported by many members of the scientific community, persuaded Congress to consolidate their research efforts into one new office, the U.S. Geological Survey.

Because of the government patronage and the historical significance of the four surveys, much of the primary fieldwork has been preserved. The field notes and records of the United States Geographical Surveys West of the 100th Meridian are archived as Record Group 77, Office of the Chief of Engineers. Many of the large-plate photographs of William Henry Jackson, Jack Hillers, Timothy O'Sullivan, and E.O Beaman, which were made while accompanying the expeditions, are held in the Still Pictures Section of the National Archives in Washington, D.C. A large collection of Powell's fieldwork is housed in the Smithsonian Institution's Bureau of American Ethnology.