Two federal acts (March 2, 1867, and March 3, 1869) authorized a major geological exploration along and near the 40th parallel in the American West. The War Department’s Engineer Corps oversaw the work, and geologist Clarence King was chosen to lead it. The goal was to map geology and resources in a broad belt near the new transcontinental rail corridor.
In 1867, King’s team began multi-season field operations across a wide swath from California through Nevada and Utah toward the Rocky Mountain region. Surveyors and scientists gathered rock, fossil, and plant specimens while topographers produced detailed maps to anchor the geology. This approach—tying geologic interpretation to careful topographic mapping—helped set a standard for later federal surveys.
Between 1867 and 1872, photographs made for the expedition created a visual record of landscapes, rock formations, and survey activities. These images supported scientific reporting and helped communicate the West’s geography to audiences in the East. The surviving photographic sets are now held by major public collections.
During the early seasons, the expedition’s plant collecting concentrated in Nevada and Utah (roughly June 1867 to August 1869). Thousands of specimens were gathered for later identification and publication. This work broadened scientific knowledge of Great Basin and Intermountain West flora.
The first major report volume to appear was Mining Industry (1870), authored by James D. Hague with geological contributions by Clarence King. It summarized mining districts and mineral resources, reflecting a central purpose of the survey: to describe the West’s economic geology in a practical way. Publication while fieldwork was still ongoing shows how quickly Congress and agencies wanted usable results.
In 1871, the survey’s Botany volume (Vol. V) was published, led by Sereno Watson with help from other specialists. It organized the Nevada–Utah collections into a formal scientific reference, including descriptions and plates. Publishing botany as a full volume signaled that the project aimed to document natural history broadly, not only minerals and routes.
In 1872, King published Mountaineering in the Sierra Nevada, blending geologic explanation with field experiences and travel narrative. The book helped make a government geologist recognizable to general readers. This wider visibility mattered later, as debates grew about how to organize and fund western surveys.
In October 1872, members of King’s survey investigated a rumored diamond discovery in the western interior and found signs the site had been “salted” with planted stones. Their findings helped reveal the episode as a fraud, now known as the Great Diamond Hoax of 1872. The incident showed how survey knowledge could protect the public and government from costly speculation.
By 1872, the survey’s main fieldwork phase had ended after several seasons of mapping and sampling across the West. The close of field operations shifted the project’s center of gravity to laboratory study, writing, and map production. Much of the survey’s long-term impact came through the major report volumes and atlases published in the following years.
In 1876, the survey issued a large Geographical and Topographical Atlas to accompany the reports. The atlas presented detailed mapping of the surveyed belt and related regions, supporting both scientific interpretation and practical use. Its quality and scale made it a landmark publication in U.S. government science and mapping.
In 1877, Descriptive Geology (Vol. II) was published by Arnold Hague and S. F. Emmons with Clarence King. It provided detailed, place-by-place geology across the survey belt, turning field notebooks and samples into a coherent regional account. This volume helped establish how large-area geologic mapping could be reported systematically.
In 1878, King’s Systematic Geology (Vol. I) appeared as a broad synthesis of the region’s geologic history and structure. It tied together stratigraphy (rock-layer order), igneous rocks, mountain building, and the survey’s cross-regional observations. As the capstone of the series, it helped define what a “big picture” federal geology report could look like.
On March 3, 1879, Congress established the United States Geological Survey (USGS), consolidating several competing western survey efforts into one civilian scientific agency in the Department of the Interior. The new law tasked the USGS with classifying public lands and examining the geology, mineral resources, and products of the national domain. This created an enduring national framework that built directly on lessons and outputs from King’s survey and its peers.
President Rutherford B. Hayes nominated King on March 20, 1879; the Senate confirmed him on April 3; and he took the oath of office on May 24. King’s appointment linked the new USGS to the methods and professional standards developed during the Fortieth Parallel Survey. His early leadership helped turn a time-limited expedition model into a permanent federal science institution.
Clarence King's Geological Exploration of the Fortieth Parallel (1867–1872)