The first significant American exploration of the borderlands region came as a result of the Mexican-American War (1846-1848) when troops and supplies needed to be sent to California from Fort Leavenworth via New Mexico and Arizona. Lieutenant Colonel William Emory accompanied these forces and led a topographical unit which charted and explored the territory from Fort Leavenworth to California.

This expedition produced the first reliable map of the Gila River Trail. After the war Emory's findings were presented to Congress as Notes of a military reconnaissance from Fort Leavenworth, in Missouri, to San Diego, in California, including Part of the Arkansas, del Norte and Gila Rivers.

When the war ended in 1848, the Treaty of Guadalupe Hidalgo recognized the annexation of Texas by the U.S. and ceded a large tract of land including the present states of New Mexico, Arizona, California, Nevada and Utah. In return the U.S. paid Mexico $15 million and assumed $3 million of claims of U.S. citizens against Mexico. A joint American / Mexican Boundary Commission was appointed to determine the U.S. / Mexican Boundary as described in the Guadalupe Hidalgo treaty. This boundary was contentious for many years because the map used by the treaty-makers was inaccurate as to the location of El Paso del Norte, one of the key markers. The original Commissioner, J.R. Bartlett, accepted a compromise offered by the Mexican ambassador, General Pedro Garcia Conde, and was reviled by Emory and other southerners for "giving away" to Mexico land that should be American. See John Russell Bartlett, Boundary Commissioner.

After the California gold rush, there was a race to develop both wagon routes and railroads from east to west, but the Gila River had been stipulated as the southern boundary of the U.S. territory in present day Arizona. Emory and other surveyors agreed that the valley of the Gila River would be impassable by a railroad and that tracks would have to be laid even further south. Thoughts turned to the wagon trail blazed by Cooke and the Mormon Battalion. That route, fifty to a hundred miles south of the Gila River, presented fewer obstacles to a railroad, but the territory was still in Mexican hands.

The Gadsden Purchase
President Franklin Pierce sent James Gadsden to Mexico City with several proposals for buying from Mexico some land to the south of the recent treaty boundaries.

The plan eventually settled on was a boundary which added 27,305 square miles to Arizona and 2335 square miles to New Mexico and established the southwestern boundary of Arizona at Yuma, where it remains today. The price paid was $10 million, and the Senate ratified the treaty on June 24, 1854. [Read a contemporary account of the Purchase by J. Ross Browne.]

This treaty brought United States control to an area which included what was later to become Cochise County, although at this point it was still part of the large area known as the New Mexico Territory. Some topographical errors were incorporated into the treaty, and this caused the U.S./Mexican border to remain a subject of dispute until Emory, who had surveyed the Gila Trail in 1846, was called on to help settle the issue. Over a period of years, Emory and his team not only surveyed the boundary but collected a wealth of geological, zoological and botanical information, in the great tradition of Lewis and Clark. Between 1856 and 1859 this information was published as the three-volume Report of the United States and Mexican Boundary Survey, finalizing the last unresolved bounday of the United States.

Recommended reading:

Altshuler, Constance Wynn. Chains of Command, Arizona and the Army, 1856-1875. Tucson, The Arizona Historical Society, 1981.

Bufkin, Don and Henry P. Walker. Historical Atlas of Arizona. Norman: University of Oklahoma Press, 1979.

Editors of Time-Life Books. The Old West: The Trailblazers. Alexandria, Virginia: Time-Life Books, 1973.

Emory, W. H. Notes of a military reconnaissance, from Fort Leavenworth, in Missouri, to San Diego, in California, including of Part the Arkansas, del Norte and Gila Rivers. Download the free Notes of a military reconnaissance e-book now. If you do not have the Microsoft e-book reader, you may download it free on the Microsoft website.

Emory, W. H. et al. Report of the United States and Mexico Boundary Survey, Three volumes. (1856, 1859) This is a rare and collectible book. Some reprints have been made. If you are lucky enough to live near a really good university or research library, you may be able to find a copy there.

Harris, Benjamin Butler, The Gila Trail: The Texas Argonauts and the California Gold Rush. Norman: University of Oklahoma Press, 1960.

Norris, L. David, James C. Milligan and Odie B. Faulk. William H. Emory: Soldier-Scientist. Tucson: University of Arizona Press, 1998.

Treaty of Guadalupe Hidalgo, ended the Mexican War

Utley, Robert M. A Life Wild and Perilous: Mountain Men and the Paths to the Pacific. New York: Henry Holt & Co., 1997.