The Bartlett-García Conde Compromise of 1850 was intended to resolve a dispute over the southern boundary of New Mexico resulting from errors in the map used by the negotiators of the Treaty of Guadalupe Hidalgo. Instead, the compromise became a partisan political issue, and the question of New Mexico's southern boundary was not finally settled until the Gadsden Purchase in 1853. The boundary sketched by the negotiators of the Treaty of Guadalupe Hidalgo on the 1847 "Map of the United Mexican States" by J. Disturnell began on the Rio Grande eight miles north of El Paso and proceeded west three degrees. Unfortunately, Disturnell's map contained two major errors: it drew the Rio Grande two degrees farther west than it really was, and it showed El Paso thirty miles farther north than it really was.
These problems did not become immediately apparent, in part because of the difficulties of the United States in settling on a commissioner. In December 1848 President James K. Polk named Ambrose Sevier as the United States commissioner, but Sevier died before he could be confirmed by the Senate. John B. Weller replaced Sevier and ran the portion of the line from the Pacific Ocean to the junction of the Gila and Colorado rivers but departed sometime after February 15, 1850, the victim of political intrigues and infighting. John C. Frémont was to be Weller's successor, but Frémont resigned upon his election as the first Senator from California.
On June 19, 1850, John Russell Bartlett was named to replace Frémont. While the United States had gone through four commissioners, Mexico had had only one: Gen. Pedro García Conde, the former Mexican secretary of war and the navy, director of the Mexican Military College at Chapultepec, and deputy from Sonora to the Mexican legislature. After Weller and García earlier that year had agreed to recess until late 1850 and to arrange for the survey of the El Paso area, at the other end of the line, Weller departed. Bartlett arrived in late November, and García Conde shortly thereafter. Bartlett later described García as "an accomplished engineer, and a most amiable and estimable gentleman," while García Conde apparently felt much the same way about Bartlett, although García later refused to budge in the compromise once it was set. This mutual respect came in handy during the dispute over the New Mexico line.
When their surveyors made astronomical observations in the field, they discovered the errors in the Disturnell map, of which García was aware even before any survey work. He argued that the line should be laid down according to the latitude and longitude shown on the map. By this reasoning, the line would have begun at a point on the Rio Grande thirty miles north of El Paso and proceeded west one degree, then north to the first tributary of the Gila, giving Mexico the Mesilla valley and the copper mines of Santa Rita del Cobre. Taken by surprise by such errors, Bartlett was nevertheless prepared to be conciliatory but argued that the negotiators of Guadalupe Hidalgo had obviously intended the southern boundary of New Mexico to extend more than one degree west.
After much discussion the two commissioners agreed on a compromise. García Conde agreed that the boundary should run three degrees west, regardless of the true position of the Rio Grande. Bartlett in turn agreed that the initial point on the Rio Grande should be at 32º22' north latitude and not eight miles north of El Paso, which was at 31º45' north. Bartlett, García Conde, and the chief Mexican surveyor, José Salazar Ylarregui, signed the agreement, but it remained unofficial without the signature of the chief United States surveyor, Andrew B. Gray, who was in Texas recovering from an illness.
On April 24, 1851, a stone marker was placed on the Rio Grande at 32º22' N. The surveyors established their headquarters at the Santa Rita mines and began working west. On July 19, however, Gray arrived and immediately concluded that Bartlett had been duped. Gray refused to sign the agreement and ordered all surveying work halted until another meeting could be held with García Conde. Gray argued that latitude and longitude should be discounted, and the line should be placed on the earth in the same relation to the town of El Paso that it had on the map, that is, eight miles north of the plaza. He believed that the area between 31º45' N and 32º22' N contained the only practicable route for a transcontinental railroad to California. Gray was replaced by Maj. William H. Emory as chief surveyor a few months later. García Conde died of typhus on December 19, 1851, but his successor, Salazar, proved equally unwilling to renegotiate the New Mexico line, since the Mexican commission had earlier been heavily criticized for giving away too much in California. In the meantime, the Bartlett-García Conde Compromise had become a political issue, with the members of the Texas congressional delegation, including Sam Houston, and other Democrats accusing the Whigs of having given up too much of New Mexico.
Emory's signature on the agreement would make it official and binding, but the Democrats wanted to leave a loophole for renegotiation. On the other hand, the secretary of state had expressly ordered the chief surveyor to sign the agreement. Emory delicately sidestepped the issue by signing the agreement but insisting that in doing so he was merely witnessing the previous agreement between Bartlett and García Conde.
Under pressure from the Democrats, the Boundary Commission was disbanded on December 22, 1852, and the United States turned its attention to surveying the Rio Grande from Laredo to the Gulf of Mexico. Just over a year later the Gadsden Treaty finally resolved the initial-point controversy by purchasing enough territory for the coveted railroad route. The surveying of the United States-Mexico line was finally completed in October 1855.