The Mexican Cession (red) and the Gadsden Purchase (orange)

The Mexican Cession is an historical name for the region of the present day southwestern United States that was ceded to the US by Mexico in 1848 under the Treaty of Guadalupe Hidalgo following the Mexican-American War. For the 38 years between 1810, when Mexico declared its independence from Spain, and 1848, the region had formed approximately one-third of the territory of Mexico; prior to that, it had been a part – albeit a remote one, largely without European settlement – of the Spanish colony of New Spain for some three centuries.

It includes all of the present-day states of California, Nevada, and Utah, as well as the portions of:

• Arizona excluding the region later annexed in the Gadsden Purchase
• Colorado west of the boundary of the former Republic of Texas
• New Mexico west of the Rio Grande and excluding the Gadsden Purchase
• Wyoming west of the former Republic of Texas boundary and south of the 42nd parallel.

The treaty also specified the U.S.-Mexican border as being at the Rio Grande. Previously the portion of Texas between the Nueces River and the Rio Grande had remained disputed throughout the existence of the Republic of Texas. The United States had already claimed the area as part of the Texas Annexation in 1845.

See also

• State of Deseret
• Historic regions of the United States