El Tratado de La Mesilla

… was signed in Mexico City on this date in 1853. The treaty settled the dispute over the exact location of the international border west of Texas and gave the U.S. approximately 29,000 square miles of land — in brief, Arizona and New Mexico south of the Gila River — for the price of $10 million. In the U.S. it’s known as the Gadsden Purchase Treaty.

The Mexican Republic agrees to designate the following as her true limits with the United States for the future: retaining the same dividing line between the two Californias as already defined and established, according to the 5th article of the treaty of Guadalupe Hidalgo, the limits between the two republics shall be as follows: Beginning in the Gulf of Mexico, three leagues from land, opposite the mouth of the Rio Grande, as provided in the 5th article of the treaty of Guadalupe Hidalgo; thence, as defined in the said article, up the middle of that river to the point where the parallel of 31° 47′ north latitude crosses the same; thence due west one hundred miles; thence south to the parallel of 31° 20′ north latitude; thence along the said parallel of 31° 20′ to the 111th meridian of longitude west of Greenwich; thence in a straight line to a point on the Colorado River twenty English miles below the junction of the Gila and Colorado rivers; thence up the middle of the said river Colorado until it intersects the present line between the United States and Mexico.

Read the entire Gadsden Purchase Treaty.