Mesilla, NM
After the Treaty of Guadalupe Hidalgo, which concluded the Mexican War in 1848, the Mexican government commisioned Cura Ramon Ortiz to settle Mesilla. He brough families from New Mexico and from Paso del Norte (modern day Ciudad Juarez) to populate the Mesilla Civil Colony Grant, which by 1850 had over 800 inhabitants.
The Treaty of Guadalupe Hildago and later misunderstandings led to the Gadsden Purchase. Named for James Gadsden, entrepreneur and diplomat. The Treaty of Guadalupe Hidalgo defined the border between the US and Mexico based on a map of questionable accuracy. One article under the treaty made the United States responsible for marauders and bandits on the frontier; the article was not enforced and later Mexico claimed millions in damages.
Supporters of a southern transcontinental railroad in the U.S. considered the best route to the Pacific to be in this disputed area, through the Mesilla Valley. When Franklin Pierce became 
president in 1853, he rejected the validity of the compromise achieved under President Millard Fillmore where Mexico retained the Mesilla Valley. Pierce sent Gadsden as minister to Mexico with instructions to purchase the territory and Lower California, if possible, for a sum not to exceed $50 million. Gadsden and the Mexican president, Antonio López de Santa Ana, whose administration was in financial need, negotiated a treaty on December 30, 1853.
Under the terms of the treaty, Mexico was to cede a border strip in exchange for $15 million; the article pertaining to Indians was abolished; and all claims for damages were cancelled. The U.S. Senate ratified the treaty on April 25, 1854, after a bitter debate, much of which centered on adding more slave territory to the U.S. The version ratified by the Senate lowered the payment to $10 million and reduced the territory to be acquired. The Southern Pacific Railroad was eventually built through the region. In Mexico the sale met with great opposition and contributed to the political downfall of Santa Ana.
Mesilla is also famous for it's part in the legend of Billy the Kid, as shown in the slideshow images, the building that now houses the Billy the Kid gift shop dates from 1850 and once housed the Capitol for the New Mexico Territory (including what is now New Mexico and Arizona). This same building later became a courthouse in which Billy the Kid was tried and sentenced to hang...by the neck until...dead.
In the central square is a station for the Butterfield Overland Trail. A mail stageline from St Louis to San Francisco, the forrunner to the Pony Express.