The Treaty of Guadalupe Hidalgo which ended the Mexican War (1846-48) designated the main channel of the Rio Grande as the Mexico-U.S. boundary. Disputes arising from frequent changes in the river's course led to the Treaty of 1884 which recognized only those river diversions resulting from natural occurences. The International Boundary Commission was established in 1889 to administer the Treaty of 1884. In 1906 the American Rio Grande Land and Irrigation Company dug an unauthorized canal about two miles south of here which altered the natural course of the Rio Grande. As a result, a 419-acre section of U.S. property called El Horcon tract was isolated south of the river. Although still U.S. territory according to the Treaty of 1884, the tract and the popular gambling and resort community of Rio Rico which flourished there during the 1920s and 1930s became increasingly subject to Mexican administration and jurisdiction. After the U.S. granted Mexico territorial rights over El Horcon tract and Rio Rico in 1970, a native of Rio Rico sued the U.S. government to guarantee his U.S. citizenship. This lawsuit began an eight-year legal battle that eventually led to U.S. citizenship for about 200 people born in Rio Rico prior to 1970. (1994)