RIO GRANDE BOUNDARY. For 1,200 miles from the Gulf of Mexico^qv to El Paso the United States and Mexico share the Rio Grande as a boundary. Under the Treaty of Guadalupe Hidalgo^qv of 1848 and a treaty in 1853, the center of the deepest channel constitutes the dividing line, but because of the meandering nature of the river, innumerable land changes have taken place, some caused by erosion and accretion, others by avulsion or changes in the river's course. The many cases arising from the river's shifting course have included jurisdiction over San Elizario Island, Morteritos Island, and the bancos^qv before 1905; cattle seizure; wing dam and fence construction; the Brownsville Wharf Case;^qv water diversion by the American Rio Grande Land and Irrigation Company; and the Chamizal Dispute.^qv Wishing to standardize the practice followed in determining the boundary line, the United States and Mexico signed the Treaty of 1884^qv and in 1889 established the International Boundary Commission (later the International Boundary and Water Commissionqv) to administer the treaty rules. However, bancos formed by tracts of land segregated from either country by a cutoff became such a problem that a special treaty had to be negotiated to exclude them from the effects of the Treaty of 1884. A treaty on March 20, 1905, provided that bancos formed on the right bank of the river go under the dominion and jurisdiction of Mexico and those on the left bank under that of the United States. Excepted from this rule were bancos with an area of more than 250 hectares or with a population of more than 200 persons. The treaty affected 215 bancos.

The Rio Grande Rectification Project^qv straightened out the river from Cordova Island^qv to Box Canyon, stabilized the boundary, provided additional flood control, and helped prevent future detachments of land from one country to another. Rio Grande water apportionment and Rio Grande flood control^qv have been major problems along the boundary, but bases for settling both have been established.

BIBLIOGRAPHY: Jacqueline Eckert, International Law and the United States-Mexican Boundary Relations (Ph.D. dissertation, University of Texas, 1939).

Jacqueline E. Timm