Boundary Treaty of 1970
|Treaty to Resolve Pending Boundary Differences and Maintain the Rio Grande and Colorado River as the International Boundary|
|Signed||November 23, 1970|
|Effective||April 18, 1972|
The 1970 Boundary Treaty between the United States and Mexico settled all then pending boundary disputes and uncertainties related to the Rio Grande (Río Bravo del Norte) border. The most significant dispute remaining after the Chamizal Settlement in 1963 involved the location of the boundary in the area of Presidio, Texas, and Ojinaga, Chihuahua. The river channel was jointly relocated to approximate conditions existing prior to the dispute which arose from changes in the course of the river in 1907. The International Boundary and Water Commission was charged with its implementation. The American-Mexican Treaty Act of October 25, 1972 authorized the United States Section's participation. The project was undertaken in 1975 and completed in 1977. 
The river was relocated in two reaches by construction of a new channel 4.7 miles (8 km) in length in one reach and 3.6 miles (6 km) in the other. The relocated channel was aligned in the reach above Presidio-Ojinaga so as to transfer from north to the south side of the river 1,606.19 acres (650.00 ha) and in the second reach downstream from the two cities so as to transfer from the south to the north side a net area of 252 acres (102 ha). It is an earth channel with dimensions patterned after the natural channel. The United States acquired 1,969.22 acres (796.92 ha) of American agricultural land that was used for the transfer of lands to Mexico and for half of the river relocation.
Also, the channel of the Rio Grande in the Hidalgo–Reynosa area was relocated to transfer from Mexico to the United States 481.68 acres (1.9493 km2) by constructing a new earth channel 1.6 miles (3 km) in length. This transfer was made in exchange for the transfer from the United States to Mexico of two tracts of land, the Horcón Tract, after 1906 located south of the Rio Grande, and Beaver Island (Isla Morteritos), located in the river south of Roma, Texas, comprising 481.68 acres (194.93 ha) in total. This final provision of the treaty transferred to Mexico the portion of the town of Río Rico, Tamaulipas located within the Horcón Tract.
The total costs of these two relocations were equally shared by the two governments, with the United States performing the greater part of the work required in the Presidio-Ojinaga area, and Mexico performing the work required in the Hidalgo-Reynosa area and a small part of the work required in the Presidio-Ojinaga area.
- Robert J. McCarthy, Executive Authority, Adaptive Treaty Interpretation, and the International Boundary and Water Commission, U.S.-Mexico, 14-2 U. Denv. Water L. Rev. 197(Spring 2011) (also available for free download at http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1839903)