New Mexico v. Texas

Background

New Mexico and Texas disputed about a roughly fifteen-mile stretch of their common border in the Rio Grande valley. Each State said the true border was the middle of the river channel as it existed in 1850, but New Mexico placed the channel on the eastern side of the valley while Texas located it mainly on the western side. The case produced thousands of pages of testimony, old surveys, maps, patents, and field notes, and a special master examined the evidence and made detailed factual findings.

Reasoning

The central question was where the river channel lay around 1850 and whether later shifts by deposits (accretions) changed the boundary. The Court accepted the master’s careful work: it found the eyewitness memories weak, gave weight to historical surveys and maps (including the Salazar-Diaz survey and Clark’s survey), and treated the re-establishment of Clark’s Monument No. 1 as controlling under the resolutions that preceded New Mexico’s statehood. Because the greater weight of documentary and map evidence supported Texas’s location, the Court concluded New Mexico failed to prove its claim.

Real world impact

The Court declares the boundary is the middle of the Rio Grande channel as located in 1850, accepts the master’s described line, and denies New Mexico’s request. The Court fixed the east-bank intersection on the 32nd parallel by reference to the re-established monument and adopted the master’s 150-foot measurement from each bank for the middle line. The decision requires an accurate survey and placement of markers and will settle which private land titles and grants lie on each side of the border.