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Oenothera primiveris, Evening Primrose Family, Herbarium specimen from Mexican Boundary Survey

While marking the U.S.-Mexico boundary, Army surveyors also studied the flora and fauna of the borderland. They published a three-volume illustrated report and collected plant and animal specimens—among them, this desert evening primrose. This flower is native to the southwestern United States and northern Mexico and well adapted to the arid climate.

Smithsonian Institution, National Museum of Natural History

Oenothera primiveris, Evening Primrose Family, Herbarium specimen from Mexican Boundary Survey

Surveying the Mexican Border

The Treaty of Guadalupe Hidalgo, approved for ratification by the U.S. Senate in 1848, set the terms for ending the Mexican War. Mexico agreed to cede more than half its territory to the United States for $15 million. A new, 2,000-mile border between the two countries was to run along the Rio Grande and Rio Gila to the Pacific Ocean with a boundary commission from each country surveying and marking its location. Congress authorized the Army Corps of Topographical Engineers to conduct the survey for the United States.