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Oenothera primiveris, photograph by Warren L. Wagner

Oenothera primiveris, the desert evening primrose, is an annual herb that grows in winter. Its four-petaled yellow flowers open at night, then fade to orange.

Smithsonian Institution, National Museum of Natural History

Oenothera primiveris, photograph by Warren L. Wagner

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.