The Mexican Cession was a treaty signed in 1848 that ended the Mexican-American War and established the Rio Grande as the border between the U.S. and Mexico. It transferred ownership of California, Nevada, Utah, and parts of four other states from Mexico to the United States for $15 million, expanding U.S. territory by over 500,000 square miles. Nicolas Trist helped negotiate the Treaty of Guadalupe Hidalgo that formalized the land transfer from Mexico to the U.S.