Which treaty transferred Alta California and Santa Fe de Nuevo México to U.S. control?

The Treaty of Guadalupe Hidalgo transferred Alta California and Santa Fe de Nuevo México to U.S. control.

Signed on February 2, 1848, the treaty ended the Mexican–American War. Mexico ceded about 55% of its prewar territory, including present-day California, Nevada, Utah, most of Arizona, and parts of New Mexico, Colorado, and Wyoming. It also recognized the Rio Grande as Texas's southern boundary.

The United States paid Mexico $15 million and accepted responsibility for certain claims by American citizens. The treaty also promised property and civil-rights protections to Mexicans living in the transferred territories, though those guarantees were often contested or undermined in practice.

A common mix-up is the Adams–Onís Treaty, which set an earlier U.S.–Spanish boundary, or the later Gadsden Purchase, which added land in present-day southern Arizona and New Mexico. The Mexican Cession itself chiefly came through Guadalupe Hidalgo.