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In page San Francisco Bay:

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The United States seized the region from Mexico during the Mexican–American War (1846–1848). On February 2, 1848, the Mexican province of Alta California was annexed to the United States with the signing of the Treaty of Guadalupe Hidalgo. A year and a half later, California requested to join the United States on December 3, 1849, and was accepted as the 31st State of the Union on September 9, 1850.[citation needed]