<P> What is now California was first settled by various Native Californian tribes before being explored by a number of European expeditions during the 16th and 17th centuries . The Spanish Empire then claimed it as part of Alta California in their New Spain colony . The area became a part of Mexico in 1821 following its successful war for independence but was ceded to the United States in 1848 after the Mexican -- American War . The western portion of Alta California then was organized and admitted as the 31st state on September 9 , 1850 . The California Gold Rush starting in 1848 led to dramatic social and demographic changes , with large - scale emigration from the east and abroad with an accompanying economic boom . </P>
<P> What is now California was first settled by various Native Californian tribes before being explored by a number of European expeditions during the 16th and 17th centuries . The Spanish Empire then claimed it as part of Alta California in their New Spain colony . The area became a part of Mexico in 1821 following its successful war for independence but was ceded to the United States in 1848 after the Mexican -- American War . The western portion of Alta California then was organized and admitted as the 31st state on September 9 , 1850 . The California Gold Rush starting in 1848 led to dramatic social and demographic changes , with large - scale emigration from the east and abroad with an accompanying economic boom . </P>
when did california become part of the united states
when did california become part of the united states
September 9 , 1850
September 9 , 1850