The 31st state of the United States is CALIFORNIA. It was admitted to the Union on September 9, 1850, becoming the 31st state. CALIFORNIA is the most populous state in the country and is home to many major cities, including Los Angeles, San Francisco, and San Diego. It is also known for its diverse geography, ranging from the Sierra Nevada mountains to the Pacific Ocean. CALIFORNIA is a major agricultural producer and is also a leader in technology and innovation.