California is a U. S. state.
California . The Greater Los Angeles Area and the San Francisco Bay Area are the nation 's second - and fifth-most populous urban regions , respectively . The Central Valley is a large , flat valley that dominates the geographical center of the U.S. state of California . Los Angeles . With a census-estimated 2017 population of 4,042,000 , it is the second-most populous city in the United States ( after New York City ) and the most populous city in the state of California .