Around ~45% of California resides in the contiguous urban area of Greater Los Angeles, representing ~17.5 million residents, compared to the rest of California with ~22 million residents. For a state this large and populous, you would have expected more evenly distributed population across multiple urban areas akin to Texas or Florida, but California seems surprisingly concentrated for its size. Of the top 10 largest US states, only New York, Illinois, and Georgia are more centralized than California into one metro area. The 5 other states (Texas, Florida, Pennsylvania, Ohio, North Carolina) are much more polycentric/decentralized than California. Michigan is similar to California, where roughly ~45% of the state lives in one metro area, Detroit.
If you were to divide California into 2 equivalent halves with ~19.7 million, it would go through the heart of the City of Los Angeles, somewhere between Wilshire and Ventura Boulevards.