2002-2004 [most recent I could find] California Department of Insurance (CDI) study showed Los Angeles County’s uninsured driver rate at 24.0% (2002), 23.4% (2003), and 23.7% (2004).

https://www.insurance.ca.gov/

Here in Washington state, it's a fine of over $500 to not be able to present insurance proof on demand when pulled over...