It would likely depend upon your situation if Washington State car insurance would be effective or accepted as coverage in California.

For example if your car is registered in Washington State because you live there permanently but you are visiting California then normally your WA coverages would conform to California's auto insurance requirements.

If instead you are attending school in CA but are still keeping your Washington State residence then your WA insurance may continue to cover you in California while you are a student and non-resident of CA. In this situation you would need to contact your insurer to make sure your coverage would continue to be in effect while you were out of state for this extended period of time.

If you have moved to California then typically you would need to register and insure your vehicle in California with an insurance company doing business there. If your Washington insurance provider also does business in California then it may be a simple process of working with your agent to change it over to a new agency in CA.

In California your insurance company is required to electronically report insurance information for all private-use vehicle liability policies so you need the CA insurer to do this if you are living in California.

To see if your Washington insurance would be effective in California for your situation you should contact your insurance agent who can discuss the specifics of your policy with you. To find out if your Washington State insurance coverages would be accepted by California for your particular situation try contacting the CA DMV and/or California Department of Insurance.