In California it is illegal to drive with an expired license. If you are caught driving by law enforcement with an expired license you should be cited under 12500 (a) of the CA Vehicle Code (VC).

California vehicle code 12500 makes it illegal, and a misdemeanor, to drive without a valid license on any highway in California. A person cited for driving without a valid license in CA may be punished by probation, time in county jail, and fines of up to $1000 plus surcharges.

12500 (a) states that a person may not drive a motor vehicle upon a highway, unless the person then holds a valid driver's license issued under this code, except those persons who are expressly exempted under this code.

Also your car might be towed and impounded since you do not hold a valid license.
22651 (p) of the vehicle code states that when the peace officer issues the driver of a vehicle a notice to appear for a violation of Section 12500, 14601, 14601.1, 14601.2, 14601.3, 14601.4, 14601.5, or 14604 and the vehicle has not been
impounded pursuant to Section 22655.5. Any vehicle so removed from the highway or any public lands, or from private property after having been on a highway or public lands, shall not be released to the registered owner or his or her agent, except upon presentation of the registered owner's or his or her agent's currently valid driver's license to operate the vehicle and proof of current vehicle registration, or upon order of a court.

From the information we have read, driving with an expired license in California appears to typically come with a fine of about $250 or so. The exact amount will be dependent upon the fine and fees your county court has in place for this infraction.

The CA DMV can give you more information on the possible penalties for having an expired license. If you have been ticketed for driving with an expired license in CA, then you can contact the court listed on the citation to tell you what penalties will be assessed.