Thanks for your question. From the California employment website here are the penalties..

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Overpayments

A Notice of Overpayment is mailed to you when you have been paid UI benefits that you were not eligible to receive. The Notice shows the amount of the overpayment and penalties, if any. It explains why you were overpaid and gives you information about your appeal rights.

The EDD classifies overpayments into two categories: non-Fraud or fraud.

Non-Fraud: When you have received benefits to which you were not entitled and you are not at fault, the overpayment is considered non-fraud. In some cases, you may not have to repay a non-fraud overpayment. You will receive a notice telling you if the overpayment must be repaid.

Fraud: When you knowingly give false information or withhold information and receive benefits that you should not have received. Withholding or giving false information to obtain unemployment insurance benefits is a serious offense that can result in criminal prosecution. With a fraud overpayment, you are assessed a penalty in the amount of 30 percent of the amount of the overpayment and a false statement disqualification of 5 to 23 weeks. Fraud overpayments and penalties must be repaid.

If you do not repay your overpayment promptly, EDD will deduct the money owed from your future weekly unemployment or state insurance benefits. This process is referred to as an offset. EDD may also:

• Reduce or totally withhold your state income tax refunds, lottery winnings, or any other money owed to you by the state.
• File a claim against you in court, charge you court costs and interest, and record a lien on your property."