Cal. Civ. Proc. Code § 1577

In addition to any damages, penalties, or fines for which a person may be liable under other provisions of law, any person who fails to report, pay, or deliver unclaimed property within the time prescribed by this chapter, unless that failure is due to reasonable cause, shall pay to the Controller interest at the rate of 12 percent per annum on that property or value thereof from the date the property should have been reported, paid, or delivered. If a holder pays or delivers unclaimed property in a timely manner, but files a report that is not in substantial compliance with the requirements of Section 1530, the interest payable shall not exceed ten thousand dollars ($10,000). The holder shall not be subject to any interest payment if the holder’s failure to report in substantial compliance with the requirements of Section 1530 is due to reasonable cause.