The instructions for CA form 540 say:
California allows personal casualty and theft loss and disaster loss deductions. If you have personal casualty and theft loss and/or disaster loss, complete another federal Form 4684, Casualties and Thefts, using California amounts. Enter the difference between the federal and California amount in column B or column C.
If you can claim a casualty loss in CA, then the cost basis for your property in CA will be lower than its cost basis for Federal tax purposes.
[Edited 04/06/25 | 9:04 AM PST]
@Banjer I have edited my answer
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