California Civil Code Section 1995.260

If a restriction on transfer of the tenant`s interest in a lease requires the landlord`s consent for transfer but provides no standard for giving or withholding consent, the restriction on transfer shall be construed to include an implied standard that the landlord`s consent may not be unreasonably withheld. Whether the landlord`s consent has been unreasonably withheld in a particular case is a question of fact on which the tenant has the burden of proof. The tenant may satisfy the burden of proof by showing that, in response to the tenant`s written request for a statement of reasons for withholding consent, the landlord has failed, within a reasonable time, to state in writing a reasonable objection to the transfer.