Cal. Probate Code § 285

(a) A disclaimer may not be made after the beneficiary has accepted the interest sought to be disclaimed. (b) For the purpose of this section, a beneficiary has accepted an interest if any of the following occurs before a disclaimer is filed with respect to that interest: (1) The beneficiary, or someone acting on behalf of the beneficiary, makes a voluntary assignment, conveyance, encumbrance, pledge, or transfer of the interest or part thereof, or contracts to do so; provided, however, that a beneficiary will not have accepted an interest if the beneficiary makes a gratuitous conveyance or transfer of the beneficiary’s entire interest in property to the person or persons who would have received the property had the beneficiary made an otherwise qualified disclaimer pursuant to this part. (2) The beneficiary, or someone acting on behalf of the beneficiary, executes a written waiver under Section 284 of the right to disclaim the interest. (3) The beneficiary, or someone acting on behalf of the beneficiary, accepts the interest or part thereof or benefit thereunder. (4) The interest or part thereof is sold at a judicial sale. (c) An acceptance does not preclude a beneficiary from thereafter disclaiming all or part of an interest if both of the following requirements are met: (1) The beneficiary became entitled to the interest because another person disclaimed an interest. (2) The beneficiary or other person acting on behalf of the beneficiary at the time of the acceptance had no knowledge of the interest to which the beneficiary so became entitled. (d) The acceptance by a joint tenant of the joint tenancy interest created when the joint tenancy is created is not an acceptance by the joint tenant of the interest created when the joint tenant survives the death of another joint tenant.