California Civil Code Section 1109

Where a grant is made upon condition subsequent, and is subsequently defeated by the non-performance of the condition, the person otherwise entitled to hold under the grant must reconvey the property to the grantor or his successors, by grant, duly acknowledged for record. (1110.) Section Eleven Hundred and Ten. An instrument purporting to be a grant of real property, to take effect upon condition precedent, passes the estate upon the performance of the condition.