Cal. Rev. & Tax. Code § 6407

The possession of, or the exercise of any right or power over, tangible personal property under a lease of such property is exempt from the use tax for any period of time for which the lessee is obligated to lease the property for an amount fixed by the lease prior to August 1, 1965. The lessee shall be deemed not to be obligated for any period of time for which he has the unconditional right to terminate the lease upon notice, whether or not the right is exercised.