CA Prob Code Section 20116

(a)

If all property does not come into the possession of the personal representative, the personal representative is entitled, and has the duty, to recover from the persons interested in the estate the proportionate amount of the estate tax with which the persons are chargeable under this chapter.

(b)

If the personal representative cannot collect from any person interested in the estate the amount of an estate tax apportioned to the person, the amount not recoverable shall be equitably prorated among the other persons interested in the estate who are subject to proration.