(Mendocino, CA)  --  A sixth Hart family member is confirmed dead after their SUV plunged off a Northern California cliff.  Mendocino County authorities have announced that a body found in the surf ten days ago near the crash site is that of twelve-year-old Sierra Hart.  Two of her siblings are still missing and presumed dead.  Investigators believe that Jennifer Hart intentionally drove off a cliff last month with a blood-alcohol level over the legal limit.  Others in the vehicle may have been drugged with a Benadryl-type medicine.  Sierra's autopsy and toxicology reports are pending.  The Washington family left its Woodland home in a hurry and drove through Oregon on its way to the rocky California coastline.