Christina A. Jefferds, 45, had been watching her granddaughter at home when the torrent of mud swept through the Stillaguamish Valley on Saturday morning.
The Snohomish County medical examiner's office said she died of "blunt impact" injuries.
Jefferds' daughter Natasha Huestis, 26, told NBC News on Wednesday that she was still desperately looking for her 4-month-old daughter, Sanoah.
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