The Tucson zoo announced Monday that 17-year-old Snow passed away in her sleep.
She was in her normal sleeping position and location, with no signs of trauma.
Snow and her brother Klondike were born at the Denver Zoo in 1994.
Snow was moved to the Tucson's Reid Park Zoo earlier this year because of allergies.
Early necropsy results may be available as early as Thursday, but final results will take several weeks.
Klondike still lives at SeaWorld Orlando.
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