In 1953 , at a sheep camp in Hamlin Valley , Elma Mackelprang observed tiny whitish flakes swirling through the air . They were part of the fallout associated with the '' Grable '' experiment , part of the Operation Upshot – Knothole series of nuclear weapon tests , the most reckless and dirtiest ever conducted in Nevada . Mackelprang later experienced symptoms of radiation poisoning
Grable
Upshot-Knothole Grable
Hamlin Valley