COSMOGENIC HE-3 AND NE-21 AGE OF THE BIG-LOST-RIVER-FLOOD, SNAKE-RIVER-PLAIN, IDAHO

The Big Lost River flood in southeastern Idaho occurred 20,500 calibra ted yr B.P., on the basis of dates derived from cosmogenic He-3 and Ne -21 measurements of samples from flood-deposited boulders and from sco ur features. This date corresponds to a date of 16,900 C-14 yr B.P. an d is close in age to several other cataclysmic flood events in western North America; it may mark evidence for widespread warming at the end of the Pleistocene in western North America. The Big Lost River flood was smaller than some other late Pleistocene floods, such as the Bonn eville flood and the Missoula floods; thus, some samples exposed after the flood had significant amounts of cosmogenic He-3 and Ne-21 that w as acquired before the flood occurred.