IMPACTS OF ICE AGE FLOODS ON PLEISTOCENE MAMMOTHS OF SOUTHEASTERN WASHINGTON

Ever wonder what happened to all of the creatures that lived in the path of Ice Age floods that emptied Glacial Lake Missoula? Well, those that were not already on high ground or could not get out of the way of the floods were likely swept to their deaths, many coming to rest in quiet slackwater areas along the floods' route including the shoreline of temporary Lake Lewis. Likewise, some older fossil remains present in the loess and other sediments scoured by the floods were likely eroded and transported away from their previous resting places. Still other fossil remains likely floated in on icebergs that accompanied the floodwaters.

Rapid burial in flood deposits is an ideal environment for preservation of fossils. Large numbers of fossils, including those of mollusks, rodents, mammoths, and other vertebrates, have been found in the Mid-Columbia Basin primarily in fine-grained slackwater deposits of the Ice Age floods. Among the most frequently found fossils in these fine-grained sediments is the Columbian Mammoth (Mammuthus columbi). Mammoth fossils are particularly common throughout Washington State, with finds numbering to several hundred. In March 1998, the Columbian Mammoth was named the “official fossil” of the State of Washington.

Recent efforts to catalog the location, elevation, geologic context, and relative age of mammoth finds in the Mid-Columbia Basin, have found a predominance of sites located at an elevation of between 300 and 380 m MSL, consistent with the maximum water level of temporary Lake Lewis. Many of these sites are disarticulated, but fairly complete skeletons, suggesting little disturbance after decomposition of the carcass. The location of these finds and their geologic context suggests that, indeed, the humungous Ice Age floods may have had catastrophic impacts on mammoths and other large mammals in southeastern Washington.