From African explorers to the Tarzan's adventures, we have heard about the mysterious elephants' graveyards. Now, researchers have revealed an Ice Age graveyard of the Ice Age's elephants: mammoths. The fossils, some of them complete skeletons of Mammuthus columbi, the Columbian mammoth, were stored in the hillsides of the current Yakima, Columbia and Walla Walla valleys (southeastern Washington). The death corpses were repeatedly deposited by the water of the ancient Lake Lewis.

Pacific Northwest National Laboratory geologists want to track down the high-water marks of these floods, the most recent taking place 12,000 to 15,000 years ago. "Now is the perfect time to collect geologic and paleontologic data," said George Last, a senior research scientist at the Department of Energy laboratory in Richland, Washington. "Winter has eroded the slopes, exposing new evidence. We're interested in researching any known or suspected mammoth find, to collected additional evidence and to improve documentation of those sites."

In 2006, PNNL team Kelsey Winsor and colleagues have detected 62 sites of known or suspected fossil finds and two more were found this spring. "We're trying to tease out as much information as we can about each and every mammoth find in the mid-Columbia basin, so that we can better understand the impacts that Ice Age floods may have had on the mammoths and other creatures, and in turn learn more about the history of Ice Age flooding." said PNNL researcher Kelsey Winsor.

Most of these Ice Age floods in eastern Washington could have rooted in glacial Lake Missoula, appeared behind ice that dammed the Clark Fork River. When the ice dam ceded, the lake released huge water amounts (up to 500 cubic miles) in a matter of seconds. After each flood, the lake slowly reformed behind the ice dam and the cycle could have repeated. The successive floods formed a distinct geological structure, the Channeled Scablands, with only one outlet, the Wallula Gap. But this outlet was too narrow, and the massive flow was retained up in the temporary Lake Lewis, from which drained to the Columbia River Gorge in a few days.

Most mammoth fossils coincide with the Lake Lewis area at elevations of 600 to 1,000 feet (200-333 m). Complete skeletons at lower elevations belonged likely to individuals buried soon after death-by-torrent, caught by the half mile (800 m) high water wall approaching with 60 miles (100 km) an hour. Some fragments could come from complete skeletons fragmented and relocated by later floods.