The Alexandria Mammoth
The tusk is most probably that of a Columbian Mammoth (Mammuthus columbi), a large non-wooly ancestor of the modern elephant, which roamed this region during the Pleistocene (1.8 million-11,000 years ago). Carbon-14 tests, completed by The Stafford Research Laboratory in Boulder, Colorado, have determined that this mammoth lived 14,570 years ago (±50 years). This date corresponds with the dates of the Missoula Floods, which comprised many episodes of innundation between 15,000 and 13,000 years ago.
About eight feet below the level of the tusk is an ancient river bed, where water flowed through the valley during the last Ice Age, more than 10,000 years ago. This riverbed is dense with basalt rock, the native rock of the Yakima Valley. The approximately 16 feet of earth that covers this ancient surface contains metamorphic pebbles from the mountains of Idaho and Montana. This layer is the rich, dark, fertile soil deposit that covers the Yakima Valley floor and represents the deposits left after the great Missoula Floods.
It is impossible to know for sure how the tusk arrived here. One theory considered by our geology consultants, Steven Lundblad of Central Washington University and David Huycke of Yakima Valley Community College, is that the body of the Alexandria Mammoth was "rafted" to Moxee in a block of ice during a flood event. This type of deposition was rather common and is evidenced by "dropstones" found in the flood deposits—large, heavy stones that could not simply flow in with water but are carried frozen inside blocks of ice, only to melt out in time. Several of these dropstones were found along with the bone remains.