LATE PLEISTOCENE MAMMOTH, BISON, BEAR, AND GROUND SQUIRREL FOSSILS FROM THE AIRPORT LANE SITE, LA GRANDE ALLUVIAL FAN TERRACE, NE OREGON

An earthmover operator removing 5 meters from the top of a distal remnant of the La Grande alluvial fan terrace in the southern part of the Grande Ronde Valley in January 2010 uncovered the tibia and two tusks from a juvenile male Columbian mammoth (Mammuthus columbi); a left radius of a large adult male bison (Bison latifrons); seven lumbar vertebrae, tailbones, and the proximal end of a left femur of a short-faced bear (Arctodus simus?); and a partial skeleton of a Columbian ground squirrel (Spermophilus columbianus), including the skull and lower jaw. The bear was lying on its left side and the vertebrae were articulated. The two mammoth tusks were found together in a position that suggests they came from the same skull, but the skull was not found. The fossils were found in grayish brown, silty, fine sand-sized river sediments with rare planktic diatoms (Aulcoseira, Fragilaria, Navicula, Nitzchia)), sponge spicules (Ephydatia fluviatilis), and very rare grass (Gramineae) and hemlock (Tsuga) pollen. It is possible that the animals were washed in from upstream during a flood caused by the failure of a glacial ice dam in the Elkhorn Mountains or during the spring when the ice was melting rapidly. Attempts to isolate DNA have been unsuccessful to date due to the poor state of preservation of the fossils. Radiocarbon dating of enamel fragments from the mammoth tusks by Geochron Laboratories yielded radiocarbon ages of 10,630 ± 490 ¹⁴C years BP for collagen and 10,650 ± 340 ¹⁴C years for bioapatite. These are the youngest late Pleistocene fossils discovered so far in the Grande Ronde Valley.