ORIGINS OF RIP-UP CLASTS IN MISSOULA FLOODS DEPOSITS OF THE WEST PLAINS, EASTERN WASHINGTON

Eastern Washington is an area with a complex catastrophic geologic history. This study is to identify the provenance of clayey rip-up clasts, located in a gravel quarry pit in Airway Heights, Washington. Our hypothesis is that these rip-up clasts were locally derived from sources such as weathered basalt, and the Miocene Latah Formation (Vantage Formation), and redeposited along with numerous basalt and bedrock boulders by the Pleistocene glacial Lake Missoula Floods onto glacial Lake Columbia. The maximum elevation of glacial Lake Columbia has been estimated 715 meters; the quarry elevation is approximately 718 to 730 meters. Clasts sizes ranged from <20 cm to approximately 1 meters. Our methods focused on classification of the rip-up clasts using grain size analysis of the rip-up clasts. Rip-up clasts were generally sourced from saprolite and weathered basalt and bedrock, Latah Formation, and possibly included prior outburst flood deposits.