MAPPING ERRATICS IN THE MID-TO-UPPER WENATCHEE RIVER VALLEY, WASHINGTON STATE

North-Central Washington State bears evidence of both continental and alpine glaciations. In addition to glacial erosion and depositional features, there is also evidence of glacial outburst floods, slack water deposits and temporary glacial lakes. Glacial erratics in the Wenatchee area were first documented by J Harlan Bretz during his work in the 30’s when he noted the wide array of erratics and properly interpreted them as flood-borne. We mapped erratics in the mid and upper Wenatchee Valley, including some originally logged in the early 90s. In addition, we collected a variety of field measurements including: dimensions, orientation, lithology, degree of weathering, location, elevation, and observed lichen growth. Glacial erratics in the upper to mid Wenatchee Valley represent a variety of lithologies, many of which apparently originated from the Mt. Stuart Batholith and surrounding bedrock units. The presence of erratics of unknown origin suggest ice-rafted erratics arrived via the Columbia River in flood slack waters, presumably from continental outburst floods, or from calving of continental ice into glacial lake waters north of Wenatchee.