Glacial Geology of the eastern Olympic Peninsula, Washington

Long, William

This paper describes the relationship of former east-flowing Olympic valley glaciers to the Puget Lobe of the Cordilleran Ice Sheet during the last two major glaciations of the Puget Lowland. Rocks of northern provenance at high points along the Olympic Mountain flank indicate the presence of the Puget Lobe. Surface granite boulders of Vashon age are fresh and abundant; those of Salmon Springs age are weathered and rare. Puget ice on the southeastern peninsula was 2,000 feet high against the range during Salmon Springs time and 700 feet higher than during Vashon time. Along the eastern Olympic flank upper limits of the Puget lobes converged to a point at 3,400 feet on Buck Mountain, but north of there, the upper ice levels coincided. The highest granite erratics on the eastern Olympic flank were found on the northwest ridge of Mount Zion at an altitude of 3,550 feet, which was the place on the northeastern peninsula where the ice sheet bifurcated into two lobes--the Puget Lobe flowing southward into the Puget Lowland and the Juan de Fuca Lobe flowing westward to the Pacific Ocean. During the Evans Creek Stade of the Fraser Glaciation alpine glaciers on the Hamma Hamma, Duckabush and Dosewallips rivers advanced east beyond the Olympic front, and alpine glaciers on the Big Quilcene River terminated behind the mountain front. Valley glaciers had retreated from their maximum stands prior to the arrival of the Puget Lobe during the Vashon Stade. After the time of the Vashon maximum, alpine glaciers twice re-advanced and deposited moraines well behind the mountain front.