Within the Mount Washington Wilderness, there are outwash plains and lateral, recessional, and terminal ground moraines. Many of these glacial deposits were created during the most recent glacial advance in the late Pleistocene, though there are Holocene glacial deposits as well. There was an ice sheet during the late Pleistocene between Mount Washington and Three Fingered Jack. The McKenzie River, fed by Clear Lake, runs south for about just west of Mount Washington before it turns west for another and meets the Willamette River near the city of Eugene.