The Puget Lowland lies between the Cascades and Olympic Mountains and once contained a plateau of glacial till not usually more than above sea level. The plateau, the most prominent single landform of the entire region, was dissected by glacial outwash, forming present-day landforms: rivers, creeks and streams; glacial lakes such as Lake Washington; and numerous kettle lakes, and Puget Sound itself. High points on the plateau remain, most of which are a drumlin (rocky glacial debris), or a bedrock intrusion that predated glaciation. Hills above 500 feet are considered exceptional.