The Puget Lowland lies between the Cascades and Olympic Mountains and once contained a plateau of glacial till not usually more than 350–450 feet (110–140 m) above sea level.
High points on the plateau remain, most of which are a drumlin (rocky glacial debris), or a bedrock intrusion that predated glaciation.
The Blue Hills of the Kitsap Peninsula are unusual in that they are composed of basalt bedrock, not glacial till.
[b] They are basalt intrusions possibly related to the Blue Hills of the Kitsap Peninsula.
Mason County's Olympic Mountains foothills are called the Satsop Hills.