Pinnacle Peak is a 1,000 ft extinct volcanic cinder cone rising up from the flat farmlands surrounding Enumclaw. This flat terrain was created by the Osceola Mudflow that spread from nearby Mount Rainier approximately 5,600 years ago. Some of Pinnacle Peak is buried beneath this mudflow since the peak predates the mudflow. Extruded outcroppings of columnar basalt can be seen along the trails near the top of the peak.