The early observers of this area described a mysterious deep blue lake in Oregon. The lake actually occupies a caldera , formed when a volcano called Mount Mazama exploded and collapsed, about 6845 years ago. This display summarizes the phases of formation of Crater Lake. The caldera gradually filled with water from rain and snow. It contained no vegetation or animal life until fish were introduced about 60 years ago.
Wizard Island is a small cinder cone that formed within the caldera, after the collapse.
An andesite dike forms Backbone Ridge. Pyroclastic eruptions produced tuff, which was cemented together in places where gas and steam passed through pipes. These areas were more resistant to erosion and stand today as The Pinnacles . Layers of volcanic ash in soil can be traced for miles. The brown layer is Mazama ash, the white is Mt. St. Helens ash from an eruption around 3400 years ago.