Smith Rock State Park years ago, a large caldera was formed when overlying rock collapsed into an underground lava chamber. This created a huge amount of rock and ash debris that filled the caldera. That material solidified into rock, becoming Smith Rock tuff. Rhyolite flows intruded along faults in the Smith Rock Tuff. A half million years ago, basalt lava flows from nearby volcanoes covered the older tuff. More recently, the Crooked River cut its way through the layers of rock to create today's geographic features. Smith Rock itself is a -high ridge (above sea level) with a sheer cliff-face overlooking a bend in
Volcanic history of the Northern Cordilleran Volcanic Province the junction of the Pelly and Yukon rivers, Volcano Mountain in central Yukon consists of a cinder cone and a series of lava flows. It is the youngest volcano in the Fort Selkirk Volcanic Field and lava flows originated from fractures in the volcano's flank. These lava flows extend northeast and southwest of the volcano. The northeastern lava flow extends from Volcano Mountain whereas the southwestern lava flow extends from the volcano. These lava flows are composed of olivine nephelinite, a type of lava not commonly found on Earth. Nephelinite lavas are usually interpreted to have originated much deeper in