The Smith Rock area is made up of layers of recent basalt flows overlaying older Clarno ash and tuff formations. Approximately 30 million 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 eventually hardened into rock, becoming Smith Rock tuff. A half million years ago, basalt lava flows from nearby volcanoes covered the older tuff. Over time the Crooked River cut its way through these layers of rock. The river has an elevation of 2600 ft above sea level and the top of Smith Rock is 600 ft higher.