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
Trap rock the Green with trap rock quarried from Eli Whitney's quarry, is a particularly colorful example of a red-orange-brown-colored, natural-faced trap rock. It was also used for foundations and railroad beds in the New Haven area. Well-known examples of outcropping trap rock include both intrusive sills and extrusive lava flows. They include the Palisades Sill, a Triassic, 200 Ma diabase intrusion that forms the Palisade along of the Hudson River in New York and New Jersey. Vast areas of trap rock in the form of thick lava flows and other volcanic rocks comprise the Deccan Traps of India and Siberian Traps