Smith Rock in Oregon. Smith Rock is a world-class climbing destination, partly due to the rigid nature of its rock. It is made of volcanic tuff, or fallout from volcanic eruptions. It also, by chance, forms the northwestern corner of the Prineville Caldera, a “super volcano” (God I hate that term) some twenty miles across east to west, that formed here between twenty and thirty million years ago. The valley and plains that surround the city of Prineville are all part of the center of this volcanic caldera, and the hills around it are craggy from the tuff produced by this eruption.