The centerpiece of the park is a narrow gorge cut through rock by a stream—Glen Creek—that was left hanging when glaciers of the Ice age deepened the Seneca valley, increasing the tributary stream gradient to create rapids and waterfalls wherever there were layers of hard rock. The area's rocks are sedimentary of Devonian age, part of a dissected plateau that was uplifted with little faulting or distortion. They consist mostly of soft shales, with some layers of harder sandstone and limestone.