Between six and nine million years ago, stretching and thinning of the Earth's crust caused movement along the Teton fault. The west block along the fault line rose to form the Teton Range, creating the youngest mountain range in the Rocky Mountains. The fault's east block fell to form the valley called Jackson Hole. The geological processes that led to the current composition of the oldest rocks in the Teton range began about 2.5 billion years ago. At that time, sand and volcanic debris settled into an ancient ocean. Additional sediment was deposited for millions of years and eventually heat and pressure metamorphosed the sediment into gneiss. Subsequently, magma was forced up through the cracks in the gneiss to form granite, anywhere from inches to hundreds of feet thick. Other intrusive igneous rocks are noticeable as the black dikes of diabase, visible on the southwest face of Mount Moran and on the Grand Teton. Starting during the Cambrian period, deep deposits of sedimentary rock were deposited in shallow seas over the metamorphic basement rocks. Erosion and uplift have exposed the metamorphic and intrusive igneous rocks now visible on the east slope of the range and in the Cathedral Group and the Paleozoic and Cenozoic sedimentary rocks on the west slope. As recently as 2.1 million years ago the Huckleberry Ridge Tuff was deposited along the west slope of the north part of the range.