The granite of the Sierra Nevada range and the glacier-carved landscape of Yosemite National Park help divide the geological history of the region into two distinct parts. First, the deposition and deformation of metamorphic rocks and the emplacement of granitic rocks during the Paleozoic and Mesozoic, and second, the uplift, erosion, and glaciation during the Cenozoic that produced the modern landscape (States -United of America). Important chapters in this geologic history include the assembly of California, the intrusion of the Sierra Nevada batholith, the building of the Sierra Nevada, and erosion by glaciers (United States of America). The glaciation gave rise to iconic monuments known around the world, such as Yosemite Falls, Yosemite Valley and Half Dome (USA). It is well known that glaciation caused Yosemite's current appearance, but it is not as well known what happened before the relatively recent glaciation that occurred about 15,000 years old. The geological history of Yosemite and its surrounding area begins 500 million years ago, in the Paleozoic era, when the region was still under the waters of the Pacific Ocean (Beatty). This area had a passive fault, similar to the eastern seaboard of the United States today. Mud and silt from the ocean were deposited in the Yosemite region and eventually became shale, siltstone, and carbonate rocks (United States of America). At the end of the Ordovician period, the fault changed from a passive to an active fault. The oceanic plate began to sink beneath the continental crust and push shales upward, forming the first mountains of the western United States. At first these were volcanic islands off the coast. This training is called the Shoo Fly Complex. T...... middle of paper ......se two tectonic plates generated intense friction and pressure that generated enough heat to melt the rocks. The descent of the denser oceanic Farallon plate into the asthenosphere produced magma made from basalt or andesite. These are dark colored rocks with little silica. The buoyant magma passed through the silica-rich continental crust, partially melting the crust it was displacing and becoming more granitic in composition. About 100 million years ago, granite magma accumulated at depths of only 2 to 5 miles below the surface (United States of America). The granite terrain that makes up the Sierra was once thought to have only local variations, but it was produced from a large mass of rock. However, hundreds of intrusions have been found to be responsible for variations in the granite found in Yosemite and the Sierra Nevada range (Huber).